Physical Review D

We study the decay B^--->DK^*- using a sample of 379×10⁶ Upsilon(4S)-->B[overline B] events collected with the BABAR detector at the PEP-II B factory. We perform a Gronau-London-Wyler analysis where the D meson decays into either a CP-even (CP+) eigenstate (K⁺K^-, pi⁺pi^-), CP-odd (CP-) eigenstate (KS⁰pi⁰, KS⁰phi, KS⁰omega) or a non-CP state (K^-pi⁺). We also analyze D meson decays into K⁺pi^- from a Cabibbo-favored [overline D]⁰ decay or doubly suppressed D⁰ decay [Atwood-Dunietz-Soni (ADS) analysis]. We measure observables that are sensitive to the Cabibbo-Kobayashi-Maskawa angle gamma: the partial-rate charge asymmetries [script A]CP±, the ratios [script R]CP± of the B-decay branching fractions in CP± and non-CP decay, the ratio [script R]ADS of the charge-averaged branching fractions, and the charge asymmetry [script A]ADS of the ADS decays: [script A]CP+=0.09±0.13±0.06, [script A]CP-=-0.23±0.21±0.07, [script R]CP+=2.17±0.35±0.09, [script R]CP-=1.03±0.27±0.13, [script R]ADS=0.066±0.031±0.010, and [script A]ADS=-0.34±0.43±0.16, where the first uncertainty is statistical and the second is systematic. Combining all the measurements and using a frequentist approach yields the magnitude of the ratio between the Cabibbo-suppressed and favored amplitudes, rB=0.31 with a one (two) sigma confidence level interval of [0.24, 0.38] ([0.17, 0.43]). The value rB=0 is excluded at the 3.3 sigma level. A similar analysis excludes values of gamma in the intervals [0, 7]°, [55, 111]°, and [175, 180]° ([85, 99]°) at the one (two) sigma confidence level.

The potential for a precise measurement of the unitarity triangle angle gamma in future experiments from the decay B⁰-->DK^*0 is well known. It has recently been suggested that the sensitivity can be significantly enhanced by analyzing the B⁰-->DK⁺pi^- Dalitz plot to extract amplitudes relative to those of the flavor-specific decay B⁰-->D2^*-K⁺. An extension to this method which includes the case where the neutral D meson is reconstructed in suppressed final states is presented. The sensitivity to gamma is estimated using this method and compared to that obtained using the B⁰-->DK^*0 decay alone. Experimental effects, such as background contamination, are also considered. This approach appears to be a highly attractive addition to the family of methods that can be used to determine gamma.

A careful reanalysis of both Argonne National Laboratory and Brookhaven National Laboratory data for weak single pion production is done. We consider deuteron nuclear effects and normalization (flux) uncertainties in both experiments. We demonstrate that these two sets of data are in good agreement. For the dipole parametrization of C5^A(Q²), we obtain C5^A(0)=1.19±0.08, MA=0.94±0.03 GeV. As an application we present the discussion of the uncertainty of the neutral current 1pi⁰ production cross section, important for the T2K neutrino oscillation experiment.

We investigate the weak nonleptonic decays of Lambdac⁺, Xic⁺, and Xic⁰ into the octet baryons (J^P=1/2⁺) and axial-vector mesons (J^P=1⁺) employing the factorization scheme for W-emission diagrams and the pole model for W-exchange contributions. Determining the baryon-baryon transition form factors in the nonrelativistic quark model and incorporating the constraints of heavy quark symmetry, we predict their branching ratios and asymmetry parameters.

We compute the next-to-leading order QCD corrections to the production of W bosons in association with three jets at the Tevatron in the leading color approximation, which we define by considering the number of colors and the number of light flavors as being of the same order of magnitude. The theoretical uncertainty in the next-to-leading order prediction for the cross section is of the order of 15%–25% which is a significant improvement compared to the leading order result.

The cosmic ray interaction event generator Sibyll is widely used in extensive air shower simulations. We describe in detail the properties of Sibyll 2.1 and the differences with the original version 1.7. The major structural improvements are the possibility to have multiple soft interactions, introduction of new parton density functions, and an improved treatment of diffraction. Sibyll 2.1 gives better agreement with fixed target and collider data, especially for the inelastic cross sections and multiplicities of secondary particles. Shortcomings and suggestions for future improvements are also discussed.

We perform a chi² analysis of nuclear parton distribution functions (NPDFs) using neutral current charged-lepton ([script-l]^±A) deeply inelastic scattering (DIS), and Drell-Yan data for several nuclear targets. The nuclear A dependence of the NPDFs is extracted in a next-to-leading order fit. We compare the nuclear corrections factors (F2^Fe/F2^D) for this charged-lepton data with other results from the literature. In particular, we compare and contrast fits based upon the charged-lepton DIS data with those using neutrino-nucleon DIS data.

We introduce a toy model implementing the proposal of using a custodial symmetry to protect the ZbL[overline b]L coupling from large corrections. This “doublet-extended standard model” adds a weak doublet of fermions (including a heavy partner of the top quark) to the particle content of the standard model in order to implement an O(4)×U(1)X~SU(2)L×SU(2)R×PLR×U(1)X symmetry in the top-quark mass generating sector. This symmetry is softly broken to the gauged SU(2)L×U(1)Y electroweak symmetry by a Dirac mass M for the new doublet; adjusting the value of M allows us to explore the range of possibilities between the O(4)-symmetric (M-->0) and standard-model-like (M-->[infinity]) limits. In this simple model, we find that the experimental limits on the ZbL[overline b]L coupling favor smaller M while the presence of a potentially sizable negative contribution to alphaT strongly favors large M. Comparison with precision electroweak data shows that the heavy partner of the top quark must be heavier than about 3.4 TeV, making it difficult to search for at LHC. This result demonstrates that electroweak data strongly limit the amount by which the custodial symmetry of the top-quark mass generating sector can be enhanced relative to the standard model. Using an effective field theory calculation, we illustrate how the leading contributions to alphaT, alphaS, and the ZbL[overline b]L coupling in this model arise from an effective operator coupling right-handed top quarks to the Z boson, and how the effects on these observables are correlated. We contrast this toy model with extradimensional models in which the extended custodial symmetry is invoked to control the size of additional contributions to alphaT and the ZbL[overline b]L coupling, while leaving the standard model contributions essentially unchanged.

A secluded U(1) sector with weak admixture to photons, O(10^-2-10^-3), and the scale of the breaking below 1 GeV represents a natural yet poorly constrained extension of the standard model. We analyze g-2 of muons and electrons together with other precision QED data, as well as radiative decays of strange particles to constrain the mass-mixing angle (mV-kappa) parameter space. We point out that mV~=214 MeV and kappa²>3×10^-5 can be consistent with the hypothesis of the HyperCP Collaboration, which seeks to explain the anomalous energy distribution of muon pairs in the Sigma⁺-->pµ⁺µ^- process by a resonance, without direct contradiction to the existing data on radiative kaon decays. The same parameters lead to an O(few×10^-9) upward correction to the anomalous magnetic moment of the muon, possibly relaxing some tension between the experimental value and theoretical determinations of g-2. The ultrafine energy resolution scan of the e⁺e^--->µ⁺µ^- cross section and dedicated analysis of lepton spectra from K⁺-->pi⁺e⁺e^- decays should be able to provide a conclusive test of this hypothesis and improve the constraints on the model.

We calculate the relic density of the lightest neutralino in a supersymmetric seesaw type-II (“triplet seesaw”) model with minimal supergravity boundary conditions at the grand unified theory (GUT) scale. The presence of a triplet below the GUT scale, required to explain measured neutrino data in this setup, leads to a characteristic deformation of the sparticle spectrum with respect to the pure minimal supergravity (mSUGRA) expectations, affecting the calculated relic dark matter (DM) density. We discuss how the DM allowed regions in the (m0,M1/2) plane change as a function of the (type-II) seesaw scale. We also compare the constraints imposed on the models parameter space form upper limits on lepton flavor violating decays to those imposed by DM. Finally, we briefly comment on uncertainties in the calculation of the relic neutralino density due to uncertainties in the measured top and bottom masses.

We study the effect of soft gluon emission in the hadroproduction of gluino-gluino and squark-antisquark pairs at the next-to-leading logarithmic accuracy within the framework of the minimal supersymmetric model. We present the calculation of the one-loop soft anomalous dimension matrices controlling the color evolution of the underlying hard-scattering processes. The numerical results for resummed cross sections for proton-proton collisions at the Large Hadron Collider are discussed in detail.

We combine the analyses for flavor changing neutral current processes and dark matter solutions in minimal-type supersymmetric grand unified theory models, SO(10) and SU(5), with a large Bs-[overline B]s mixing phase and large tanbeta. For large tanbeta, the double-penguin diagram dominates the supersymmetry contribution to the Bs-[overline B]s mixing amplitude. Also, the Br(Bs-->µµ) constraint becomes important as it grows as tan⁶beta, although it can still be suppressed by a large pseudoscalar Higgs mass mA. We investigate the correlation between Bs-->µµ and the dark matter direct detection cross section through their dependence on mA. In the minimal-type of SU(5) with type I seesaw, the large mixing in neutrino Dirac couplings results in a large lepton flavor violating decay process tau-->µgamma, which in turn sets the upper bound on mA. In the SO(10) case, the large mixing can be chosen to be in the Majorana couplings instead, and the constraint from Br(tau-->µgamma) can be avoided. The heavy Higgs funnel region turns out to be an interesting possibility in both cases and the direct dark matter detection should be possible in the near future in these scenarios.

We construct a model of an unparticle sector consisting of a supersymmetric SU(N) gauge theory with the number of flavors in the Seiberg conformal window. We couple this sector to the minimal supersymmetric standard model via heavy messengers. The resulting low energy theory has a Higgs coupling to unparticles. The Higgs vev drives the hidden Seiberg sector to a new conformal fixed point. The coupling to the Higgs mediates supersymmetry breaking to the Seiberg sector, and breaks conformal invariance at a lower scale. The low energy theory contains light stable and metastable mesons. Higgs decay into this sector gives signatures which are similar to those of “hidden valley” models. Decays of the lightest superpartner of standard model particles into the hidden sector reveal potentially observable unparticle kinematics.

The exchange of electroweak gauginos in the t or u channel allows squark pair production at hadron colliders without color exchange between the squarks. This can give rise to events where little or no energy is deposited in the detector between the squark decay products. We discuss the potential for detection of such rapidity-gap events at the Large Hadron Collider. Our numerical analysis is divided into two parts. First, we evaluate in a simplified framework the rapidity-gap signal at the parton level. The second part covers an analysis with full event simulation using PYTHIA as well as Herwig++, but without detector simulation. We analyze the transverse energy deposited between the jets from squark decay, as well as the probability of finding a third jet in between the two hardest jets. For the minimal supergravity benchmark point SPS1a we find statistically significant evidence for a color-singlet exchange contribution. The systematical differences between current versions of PYTHIA and HERWIG++ are larger than the physical effect from color-singlet exchange; however, these systematic differences could be reduced by tuning both Monte Carlo generators on normal QCD dijet data.

Although gauge-boson propagators in asymptotically-free gauge theories satisfy a dispersion relation, they do not satisfy the Källen-Lehmann (KL) representation because the spectral function changes sign. We argue that this is a simple consequence of asymptotic freedom. On the basis of the QED-like Ward identities of the pinch technique (PT) we claim that the product of the coupling g² and the scalar part d^(q²) of the PT propagator, which is both gauge invariant and renormalization-group invariant, can be factored into the product of the running charge [overline g]²(q²) and a term H^(q²) both of which satisfy the KL representation although their product does not. We show that this behavior is consistent with some simple analytic models that mimic the gauge-invariant PT Schwinger-Dyson equations (SDE), provided that the dynamic gauge-boson mass is sufficiently large. The PT SDEs do not depend directly on the PT propagator through d^ but only through H^.

We determine the first independent part of the g⁶ coefficient in the weak coupling expansion of the QCD pressure at high temperatures, the one proportional to the maximal power of the number of quark flavors Nf. In addition to introducing and developing computational methods that can be used in evaluating other parts of the expansion, our calculation provides a result that becomes dominant in the limit of large Nf and a fixed effective coupling geff²[equivalent]g²Nf/2.