A new free weekly publication from APS

Physics - A new free weekly publication from APS
Please visit physics.aps.org
 

SELECTED ARTICLES (0)

Physical Review C

(Nuclear Physics)

November 2009

Volume 80, Number 5 , partial issue

Click on icons for further information Rapid Communication icon   Physics Viewpoint icon   Focus icon   Free to Read icon

Rapid Communication icon  Rapid Communication
     Close

     Close
Physics Viewpoint icon  Physics Viewpoint
Selected for a Viewpoint in Physics. Please visit http://physics.aps.org/.
     Close
Focus icon  Featured in Phys. Rev. Focus
Please visit http://focus.aps.org.
     Close
Free to Read icon  Free to Read
Marks articles whose full text is available without a subscription. See the FREE TO READ FAQ.
     Close

RAPID COMMUNICATIONS
Rapid

Interaction current in pp-->ppgamma
K. Nakayama and H. Haberzettl
Published 11 November 2009 (5 pages)
051001(R)  Full Text: PDF (240 kB)  | Buy Article
+
Show Abstract
The nucleon-nucleon bremsstrahlung reaction is investigated based on a fully gauge-invariant relativistic meson-exchange model approach. To account consistently for the complicated part of the interaction current (which at present is too demanding to be calculated explicitly), a generalized contact current is introduced following the approach of H. Haberzettl, K. Nakayama, and S. Krewald [Phys. Rev. C 74, 045202 (2006)]. The contact interaction current is constructed phenomenologically such that the resulting full bremsstrahlung amplitude satisfies the generalized Ward-Takahashi identity. The formalism is applied to describe the high-precision proton-proton bremsstrahlung data at 190 MeV obtained at KVI [H. Huisman et al., Phys. Rev. C 65, 031001(R) (2002)]. The present results show good agreement with the data, thus removing the long-standing discrepancy between the theoretical predictions and experimental data. The present investigation, therefore, points to the importance of properly taking into account the interaction current for this reaction.
Rapid

Gamow shell-model calculations of drip-line oxygen isotopes
K. Tsukiyama, M. Hjorth-Jensen, and G. Hagen
Published 4 November 2009 (5 pages)
051301(R)  Full Text: PDF (200 kB)  | Buy Article
+
Show Abstract
We employ the Gamow shell model (GSM) to describe low-lying states of the oxygen isotopes 24O and 25O. The many-body Schrödinger equation is solved starting from a two-body Hamiltonian defined by a renormalized low-momentum nucleon-nucleon (NN) interaction and a spherical Berggren basis. The Berggren basis treats bound, resonant, and continuum states on an equal footing and is therefore an appropriate representation of loosely bound and unbound nuclear states near threshold. We show that the inclusion of continuum effects has a significant effect on the low-lying 1+ and 2+ excited states in 24O. On the other hand, we find that a correct description of binding energy systematics of the ground states is driven by the proper treatment and inclusion of many-body correlation effects. This is supported by the fact that we get 25O unstable with respect to 24O in both oscillator and Berggren representations starting from a 22O core. Furthermore, we show that the structure of these loosely bound or unbound isotopes is strongly influenced by the 1S0 component of the NN interaction. This has important consequences for our understanding of nuclear stability.
Rapid

Precision test of the isobaric multiplet mass equation for the A=32, T=2 quintet
A. A. Kwiatkowski, B. R. Barquest, G. Bollen, C. M. Campbell, D. L. Lincoln, D. J. Morrissey, G. K. Pang, A. M. Prinke, J. Savory, S. Schwarz, C. M. Folden III, D. Melconian, S. K. L. Sjue, and M. Block
Published 9 November 2009 (4 pages)
051302(R)  Full Text: PDF (217 kB)  | Buy Article
+
Show Abstract
Masses of the radionuclides 32,33Si and 34P and of the stable nuclides 32S and 31P have been measured with the Low Energy Beam and Ion Trap (LEBIT) Penning trap mass spectrometer. Relative mass uncertainties as low as 3×10-9 have been achieved. The measured mass value of 32Si differs from the literature value by four standard deviations. The precise mass determination of 32Si and 32S have been employed to test the validity of the quadratic form of the isobaric multiplet mass equation (IMME) for the most well known A=32, T=2 isospin quintet. The new experimental results indicate a dramatic breakdown of the model.
Rapid

Microscopic calculation of alpha-decay half-lives with a deformed potential
Dongdong Ni and Zhongzhou Ren
Published 12 November 2009 (5 pages)
051303(R)  Full Text: PDF (276 kB)  | Buy Article
+
Show Abstract
A new version of the generalized density-dependent cluster model is presented to describe an alpha particle tunneling through a deformed potential barrier. The microscopic deformed potential is numerically constructed in the double-folding model by the multipole expansion method. The decay width is computed using the coupled-channel Schrödinger equation with outgoing wave boundary conditions. We perform a systematic calculation on alpha-decay half-lives of even-even nuclei ranging from Z=52 to Z=104, including 65 well-deformed ones. The calculated alpha-decay half-lives are found to be in good agreement with the experimental values. There also exists good agreement with the available experimental branching ratios for well-deformed systems.
Rapid

Four-body continuum-discretized coupled-channels calculations
M. Rodríguez-Gallardo, J. M. Arias, J. Gómez-Camacho, A. M. Moro, I. J. Thompson, and J. A. Tostevin
Published 2 November 2009 (5 pages)
051601(R)  Full Text: PDF (382 kB)  | Buy Article
+
Show Abstract
The development of a continuum-bin scheme of discretization for three-body projectiles is necessary for studies of reactions of Borromean nuclei such as 6He within the continuum-discretized coupled-channels approach. Such a procedure, for constructing bin states on selected continuum energy intervals, is formulated and applied for the first time to reactions of a three-body projectile. The continuum representation uses the eigenchannel expansion of the three-body S matrix. The method is applied to the challenging case of the 6He+208Pb reaction at 22 MeV, where an accurate treatment of both the Coulomb and the nuclear interactions with the target is necessary.
Rapid

Scaling patterns of the suppression of pi0 yields in Au+Au collisions at sqrt(s[sub NN])=200 GeV: Links to the transport properties of the QGP
Roy A. Lacey, N. N. Ajitanand, J. M. Alexander, X. Gong, J. Jia, A. Taranenko, and Rui Wei
Published 3 November 2009 (4 pages)
051901(R)  Full Text: PDF (313 kB)  | Buy Article
+
Show Abstract
Suppression measurements for neutral pions (pi0) are used to investigate the predicted path length L and transverse momentum pT dependent jet quenching patterns of the hot QCD medium produced in Au+Au collisions at sqrt(s[sub NN])=200 GeV. The observed scaling patterns show the predicted trends for jet-medium interactions dominated by radiative energy loss. They also allow simple estimates of the transport coefficient q-hat and the ratio of viscosity to entropy density eta/s. These estimates indicate that the short mean free path lambda in the QCD medium leading to hydrodynamic-like flow with a small value of eta/s is also responsible for the strong suppression observed.
Rapid

Size fluctuations of the initial source and event-by-event transverse momentum fluctuations in relativistic heavy-ion collisions
Wojciech Broniowski, Mikolaj Chojnacki, and Lukasz Obara
Published 9 November 2009 (5 pages)
051902(R)  Full Text: PDF (338 kB)  | Buy Article
+
Show Abstract
We show that the event-by-event fluctuations of the transverse size of the initial source, which follow directly from the Glauber treatment of the earliest stage of relativistic heavy-ion collisions, cause, after hydrodynamic evolution, fluctuations of the transverse flow velocity at hadronic freeze-out. This, in turn, leads to event-by-event fluctuations of the average transverse momentum, <pT>. Simulations with GLISSANDO for the Glauber phase, followed by a realistic hydrodynamic evolution and statistical hadronization carried out with THERMINATOR, lead to agreement with the Relativistic Heavy Ion Collider (RHIC) data. In particular, the magnitude of the effect, its centrality dependence, and the weak dependence on the incident energy are properly reproduced. Our results show that the bulk of the observed event-by-event <pT> fluctuations may be explained by the fluctuations of the size of the initial source.

ARTICLES

Nucleon-Nucleon Interaction, Few-Body Systems

Target polarization for 2H-vector(e,e'p)n at GeV energies
Sabine Jeschonnek and J. W. Van Orden
Published 9 November 2009 (15 pages)
054001  Full Text: PDF (1950 kB)  | Buy Article
+
Show Abstract
We perform a fully relativistic calculation of the 2H-vector(e,e'p)n reaction in the impulse approximation employing the Gross equation to describe the deuteron ground state, and we use the SAID parametrization of the full NN scattering amplitude to describe the final state interactions (FSIs). The formalism for treating target polarization with arbitrary polarization axes is discussed, and general properties of some asymmetries are derived from it. We show results for momentum distributions and angular distributions of various asymmetries that can only be accessed with polarized targets.

Coordinate space proton-deuteron scattering calculations including Coulomb force effects
S. Ishikawa
Published 18 November 2009 (14 pages)
054002  Full Text: PDF (1063 kB)  | Buy Article
+
Show Abstract
We present a practical method to solve the proton-deuteron scattering problem at energies above the three-body breakup threshold, in which we treat three-body integral equations in coordinate space accommodating long-range proton-proton Coulomb interactions. The method is examined for phase shift parameters and then applied to calculations of differential cross sections in elastic and breakup reactions, analyzing powers, etc., with a realistic nucleon-nucleon force and three-nucleon forces. The effects of the Coulomb force and the three-nucleon forces on these observables are discussed in comparison with experimental data.

Nuclear Structure

Excited state g factors in 125Te
S. K. Chamoli, A. E. Stuchbery, and M. C. East
Published 3 November 2009 (7 pages)
054301  Full Text: PDF (322 kB)  | Buy Article
+
Show Abstract
The transient-field technique has been used to measure, with considerably improved precision, the g factors of the 3/2+ and 5/2+ states in 125Te at 444 and 463 keV, respectively, relative to the g factor of the first excited state in 126Te. Together with shell model and weak-coupling core-excitation model calculations, the g-factor measurements provide insight into the orbital occupation of the odd neutron for the low-excitation states in 125Te. A new 9/2+ level at 1029 keV, together with a firm 7/2+ spin assignment for the level at 1018 keV, identifies candidate states for the coupling of the s1/2 neutron to the 4+ core excitation.

Electric quadrupole moments of the 2<sub>1</sub><sup>+</sup> states in 100,102,104Cd
A. Ekström, J. Cederkäll, D. D. DiJulio, C. Fahlander, M. Hjorth-Jensen, A. Blazhev, B. Bruyneel, P. A. Butler, T. Davinson, J. Eberth, C. Fransen, K. Geibel, H. Hess, O. Ivanov, J. Iwanicki, O. Kester, J. Kownacki, U. Köster, B. A. Marsh, P. Reiter, M. Scheck, B. Siebeck, S. Siem, I. Stefanescu, H. K. Toft, G. M. Tveten, J. Van de Walle, D. Voulot, N. Warr, D. Weisshaar, F. Wenander, K. Wrzosek, and M. Zielińska
Published 3 November 2009 (11 pages)
054302  Full Text: PDF (636 kB)  | Buy Article
+
Show Abstract
Using the REX-ISOLDE facility at CERN the Coulomb excitation cross sections for the 0gs<sup>+</sup>-->21<sup>+</sup> transition in the beta-unstable isotopes 100,102,104Cd have been measured for the first time. Two different targets were used, which allows for the first extraction of the static electric quadrupole moments Q(21<sup>+</sup>) in 102,104Cd. In addition to the B(E2) values in 102,104Cd, a first experimental limit for the B(E2) value in 100Cd is presented. The data was analyzed using the maximum likelihood method. The provided probability distributions impose a test for theoretical predictions of the static and dynamic moments. The data are interpreted within the shell-model using realistic matrix elements obtained from a G-matrix renormalized CD-Bonn interaction. In view of recent results for the light Sn isotopes the data are discussed in the context of a renormalization of the neutron effective charge. This study is the first to use the reorientation effect for post-accelerated short-lived radioactive isotopes to simultaneously determine the B(E2) and the Q(21<sup>+</sup>) values.

Reviewing the evidence for two-proton emission from the high-spin isomer in 94Ag
David G. Jenkins
Published 4 November 2009 (6 pages)
054303  Full Text: PDF (188 kB)  | Buy Article
+
Show Abstract
The emission of two protons, a highly exotic decay process, has been reported from the high-spin 21+ isomer in 94Ag [I. Mukha et al., Nature (London) 439, 298 (2006)]. Recent experimental results from gamma-ray spectroscopy and Penning trap mass measurements, as well as theoretical predictions, are difficult to reconcile with this claim. These anomalies motivate a closer look at the supporting evidence. A detailed review of this evidence suggests that is it unsafe to conclude that the methods used in the two-proton identification experiment demonstrate an “unambiguous signature” for two-proton emission. Because the apparatus used could not distinguish protons from positrons and electrons, the identification stands or falls on coincidences with gamma rays in the daughter nucleus 92Rh. It is shown that spurious peaks from Compton-scattered gamma rays associated with the dominant background from 94Ag beta decay could have been misidentified as 92Rh gamma rays.

beta decay of the pif5/2 ground state of 77Cu studied with 225 MeV and 0.2 MeV purified radioactive beams
S. V. Ilyushkin, J. A. Winger, C. J. Gross, K. P. Rykaczewski, J. C. Batchelder, L. Cartegni, I. G. Darby, C. Goodin, R. Grzywacz, J. H. Hamilton, A. Korgul, W. Królas, S. N. Liddick, C. Mazzocchi, S. Padgett, A. Piechaczek, M. M. Rajabali, D. Shapira, and E. F. Zganjar
Published 6 November 2009 (10 pages)
054304  Full Text: PDF (768 kB)  | Buy Article
+
Show Abstract
Isobarically purified beams of 77Cu with energies of 225 and 0.2 MeV were used at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory to study beta decay into states in 77Zn. Data taken at 225 MeV allowed the determination of absolute branching ratios relative to the decay of 77Cu for this beta decay as well as its daughters. From these we obtained a refined beta-delayed neutron emission probability of 30.3(22)% and a probability that the decay proceeds through 77Zng of 49.1(26)%. A total of 64  gamma rays were placed in a level scheme for 77Zn containing 35 excited states including one state above the neutron separation energy, whereas two gamma rays were observed for the betan branch to states in 76Zn. The growth and decay curves of some prominent gamma rays indicate a single beta-decaying state with a half-life of 480(9)  ms. The decay pattern for 77Cu, with observed feeding of 8(3)% to 7/2+  77Zng and 6(3)% to 1/2-  77Znm, in contrast to the large feeding observed for decay of pip3/2 73Cug to 1/2-  73Zng, strongly suggests a pif5/2 ground state for the studied 77Cu activity.

Momentum distributions in medium and heavy exotic nuclei
M. K. Gaidarov, G. Z. Krumova, P. Sarriguren, A. N. Antonov, M. V. Ivanov, and E. Moya de Guerra
Published 11 November 2009 (13 pages)
054305  Full Text: PDF (1203 kB)  | Buy Article
+
Show Abstract
We study nucleon momentum distributions of even-even isotopes of Ni, Kr, and Sn in the framework of deformed self-consistent mean-field Skyrme HF  +  BCS method, as well as of theoretical correlation methods based on light-front dynamics and local density approximation. The isotopic sensitivities of the calculated neutron and proton momentum distributions are investigated together with the effects of pairing and nucleon-nucleon correlations. The role of deformation on the momentum distributions in even-even Kr isotopes is discussed. For comparison, the results for the momentum distribution in nuclear matter are also presented.

Projected shell model description for high-spin states in neutron-rich Fe isotopes
Yang Sun, Ying-Chun Yang, Hong-Liang Liu, Kazunari Kaneko, Munetake Hasegawa, and Takahiro Mizusaki
Published 12 November 2009 (11 pages)
054306  Full Text: PDF (911 kB)  | Buy Article
+
Show Abstract
A systematic study of neutron-rich even-even Fe isotopes with a neutron number from 32 to 42 is carried out by using the projected shell model. Calculations are performed up to the spin I=20 state. Irregularities found in the yrast spectra and in B  (E2) values are discussed in terms of neutron excitations to the high-j orbital g9/2. Furthermore, the neutron two-quasiparticle structure of a low-K negative-parity band and the proton two-quasiparticle structure of a high-K positive-parity band are predicted to exist near the yrast region. Our study reveals a soft nature for the ground state of N[approximate]40 isotopes and emphasizes the important role of the neutron g9/2 orbital in determining the structure properties for both low- and high-spin states in these nuclei.

Measurement of the branching ratio of the 6He beta-decay channel into the alpha+d continuum
R. Raabe, J. Büscher, J. Ponsaers, F. Aksouh, M. Huyse, O. Ivanov, S. R. Lesher, I. Mukha, D. Pauwels, M. Sawicka, D. Smirnov, I. Stefanescu, J. Van de Walle, P. Van Duppen, C. Angulo, J. Cabrera, N. de Séréville, I. Martel, A. M. Sánchez-Benítez, and C. Aa. Diget
Published 16 November 2009 (6 pages)
054307  Full Text: PDF (241 kB)  | Buy Article
+
Show Abstract
We measured the deuteron-emission branch of the beta decay of the halo nucleus 6He using the technique of implantation into a highly segmented silicon detector. The method, used here for the first time with a beam of 6He ions, ensures precise normalization; the value obtained for the branching ratio is [overline B]=(1.65±0.10)×10-6 (6% error). The summed energy spectra of the emitted alpha and d particles has also been measured. The results allow us to compare calculations from various models, potentially setting strong constraints on the precision required for the description of the 6He ground-state wave function.

Statistical properties of E(5) and X(5) symmetries
Zhan-feng Hou (侯占峰), Yu Zhang (张宇), and Yu-xin Liu (刘玉鑫)
Published 16 November 2009 (6 pages)
054308  Full Text: PDF (518 kB)  | Buy Article
+
Show Abstract
We investigate the statistical properties of the E(5) and X(5) symmetries, which describe states at the critical points of nuclear shape phase transitions in the geometric model, and analyze the fluctuations in both the energy spectrum and the E2 transition intensities using different angular momenta and Hamiltonian parameters. The results indicate that the spectrum of the E(5) symmetry exhibits highly regular statistical behavior and that the X(5) symmetric states are also nearly regular, with little deviation for different angular momenta and Hamiltonian parameters.

Candidates for low-lying mixed-symmetry states in 140Nd
E. Williams, R. J. Casperson, V. Werner, H. Ai, P. Boutachkov, M. Chamberlain, G. Gürdal, A. Heinz, E. A. McCutchan, J. Qian, and R. Winkler
Published 17 November 2009 (10 pages)
054309  Full Text: PDF (531 kB)  | Buy Article
+
Show Abstract
The nucleus 140Nd was investigated using gamma-gamma coincidence and angular-correlation techniques following the epsilon/beta+ decay of 140Sm and 140Pr. Spins, gamma-decay intensities, and E2/M1 mixing ratios were extracted from the data. The 23<sup>+</sup> and 24<sup>+</sup> states were identified as possible mixed-symmetry states, based on mixing ratios obtained for observed decays to the 21<sup>+</sup> state. The relationship between the decay pattern of these two candidate states and underlying shell structure in this mass region is discussed.

Experimental energy-dependent nuclear spin distributions
T. von Egidy and D. Bucurescu
Published 17 November 2009 (19 pages)
054310  Full Text: PDF (794 kB)  | Buy Article
+
Show Abstract
A new method is proposed to determine the energy-dependent spin distribution in experimental nuclear-level schemes. This method compares various experimental and calculated moments in the energy-spin plane to obtain the spin-cutoff parameter sigma as a function of mass A and excitation energy using a total of 7202 levels with spin assignment in 227 nuclei between F and Cf. A simple formula, sigma2=0.391  A0.675(E-0.5Pa')0.312, is proposed up to about 10 MeV that is in very good agreement with experimental sigma values and is applied to improve the systematics of level-density parameters.

Description of proton-neutron mixed-symmetry states near 132Sn within a realistic large scale shell model
K. Sieja, G. Martínez-Pinedo, L. Coquard, and N. Pietralla
Published 18 November 2009 (10 pages)
054311  Full Text: PDF (489 kB)  | Buy Article
+
Show Abstract
Large scale shell-model calculations with an effective interaction derived from the realistic G-matrices were performed for N=80 isotones for which so-called mixed-symmetry states were recently observed experimentally. Calculated spectra are shown to be in good agreement with data. The calculated transition rates reveal the necessity of modifying the strength of the pairing interaction. The structure of mixed-symmetry 2+ states is analyzed in terms of seniority components and by decomposition into the Q-phonon scheme.

High-spin states in 127Ce and 129Ce: Further evidence for triaxial nuclear shapes
E. S. Paul, J. P. Revill, M. Mustafa, S. V. Rigby, A. J. Boston, C. Foin, J. Genevey, A. Gizon, J. Gizon, I. M. Hibbert, D. T. Joss, P. J. Nolan, B. M. Nyakó, N. J. O'Brien, C. M. Parry, A. T. Semple, S. L. Shepherd, J. Timár, R. Wadsworth, and L. Zolnai
Published 19 November 2009 (13 pages)
054312  Full Text: PDF (696 kB)  | Buy Article
+
Show Abstract
High-spin states have been studied in the neutron-deficient odd-N 127Ce and 129Ce isotopes, produced in 100Mo(32S,5ngamma) and 100Mo(34S,5ngamma) reactions, using the Euroball and Eurogam gamma-ray spectrometers, respectively. A quadruples analysis (gamma4) of the coincident gamma-ray data has established new band structures in 127,129Ce and extended the known bands to higher spin. In addition, links have been established between two positive-parity bands in 127Ce allowing a reassignment of Ipi=1/2+ to the ground state of this nucleus. Configuration assignments are made by comparison of band properties with cranked Woods-Saxon calculations and systematics of other light odd-N cerium isotopes. Unusually large signature splitting in the negative-parity bands is discussed in terms of nonaxial nuclear shapes induced by the core-polarization effects of h11/2 neutrons.

Nuclear Reactions

Glauber model for alpha-nucleus total reaction cross section
Deeksha Chauhan and Z. A. Khan
Published 10 November 2009 (9 pages)
054601  Full Text: PDF (437 kB)  | Buy Article
+
Show Abstract
The Coulomb-modified Glauber model is employed to calculate the total reaction cross section (sigmaR) for alpha particles from 9Be, 12C, 16O, 28Si, 40Ca, 58,60Ni, 112,116,120,124Sn, and 208Pb at 117.2, 163.9, and 192.4 MeV and from the lighter nuclei also at 69.6 MeV. Our main focus in this work is to assess the suitability of semiphenomenological parametrization of the NN amplitude (SPNN), used recently [Deeksha Chauhan and Z. A. Khan, Eur. Phys. J. A 41, 179 (2009)], in the analysis of sigmaR at the energies under consideration. Using the realistic form factors for the colliding nuclei, it is found that the SPNN works reasonably well and we have quite a satisfactory account of the sigmaR data in all the cases. Moreover, our analysis suggests that the SPNN could be taken as fairly stable to describe simultaneously the elastic angular distribution and the sigmaR for a wide range of target nuclei in the relatively low-energy region.

Global optical potential for the elastic scattering of 6He at low energies
Y. Kucuk, I. Boztosun, and T. Topel
Published 11 November 2009 (7 pages)
054602  Full Text: PDF (542 kB)  | Buy Article
+
Show Abstract
A set of global optical potentials has been derived to describe the interactions of 6He at low energies. The elastic scattering angular distribution data measured so far for many systems, ranging from 12C to 209Bi, have been considered within the framework of the optical model to find a global potential set to describe the experimental data consistently. We report that very good agreement between theoretical and experimental results has been obtained with small chi2/N values by using the derived potential set. The reaction cross section and volume integrals of the potentials have been deduced from the theoretical calculations for all studied systems at relevant energies.

Determination of nuclear radii for unstable states in 12C with diffraction inelastic scattering
A. N. Danilov, T. L. Belyaeva, A. S. Demyanova, S. A. Goncharov, and A. A Ogloblin
Published 12 November 2009 (9 pages)
054603  Full Text: PDF (606 kB)  | Buy Article
+
Show Abstract
We propose a method for determining the nuclear radii for the excited states lying above the particle breakup threshold based on the diffraction model of scattering. The method is applied to analyzing the diffraction structure of the elastic and inelastic scattering of 2He, 3He, 4He, 6Li, and 12C ions on 12C at energies below 100 MeV/A. We study the radii of 12C in the excited states up to Ex[approximate]11 MeV and show that the diffraction radii for the ground and the first 2+ (4.44 MeV) excited states are approximately the same. The diffraction radii for the 02<sup>+</sup> (7.65 MeV) Hoyle state and 3- (9.64 MeV) states located above the 12C -->3alpha threshold are larger by [approximate]0.5 fm. This difference does not depend on the energy or on the kind of projectiles (deuterons are an exception). This fact justifies an application of the proposed method to the determination of the root-mean-square radii of the above-threshold states. We found that the rms radii for the 02<sup>+</sup> (7.65 MeV) and 3- (9.64 MeV) states are a factor of 1.2 larger than the rms radius for the ground state of 12C. Also, we estimated the rms radii for the above-threshold 2+ (9.9 MeV), 0+ (10.3 MeV), and 1- (10.84 MeV) states.

Variation of nonequilibrium processes in the p+Ni system with beam energy
A. Budzanowski et al. (PISA Collaboration)
Published 13 November 2009 (8 pages)
054604  Full Text: PDF (1102 kB)  | Buy Article
+
Show Abstract
The energy and angular dependence of double differential cross sections d2sigma/dOmegadE were measured for p,d,t,3,4He, 6,7Li, 7,9Be, and 10,11B produced in collisions of 0.175 GeV protons with a Ni target. The analysis of measured differential cross sections allowed the extraction of total production cross sections for the ejectiles listed above. The shape of the spectra and angular distributions indicates the presence of other nonequilibrium processes besides the emission of nucleons from the intranuclear cascade and the evaporation of various particles from remnants of intranuclear cascade. These nonequilibrium processes consist of the coalescence of nucleons into light-charged particles during the intranuclear cascade, of the fireball emission, which contributes to the cross sections of protons and deuterons, and of the breakup of the target nucleus, which leads to the emission of intermediate mass fragments. All such processes were found earlier at beam energies 1.2, 1.9, and 2.5 GeV for Ni and Au targets; however, significant differences in the properties of these processes at high and low beam energy are observed in the present study.

Analytical transformed harmonic oscillator basis for continuum discretized coupled channels calculations
A. M. Moro, J. M. Arias, J. Gómez-Camacho, and F. Pérez-Bernal
Published 16 November 2009 (10 pages)
054605  Full Text: PDF (512 kB)  | Buy Article
+
Show Abstract
A new method for continuum discretization in continuum-discretized coupled-channels calculations is proposed. The method is based on an analytic local-scale transformation of the harmonic-oscillator wave functions proposed for other purposes in a recent work [Karatagladis et al., Phys. Rev. C 71, 064601 (2005)]. The new approach is compared with the standard method of continuum discretization in terms of energy bins for the reactions d+58Ni at 80 MeV, 6Li+40Ca at 156 MeV, and 6He+208Pb at 22 MeV and 240 MeV/nucleon. In all cases very good agreement between both approaches is found.

Symmetry energy from fragment observables in the canonical thermodynamic model
G. Chaudhuri, F. Gulminelli, and S. Das Gupta
Published 18 November 2009 (7 pages)
054606  Full Text: PDF (295 kB)  | Buy Article
+
Show Abstract
Different formulas relating measurable fragment isotopic observables to the symmetry energy of excited nuclei were proposed and applied to the analysis of heavy ion collision data in the recent literature. In this article, we examine the quality of the different expressions in the framework of the McGill canonical thermodynamic model (CTM). We show that even in the idealized situation of canonical equilibrium and in the absence of secondary decay, these formulas do not give a precise reconstruction of the symmetry energy of the fragmenting source. However, both isotopic widths and isoscaling appear very well correlated to the physical symmetry energy.

Quantum molecular dynamics study of the mass distribution of products in 7.0A MeV 238U+238U collisions
Kai Zhao, Xizhen Wu, and Zhuxia Li
Published 18 November 2009 (7 pages)
054607  Full Text: PDF (1045 kB)  | Buy Article
+
Show Abstract
Within the improved quantum molecular dynamics (ImQMD) model incorporating the statistical decay model, the reactions of 238U+238U at an energy of 7.0A MeV have been studied. The charge, mass, and excitation energy distributions of primary fragments are investigated within the ImQMD model, and de-excitation processes of these primary fragments are described by a statistical decay model. The mass distribution of the final products in 238U+238U collisions is obtained and compared with the recently obtained experimental data.

Synthesis of superheavy element 120 via 50Ti+ACf hot fusion reactions
Z. H. Liu and Jing-Dong Bao
Published 20 November 2009 (5 pages)
054608  Full Text: PDF (458 kB)  | Buy Article
+
Show Abstract
Synthesis of superheavy element 120 in terms of the 50Ti+249-252Cf fusion-evaporation reactions is evaluated and discussed. It is found that the reactions of 250,251Cf(50Ti,3n)297,298120 and 251,252Cf(50Ti,4n)297,298120 are relatively favorable with the maximum evaporation-residue cross sections of 0.12, 0.09, 0.11, and 0.25 pb, respectively. However, 252Cf may be difficult to be target because its spontaneous fission will bring about serious background in the experiment. Fusion probabilities for different target-projectile combinations leading to the formation of surperheavy nucleus 302120 are estimated with the “fusion-by-diffusion” model and presented as a function of the Coulomb parameter Z1Z2/(A1<sup>1/3</sup>+A2<sup>1/3</sup>). Among the reactions 50Ti+252Cf, 54Cr+248Cm, 58Fe+244Pu, and 64Ni+238U, the reaction 50Ti+252Cf has the largest fusion probability. Synthesis of superheavy element 120 is of essential importance for determining whether the magic proton shell should be at Z=114 or at higher proton numbers Z=120–126. Therefore, the experiment to produce isotopes with Z=120 in the fusion reactions 50Ti+250,251Cf is of great interest.

Relativistic Nuclear Collisions

Photoproduction of rho0 mesons in ultraperipheral heavy ion collisions at energies available at the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC)
V. P. Gonçalves and M. V. T. Machado
Published 2 November 2009 (6 pages)
054901  Full Text: PDF (250 kB)  | Buy Article
+
Show Abstract
We investigate the photoproduction of rho mesons in ultraperipheral heavy ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC) energies in the dipole approach and within two phenomenological models based on the color glass condensate (CGC) formalism. We estimate the integrated cross section and rapidity distribution for meson production and compare our predictions with the data from the STAR Collaboration. In particular, we demonstrate that the total cross section at RHIC is strongly dependent on the energy behavior of the dipole-target cross section at low energies, which is not well determined in the dipole approach. In contrast, the predictions at midrapidities at RHIC and in the full rapidity at LHC are under theoretical control and can be used to test QCD dynamics at high energies.

Light-cone wave function approach to open heavy flavor dynamics in QCD matter
Rishi Sharma, Ivan Vitev, and Ben-Wei Zhang
Published 4 November 2009 (17 pages)
054902  Full Text: PDF (973 kB)  | Buy Article
+
Show Abstract
We calculate the lowest-order charm and beauty parton distribution functions in and fragmentation functions into D and B mesons using the operator definitions of factorized perturbative quantum chromodynamics (QCD). In the vacuum, we find the leading corrections that arise from the structure of the final-state hadrons. Quark-antiquark potentials extracted from the lattice are employed to demonstrate the existence of open heavy flavor bound-state solutions in the quark-gluon plasma in the vicinity of the critical temperature. We provide first results for the in-medium modification of the heavy-quark distribution and decay probabilities in a comoving plasma. In an improved perturbative QCD description of heavy-flavor dynamics in the thermal medium, we combine D- and B-meson formation and dissociation with parton-level charm and beauty quark quenching to obtain predictions for the heavy-meson and nonphotonic-electron suppression in Cu+Cu and Pb+Pb collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider, respectively.

Initial eccentricity in deformed 197Au+197Au and 238U+238U collisions at sqrt(s[sub NN])=200 GeV at the BNL Relativistic Heavy Ion Collider
Peter Filip, Richard Lednicky, Hiroshi Masui, and Nu Xu
Published 5 November 2009 (5 pages)
054903  Full Text: PDF (639 kB)  | Buy Article
+
Show Abstract
Initial eccentricity and eccentricity fluctuations of the interaction volume created in relativistic collisions of deformed 197Au and 238U nuclei are studied using optical and Monte Carlo (MC) Glauber simulations. It is found that the nonsphericity noticeably influences the average eccentricity in central collisions, and eccentricity fluctuations are enhanced from deformation. Quantitative results are obtained for Au+Au and U+U collisions at energy sqrt(s[sub NN])=200 GeV.

Nuclear structure functions at small x
Jamal Jalilian-Marian
Published 6 November 2009 (6 pages)
054904  Full Text: PDF (290 kB)  | Buy Article
+
Show Abstract
I study the nuclear structure function F2<sup>A</sup> and its logarithmic derivative in the high-energy limit (small-x region) using the color glass condensate formalism. In this limit the structure function F2 depends on the quark-antiquark dipole-target scattering cross section NF(xbj,rt,bt). The same dipole cross section appears in single-hadron and hadron-photon production cross sections in the forward rapidity region in deuteron (proton)-nucleus collisions at high energy, that is, at energies available at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). I use a parametrization of the dipole cross section, which has successfully been used to describe the deuteron-gold data at the RHIC, to compute the nuclear structure function F2<sup>A</sup> and its log Q2 derivative (which is related to gluon distribution function in the double log limit). I provide a quantitative estimate of the nuclear shadowing of F2<sup>A</sup> and the gluon distribution function in the kinematic region relevant to a future electron-ion collider.

Baryon stopping and saturation physics in relativistic collisions
Yacine Mehtar-Tani and Georg Wolschin
Published 9 November 2009 (9 pages)
054905  Full Text: PDF (526 kB)  | Buy Article
+
Show Abstract
We investigate baryon transport in relativistic heavy-ion collisions at energies reached at the CERN Super Proton Synchrotron (SPS), BNL Relativistic Heavy-Ion Collider (RHIC), and CERN's Large Hadron Collider (LHC) in the model of saturation. An analytical scaling law is derived within the color glass condensate framework based on small-coupling QCD. Transverse momentum spectra, net-baryon rapidity distributions, and their energy, mass, and centrality dependencies are well described. In comparison with RHIC data in Au+Au collisions at sqrt(s[sub NN])=62.4 and 200 GeV, the gradual approach to the gluon saturation regime is investigated and limits for the saturation-scale exponent are determined. Predictions for net-baryon rapidity spectra and the mean rapidity loss in central Pb+Pb collisions at LHC energies of sqrt(s[sub NN])=5.52 TeV are made.

Effects of bulk viscosity at freezeout
Akihiko Monnai and Tetsufumi Hirano
Published 12 November 2009 (10 pages)
054906  Full Text: PDF (385 kB)  | Buy Article
+
Show Abstract
We investigate particle spectra and elliptic flow coefficients in relativistic heavy-ion collisions by taking into account the distortion of phase space distributions by bulk viscosity at freezeout. We first calculate the distortion of phase space distributions in a multicomponent system with Grad's 14-moment method. We find some subtle issues when macroscopic variables are matched with microscopic momentum distributions in a multicomponent system, and we develop a consistent procedure to uniquely determine the corrections to the phase space distributions. Next, we calculate particle spectra by using the Cooper-Frye formula to see the effect of the bulk viscosity. Despite the relative smallness of the bulk viscosity, we find that it is likely to have a visible effect on particle spectra and elliptic flow coefficients. This indicates the importance of taking into account bulk viscosity together with shear viscosity to constrain the transport coefficients with better accuracy from comparison with experimental data.

High-pT  pi0 production with respect to the reaction plane in Au+Au collisions at sqrt(s[sub NN])=200 GeV
S. Afanasiev et al. (PHENIX Collaboration)
Published 13 November 2009 (29 pages)
054907  Full Text: PDF (1688 kB)  | Buy Article
+
Show Abstract
Measurements of the azimuthal anisotropy of high-pT neutral pion (pi0) production in Au+Au collisions at sqrt(s[sub [sub NN]])=200 GeV by the PHENIX experiment are presented. The data included in this article were collected during the 2004 Relativistic Heavy Ion Collider running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of pi0 mesons detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v2) of the angular distributions are presented as a function of pi0 transverse momentum (pT) for different bins in collision centrality. Measured reaction plane dependent pi0 yields are used to determine the azimuthal dependence of the pi0 suppression as a function of pT, RAA(Deltaphi,pT). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the pi0 suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.

Fate of the initial state perturbations in heavy ion collisions
Edward Shuryak
Published 13 November 2009 (14 pages)
054908  Full Text: PDF (798 kB)  | Buy Article
+
Show Abstract
Heavy ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) are well described by the (nearly ideal) hydrodynamics. In the present paper, we study the propagation of perturbations induced by moving charges (jets) on top of the expanding fireball, using hydrodynamics and (dual) magnetohydrodynamics. Two experimentally observed structures, called a “cone” and a “hard ridge”, have been discovered in a dihadron correlation function with a large-pt trigger, while a “soft ridge” is a similar structure seen without a hard trigger. All three can be viewed as traces left by a moving charge in matter, on top of overall expansion. A puzzle is why those perturbations are apparently rather well preserved at the time of the fireball freeze-out. We study two possible solutions: (A) a “wave-splitting” acoustic option and (B) a “metastable electric flux tube” option. In the first case, we show that rapidly variable speed of sound under certain conditions leads to secondary sound waves, which are at freeze-out time closer to the original location and have larger intensities than the first wave. In the latter case, we rely on (dual) magnetohydrodynamics, which also predicts two cones or cylinders of the waves. We also briefly discuss metastable electric flux tubes in the near-Tc phase and their relation to clustering data.

Jet energy loss, photon production, and photon-hadron correlations at energies available at the BNL Relativistic Heavy Ion Collider (RHIC)
Guang-You Qin, Jörg Ruppert, Charles Gale, Sangyong Jeon, and Guy D. Moore
Published 16 November 2009 (10 pages)
054909  Full Text: PDF (571 kB)  | Buy Article
+
Show Abstract
Jet energy loss, photon production, and photon-hadron correlations are studied together at high transverse momentum in relativistic heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) energies. The modification of hard jets traversing a hot and dense nuclear medium is evaluated by consistently taking into account induced gluon radiation and elastic collisions. The production of high-transverse-momentum photons in Au+Au collisions at RHIC is calculated by incorporating a complete set of photon-production channels. Comparison with experimental photon production and photon-hadron correlation data is performed, using a (3+1)-dimensional relativistic hydrodynamic description of the thermalized medium created in these collisions. Our results demonstrate that the interaction between the hard jets and the soft medium is important for the study of photon production and of photon-hadron correlation at RHIC.

Centrality and system size dependence of (multi-strange) hyperons at 40A and 158A GeV: A comparison between a binary collision model and a Boltzmann + hydrodynamic hybrid model
Hannah Petersen, Michael Mitrovski, Tim Schuster, and Marcus Bleicher
Published 17 November 2009 (8 pages)
054910  Full Text: PDF (435 kB)  | Buy Article
+
Show Abstract
We present results on the centrality and system size dependence of (multi-strange) hyperons in Pb+Pb collisions at 40A and 158A GeV from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD-v2.3) model and a coupled Boltzmann + hydrodynamics calculation. The second approach is realized in a hybrid fashion based on UrQMD, with an intermediate hydrodynamical evolution for the hot and dense stage of the collision. This implementation allows a comparison of microscopic transport calculations with hydrodynamic simulations to explore the transition from a system that is not fully equilibrated, such as C+C or Si+Si collisions, to a supposedly fully equilibrated system, such as that created in Pb+Pb reactions. The results of our calculations are compared to measurements of the (anti-)hyperon yields at midrapidity (|y|<=0.5) and total multiplicities performed by the NA49 and NA57 Collaborations at 40A and 158A GeV. Furthermore, we compare our predictions to the centrality dependence of Lambda,[overline Lambda ], and Xi- rapidity spectra and total multiplicities at 40A and 158A GeV, where possible.

Spin susceptibility of degenerate quark matter
Kausik Pal and Abhee K. Dutt-Mazumder
Published 19 November 2009 (6 pages)
054911  Full Text: PDF (201 kB)  | Buy Article
+
Show Abstract
The expression for spin susceptibility chi of degenerate quark matter is derived with corrections up to [script O](g4ln  g2). It is shown that, at low density, chi-1 changes sign and turns negative, indicating a ferromagnetic phase transition. To this order, we also calculate sound velocity c1 and incompressibility K with arbitrary spin polarization. The estimated values of c1 and K show that the equation of state of the polarized matter is stiffer than that of unpolarized matter. Finally, we determine the finite temperature corrections to the exchange energy and derive corresponding results for the spin susceptibility.

Hadronic Physics and QCD

Photoproduction of pseudoscalar mesons off nuclei at forward angles
S. Gevorkyan, A. Gasparian, L. Gan, I. Larin, and M. Khandaker
Published 6 November 2009 (8 pages)
055201  Full Text: PDF (495 kB)  | Buy Article
+
Show Abstract
With the advent of new photon-tagging facilities and novel experimental technologies, it has become possible to perform photoproduction cross-sectional measurements of pseudoscalar mesons on nuclei with percent-level accuracy. The extraction of the radiative decay widths from these measurements at forward angles is done by the Primakoff method, which requires theoretical treatment of all processes participating in these reactions at the same percent level. In this work, we review the theoretical approach to meson photoproduction amplitudes in the electromagnetic and strong fields of nuclei at forward angles. The most updated description of these processes are presented based on the Glauber theory of multiple scattering. In particular, the effects of final-state interactions, corrections for light nuclei, and photon shadowing in nuclei are discussed.

Photoproduction of eta and eta' mesons off protons
V. Crede et al. (CBELSA/TAPS Collaboration)
Published 6 November 2009 (12 pages)
055202  Full Text: PDF (923 kB)  | Buy Article
+
Show Abstract
Total and differential cross sections for eta and eta'photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The eta mesons are detected in their two neutral decay modes, eta-->gammagamma and eta-->3pi0-->6gamma, and for the first time, cover the full angular range in cos  thetac.m. of the eta meson. These new eta photoproduction data are consistent with the earlier CB-ELSA results. The eta' mesons are observed in their neutral decay to pi0pi0eta-->6gamma and also extend the coverage in angular range.

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction
I. G. Aznauryan et al. (CLAS Collaboration)
Published 10 November 2009 (22 pages)
055203  Full Text: PDF (1152 kB)  | Buy Article
+
Show Abstract
We present results on the electroexcitation of the low mass resonances Delta(1232)P33, N(1440)P11, N(1520)D13, and N(1535)S11 in a wide range of Q2. The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for pi electroproduction off the proton. The data were analyzed using two conceptually different approaches—fixed-t dispersion relations and a unitary isobar model—allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the Delta(1232)P33 show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q2<=6 GeV2. For the Roper resonance, N(1440)P11, the data provide strong evidence that this state is a predominantly radial excitation of a three-quark (3q) ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N(1535)S11 allowed us to obtain the branching ratios of this state to the piN and etaN channels via comparison with the results extracted from eta electroproduction. The extensive CLAS data also enabled the extraction of the gamma*p-->N(1520)D13 and N(1535)S11 longitudinal helicity amplitudes with good precision. For the N(1535)S11, these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a 3q excitation. The transverse amplitudes for the N(1520)D13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q2>1 GeV2, confirming a long-standing prediction of the constituent quark model.

Pion-nucleon scattering in Kadyshevsky formalism. I. Meson exchange sector
J. W. Wagenaar and T. A. Rijken
Published 12 November 2009 (14 pages)
055204  Full Text: PDF (360 kB)  | Buy Article
+
Show Abstract
In a series of two articles we present the theoretical results of piN/meson-baryon scattering in the Kadyshevsky formalism. In this article the results are given for meson exchange diagrams. On the formal side we show, by means of an example how general couplings, i.e., couplings containing multiple derivatives and/or higher spin fields, should be treated. We do this by introducing and applying the Takahashi-Umezawa and the Gross-Jackiw method. For practical purposes we introduce the [overline P] method. We also show how the Takashashi-Umezawa method can be derived using the theory of Bogoliubov and collaborators and the Gross-Jackiw method is also used to study the n dependence of the Kadyshevsky integral equation. Last but not least we present the second quantization procedure of the quasiparticle in Kadyshevsky formalism.

Pion-nucleon scattering in Kadyshevsky formalism. II. Baryon exchange sector
J. W. Wagenaar and T. A. Rijken
Published 12 November 2009 (23 pages)
055205  Full Text: PDF (443 kB)  | Buy Article
+
Show Abstract
In this article, which is the second part in a series of two, we construct tree-level baryon exchange and resonance amplitudes for piN/MB scattering in the framework of the Kadyshevsky formalism. We use this formalism to formally implement absolute pair suppression, where we make use of the method of Takahashi and Umezawa. The resulting amplitudes are Lorentz invariant and causal. We continue studying the frame dependence of the Kadyshevsky integral equation using the method of Gross and Jackiw. The invariant amplitudes, including those for meson exchange, are linked to the phase shifts using the partial-wave basis.

Dynamically generated open-charm baryons beyond the zero-range approximation
C. E. Jiménez-Tejero, A. Ramos, and I. Vidaña
Published 18 November 2009 (11 pages)
055206  Full Text: PDF (400 kB)  | Buy Article
+
Show Abstract
The interaction of the low-lying pseudoscalar mesons with the ground-state baryons in the charm sector is studied within a coupled-channel approach using a t-channel vector-exchange driving force. The amplitudes describing the scattering of the pseudoscalar mesons off the ground-state baryons are obtained by solving the Lippmann-Schwinger equation. We analyze in detail the effects of going beyond the t=0 approximation. Our model predicts the dynamical generation of several open-charm baryon resonances in different isospin and strangeness channels, some of which can be clearly identified with recently observed states.

Differential cross sections of the charge-exchange reaction pi-p-->pi0n in the momentum range from 103 to 178 MeV/c
D. Mekterović et al. (Crystal Ball Collaboration)
Published 20 November 2009 (12 pages)
055207  Full Text: PDF (482 kB)  | Buy Article
+
Show Abstract
Measured values of the differential cross sections for pion-nucleon charge exchange, pi-p-->pi0n, are presented for pi- momenta of 103,112,120,130,139,152, and 178 MeV/c. Complete angular distributions were obtained by using the Crystal Ball detector at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Statistical uncertainties of the differential cross sections vary from 3 to 6% in the backward angle region and from 6 to about 20% in the forward region with the exception of the two most forward angles. The systematic uncertainties are estimated to be about 3% for all momenta.

Electroweak Interaction, Symmetries

Weak-interaction strength from charge-exchange reactions versus beta decay in the A=40 isoquintet
M. Bhattacharya, C. D. Goodman, and A. García
Published 19 November 2009 (6 pages)
055501  Full Text: PDF (393 kB)  | Buy Article
+
Show Abstract
We report a measurement of the Gamow-Teller (GT) strength distribution for 40Ar-->40K using the 0°(p,n) reaction. The measurement extends observed GT strength distribution in the A=40 system up to an excitation energy of ~8 MeV. In comparing our results with those from the beta decay of the isospin mirror nucleus 40Ti, we find that, within the excitation energy region probed by the beta-decay experiment, we observe a total GT strength that is in fair agreement with the beta-decay measurement. However, we find that the relative strength of the two strongest transitions differs by a factor of ~1.8 in comparing our results from (p,n) reactions with the beta decay of 40Ti. Using our results we present the neutrino-capture cross section for 40Ar.

Nuclear Astrophysics

Calculation of stellar electron-capture cross sections on nuclei based on microscopic Skyrme functionals
N. Paar, G. Colò, E. Khan, and D. Vretenar
Published 11 November 2009 (15 pages)
055801  Full Text: PDF (553 kB)  | Buy Article
+
Show Abstract
A fully self-consistent microscopic framework for the evaluation of nuclear weak-interaction rates at finite temperature is introduced, based on Skyrme functionals. The single-nucleon basis and the corresponding thermal occupation factors of the initial nuclear state are determined in the finite-temperature Skyrme Hartree-Fock model and charge-exchange transitions to excited states are computed using the finite-temperature random-phase approximation (RPA). Effective interactions are implemented self-consistently: Both the finite-temperature single-nucleon Hartree-Fock equations and the matrix equations of RPA are based on the same Skyrme energy density functional. Using a representative set of Skyrme functionals, the model is applied in the calculation of stellar electron-capture cross sections for selected nuclei in the iron mass group and for neutron-rich Ge isotopes.

gamma-ray spectroscopy study of states in 27Si relevant for the 26Alm(p,gamma)27Si reaction in novae and supernovae
G. Lotay, P. J. Woods, D. Seweryniak, M. P. Carpenter, R. V. F. Janssens, and S. Zhu
Published 13 November 2009 (9 pages)
055802  Full Text: PDF (399 kB)  | Buy Article
+
Show Abstract
The heavy-ion, fusion-evaporation reaction 12C(16O,n) was used to identify gamma-decay transitions from excited states in 27Si above the proton threshold. The precise level energy measurements, Jpi assignments, and lifetime measurements of astrophysically important 26Alm+p resonances have allowed an evaluation of the 26Alm(p,gamma)27Si reaction rate. An lp=0 resonance has been newly identified at a center-of-mass energy in the 26Alm+p system of 146.3(3) keV and is expected to dominate the rate for low stellar temperatures. In addition, an lp=1 resonance has been identified at 378.3(30) keV and is likely to dominate the rate at high astrophysical temperatures, such as those found in oxygen-neon novae and core-collapse supernovae.

Photoexcitation of astrophysically important states in 26Mg
R. Longland, C. Iliadis, G. Rusev, A. P. Tonchev, R. J. deBoer, J. Görres, and M. Wiescher
Published 16 November 2009 (8 pages)
055803  Full Text: PDF (408 kB)  | Buy Article
+
Show Abstract
We performed a nuclear resonance fluorescence experiment to determine the energy and quantum numbers of excited states in 26Mg. Spin-parity ambiguities of excited states in 26Mg, the compound nucleus for the s-process neutron source 22Ne(alpha,n)25Mg, result in large uncertainties in the reaction rates. The present work uses the monoenergetic gamma-ray beam from the High-Intensity gamma-ray Source to probe states in the excitation energy range of Ex=10.8 to 11.4 MeV. Five excited states were observed and unambiguous quantum numbers were assigned at Ex=10  573.3(8) keV (Jpi=1-), Ex=10  647.3(8) keV (Jpi=1+), Ex=10  805.7(7) keV (Jpi=1-), Ex=10  949.1(8) keV (Jpi=1-), and Ex=11  153.5(10) keV (Jpi=1+). The two natural parity states, located between the alpha-particle and neutron thresholds, are expected to significantly influence the rate of the competing 22Ne(alpha,gamma)26Mg reaction. An important finding of this work is that the Ex=11  154 keV level has unnatural parity, contrary to previous results, and thus does not contribute to the 22Ne+alpha reaction rates.

High-precision (p,t) reaction measurement to determine 18Ne(alpha,p)21Na reaction rates
A. Matic, A. M. van den Berg, M. N. Harakeh, H. J. Wörtche, G. P. A. Berg, M. Couder, J. L. Fisker, J. Görres, P. LeBlanc, S. O'Brien, M. Wiescher, K. Fujita, K. Hatanaka, Y. Sakemi, Y. Shimizu, Y. Tameshige, A. Tamii, M. Yosoi, T. Adachi, Y. Fujita, Y. Shimbara, H. Fujita, T. Wakasa, P. O. Hess, B. A. Brown, and H. Schatz
Published 16 November 2009 (18 pages)
055804  Full Text: PDF (846 kB)  | Buy Article
+
Show Abstract
x-ray bursts are identified as thermonuclear explosions in the outer atmosphere of accreting neutron stars. The thermonuclear runaway is fueled by the alphap process that describes a sequence of (alpha,p) reactions triggered by the 18Ne(alpha,p)21Na breakout reaction from the hot CNO cycles. We studied the level structure of the compound nucleus 22Mg by measuring the 24Mg(p,t)22Mg reaction at the Grand Raiden spectrometer at Research Center for Nuclear Physics, Osaka. A large number of alpha-unbound states was identified and precise excitation energies were determined. Based on shell model and alpha-cluster model calculations we predict the level parameters for determining the stellar reaction rate of 18Ne(alpha,p)21Na for a wide temperature range. x-ray burst simulations have been performed to study the impact of the reaction on the x-ray burst luminosity.

Spin response of a normal Fermi liquid with noncentral interactions
C. J. Pethick and A. Schwenk
Published 20 November 2009 (8 pages)
055805  Full Text: PDF (330 kB)  | Buy Article
+
Show Abstract
We consider the spin response of a normal Fermi liquid with noncentral interactions under conditions intermediate between the collisionless and hydrodynamic regimes. This problem is of importance for calculations of neutrino properties in dense matter. By expressing the deviation of the quasiparticle distribution function from equilibrium in terms of eigenfunctions of the transport equation under the combined influence of collisions and an external field, we derive a closed expression for the spin-density–spin-density response function and compare its predictions with that of a relaxation-time approximation. Our results indicate that the relaxation-time approximation is reliable for neutrino properties under astrophysically relevant conditions.

BRIEF REPORTS

Analytic expressions for alpha particle preformation in heavy nuclei
H. F. Zhang, G. Royer, Y. J. Wang, J. M. Dong, W. Zuo, and J. Q. Li
Published 2 November 2009 (4 pages)
057301  Full Text: PDF (398 kB)  | Buy Article
+
Show Abstract
Experimental alpha decay energies and half-lives are investigated systematically to extract alpha particle preformation in heavy nuclei. Formulas for the preformation factors are proposed that can be used to guide microscopic studies on preformation factors and perform accurate calculations of the alpha decay half-lives. There is little evidence for the existence of an island of long stability of superheavy nuclei.

Giant monopole resonance in Pb isotopes
E. Khan
Published 5 November 2009 (3 pages)
057302  Full Text: PDF (101 kB)  | Buy Article
+
Show Abstract
The extraction of the nuclear incompressibility from isoscalar giant monopole resonance (GMR) measurements is analyzed. Pairing may play a role in the shift of the GMR energy between the doubly closed shell 208Pb nucleus and other Pb isotopes. Pairing effects are predicted microscopically using the constrained Hartree-Fock-Bogoliubov method. Accurate measurements of the GMR in open-shell Pb isotopes are necessary.

g factor of the 2<sub>1</sub><sup>+</sup> state of 172Hf
Z. Berant, E. Oster, R. J. Casperson, A. Wolf, V. Werner, A. Heinz, R. F. Casten, G. Gurdal, E. A. McCutchan, D. S. Brenner, J. R. Terry, R. Winkler, E. Williams, J. Qian, A. Schmidt, M. K. Smith, T. Ahn, C. W. Beausang, P. H. Regan, T. Ross, M. Bunce, B. Darakchieva, D. A. Meyer, J. LeBlanc, K. Dudziak, C. Bauer, and G. Henning
Published 10 November 2009 (4 pages)
057303  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
The g factor of the 21<sup>+</sup> state of 172Hf was measured using the perturbed angular correlation technique in a static external magnetic field. The result, g(21<sup>+</sup>)=0.25(5), is discussed in relation to the systematics of the previously reported g factors in the Hf isotopes and compared with the predictions of several models. An interesting outcome of the analysis presented in this paper is the agreement between the calculated g factors within the interacting boson approximation (IBA) and the results of a large-scale shell model calculation. This agreement supports the emphasis in the IBA on the valence space. The undershooting of the empirical g factors near midshell in both models suggests that they underestimate the role of the saturation of collectivity, which is explicitly incorporated into a phenomenological model that agrees better with the data.

Isobaric incompressibility of isospin asymmetric nuclear matter
D. N. Basu, P. Roy Chowdhury, and C. Samanta
Published 18 November 2009 (3 pages)
057304  Full Text: PDF (123 kB)  | Buy Article
+
Show Abstract
The isospin dependence of the saturation properties of asymmetric nuclear matter, particularly the incompressibility K[infinity](X)=K[infinity]+KtauX2+O(X4) at saturation density, is systematically studied using density-dependent M3Y interaction. Ktau characterizes the isospin dependence of the incompressibility at saturation density rho0. The approximate expression Kasy[approximate]Ksym-6L is often used for Ktau where L and Ksym represent the slope and curvature parameters of the symmetry energy at rho0, respectively. It can be expressed accurately as Ktau=Ksym-6L-(Q0/K[infinity])L, where Q0 is the third-order-derivative parameter of symmetric nuclear matter at rho0. The results of this addendum to [Phys. Rev. C 80, 011305(R) (2009)] indicate that the Q0 contribution to Ktau is not insignificant.

Production of new superheavy Z=108–114 nuclei with 238U, 244Pu, and 248,250Cm targets
Zhao-Qing Feng, Gen-Ming Jin, and Jun-Qing Li
Published 4 November 2009 (4 pages)
057601  Full Text: PDF (342 kB)  | Buy Article
+
Show Abstract
Within the framework of the dinuclear system (DNS) model, production cross sections of new superheavy nuclei with charged numbers Z=108–114 are analyzed systematically. Possible combinations based on the actinide nuclides 238U, 244Pu, and 248,250Cm with the optimal excitation energies and evaporation channels are pointed out to synthesize new isotopes that lie between the nuclides produced in the cold fusion reactions and the 48Ca-induced fusion reactions experimentally, which are feasible to be constructed experimentally. It is found that the production cross sections of superheavy nuclei decrease drastically with the charged numbers of compound nuclei. Larger mass asymmetries of the entrance channels enhance the cross sections in 2n–5n channels.

Gauge-invariant interaction of spin-(3/2) resonances
V. Shklyar and H. Lenske
Published 16 November 2009 (4 pages)
058201  Full Text: PDF (105 kB)  | Buy Article
+
Show Abstract
We show that the gauge-invariant coupling suggested by Pascalutsa removes non-pole terms from the spin-(3/2) propagator only for a specific choice of free parameter. For the general case, the problem can be solved by demanding the invariance of the full Lagrangian under the point-like transformations. It is shown that apart from gauge invariance, the original Rarita-Schwinger (R-S) constraint ensures a correct number of physical degrees of freedom. This is used to constrain couplings in the various applications of the half-integer R-S theories in hadron physics.

ERRATA

Publisher's Note: Cluster structures and superdeformation in 28Si [Phys. Rev. C 80, 044316 (2009)]
Yasutaka Taniguchi, Yoshiko Kanada-En'yo, and Masaaki Kimura
Published 6 November 2009 (1 page)
059903(E)  Full Text: PDF (22 kB) 
No abstract available.

Erratum: Coulomb dissociation of 15C and radiative neutron capture on 14C [Phys. Rev. C 80, 024608 (2009)]
H. Esbensen and R. Reifarth
Published 11 November 2009 (2 pages)
059904(E)  Full Text: PDF (103 kB) 
No abstract available.