Wed·Jul 1, 2009Wednesday·July 1, 2009

1. 01*

   J/psi azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon

   F. Prino (INFN, Torino) (for the NA50 collaboration)

   The J/$\psi$ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J/$\psi$ mesons at SPS energies. Hence, the measurement of J/$\psi$ elliptic anisotropy, quantified by the Fourier coefficient v${}_2$ of the J/$\psi$ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J/$\psi$ suppression observed in Pb-Pb collisions. We present the measured J/$\psi$ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v${}_2$ as a function of the collision centrality and of the J/$\psi$ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or p${}_{\mathrm{T}}$ sub-samples. The extracted v${}_2$ values are significantly larger than zero for non-central collisions and are seen to increase with p${}_{\mathrm{T}}$.

   nucl-exEPJC(2009)·7 citations
2. 02*

   The beta-gamma decay of 21Na

   N.L. Achouri🇫🇷 · J.-C. Angélique🇫🇷 · G. Ban🇫🇷 · B. Bastin🇫🇷 · B. Blank🇫🇷 · S. Dean🇳🇱 · P. Dendooven🇳🇱 · J. Giovinazzo🇫🇷 · S. Grévy🇫🇷 · K. Jungmann🇳🇱 · B. Laurent🇫🇷 · E. Liénard🇫🇷 and 6 other authors

   A new and independent determination of the Gamow-Teller branching ratio in the beta-decay of 21Na is reported. The value obtained of 5.13 +- 0.43 % is in agreement with the currently adopted value and the most recent measurement. In contrast to previous experiments, the present method was based on the counting of the parent 21Na ions and the resulting 351 keV gamma-rays without coincident beta-particle detection.

   nucl-exJ.Phys.G(2010)·7 citations
3. 03*

   The NJL-jet model for quark fragmentation functions

   T. Ito🇯🇵 · W. Bentz🇯🇵 · I. C. Cloët🇺🇸 · A. W. Thomas🇺🇸 · K. Yazaki🇯🇵

   A description of fragmentation functions which satisfy the momentum and isospin sum rules is presented in an effective quark theory. Concentrating on the pion fragmentation function, we first explain why the elementary (lowest order) fragmentation process q --> q \pi is completely inadequate to describe the empirical data, although the "crossed" process \pi --> q \bar{q} describes the quark distribution functions in the pion reasonably well. Taking into account cascade-like processes in a generalized jet-model approach, we then show that the momentum and isospin sum rules can be satisfied naturally, without the introduction of ad hoc parameters. We present results for the Nambu--Jona-Lasinio (NJL) model in the invariant mass regularization scheme and compare them with the empirical parametrizations. We argue that the NJL-jet model, developed herein, provides a useful framework with which to calculate the fragmentation functions in an effective chiral quark theory.

   ↳ nucl-thhep-exhep-phnucl-exPRD(2009)·61 citations
4. 04*

   A simple model for the nuclear unintegrated gluon distribution

   M.A. Betemps🇧🇷 · M.V.T. Machado🇧🇷

   The solution of non-linear evolution equations for dense nuclear gluon density has been suggested as one of the relevant mechanisms of pA and AA collisions at collider energies. Here we study a simple parameterization for the unintegrated gluon distribution using the knowledge of asymptotic solutions of the Balitsky-Kovchegov equation, describing high-energy QCD in the presence of saturation effects. A satisfactory description of nuclear shadowing at small-x is obtained and it allows us to understand the qualitative behavior shown by data.

   ↳ hep-phnucl-exnucl-thEPJC(2010)·13 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.