Mon·Jul 25, 2011Monday·July 25, 2011

1. 01*

   Event-by-event mean p_T fluctuations in pp and Pb-Pb collisions measured by the ALICE experiment at the LHC

   S. T. Heckel (for the ALICE collaboration)🇩🇪

   Non-statistical event-by-event fluctuations of the mean transverse momentum of charged particles in pp and Pb-Pb collisions are studied using the ALICE experiment at the LHC. Little collision energy dependence is observed in pp. The data indicate a common scaling behaviour with event multiplicity from pp to semi-central Pb-Pb collisions. In central Pb-Pb, the results deviate from this trend, exhibiting a significant reduction of the fluctuation strength. The results are compared with measurements in Au-Au collisions at lower energies and with Monte Carlo simulations.

   nucl-exhep-exhep-phnucl-thJ.Phys.G(2011)·15 citations
2. 02*

   Revision of the 15N(p,{\gamma})16O reaction rate and oxygen abundance in H-burning zones

   A. Caciolli🇮🇹 · C. Mazzocchi🇮🇹 · V. Capogrosso · D. Bemmerer🇩🇪 · C. Broggini🇮🇹 · P. Corvisiero🇮🇹 · H. Costantini · Z. Elekes🇭🇺 · A. Formicola🇮🇹 · Zs. Fulop🇭🇺 · G. Gervino🇮🇹 · A. Guglielmetti🇮🇹 and 18 other authors

   The NO cycle takes place in the deepest layer of a H-burning core or shell, when the temperature exceeds T {\simeq} 30 {\cdot} 106 K. The O depletion observed in some globular cluster giant stars, always associated with a Na enhancement, may be due to either a deep mixing during the RGB (red giant branch) phase of the star or to the pollution of the primordial gas by an early population of massive AGB (asymptotic giant branch) stars, whose chemical composition was modified by the hot bottom burning. In both cases, the NO cycle is responsible for the O depletion. The activation of this cycle depends on the rate of the 15N(p,{\gamma})16O reaction. A precise evaluation of this reaction rate at temperatures as low as experienced in H-burning zones in stellar interiors is mandatory to understand the observed O abundances. We present a new measurement of the 15N(p,{\gamma})16O reaction performed at LUNA covering for the first time the center of mass energy range 70-370 keV, which corresponds to stellar temperatures between 65 {\cdot} 106 K and 780 {\cdot}106 K. This range includes the 15N(p,{\gamma})16O Gamow-peak energy of explosive H-burning taking place in the external layer of a nova and the one of the hot bottom burning (HBB) nucleosynthesis occurring in massive AGB stars. With the present data, we are also able to confirm the result of the previous R-matrix extrapolation. In particular, in the temperature range of astrophysical interest, the new rate is about a factor of 2 smaller than reported in the widely adopted compilation of reaction rates (NACRE or CF88) and the uncertainty is now reduced down to the 10% level.

   ↳ astro-ph.SRnucl-exAstron.Astrophys.(2011)·47 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.