Physical Review D (Particles and Fields) -- 1 April 2009

Top quark mass measurement in the lepton plus jets channel using a modified matrix element method

T. Aaltonen et al. (CDF Collaboration)

Published 10 April 2009 (23 pages)

072001 Full Text: PDF (875 kB) | Buy Article

+

Show Abstract

We report a measurement of the top quark mass, mt, obtained from p[overline p] collisions at sqrt(s)=1.96 TeV at the Fermilab Tevatron using the CDF II detector. We analyze a sample corresponding to an integrated luminosity of 1.9 fb^-1. We select events with an electron or muon, large missing transverse energy, and exactly four high-energy jets in the central region of the detector, at least one of which is tagged as coming from a b quark. We calculate a signal likelihood using a matrix element integration method, where the matrix element is modified by using effective propagators to take into account assumptions on event kinematics. Our event likelihood is a function of mt and a parameter JES (jet energy scale) that determines in situ the calibration of the jet energies. We use a neural network discriminant to distinguish signal from background events. We also apply a cut on the peak value of each event likelihood curve to reduce the contribution of background and badly reconstructed events. Using the 318 events that pass all selection criteria, we find mt=172.7±1.8(stat+JES)±1.2(syst) GeV/c².

Neutrino flux prediction at MiniBooNE

A. A. Aguilar-Arevalo et al. (MiniBooNE Collaboration)

Published 15 April 2009 (38 pages)

072002 Full Text: PDF (3891 kB) | Buy Article

+

Show Abstract

The booster neutrino experiment (MiniBooNE) searches for nuµ-->nue oscillations using the [script O](1 GeV) neutrino beam produced by the booster synchrotron at the Fermi National Accelerator Laboratory). The booster delivers protons with 8 GeV kinetic energy (8.89 GeV/c momentum) to a beryllium target, producing neutrinos from the decay of secondary particles in the beam line. We describe the Monte Carlo simulation methods used to estimate the flux of neutrinos from the beam line incident on the MiniBooNE detector for both polarities of the focusing horn. The simulation uses the Geant4 framework for propagating particles, accounting for electromagnetic processes and hadronic interactions in the beam line materials, as well as the decay of particles. The absolute double differential cross sections of pion and kaon production in the simulation have been tuned to match external measurements, as have the hadronic cross sections for nucleons and pions. The statistical precision of the flux predictions is enhanced through reweighting and resampling techniques. Systematic errors in the flux estimation have been determined by varying parameters within their uncertainties, accounting for correlations where appropriate.

Constraints on the CKM angle gamma in B⁰-->[overline D]⁰K^*0 and B⁰-->D⁰K^*0 from a Dalitz analysis of D⁰ and [overline D]⁰ decays to K_Spi⁺pi^-

B. Aubert et al. (BABAR Collaboration)

Published 15 April 2009 (10 pages)

072003 Full Text: PDF (338 kB) | Buy Article

+

Show Abstract

We present constraints on the angle gamma of the unitarity triangle with a Dalitz analysis of neutral D decays to KSpi⁺pi^- from the processes B⁰-->[overline D]⁰K^*0 ([overline B]⁰-->D⁰[overline K]^*0) and B⁰-->D⁰K^*0 ([overline B]⁰-->[overline D]⁰[overline K]^*0) with K^*0-->K⁺pi^- ([overline K]^*0-->K^-pi⁺). Using a sample of 371×10⁶ B[overline B] pairs collected with the BABAR detector at PEP-II, we constrain the angle gamma as a function of rS, the magnitude of the average ratio between b-->u and b-->c amplitudes.

Time-dependent Dalitz plot measurement of CP parameters in B⁰-->K_S⁰pi⁺pi^- decays

J. Dalseno et al. (Belle Collaboration)

Published 16 April 2009 (17 pages)

072004 Full Text: PDF (449 kB) | Buy Article

+

Show Abstract

We present a time-dependent Dalitz plot measurement of CP violation parameters in B⁰-->KS⁰pi⁺pi^- decays. These results are obtained from a large data sample that contains 657×10⁶ B[overline B] pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. For the CP violation parameters, we obtain two consistent solutions that describe the data well. The first of these solutions may be preferred by external information from other measurements. There is no evidence for direct CP violation in B⁰-->rho⁰(770)KS⁰, B⁰-->f0(980)KS⁰ and B⁰-->K^*+(892)pi^-, while measurements of mixing-induced CP violation in B⁰-->rho⁰(770)KS⁰ and B⁰-->f0(980)KS⁰ decays are consistent with that of b-->c[overline c]s decays. We also measured the phase difference between B⁰-->K^*+(892)pi^- and [overline B]⁰-->K^*-(892)pi⁺, which may be used to extract phi3.

Measurement of the top quark mass at CDF using the “neutrino phi weighting” template method on a lepton plus isolated track sample

T. Aaltonen et al. (CDF Collaboration)

Published 16 April 2009 (18 pages)

072005 Full Text: PDF (1426 kB) | Buy Article

+

Show Abstract

We present a measurement of the top quark mass with t[overline t] dilepton events produced in p[overline p] collisions at the Fermilab Tevatron (sqrt(s)=1.96 TeV) and collected by the CDF II detector. A sample of 328 events with a charged electron or muon and an isolated track, corresponding to an integrated luminosity of 2.9 fb^-1, are selected as t[overline t] candidates. To account for the unconstrained event kinematics, we scan over the phase space of the azimuthal angles (phinu1,phinu2) of neutrinos and reconstruct the top quark mass for each phinu1, phinu2 pair by minimizing a chi² function in the t[overline t] dilepton hypothesis. We assign chi²-dependent weights to the solutions in order to build a preferred mass for each event. Preferred mass distributions (templates) are built from simulated t[overline t] and background events, and parametrized in order to provide continuous probability density functions. A likelihood fit to the mass distribution in data as a weighted sum of signal and background probability density functions gives a top quark mass of 165.5-3.3^+3.4(stat)±3.1(syst) GeV/c².

Dalitz plot analysis of B^±-->pi^±pi^±pi^-/+ decays

B. Aubert et al. (BABAR Collaboration)

Published 22 April 2009 (15 pages)

072006 Full Text: PDF (431 kB) | Buy Article

+

Show Abstract

We present a Dalitz plot analysis of charmless B^± decays to the final state pi^±pi^±pi^-/+ using a sample of (465±5)×10⁶ B[overline B] pairs collected by the BABAR experiment at sqrt(s)=10.58 GeV. We measure the branching fractions [script B](B^±-->pi^±pi^±pi^-/+)=(15.2±0.6±1.2±0.4)×10^-6, [script B](B^±-->rho⁰(770)pi^±)=(8.1±0.7±1.2-1.1^+0.4)×10^-6, [script B](B^±-->f2(1270)pi^±)=(1.57±0.42±0.16-0.19^+0.53)×10^-6, and [script B](B^±-->pi^±pi^±pi^-/+ nonresonant)=(5.3±0.7±0.6-0.5^+1.1)×10^-6, where the uncertainties are statistical, systematic, and model-dependent, respectively. Measurements of branching fractions for the modes B^±-->rho⁰(1450)pi^± and B^±-->f0(1370)pi^± are also presented. We observe no significant direct CP asymmetries for the above modes, and there is no evidence for the decays B^±-->f0(980)pi^±, B^±-->chic0pi^±, or B^±-->chic2pi^±.

New measurement of exclusive decays of the chi_c0 and chi_c2 to two-meson final states

D. M. Asner et al. (CLEO Collaboration)

Published 22 April 2009 (4 pages)

072007 Full Text: PDF (218 kB) | Buy Article

+

Show Abstract

Using a sample of 2.59×10⁷ psi(2S) decays collected by the CLEO-c detector, we present results of a study of chic0 and chic2 decays into two-meson final states. We present the world's most precise measurements of the chicJ,(J=0,2)-->pi⁺pi^-, pi⁰pi⁰, K⁺K^-, KS⁰KS⁰, etaeta, and eta^[prime]eta^[prime] branching fractions, and a search for chic decays into etaeta^[prime]. These results shed light on the mechanism of charmonium decays into pseudoscalar mesons.

Dalitz plot analysis of D_s⁺-->K⁺K^-pi⁺

R. E. Mitchell et al. (CLEO Collaboration)

Published 24 April 2009 (13 pages)

072008 Full Text: PDF (1384 kB) | Buy Article

+

Show Abstract

We perform a Dalitz plot analysis of the decay Ds⁺-->K⁺K^-pi⁺ with the CLEO-c data set of 586 pb^-1 of e⁺e^- collisions accumulated at sqrt(s)=4.17 GeV. This corresponds to about 0.57×10⁶ Ds^[plus-minus]Ds^*-/+ pairs from which we select 14 400 candidates with a background of roughly 15%. In contrast to previous measurements we find good agreement with our data only by including an additional f0(1370)pi⁺ contribution. We measure the magnitude, phase, and fit fraction of K^*(892)⁰K⁺, phi(1020)pi⁺, K0^*(1430)K⁺, f0(980)pi⁺, f0(1710)pi⁺, and f0(1370)pi⁺ contributions and limit the possible contributions of other KK and Kpi resonances that could appear in this decay.

Measurement of time-dependent CP asymmetry in B⁰-->c[overline c]K^(*)0 decays

B. Aubert et al. (BABAR Collaboration)

Published 29 April 2009 (13 pages)

072009 Full Text: PDF (455 kB) | Buy Article

+

Show Abstract

We present updated measurements of time-dependent CP asymmetries in fully reconstructed neutral B decays containing a charmonium meson. The measurements reported here use a data sample of (465±5)×10⁶ Upsilon(4S)-->B[overline B] decays collected with the BABAR detector at the PEP-II asymmetric energy e⁺e^- storage rings operating at the SLAC National Accelerator Laboratory. The time-dependent CP asymmetry parameters measured from JpsiKS⁰, JpsiKL⁰, psi(2S)KS⁰, etacKS⁰, chic1KS⁰, and J/psiK^*(892)⁰ decays are: Cf=0.024±0.020(stat)±0.016(syst) and -etafSf=0.687±0.028(stat)±0.012(syst).

Top quark mass measurement in the t[overline t] all hadronic channel using a matrix element technique in p[overline p] collisions at sqrt(s)=1.96 TeV

T. Aaltonen et al. (CDF Collaboration)

Published 30 April 2009 (28 pages)

072010 Full Text: PDF (1124 kB) | Buy Article

+

Show Abstract

We present a measurement of the top quark mass in the all hadronic channel (t[overline t]-->b[overline b]q1[overline q]2q3[overline q]4) using 943 pb^-1 of p[overline p] collisions at sqrt(s)=1.96 TeV collected at the CDF II detector at Fermilab (CDF). We apply the standard model production and decay matrix element (ME) to t[overline t] candidate events. We calculate per-event probability densities according to the ME calculation and construct template models of signal and background. The scale of the jet energy is calibrated using additional templates formed with the invariant mass of pairs of jets. These templates form an overall likelihood function that depends on the top quark mass and on the jet energy scale (JES). We estimate both by maximizing this function. Given 72 observed events, we measure a top quark mass of 171.1±3.7(stat+JES)±2.1(syst) GeV/c². The combined uncertainty on the top quark mass is 4.3 GeV/c².

Cosmic ray primary composition in the energy range 10–1000 TeV obtained by passive balloon-borne detector: Reanalysis of the RUNJOB experiment

V. Kopenkin and T. Sinzi

Published 30 April 2009 (18 pages)

072011 Full Text: PDF (566 kB) | Buy Article

+

Show Abstract

We search for a consistent view on the RUNJOB experiment and present an alternative analysis based on explicitly reported and published numerical data. Here we show that there is more than one interpretation to the reported observational data. It is demonstrated that, contrary to the wide-spread opinion, the RUNJOB data are not inconsistent with an increase of the average mass near the knee region of the cosmic ray spectrum. Considering very low statistics and systematic uncertainties, especially in the high energy region, we suggest that peculiarities of the methodical origin were the most likely source of those RUNJOB conclusions which contradicted previous observations reported by other groups.

Unified triminimal parametrizations of quark and lepton mixing matrices

Xiao-Gang He, Shi-Wen Li, and Bo-Qiang Ma

Published 6 April 2009 (15 pages)

073001 Full Text: PDF (192 kB) | Buy Article

+

Show Abstract

We present a detailed study on triminimal parametrizations of quark and lepton mixing matrices with different basis matrices. We start with a general discussion on the triminimal expansion of the mixing matrix and on possible unified quark and lepton parametrization using quark-lepton complementarity. We then consider several interesting basis matrices and compare the triminimal parametrizations with the Wolfenstein-like parametrizations. The usual Wolfenstein parametrization for quark mixing is a triminimal expansion around the unit matrix as the basis. The corresponding quark-lepton complementarity lepton mixing matrix is a triminimal expansion around the bimaximal basis. Current neutrino oscillation data show that the lepton mixing matrix is very well represented by the tribimaximal mixing. It is natural to take it as an expanding basis. The corresponding zeroth order basis for quark mixing in this case makes the triminimal expansion converge much faster than the usual Wolfenstein parametrization. The triminimal expansion based on tribimaximal mixing can be converted to the Wolfenstein-like parametrizations discussed in the literature. We thus have a unified description between different kinds of parametrizations for quark and lepton sectors: the standard parametrizations, the Wolfenstein-like parametrizations, and the triminimal parametrizations.

Fourth generation leptons and muon g-2

Wei-Shu Hou, Fei-Fan Lee, and Chien-Yi Ma

Published 6 April 2009 (7 pages)

073002 Full Text: PDF (298 kB) | Buy Article

+

Show Abstract

We consider the contributions to gµ-2 from fourth generation heavy neutral and charged leptons N and E, respectively, at the one-loop level. Diagrammatically, there are two types of contributions: boson-boson-N and E-E-boson in the loop diagram. In general, the effect from N is suppressed by off-diagonal lepton mixing matrix elements. For E, we consider flavor changing neutral couplings arising from various new physics models, which are stringently constrained by µ-->egamma. We assess how the existence of a fourth generation would affect these new physics models.

Radiative neutrino mass in type III seesaw model

Yi Liao, Ji-Yuan Liu, and Guo-Zhu Ning

Published 7 April 2009 (11 pages)

073003 Full Text: PDF (205 kB) | Buy Article

+

Show Abstract

The simplest type III seesaw model as originally proposed introduces one lepton triplet. It thus contains four active neutrinos, two massive and two massless at tree level. We determine the radiative masses that the latter receive first at two loops. The masses are generally so tiny that they are definitely excluded by the oscillation data, if the heavy leptons are not very heavy, say, within the reach of the CERN LHC. To accommodate the data on masses, the seesaw scale must be as large as the scale of grand unification. This indicates that the most economical type III model would entail no new physics at low energies beyond the tiny neutrino masses.

Rare muon decay µ⁺-->e⁺e^-e⁺nu_e[overline nu ]_µ

Rashid M. Djilkibaev and Rostislav V. Konoplich

Published 8 April 2009 (7 pages)

073004 Full Text: PDF (214 kB) | Buy Article

+

Show Abstract

An analytical expression for the spin-averaged amplitude squared of the rare muon decay µ⁺-->e⁺e^-e⁺nue[overline nu ]µ is calculated. Monte Carlo phase space simulation using the analytical expression for the amplitude has been used to get various differential distributions of charged leptons. The approximate analytical expression for the total energy spectrum of charged leptons near the end point is presented. The dependence of the branching ratio on cuts in the total energy of charged leptons is studied taking into account an experimental energy resolution. It is shown that the measured branching ratio is very sensitive to the energy resolution.

Light sterile neutrino effects at theta₁₃-driven reactor neutrino experiments

André de Gouvêa and Thomas Wytock

Published 9 April 2009 (11 pages)

073005 Full Text: PDF (1207 kB) | Buy Article

+

Show Abstract

We study the impact of very light sterile neutrinos (Deltamnew²[is-an-element-of][1,10]×10^-2 eV², sin²2thetanew<10^-1) on analyses of upcoming theta13-driven reactor antineutrino experiments like Double CHOOZ and Daya Bay. Oscillations driven by these values of Deltamnew² affect data in the near and far detectors differently and hence potentially modify the capability of these experimental setups to constrain and measure sin²2theta13. We find that the hypothesis thetanew[not-equal]0 negatively impacts one's ability to place an upper bound on sin²2theta13 in the advent of a no-oscillation signal or to measure sin²2theta13 if a theta13-driven signal is observed. The impact of sterile neutrino effects, however, depends dramatically on one's ability to measure the recoil positron energy spectrum. If sin²2thetanew>~10^-2, upcoming theta13-driven reactor antineutrino experiments should be able to measure sin²2thetanew and Deltamnew², along with sin²2theta13, as long as one is sensitive to distortions in the recoil positron energy spectrum in the near (and far) detectors.

Reconstruction of quark mass matrices with weak basis texture zeroes from experimental input

D. Emmanuel-Costa and C. Simoes

Published 9 April 2009 (9 pages)

073006 Full Text: PDF (161 kB) | Buy Article

+

Show Abstract

All quark mass matrices with texture zeroes obtained through weak basis transformations are confronted with the experimental data. The reconstruction of the quark mass matrices Mu and Md at the electroweak scale is performed in a weak basis where the matrices are Hermitian and have a maximum of three vanishing elements. The same procedure is also accomplished for the Yukawa coupling matrices at the grand unification scale in the context of the standard model and its minimal supersymmetric extension as well as of the two Higgs doublet model. The analysis of all viable power structures on the quark Yukawa coupling matrices that could naturally appear from a Froggatt-Nielsen mechanism is also presented.

Experimental requirements to determine the neutrino mass hierarchy using reactor neutrinos

Liang Zhan, Yifang Wang, Jun Cao, and Liangjian Wen

Published 14 April 2009 (5 pages)

073007 Full Text: PDF (373 kB) | Buy Article

+

Show Abstract

This paper presents experimental requirements to determine the neutrino mass hierarchy using reactor neutrinos. The detector shall be located at a baseline around 58 km from the reactor(s) to measure the energy spectrum of electron antineutrinos ([overline nu ]e) precisely. By applying Fourier cosine and sine transforms to the L/E spectrum, features of the neutrino mass hierarchy can be extracted from the |Deltam31²| and |Deltam32²| oscillations. To determine the neutrino mass hierarchy above 90% probability, requirements to the baseline, the energy resolution, the energy scale uncertainty, the detector mass, and the event statistics are studied at different values of sin²(2theta13).

Neutral current neutrino-nucleus interactions at high energies

M. B. Gay Ducati, M. M. Machado, and M. V. T. Machado

Published 14 April 2009 (7 pages)

073008 Full Text: PDF (240 kB) | Buy Article

+

Show Abstract

We present a QCD analysis of the neutral current (NC) neutrino-nucleus interaction at the small-x region using the color dipole formalism. This phenomenological approach is quite successful in describing experimental results in deep inelastic ep scattering and charged current neutrino-nucleus interactions at high energies. We present theoretical predictions for the relevant structure functions and the corresponding implications for the total NC neutrino cross section. It is shown that at small x, the NC boson-nucleon cross section should exhibit the geometric scaling property that has important consequences for ultrahigh energy neutrino phenomenology.

Nonunitarity effects in a realistic low-scale seesaw model

Michal Malinský, Tommy Ohlsson, and He Zhang

Published 16 April 2009 (6 pages)

073009 Full Text: PDF (211 kB) | Buy Article

+

Show Abstract

We analyze the structure of the nonunitary leptonic mixing matrix in the inverse seesaw model with heavy singlets accessible at the LHC. In this model, unlike in the usual TeV seesaw scenarios, the low-scale right-handed neutrinos do not suffer from naturalness issues. Underlying correlations among various parameters governing the nonunitarity effects are established, which leads to a considerable improvement of the generic nonunitarity bounds. In view of this, we study the discovery potential of the nonunitarity effects at future experiments, focusing on the sensitivity limits at a neutrino factory.

Light sterile neutrinos, spin flavor precession, and the solar neutrino experiments

C. R. Das, João Pulido, and Marco Picariello

Published 16 April 2009 (9 pages)

073010 Full Text: PDF (383 kB) | Buy Article

+

Show Abstract

We generalize to three active flavors a previous two-flavor model for the resonant spin flavor conversion of solar neutrinos to sterile ones, a mechanism which is added to the well-known large mixing angle (LMA) one. The transition magnetic moments from the muon and tau neutrinos to the sterile play the dominant role in fixing the amount of active flavor suppression. We also show, through numerical integration of the evolution equations, that the data from all solar neutrino experiments except Borexino exhibit a clear preference for a sizable magnetic field either in the convection zone or in the core and radiation zone. This is possibly related to the fact that the data from the first set are average ones taken during a period of mostly intense solar activity, whereas in contrast Borexino data were taken during a period of quiet Sun. We argue that the solar neutrino experiments are capable of tracing the possible modulation of the solar magnetic field. Those monitoring the high-energy neutrinos, namely, the ⁸B flux, appear to be sensitive to a field modulation either in the convection zone or in the core and radiation zone. Those monitoring the low-energy fluxes will be sensitive to the second type of solar field profiles only. In this way Borexino alone may play an essential role, since it examines both energy sectors, although experimental redundancy from other experiments will be most important.

Unparticle physics and neutrino phenomenology

J. Barranco, A. Bolaños, O. G. Miranda, C. A. Moura, and T. I. Rashba

Published 17 April 2009 (9 pages)

073011 Full Text: PDF (353 kB) | Buy Article

+

Show Abstract

We have constrained unparticle interactions with neutrinos and electrons using available data on neutrino-electron elastic scattering and the four CERN LEP experiments data on mono photon production. We have found that, for neutrino-electron elastic scattering, the MUNU experiment gives better constraints than previous reported limits in the region d>1.5. The results are compared with the current astrophysical limits, pointing out the cases where these limits may or may not apply. We also discuss the sensitivity of future experiments to unparticle physics. In particular, we show that the measurement of coherent reactor neutrino scattering off nuclei could provide a good sensitivity to the couplings of unparticle interaction with neutrinos and quarks. We also discuss the case of future neutrino-electron experiments as well as the International Linear Collider.

Hadronic light-by-light scattering in the muon g-2: A new short-distance constraint on pion exchange

Andreas Nyffeler

Published 20 April 2009 (13 pages)

073012 Full Text: PDF (290 kB) | Buy Article

+

Show Abstract

Recently it was pointed out that for the evaluation of the numerically dominant pion-exchange contribution to the hadronic light-by-light scattering correction in the muon g-2, a fully off-shell pion-photon-photon form factor should be used. Following this proposal, we first derive a new short-distance constraint on the off-shell form factor which enters at the external vertex for the muon g-2 and show that it is related to the quark condensate magnetic susceptibility in QCD. We then evaluate the pion-exchange contribution in the framework of large-NC QCD using an off-shell form factor which fulfills all short-distance constraints. With a value for the magnetic susceptibility as estimated in the same large-NC framework, we obtain the result amu^{LbyL;pi[sup 0]}=(72±12)×10^-11. Updating our earlier results for the contributions from the exchanges of the eta and eta^[prime] using simple vector-meson dominance form factors, we obtain amu^LbyL;PS=(99±16)×10^-11 for the sum of all light pseudoscalars. Combined with available evaluations for the other contributions to hadronic light-by-light scattering this leads to the new estimate amu^LbyL;had=(116±40)×10^-11.

Higgs boson exchange effects in l⁺l^--->W⁺W^- at high energy

U. Baur and E. Brewer

Published 21 April 2009 (9 pages)

073013 Full Text: PDF (540 kB) | Buy Article

+

Show Abstract

We consider the prospects for detecting effects due to the Higgs exchange diagram in high energy µ⁺µ^-, e⁺e^-, and tau⁺tau^- collisions producing a pair of W bosons. The processes l⁺l^--->W⁺W^- (with l=µ, e, tau) are analyzed, analytically and via numerical simulations, to determine the center of mass energy, sqrt(s[sub H]), where the effects from Higgs exchange become relevant. The scaling of sqrt(s[sub H]) with the mass of the incoming leptons is also studied. Special consideration is given to the W⁺W^--->l^±nuljj final state after experimental acceptance cuts are imposed. Angular cuts are shown to be able to significantly lower sqrt(s[sub H]). The center of mass energy for which Higgs exchange effects become relevant in l⁺l^--->W⁺W^- is found to be much higher than that in l⁺l^--->[overline nu ]nuW⁺W^-. Higgs boson exchange effects in W-pair production thus will not be relevant for the e⁺e^- and µ⁺µ^- colliders currently on the drawing board.

Model calculations of the Sivers function satisfying the Burkardt sum rule

A. Courtoy, S. Scopetta, and V. Vento

Published 6 April 2009 (5 pages)

074001 Full Text: PDF (204 kB) | Buy Article

+

Show Abstract

It is shown that, at variance with previous analyses, the MIT bag model can explain the available data of the Sivers function and satisfies the Burkardt sum rule to a few percent accuracy. The agreement is similar to the one recently found in the constituent quark model. Therefore, these two model calculations of the Sivers function are in agreement with the present experimental and theoretical wisdom.

Hadronic quarkonium decays at order v⁷

Nora Brambilla, Antonio Vairo, and Emanuele Mereghetti

Published 6 April 2009 (23 pages)

074002 Full Text: PDF (551 kB) | Buy Article

+

Show Abstract

We compute the complete imaginary part of the nonrelativistic QCD (NRQCD) Lagrangian at order 1/M⁴ in the heavy-quark mass expansion, which includes center of mass operators, and at order alphas² in the matching coefficients. We also compute the imaginary part of the NRQCD Lagrangian at order 1/M⁶ and at order alphas² that contributes to the S-wave and P-wave inclusive decay widths of heavy quarkonium into light hadrons at order v⁷ in the heavy-quark velocity expansion. If we count alphas(M)~v², the calculation provides the complete next-to-leading order corrections to the P-wave hadronic widths, and in the original NRQCD power counting, the complete next-to-leading order corrections to the vector S-wave widths, and part of the next-to-next-to leading order corrections to the pseudoscalar S-wave widths. In the S-wave case, we confirm previous findings and add new terms in a more conservative power counting. In the P-wave case, our results are in disagreement with previous ones. Constraints induced by Poincaré invariance on the NRQCD four-fermion sector are studied for the first time and provide an additional check of the calculation. Perspectives for phenomenological applications are discussed.

Skyrmion vibrational energies together with a generalized mass term

Merlin C. Davies and Luc Marleau

Published 6 April 2009 (9 pages)

074003 Full Text: PDF (267 kB) | Buy Article

+

Show Abstract

We study various properties of a one-parameter mass term for the Skyrme model, originating from the works of Kopeliovich, Piette and Zakrzewski [V. B. Kopeliovich, B. Piette, and W. J. Zakrzewski, Phys. Rev. D 73, 014006 (2006).], through the use of axially symmetric solutions obtained numerically by simulated-annealing. These solutions allow us to observe asymptotic behaviors of the B=2 binding energies that differ to those previously obtained [B. Piette and W. J. Zakrzewski, Phys. Rev. D 77, 074009 (2008).]. We also decipher the characteristics of three distinct vibrational modes that appear as eigenstates of the vibrational Hamiltonian. This analysis further examine the assertion that the one-parameter mass term offers a better account of baryonic matter than the traditional mass term.

Leading twist distribution amplitudes of P-wave nonrelativistic mesons

V. V. Braguta, A. K. Likhoded, and A. V. Luchinsky

Published 7 April 2009 (7 pages)

074004 Full Text: PDF (132 kB) | Buy Article

+

Show Abstract

This paper is devoted to the study of the leading twist distribution amplitudes of P-wave nonrelativistic mesons. It is shown that at the leading order approximation in relative velocity of quark-antiquark pair inside the mesons these distribution amplitudes can be expressed through one universal function. As an example, the distribution amplitudes of P-wave charmonia mesons are considered. Within QCD sum rules the model for the universal function of P-wave charmonia mesons is built. In addition, relations are found between the moments of the universal function and the nonrelativistic QCD matrix elements that control relativistic corrections to any amplitude involving P-wave charmonia. Our calculation shows that characteristic size of these corrections is of order of ~30%.

Precision determination of invisible-particle masses at the CERN LHC. II.

Alan J. Barr, Alex Pinder, and Mario Serna

Published 7 April 2009 (14 pages)

074005 Full Text: PDF (770 kB) | Buy Article

+

Show Abstract

We further develop the constrained mass variable techniques to determine the mass scale of invisible particles pair-produced at hadron colliders. We introduce the constrained mass variable M3C which provides an event-by-event lower bound and upper bound to the mass scale given the two mass differences between the lightest three new particle states. This variable is most appropriate for short symmetric cascade decays involving two-body decays and on-shell intermediate states which end in standard-model particles and two dark-matter particles. An important feature of the constrained mass variables is that they do not rely simply on the position of the end point but use the additional information contained in events which lie far from the end point. To demonstrate our method we study the supersymmetric model SPS 1a. We select cuts to study events with two chi-tilde2^o each of which decays to chi-tilde1^o, and two opposite-sign same-flavor charged leptons through an intermediate on-shell slepton. We find that with 300 fb^-1 of integrated luminosity the invisible-particle mass can be measured to Mchi-tilde[sub 1][sup o]=96.4±2.4 GeV. Combining fits to the shape of the M3C constrained mass variable distribution with the maxmll edge fixes the mass differences to ±0.2 GeV.

omega-phi mixing and weak annihilation in D_s decays

Michael Gronau and Jonathan L. Rosner

Published 8 April 2009 (8 pages)

074006 Full Text: PDF (315 kB) | Buy Article

+

Show Abstract

The mixing between nonstrange and strange quark wave functions in the omega and phi mesons leads to a small predicted branching ratio [script B](Ds⁺-->omegae⁺nue)=[script O](10^-4)(delta/3.34°)², where delta is the mixing angle. The value delta=-3.34° is obtained in a mass-independent analysis, while a mass-dependent analysis gives delta=-0.45° at m(omega) and -4.64° at m(phi). Measurement of this branching ratio thus can tell whether the decay is dominated by phi-omega mixing, or additional nonperturbative processes commonly known as “weak annihilation” (WA) contribute. The role of WA in the decay Ds⁺-->omegapi⁺ and its possible use in estimating WA effects in Ds⁺-->omegae⁺nue are also discussed. Assuming that the dynamics of WA in Ds⁺-->omegapi⁺ is similar in Ds⁺-->omegae⁺nue we estimate [script B](Ds⁺-->omegae⁺nue)=(1.3±0.5)×10^-3.

B-->K₀^*(1430)l⁺l^- decays in supersymmetric theories

M. Jamil Aslam, Cai-Dian Lü, and Yu-Ming Wang

Published 9 April 2009 (13 pages)

074007 Full Text: PDF (3338 kB) | Buy Article

+

Show Abstract

The weak decays of B-->K0^*(1430)l⁺l^- (l=µ, tau) are investigated in minimal supersymmetric standard model (MSSM) and also in supersymmetric (SUSY) SO(10) grand unified theory (GUT) models. Neutral Higgs bosons are the point of main focus in MSSM because they make quite a large contribution in exclusive B-->Xsl⁺l^- decays at large tanbeta regions of parameter space of SUSY models, as part of SUSY contributions is proportional to tan³beta. The analysis of decay rate, forward-backward asymmetries and lepton polarization asymmetries in B-->K0^*(1430)l⁺l^- show that the values of these physical observables are greatly modified by the effects of neutral Higgs bosons. In SUSY SO(10) grand unified model, the new physics contribution comes from the operators which are induced by the neutral Higgs boson penguins and also from the operators with chirality opposite to that of the corresponding standard model operators. SUSY SO(10) effects show up only in the decay B-->K0^*µ⁺µ^- where the transverse lepton polarization asymmetries deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries, the longitudinal and normal lepton polarization asymmetries are very mild. The transverse lepton polarization asymmetry is almost zero in SM and in MSSM model, whereas it can reach to -0.3 in SUSY SO(10) GUT model which could be seen at the future colliders; hence this asymmetry observable can be used to discriminate between different SUSY models.

Radiative corrections to the lattice gluon action for highly improved staggered quarks and the effect of such corrections on the static potential

A. Hart et al. (HPQCD Collaboration)

Published 9 April 2009 (10 pages)

074008 Full Text: PDF (263 kB) | Buy Article

+

Show Abstract

We perform a perturbative calculation of the influence of dynamical highly improved staggered quark fermions on the perturbative improvement of the gluonic action in the same way as we have previously done for asqtad fermions. We find the fermionic contributions to the radiative corrections in the Lüscher-Weisz gauge action to be somewhat larger for highly improved staggered quark fermions than for asqtad. Using one-loop perturbation theory as a test, we estimate that omission of the fermion-induced radiative corrections in dynamical asqtad simulations will give a measurable effect. The one-loop result gives a systematic shift of about -0.6% in r^1 on the coarsest asqtad improved staggered ensembles. This is the correct sign and magnitude to explain the scaling violations seen in PhiB=fBsqrt(M[sub B]) on dynamical lattice ensembles.

Vector meson-vector meson interaction in a hidden gauge unitary approach

L. S. Geng and E. Oset

Published 10 April 2009 (20 pages)

074009 Full Text: PDF (739 kB) | Buy Article

+

Show Abstract

The formalism developed recently to study vector meson-vector meson interaction, and applied to the case of rhorho, is extended to study the interaction of the nonet of vector mesons among themselves. The interaction leads to poles of the scattering matrix corresponding to bound states or resonances. We show that 11 states (either bound or resonant) get dynamically generated in nine strangeness-isospin-spin channels. Five of them can be identified with those reported in the PDG, i.e., the f0(1370), f0(1710), f2(1270), f2^[prime](1525), and K2^*(1430). The masses of the latter three tensor states have been used to fine-tune the free parameters of the unitary approach, i.e., the subtraction constants in evaluating the vector meson-vector meson loop functions in the dimensional regularization scheme. The branching ratios of these five dynamically generated states are found to be consistent with data. The existence of the other six states should be taken as predictions to be tested by future experiments.

Exotic meson-meson molecules and compact four-quark states

J. Vijande, A. Valcarce, and N. Barnea

Published 10 April 2009 (16 pages)

074010 Full Text: PDF (346 kB) | Buy Article

+

Show Abstract

We present an exact calculation of S and P wave QQ[overline n][overline n] states using different standard nonrelativistic quark-quark potentials. We explore in detail the charm and bottom sectors looking for bound states that could be measured within existing facilities. Against the proliferation of four-quark states sometimes predicted in the literature, we found a small number of candidates to be stable. We analyze their properties in a trial to distinguish between compact and molecular states. Possible decay modes are discussed.

Mesonic excitations and pi-pi scattering lengths at finite temperature in the two-flavor Polyakov–Nambu–Jona-Lasinio model

Wei-jie Fu (付伟杰) and Yu-xin Liu (刘玉鑫)

Published 13 April 2009 (12 pages)

074011 Full Text: PDF (745 kB) | Buy Article

+

Show Abstract

The mesonic excitations and s-wave pi-pi scattering lengths at finite temperature are studied in the two-flavor Polyakov–Nambu–Jona-Lasinio (PNJL) model. The masses of the pi and sigma mesons, pion-decay constant, the pion-quark coupling strength, and the scattering lengths a0 and a2 at finite temperature are calculated in the PNJL model with two forms of Polyakov-loop effective potential. The obtained results are almost independent of the choice of the effective potentials. The calculated results in the PNJL model are also compared with those in the conventional Nambu–Jona-Lasinio model and indicate that the effect of color confinement screens the effect of temperature below the critical one in the PNJL model. Furthermore, the Goldberger-Treiman relation and the Gell-Mann–Oakes–Renner relation are extended to the case at finite temperature in the PNJL model.

Top quark jets at the LHC

Leandro G. Almeida, Seung J. Lee, Gilad Perez, Ilmo Sung, and Joseph Virzi

Published 16 April 2009 (25 pages)

074012 Full Text: PDF (1309 kB) | Buy Article

+

Show Abstract

We investigate the reconstruction of high pT hadronically decaying top quarks at the Large Hadron Collider. One of the main challenges in identifying energetic top quarks is that the decay products become increasingly collimated. This reduces the efficacy of conventional reconstruction methods that exploit the topology of the top quark decay chain. We focus on the cases where the decay products of the top quark are reconstructed as a single jet, a “top jet.” The most basic “top-tagging” method based on jet mass measurement is considered in detail. To analyze the feasibility of the top-tagging method, both theoretical and experimental aspects of the large QCD jet background contribution are examined. Based on a factorization approach, we derive a simple analytic approximation for the shape of the QCD jet mass spectrum. We observe very good agreement with the Monte Carlo simulation. We consider high-pT t[overline t] production in the standard model as an example, and show that our theoretical QCD jet mass distributions can efficiently characterize the background via sideband analyses. We show that with 25 fb^-1 of data, our approach allows us to resolve top jets with pT>=1 TeV, from the QCD background, and about 1.5 TeV top jets with 100 fb^-1, without relying on b-tagging. To further improve the significance we consider jet shapes (recently analyzed in 10), which resolve the substructure of energy flow inside cone jets. A method of measuring the top quark polarization by using the transverse momentum of the bottom quark is also presented. The main advantages of our approach are (i) the mass distributions are driven by first principle calculations, instead of relying solely on Monte Carlo simulation; (ii) for high pT jets (pT>=1 TeV), IR-safe jet shape variables are robust against detector resolution effects. Our analysis can be applied to other boosted massive particles such as the electroweak gauge bosons and the Higgs.

Multiparton correlations and “exclusive” cross sections

G. Calucci and D. Treleani

Published 16 April 2009 (11 pages)

074013 Full Text: PDF (157 kB) | Buy Article

+

Show Abstract

In addition to the inclusive cross sections discussed within the QCD-parton model, in the regime of multiple parton interactions, different and more exclusive cross sections become experimentally viable and may be suitably measured. Indeed, in its study of double parton collisions, the quantity measured by the CDF was an “exclusive” rather than an inclusive cross section. The nonperturbative input to the “exclusive” cross sections is different with respect to the nonperturbative input of the inclusive cross sections and involves correlation terms of the hadron structure already at the level of single parton collisions. The matter is discussed in details keeping explicitly into account the effects of double and of triple parton collisions.

Global aspects of the scalar meson puzzle

Amir H. Fariborz, Renata Jora, and Joseph Schechter

Published 16 April 2009 (12 pages)

074014 Full Text: PDF (459 kB) | Buy Article

+

Show Abstract

A generalized linear sigma model for low-energy QCD is employed to study the quark structure of eight low-lying scalar isomultiplets as well as eight low-lying pseudoscalar isomultiplets. The model, building on earlier work, assumes the possible mixing of quark antiquark states with others made of two quarks and two antiquarks. No a priori assumption is made about the quark contents of the states, which emerge as predictions. An amusing and contrasting pattern for the quark structure is found; the lighter conventional pseudoscalars are, as expected, primarily of two-quark type whereas the lighter scalars have very large four-quark admixtures. The new feature of the present paper compared to earlier ones in this series involves the somewhat subtle and complicated effects of SU(3) flavor breaking. They do not alter the general pattern of two-quark vs four-quark mixing obtained in the SU(3)symmetric case but, of course, give a more detailed picture.

Isentropic thermodynamics in the Polyakov–Nambu–Jona-Lasinio model

Kenji Fukushima

Published 16 April 2009 (9 pages)

074015 Full Text: PDF (854 kB) | Buy Article

+

Show Abstract

We discuss the isentropic trajectories on the QCD phase diagram in the temperature and the quark chemical potential plane using the Nambu–Jona-Lasinio model with the Polyakov loop coupling. We impose a constraint on the strange quark chemical potential so that the strange quark density is zero, which is the case in the ultra relativistic heavy-ion collisions. We compare our numerical results with the truncated estimates by the Taylor expansion in terms of the chemical potential to quantify the reliability of the expansion used in the lattice QCD simulation. We finally discuss the strange quark chemical potential induced by the strangeness neutrality condition and relate it to the ratio of the Polyakov loop and the anti-Polyakov loop.

Topology and chiral random matrix theory at nonzero imaginary chemical potential

C. Lehner, M. Ohtani, J. J. M. Verbaarschot, and T. Wettig

Published 17 April 2009 (11 pages)

074016 Full Text: PDF (536 kB) | Buy Article

+

Show Abstract

We study the effect of topology for a random matrix model of QCD at nonzero imaginary chemical potential or nonzero temperature. Nonuniversal fluctuations of Dirac eigenvalues lead to normalization factors that contribute to the theta dependence of the partition function. These normalization factors have to be canceled in order to reproduce the theta dependence of the QCD partition function. The reason for this behavior is that the topological domain of the Dirac spectrum (the region of the Dirac spectrum that is sensitive to the topological charge) extends beyond the microscopic domain at nonzero imaginary chemical potential or temperature. Such behavior could persist in certain lattice formulations of QCD.

Substructure of high-p_T jets at the LHC

Leandro G. Almeida, Seung J. Lee, Gilad Perez, George Sterman, Ilmo Sung, and Joseph Virzi

Published 17 April 2009 (6 pages)

074017 Full Text: PDF (252 kB) | Buy Article

+

Show Abstract

We study high-pT jets from QCD and from highly boosted massive particles such as tops, W, Z, and Higgs bosons, and argue that infrared-safe observables can help reduce QCD backgrounds. Jets from QCD are characterized by different patterns of energy flow compared to the products of highly boosted heavy particle decays, and we employ a variety of jet shapes, observables restricted to energy flow within a jet, to explore this difference. Results from Monte Carlo generators and arguments based on perturbation theory support the discriminating power of the shapes we refer to as planar flow and angularities. We emphasize that for massive jets, these and other observables can be analyzed perturbatively.

Double charmonium production at B factories within light cone formalism

V. V. Braguta

Published 20 April 2009 (12 pages)

074018 Full Text: PDF (243 kB) | Buy Article

+

Show Abstract

This paper is devoted to the study of the processes e⁺e^--->J/Psietac, J/Psietac^[prime], psi^[prime]etac, psi^[prime]etac^[prime] within light cone formalism. It is shown that if one disregards the contribution of higher Fock states, the twist-3 distribution amplitudes needed in the calculation can be unambiguously determined from the twist-2 distribution amplitudes and equations of motion. Using models of the twist-2 distribution amplitudes the cross sections of the processes under study are calculated. The results of the calculation are in agreement with Belle and BABAR experiments. It is also shown that relativistic and radiative corrections to the cross sections play a crucial role in the achievement of the agreement between the theory and experiments. A comparison of the results of this paper with the results obtained in other papers is carried out. In particular, it is shown that the results of the papers where relativistic and radiative corrections were calculated within nonrelativistic QCD are overestimated by a factor of ~1.5.

Effects of unparticles on top spin correlation at the Large Hadron Collider

Masato Arai, Nobuchika Okada, and Karel Smolek

Published 21 April 2009 (10 pages)

074019 Full Text: PDF (456 kB) | Buy Article

+

Show Abstract

We study effects of the scale-invariant hidden sector, the unparticle, proposed by Georgi, on top spin correlation at the Large Hadron Collider. Assuming no flavor-changing interaction between the unparticles and the standard model particles, the top-antitop quark pair production process arises through virtual unparticle exchanges in the s channel, in addition to the standard model processes. In particular, we consider contributions of scalar and vector unparticles and find that these make sizable deviations of the top spin correlation from the standard model one.

B_s1(5830) and B_s2*(5840)

Zhi-Gang Luo (罗志刚), Xiao-Lin Chen (陈晓林), and Xiang Liu (刘翔)

Published 24 April 2009 (10 pages)

074020 Full Text: PDF (389 kB) | Buy Article

+

Show Abstract

In this paper we investigate the strong decays of the two newly observed bottom-strange mesons Bs1(5830) and Bs2^*(5840) in the framework of the quark pair creation model. The two-body strong decay widths of Bs1(5830)⁰-->B^*+K^- and Bs2^*(5840)⁰-->B⁺K^-, B^*+K^- are calculated by considering Bs1(5830) to be a mixture between |¹P1> and |³P1> states, and Bs2^*(5840) to be a |³P2> state. The double pion decay of Bs1(5830) and Bs2^*(5840) is supposed to occur via the intermediate state sigma and f0(980). Although the double pion decay widths of Bs1(5830) and Bs2^*(5840) are smaller than the two-body strong decay widths of Bs1(5830) and Bs2^*(5840), one suggests future experiments to search the double pion decays of Bs1(5830) and Bs2^*(5840) due to their sizable decay widths.

Some remarks on dipole showers and the DGLAP equation

Peter Skands and Stefan Weinzierl

Published 24 April 2009 (16 pages)

074021 Full Text: PDF (2447 kB) | Buy Article

+

Show Abstract

It has been argued recently that parton showers based on color dipoles conflict with collinear factorization and do not lead to the correct Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equation. We show that this conclusion is based on an inappropriate assumption, namely, the choice of the gluon energy as evolution variable. We further show numerically that Monte Carlo programs based on dipole showers with “infrared-sensible” evolution variables reproduce the DGLAP equation both in asymptotic form as well as in comparison to the leading behavior of second-order QCD matrix elements.

D_s inclusive decays

Michael Gronau and Jonathan L. Rosner

Published 27 April 2009 (12 pages)

074022 Full Text: PDF (170 kB) | Buy Article

+

Show Abstract

The availability of branching fractions for a large majority of Ds decays permits the prediction of inclusive branching fractions. This is achieved with the help of a modest amount of input from an isospin statistical model applied to nonresonant multibody Ds decays. A systematic uncertainty in these mostly small branching ratios is estimated by comparing predictions of this model with those of a model involving quark-antiquark pair production. The calculated inclusive branching fractions can be compared with data (for example, from a large sample of Ds⁺Ds^*-+Ds^*+Ds^- obtained by the CLEO Collaboration) and examined for specific final states which can shed light on strong and weak decay mechanisms.

Dynamical next-to-next-to-leading order parton distributions

P. Jimenez-Delgado and E. Reya

Published 27 April 2009 (15 pages)

074023 Full Text: PDF (1799 kB) | Buy Article

+

Show Abstract

Utilizing recent deep inelastic scattering measurements (sigmar,F2,3,L) and data on hadronic dilepton production we determine at next-to-next-to-leading order (NNLO) (3-loop) of QCD the dynamical parton distributions of the nucleon generated radiatively from valencelike positive input distributions at an optimally chosen low resolution scale (Q0²<1 GeV²). These are compared with “standard” NNLO distributions generated from positive input distributions at some fixed and higher resolution scale (Q0²>1 GeV²). Although the NNLO corrections imply in both approaches an improved value of chi², typically chiNNLO²~=0.9chiNLO², present deep inelastic scattering data are still not sufficiently accurate to distinguish between NLO results and the minute NNLO effects of a few percent, despite the fact that the dynamical NNLO uncertainties are somewhat smaller than the NLO ones and both are, as expected, smaller than those of their standard counterparts. The dynamical predictions for FL(x,Q²) become perturbatively stable already at Q²=2–3 GeV² where precision measurements could even delineate NNLO effects in the very small-x region. This is in contrast to the common standard approach but NNLO/NLO differences are here less distinguishable due to the larger 1sigma uncertainty bands. Within the dynamical approach we obtain alphas(MZ²)=0.1124±0.0020, whereas the somewhat less constrained standard fit gives alphas(MZ²)=0.1158±0.0035.

S-waves and the measurement of CP violating phases in B_s decays

S. Stone and L. Zhang

Published 29 April 2009 (5 pages)

074024 Full Text: PDF (1836 kB) | Buy Article

+

Show Abstract

Heavy, as yet undiscovered particles, can affect measurements of CP violation in the B system. Measuring CP violation in the Bs system provides an excellent place to observe such effects since standard model sources are predicted to produce very small effects. The angle -2betas, the “phase of Bs-[overline B]s mixing,” thought to be best measured in Bs-->J/psiphi decays is of order -0.04, while the CP violating asymmetry in Bs-->phiphi is predicted to be zero, due to the cancellation of the mixing phase with the decay phase. Recent measurements of betas in J/psiphi, while not definitive, are much larger than the standard model predictions. Measurements in the B⁰ and Ds⁺ systems of analogous modes point toward a 5–10% contamination of S-wave K⁺K^- under the phi peak. This S-wave was not taken into account in these recent analyses. Furthermore this S-wave can also materialize as a f0(980) meson that decays to pi⁺pi^-, making the final state J/psif0 useful for measuring betas with the added advantage of not requiring an angular analysis. Rate estimates, while not precise, predict four to five times fewer such events than those in the J/psiphi mode. The error on betas, however, may be similar. We also remark on S-wave problems with the Bs-->phiphi mode, and possible systematic checks using Bs-->phif0.

Sigma meson in QCD sum rules using a two-quark current with derivatives

Su Houng Lee, Kenji Morita, and Kazuaki Ohnishi

Published 30 April 2009 (5 pages)

074025 Full Text: PDF (163 kB) | Buy Article

+

Show Abstract

We study the sigma meson in QCD sum rules using a two-quark interpolating field with derivatives. In the constituent quark model, the sigma meson is composed of a quark and an antiquark in the relative p-wave state and is thus expected to have a larger overlap with an interpolating field that measures the derivative of the relative quark wave function. While the sum rule with a current without derivative gives a pole mass of around 1 GeV, the present sum rule with derivative current gives a mass of around 550 MeV and a width of 400 MeV, that could be identified with the sigma meson.

Radiative and leptonic decays of the pseudoscalar charmonium state eta_c

Mao-Zhi Yang

Published 30 April 2009 (9 pages)

074026 Full Text: PDF (229 kB) | Buy Article

+

Show Abstract

The radiative and leptonic decays of etac-->gammagamma and etac-->l⁺l^- are studied. For a etac-->gammagamma decay, the second-order electromagnetic tree-level diagram gives the leading contribution. The decay rate of etac-->gammagamma is calculated, the prediction is in good agreement with the experimental data. For etac-->l⁺l^-, both the tree and loop diagrams are calculated. The analysis shows that the loop contribution dominates; the contribution of tree diagram with a Z⁰ intermediate state can only modify the decay rate by less than 1%. The prediction of the branching ratios of etac-->e⁺e^- and µ⁺µ^- are very tiny within the standard model. The smallness of these predictions within the standard model makes the leptonic decays of etac sensitive to physics beyond the standard model. Measurement of the leptonic decay may give information about new physics.

Tensor charges of light baryons in the infinite momentum frame

Cédric Lorcé

Published 30 April 2009 (13 pages)

074027 Full Text: PDF (279 kB) | Buy Article

+

Show Abstract

We have used the chiral-quark soliton model formulated in the infinite momentum frame to investigate the octet, decuplet, and antidecuplet tensor charges up to the 5Q sector. Using flavor SU(3) symmetry we have obtained for the proton deltau=1.172 and deltad=-0.315 in fair agreement with previous model estimations. The 5Q contribution allowed us to estimate also the strange contribution to the proton tensor charge deltas=-0.011. All those values have been obtained at the model scale Q0²=0.36 GeV².

Effect of multiple Higgs fields on the phase structure of the SU(2)-Higgs model

Mark Wurtz, Randy Lewis, and T. G. Steele

Published 3 April 2009 (6 pages)

074501 Full Text: PDF (568 kB) | Buy Article

+

Show Abstract

The SU(2)-Higgs model, with a single Higgs field in the fundamental representation and a quartic self-interaction, has a Higgs region and a confinement region which are analytically connected in the parameter space of the theory; these regions thus represent a single phase. The effect of multiple Higgs fields on this phase structure is examined via Monte Carlo lattice simulations. For the case of N>=2 identical Higgs fields, there is no remaining analytic connection between the Higgs and confinement regions, at least when Lagrangian terms that directly couple different Higgs flavors are omitted. An explanation of this result in terms of enhancement from overlapping phase transitions is explored for N=2 by introducing an asymmetry in the hopping parameters of the Higgs fields. It is found that an enhancement of the phase transitions can still occur for a moderate (10%) asymmetry in the resulting hopping parameters.

Thermodynamics of free domain wall fermions

R. V. Gavai and Sayantan Sharma

Published 3 April 2009 (11 pages)

074502 Full Text: PDF (437 kB) | Buy Article

+

Show Abstract

Studying various thermodynamic quantities for the free domain wall fermions for both finite and infinite fifth dimensional extent N5, we find that the lattice corrections are minimal for NT>=10 for both energy density and susceptibility, for its irrelevant parameter M in the range 1.45–1.50. The correction terms are, however, quite large for small lattice sizes of NT<=8. We propose modifications of the domain wall operator, as well as the overlap operator, to reduce the finite cutoff effects to within 10% of the continuum results of the thermodynamic quantities for the currently used NT=6–8 lattices. Incorporating the chemical potential, we show that divergences proportional to µ²/a² are absent for a large class of such domain wall fermion actions although the chiral symmetry is broken for µ[not-equal]0 at any finite lattice spacing.

pipi scattering in twisted mass chiral perturbation theory

Michael I. Buchoff, Jiunn-Wei Chen, and André Walker-Loud

Published 8 April 2009 (7 pages)

074503 Full Text: PDF (168 kB) | Buy Article

+

Show Abstract

In this report we describe both I=2 and I=0 pipi scattering for twisted mass lattice QCD utilizing twisted mass chiral perturbation theory at next-to-leading order. Focusing on the lattice spacing (b) corrections, we demonstrate that in the exotic I=2, I3=±2 channels (pi^±pi^±), the leading scaling violations of pipi scattering at maximal twist begin at [script O](mpi²b²). This is not the case in any other isospin channel, for which the scaling violations at maximal twist begin at [script O](b²). Furthermore, we demonstrate the existence of a mixing between the I=2, I3=0 and I=0 scattering channels due to the breaking of isospin symmetry by the twisted mass term. The mixing term, although formally next-to-leading order, is relatively large, thus necessitating the use of a coupled channel analysis. We argue that this mixing likely renders the computation of the I=0 channel impractical with twisted mass lattice QCD.

Infrared behavior and Gribov ambiguity in SU(2) lattice gauge theory

V. G. Bornyakov, V. K. Mitrjushkin, and M. Müller-Preussker

Published 9 April 2009 (8 pages)

074504 Full Text: PDF (354 kB) | Buy Article

+

Show Abstract

For SU(2) lattice gauge theory, we study numerically the infrared behavior of the Landau-gauge ghost and gluon propagators with a special accent on the Gribov copy dependence. Applying a very efficient gauge-fixing procedure and generating up to 80 gauge copies, we find that the Gribov copy effect for both propagators is essential in the infrared. In particular, our best copy dressing function of the ghost propagator approaches a plateau in the infrared, while for the random first copy it continues to grow. Our best copy zero-momentum gluon propagator shows a tendency to decrease with growing lattice size, which excludes singular solutions. Our results seem compatible with the so-called decoupling solution with a nonsingular gluon propagator. However, we do not yet consider the Gribov copy problem to be resolved.

Baryon number, strangeness, and electric charge fluctuations in QCD at high temperature

M. Cheng, P. Hegde, C. Jung, F. Karsch, O. Kaczmarek, E. Laermann, R. D. Mawhinney, C. Miao, P. Petreczky, C. Schmidt, and W. Soeldner

Published 10 April 2009 (12 pages)

074505 Full Text: PDF (394 kB) | Buy Article

+

Show Abstract

We analyze baryon number, strangeness, and electric charge fluctuations as well as their correlations in QCD at high temperature. We present results obtained from lattice calculations performed with an improved staggered fermion action (p4 action) at two values of the lattice cutoff with almost physical up and down quark masses and a physical value for the strange quark mass. We compare these results, with an ideal quark gas at high temperature and a hadron resonance gas model at low temperature. We find that fluctuations and correlations are well described by the former already for temperatures about 1.5 times the transition temperature. At low temperature qualitative features of the lattice results are quite well described by a hadron resonance gas model. Higher order cumulants, which become increasingly sensitive to the light pions, however, show deviations from a resonance gas in the vicinity of the transition temperature.

Electromagnetic form factor of the pion from twisted-mass lattice QCD at N_f=2

R. Frezzotti, V. Lubicz, and S. Simula

Published 15 April 2009 (31 pages)

074506 Full Text: PDF (2482 kB) | Buy Article

+

Show Abstract

We present a lattice calculation of the electromagnetic form factor of the pion obtained using the tree-level Symanzik improved gauge action with two flavors of dynamical twisted Wilson quarks. The simulated pion masses range approximately from 260 to 580 MeV, and the lattice box sizes are chosen in order to guarantee that MpiL>~4. Accurate results for the form factor are obtained using all-to-all quark propagators evaluated by a stochastic procedure. The momentum dependence of the pion form factor is investigated up to values of the squared four-momentum transfer Q²~=0.8 GeV² and, thanks to the use of twisted boundary conditions, down to Q²~=0.05 GeV². Volume and discretization effects on the form factor appear to be within the statistical errors. Our results for the pion mass, decay constant and form factor are analyzed using (continuum) chiral perturbation theory at next-to-next-to-leading order. The extrapolated value of the pion charge radius is <r²>^phys=0.456±0.030stat±0.024syst in nice agreement with the experimental result. The extrapolated values of the pion form factor agree very well with the experimental data up to Q²~=0.8 GeV² within uncertainties which become competitive with the experimental errors for Q²>~0.3 GeV². The relevant low-energy constants appearing in the chiral expansion of the pion form factor are extracted from our lattice data, which come essentially from a single lattice spacing, adding the experimental value of the pion scalar radius in the fitting procedure. Our findings are in nice agreement with the available results of chiral perturbation theory analyses of pi-pi scattering data as well as with other analyses of our collaboration.

Strange baryon electromagnetic form factors and SU(3) flavor symmetry breaking

Huey-Wen Lin and Kostas Orginos

Published 20 April 2009 (16 pages)

074507 Full Text: PDF (1221 kB) | Buy Article

+

Show Abstract

We study the nucleon, Sigma and cascade octet baryon electromagnetic form factors and the effects of SU(3) flavor symmetry breaking from 2+1-flavor lattice calculations. We find that electric and magnetic radii are similar; the maximum discrepancy is about 10%. In the pion-mass region we explore, both the quark-component and full-baryon moments have small SU(3) symmetry breaking. We extrapolate the charge radii and the magnetic moments using three-flavor heavy-baryon chiral perturbation theory. The systematic errors due to chiral and continuum extrapolations remain significant, giving rise to charge radii for p and Sigma^- that are 3–4 standard deviations away from the known experimental ones. Within these systematics the predicted Sigma⁺ and Xi^- radii are 0.67(5) and 0.306(15) fm², respectively. When the next-to-next-to-leading order of heavy-baryon chiral perturbation theory is included, the extrapolated magnetic moments are less than 3 standard deviations away from Particle Data Group values, and the discrepancy is possibly due to remaining chiral and continuum extrapolation errors.

Lattice study of flavor SU(3) breaking in hyperon beta decay

Shoichi Sasaki and Takeshi Yamazaki

Published 20 April 2009 (24 pages)

074508 Full Text: PDF (901 kB) | Buy Article

+

Show Abstract

We present a quenched lattice calculation of all six form factors: vector [f1(q²)], weak-magnetism [f2(q²)], induced scalar [f3(q²)], axial-vector [g1(q²)], weak electricity [g2(q²)], and induce pseudoscalar [g3(q²)] form factors, in hyperon semileptonic decay Xi⁰-->Sigma⁺l[overline nu ] using domain wall fermions. The q² dependences of all form factors in the relatively low q² region are examined in order to evaluate their values at zero momentum transfer. The Xi⁰-->Sigma⁺ transition is highly sensitive to flavor SU(3) breaking since this decay corresponds to the direct analogue of neutron beta decay under the exchange of the down quark with the strange quark. The pattern of flavor SU(3) breaking effects in the hyperon beta decay is easily exposed in a comparison to results for neutron beta decay. We measure SU(3)-breaking corrections to f1(0), f2(0)/f1(0), and g1(0)/f1(0). A sign of the leading-order corrections, of which the size is less than a few percent, on f1(0) is likely negative, while f2(0)/f1(0) and g1(0)/f1(0) receive positive corrections of order 16% and 5%, respectively. The observed pattern of the deviation from the values in the exact SU(3) limit does not support some of the model estimates. We show that there are nonzero second-class form factors in the Xi⁰-->Sigma⁺ decay, measuring f3(0)/f1(0)=0.14(9) and g2(0)/g1(0)=0.68(18), which are comparable to the size of first-order SU(3) breaking. It is also found that the SU(3) breaking effect on g3(0)/g1(0) agrees with the prediction of the generalized pion-pole dominance.

Pseudoscalar-meson-octet-baryon coupling constants in two-flavor lattice QCD

Güray Erkol, Makoto Oka, and Toru T. Takahashi

Published 24 April 2009 (6 pages)

074509 Full Text: PDF (378 kB) | Buy Article

+

Show Abstract

We evaluate the piNN, piSigmaSigma, piLambdaSigma, KLambdaN and KSigmaN coupling constants and the corresponding monopole masses in lattice QCD with two flavors of dynamical quarks. The parameters representing the SU(3)-flavor symmetry are computed at the point where the three quark flavors are degenerate at the physical s-quark mass. In particular, we obtain alpha[equivalent]F/(F+D)=0.395(6). The quark-mass dependences of the coupling constants are obtained by changing the u- and the d-quark masses. We find that the SU(3)-flavor parameters have weak quark-mass dependence and thus the SU(3)-flavor symmetry is broken by only a few percent at each quark-mass point we consider.

Lattice study of the vacuum polarization function and determination of the strong coupling constant

E. Shintani et al. (JLQCD and TWQCD Collaboration)

Published 30 April 2009 (11 pages)

074510 Full Text: PDF (533 kB) | Buy Article

+

Show Abstract

We calculate the vacuum polarization functions on the lattice using the overlap fermion formulation. By matching the lattice data at large momentum scales with the perturbative expansion supplemented by the operator product expansion (OPE), we extract the strong coupling constant alphas(µ) in two-flavor QCD as Lambda[overline MS]⁽²⁾=0.234(9)(((+16)/(-0))) GeV, where the errors are statistical and systematic, respectively. In addition, from the analysis of the difference between the vector and axial-vector channels, we obtain some of the four-quark condensates.

Broken electroweak phase at high temperature in the littlest Higgs model with T parity

S. Aziz, B. Ghosh, and G. Dey

Published 1 April 2009 (10 pages)

075001 Full Text: PDF (1675 kB) | Buy Article

+

Show Abstract

We have examined in detail the nonrestoration of symmetry at high temperature in a finite-temperature littlest Higgs model, without and with T parity, by evaluating the one-loop-order finite-temperature integrals of the effective potential numerically, without the high-temperature approximation T>>mi. We observe that in the model without T parity it is not possible to find a transition temperature within the allowed temperature range of the model (0<T<4f) if the UV completion factors are those which give the standard model electroweak minimum, as the effective potential always increases with temperature in the positive direction. However, in the case of the model with T parity, it is possible to find a transition temperature with the same set of UV completion factors, as, with the increase of temperature, the effective potential decreases in magnitude in the positive side, becomes negative, and increases in magnitude in the negative side, indicating symmetry breaking at high temperature. This type of symmetry nonrestoration at high temperature has been observed earlier in some models involving pseudo-Nambu-Goldstone bosons. The behavior of the global structure of the effective potential with T parity in the theory indicates a strong first-order electroweak phase transition, conducive to baryogenesis in the early Universe.

Theoretical framework for R-parity violation

Minoru Kurimaya, Hiroto Nakajima, and Taizan Watari

Published 3 April 2009 (43 pages)

075002 Full Text: PDF (1443 kB) | Buy Article

+

Show Abstract

We propose a theoretical framework for R-parity violation. It is realized by a class of Calabi-Yau compactification of heterotic string theory. Trilinear R-parity violation in superpotential is either absent or negligibly small without an unbroken symmetry, due to a selection rule based on charge counting of a spontaneously broken U(1) symmetry. Although such a selection rule cannot be applied in general to nonrenormalizable operators in the low-energy effective superpotential, it is valid for terms trilinear in low-energy degrees of freedom, and hence can be used as a solution to the dimension-4 proton decay problem in the minimal supersymmetric standard model. Bilinear R-parity violation is generated, but there are good reasons why it is small enough to satisfy its upper bounds from neutrino mass and washout of baryon/lepton asymmetry. All R-parity violating dimension-5 operators can be generated. In this theoretical framework, nucleons can decay through squark-exchange diagrams combining dimension-5 and bilinear R-parity violating operators. B-L breaking neutron decay is predicted.

Realistic composite Higgs models

Charalampos Anastasiou, Elisabetta Furlan, and José Santiago

Published 3 April 2009 (16 pages)

075003 Full Text: PDF (467 kB) | Buy Article

+

Show Abstract

We study the role of fermionic resonances in realistic composite Higgs models. We consider the low energy effective description of a model in which the Higgs arises as the pseudo-Goldstone boson of an SO(5)/SO(4) global symmetry breaking pattern. Assuming that only fermionic resonances are present below the cutoff of our effective theory, we perform a detailed analysis of the electroweak constraints on such a model. This includes the exact one-loop calculation of the T parameter and the anomalous ZbL[overline b]L coupling for arbitrary new fermions and couplings. Other relevant observables like b-->sgamma and DeltaB=2 processes have also been examined. We find that, while minimal models are difficult to make compatible with electroweak precision tests, models with several fermionic resonances, such as the ones that appear in the spectrum of viable composite Higgs models from warped extra dimensions, are fully realistic in a large region of parameter space. These fermionic resonances could be the first observable signature of the model at the CERN LHC.

Generalized bottom-up holography and walking technicolor

Dennis D. Dietrich and Chris Kouvaris

Published 6 April 2009 (11 pages)

075004 Full Text: PDF (263 kB) | Buy Article

+

Show Abstract

In extradimensional holographic approaches the flavor symmetry is gauged in the bulk, that is, treated as a local symmetry. Imposing such a local symmetry admits fewer terms coupling the (axial) vectors and (pseudo)scalars than if a global symmetry is imposed. The latter is the case in standard low-energy effective Lagrangians. Here we incorporate these additional, a priori only globally invariant terms into a holographic treatment by means of a Stückelberg completion. This work was motivated by our investigations concerning dynamical electroweak symmetry breaking by walking technicolor and we apply our findings to these theories.

Supersymmetric B-L dark matter model and the observed anomalies in the cosmic rays

Rouzbeh Allahverdi, Bhaskar Dutta, Katherine Richardson-McDaniel, and Yudi Santoso

Published 8 April 2009 (5 pages)

075005 Full Text: PDF (614 kB) | Buy Article

+

Show Abstract

We propose a simple model of supersymmetric dark matter that can explain recent results from PAMELA and ATIC experiments. It is based on a U(1)B-L extension of the minimal supersymmetric standard model. The dark matter particle is a linear combination of the U(1)B-L gaugino and Higgsino partners of Higgs fields that break the B-L around 1 TeV. The dominant mode of dark matter annihilation is to the lightest of the new Higgs fields, which has a mass in the GeV range, and its subsequent decay mainly produces taus or muons by the virtue of B-L charges. This light Higgs also results in Sommerfeld enhancement of the dark matter annihilation cross section, which can be >~10³. For a dark matter mass in the 1–2 TeV range, the model provides a good fit to the PAMELA data and a reasonable fit to the ATIC data. We also briefly discuss the prospects of this model for direct detection experiments and the LHC.

Double-lepton polarization asymmetries in B_s-->phi[script-l]⁺[script-l]^- decay in the fourth-generation standard model

S. M. Zebarjad, F. Falahati, and H. Mehranfar

Published 9 April 2009 (15 pages)

075006 Full Text: PDF (756 kB) | Buy Article

+

Show Abstract

In this paper, we investigate the effects of the fourth generation of quarks on the double-lepton polarization asymmetries in the Bs-->phi[script-l]⁺[script-l]^- decay. It is shown that most of these asymmetries in Bs-->phi[script-l]⁺[script-l]^- are quite sensitive to the fourth-generation parameters. We also compare these asymmetries with those of B-->K[script-l]⁺[script-l]^- decay and show that <PLT>, <PTL>, <PNN>, and <PTT> in Bs-->phitau⁺tau^- decay are more sensitive to the fourth-generation parameters in comparison with those of B-->Ktau⁺tau^- decay. We conclude that an efficient way to establish the existence of the fourth generation of quarks could be the study of these asymmetries in the Bs-->phi[script-l]⁺[script-l]^- decay.

Angular distributions as a probe of anomalous ZZH and gammaZH interactions at a linear collider with polarized beams

Saurabh D. Rindani and Pankaj Sharma

Published 10 April 2009 (11 pages)

075007 Full Text: PDF (320 kB) | Buy Article

+

Show Abstract

We examine the contribution of general Z^*ZH and gamma^*ZH three-point interactions arising from new physics to the Higgs production process e⁺e^--->HZ. From Lorentz covariance, each of these vertices may be written in terms of three (complex) form factors, whose real and imaginary parts together make six independent couplings. We take into account possible longitudinal or transverse beam polarization likely to be available at a linear collider. We show how partial cross sections and angular asymmetries in suitable combinations with appropriate beam polarizations can be used to disentangle various couplings from one another. A striking result is that using transverse polarization, one of the gammaZH couplings, not otherwise accessible, can be determined independently of all other couplings. Transverse polarization also helps in the independent determination of a combination of two other couplings, in contrast to a combination of four accessible with unpolarized or longitudinally polarized beams. We also obtain the sensitivity of the various observables in constraining the new-physics interactions at a linear collider operating at a center-of-mass energy of 500 GeV with longitudinal or transverse polarization.

Dark matter through the axion portal

Yasunori Nomura and Jesse Thaler

Published 15 April 2009 (6 pages)

075008 Full Text: PDF (115 kB) | Buy Article

+

Show Abstract

Motivated by the galactic positron excess seen by PAMELA and ATIC/PPB-BETS, we propose that dark matter is a TeV-scale particle that annihilates into a pseudoscalar “axion.” The positron excess and the absence of an antiproton or gamma ray excess constrain the axion mass and branching ratios. In the simplest realization, the axion is associated with a Peccei-Quinn symmetry, in which case it has a mass around 360–800 MeV and decays into muons. We present a simple and predictive supersymmetric model implementing this scenario, where both the Higgsino and dark matter obtain masses from the same source of TeV-scale spontaneous symmetry breaking.

Gauge coupling unification in the minimal supersymmetric standard model plus five flavors

Jeff L. Jones

Published 15 April 2009 (11 pages)

075009 Full Text: PDF (430 kB) | Buy Article

+

Show Abstract

We investigate gauge coupling unification at 2-loops for theories with 5 extra vectorlike SU(5) fundamentals added to the minimal supersymmetric standard model (MSSM). This is a borderline case where unification is only predicted in certain regions of parameter space. We establish a lower bound on the scale for the masses of the extra flavors, as a function of the sparticle masses. Models far outside of the bound do not predict unification at all (but may be compatible with unification), and models outside but near the boundary cannot reliably claim to predict it with an accuracy comparable to the MSSM prediction. Models inside the boundary can work just as well as the MSSM.

Bottom-up reconstruction scenarios for (un)constrained MSSM parameters at the CERN LHC

J.-L. Kneur and N. Sahoury

Published 16 April 2009 (36 pages)

075010 Full Text: PDF (3446 kB) | Buy Article

+

Show Abstract

We consider some specific inverse problem or “bottom-up” reconstruction strategies at the CERN LHC for both general and constrained minimal supersymmetric standard model (MSSM) parameters, starting from a plausibly limited set of sparticle identification and mass measurements, using mainly gluino/squark cascade decays, plus eventually the lightest Higgs boson mass. For the three naturally separated sectors of gaugino/Higgsino, squark/slepton, and Higgs parameters, we examine different step-by-step algorithms based on rather simple, entirely analytical, inverted relations between masses and basic MSSM parameters. This includes also reasonably good approximations of some of the relevant radiative correction calculations. We distinguish the constraints obtained for a general MSSM from those obtained with universality assumptions in the three different sectors. Our results are compared at different stages with the determination from more standard “top-down” fit of models to data, and finally combined into a global determination of all the relevant parameters. Our approach gives complementary information to more conventional analysis, and is not restricted to the specific LHC measurement specificities. In addition, the bottom-up renormalization group evolution of general MSSM parameters, being an important ingredient in this framework, is illustrated as a new publicly available option of the MSSM spectrum calculation code SuSpect.

Discriminating between technicolor and warped extra dimensional model via pp-->ZZ channel

O. Antipin and K. Tuominen

Published 17 April 2009 (11 pages)

075011 Full Text: PDF (219 kB) | Buy Article

+

Show Abstract

We explore the possibility to discriminate between certain strongly coupled technicolor (TC) models and warped extra dimensional models where the standard model fields are propagating in the extra dimension. We consider a generic QCD-like TC model with running coupling as well as two TC models with walking dynamics. We argue that, due to the different production mechanisms for the lowest-lying composite tensor state in these TC theories compared to the first Kaluza-Klein graviton mode of the warped extra dimensional case, it is possible to distinguish between these models based on the angular analysis of the reconstructed longitudinal Z bosons in the pp-->ZZ-->4 charged leptons channel.

Unparticles in diphoton production to next-to-leading order in QCD at the LHC

M. C. Kumar, Prakash Mathews, V. Ravindran, and Anurag Tripathi

Published 20 April 2009 (7 pages)

075012 Full Text: PDF (270 kB) | Buy Article

+

Show Abstract

We compute to next-to-leading order in QCD the tensor unparticle contribution to the diphoton production at the LHC, wherein the unparticle sector is a consequence of (a) scale invariance but not full conformal invariance and (b) conformal invariance. We use the semianalytical two cutoff phase-space slicing method to handle the [script O](alphas) corrections to the pp-->gammagammaX and show that our results are insensitive to the soft and collinear cutoffs. In order to avoid the contribution of the photons due to fragmentation, we employ the smooth cone isolation criterion. Significance of the QCD corrections to the diphoton events including unparticles is highlighted.

Precision measurements of little Higgs parameters at the International Linear Collider

Eri Asakawa, Masaki Asano, Keisuke Fujii, Tomonori Kusano, Shigeki Matsumoto, Rei Sasaki, Yosuke Takubo, and Hitoshi Yamamoto

Published 20 April 2009 (12 pages)

075013 Full Text: PDF (627 kB) | Buy Article

+

Show Abstract

We investigate the possibility of precision measurements for parameters of the littlest Higgs model with T parity at the International Linear Collider. The model predicts new gauge bosons (AH, ZH, and WH), among which the heavy photon (AH) is a candidate for dark matter. The masses of these new gauge bosons strongly depend on the vacuum expectation value that breaks a global symmetry of the model. Through Monte Carlo simulations of the processes, e⁺e^--->AHZH and e⁺e^--->WH⁺WH^-, we show how precisely the masses can be determined at the International Linear Collider for a representative parameter point of the model. We also discuss the determination of the little Higgs parameters and their impact on the future measurement of the thermal abundance of the dark matter relics in our Universe.

Light scalar as the messenger of electroweak and flavor symmetry breaking

J. D. Lykken, Z. Murdock, and S. Nandi

Published 20 April 2009 (14 pages)

075014 Full Text: PDF (483 kB) | Buy Article

+

Show Abstract

We propose a new framework for understanding the hierarchies of fermion masses and mixings. The masses and mixings of all standard model (SM) charged fermions other than top arise from higher dimensional operators involving a messenger scalar S and flavon scalars Fi. The flavons spontaneously break SM flavor symmetries at around the TeV scale. The SM singlet scalar S couples directly to the Higgs H and spontaneously breaks another U(1) at the electroweak scale. At the TeV scale, SM quarks and charged leptons have renormalizable couplings to S, but not to H or Fi. These couplings involve new heavy vectorlike fermions. Integrating out these fermions produces a pattern of higher dimensional operators that reproduce the observed hierarchies of the SM masses and mixings in terms of powers of the “little hierarchy”: the ratio of the electroweak scale to the flavor-breaking scale. The framework has important phenomenological implications. Flavor-changing neutral currents are within experimental limits but D⁰-[overline D]⁰ mixing and Bs-->µ⁺µ^- could be close to current sensitivities. The neutral scalar s of the messenger field mixes with the light Higgs of the SM, which can have strong effects on Higgs decay branching fractions. The s mass eigenstate may be lighter than the Higgs, and could be detected at the Tevatron or the LHC.

Complete Michel parameter analysis of the inclusive semileptonic b-->c transition

Benjamin Dassinger, Robert Feger, and Thomas Mannel

Published 20 April 2009 (12 pages)

075015 Full Text: PDF (229 kB) | Buy Article

+

Show Abstract

We perform a complete “Michel parameter” analysis of all possible helicity structures which can appear in the process B-->Xc[script-l][overline nu ][script-l]. We take into account the full set of operators parametrizing the effective Hamiltonian and include the complete one-loop QCD corrections as well as the nonperturbative contributions. The moments of the leptonic energy as well as the combined moments of the hadronic energy and hadronic invariant mass are calculated including the nonstandard contributions.

Z-->b[overline b] and chiral currents in Higgsless models

Tomohiro Abe, R. Sekhar Chivukula, Neil D. Christensen, Ken Hsieh, Shinya Matsuzaki, Elizabeth H. Simmons, and Masaharu Tanabashi

Published 21 April 2009 (14 pages)

075016 Full Text: PDF (530 kB) | Buy Article

Article Lookup:

A new free weekly publication from APS

SELECTED ARTICLES (0)

SELECTED ARTICLES (0)

Physical Review D

April 2009

Volume 79, Number 7 , Articles (07xxxx)

RAPID COMMUNICATIONS

ARTICLES