Wed·Jul 6, 2011Wednesday·July 6, 2011

1. 01*

   New Precision Limit on the Strange Vector Form Factors of the Proton

   HAPPEX collaboration: Z. Ahmed🇺🇸 · K. Allada🇺🇸 · K. A. Aniol🇺🇸 · D. S. Armstrong🇺🇸 · J. Arrington🇺🇸 · P. Baturin🇺🇸 · V. Bellini🇮🇹 · J. Benesch🇺🇸 · R. Beminiwattha🇺🇸 · F. Benmokhtar🇺🇸 · M. Canan🇺🇸 · A. Camsonne🇺🇸 and 92 other authors

   The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2 = 0.624 GeV and beam energy E =3.48 GeV to be A_PV = -23.80 +/- 0.78 (stat) +/- 0.36 (syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic form factors G_E^s + 0.517 G_M^s = 0.003 +/- 0.010 (stat) +/- 0.004 (syst) +/- 0.009 (ff), where the third error is due to the limits of precision on the electromagnetic form factors and radiative corrections. With this measurement, the world data on strange contributions to nucleon form factors are seen to be consistent with zero and not more than a few percent of the proton form factors.

   nucl-exPRL(2012)·135 citations
2. 02*

   Cross section normalization in proton-proton collisions at $\sqrt{s}$ = 2.76 TeV and 7 TeV, with ALICE at LHC

   Ken Oyama (for the ALICE Collaboration)🇯🇵

   Measurements of the cross sections of the reference processes seen by the ALICE trigger system were obtained based on beam properties measured from van der Meer scans. The measurements are essential for absolute cross section determinations of physics processes. The paper focuses on instrumental and technical aspects of detectors and accelerators, including a description of the extraction of beam properties from the van der Meer scan. As a result, cross sections of reference processes seen by the ALICE trigger system are given for proton-proton collisions at two energies; $\sqrt{s}$=2.76 TeV and 7 TeV, together with systematic uncertainties originating from beam intensity measurements and other detector effects. Consistency checks were performed by comparing to data from other experiments in LHC.

   ↳ physics.ins-dethep-exnucl-exphysics.acc-phJ.Phys.G(2011)·16 citations
3. 03*

   Photons at RHIC: The role of viscosity and of initial state fluctuations

   Maxime Dion🇨🇦 · Charles Gale🇨🇦 · Sangyong Jeon🇨🇦 · Jean-Francois Paquet🇨🇦 · Bjoern Schenke🇺🇸 · Clint Young🇨🇦

   We study real photons produced in heavy ion collisions at RHIC, and we calculate their spectrum and its azimuthal momentum anisotropy. The photons from a variety of sources are included, and the interplay and the time-evolution of those sources are modelled in a full 3D hydrodynamic simulation. We quantify the v_2 of thermal photons produced in ideal and viscous fluids, and the consequences of using different initial conditions are explored.

   ↳ hep-phnucl-exnucl-thJ.Phys.G(2011)·18 citations
4. 04*

   R-Process Nucleosynthesis in Dynamically Ejected Matter of Neutron Star Mergers

   Stephane Goriely (1)🇧🇪 · Andreas Bauswein (2)🇩🇪 · H.-Thomas Janka (2) ((1) Universite Libre de Bruxelles, (2) MPI for Astrophysics, Garching)🇩🇪

   Although the rapid neutron-capture process, or r-process, is fundamentally important for explaining the origin of approximately half of the stable nuclei with A > 60, the astrophysical site of this process has not been identified yet. Here we study r-process nucleosynthesis in material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars (NSs) and within milliseconds afterwards. For the first time we make use of relativistic hydrodynamical simulations of such events, defining consistently the conditions that determine the nucleosynthesis, i.e., neutron enrichment, entropy, early density evolution and thus expansion timescale, and ejecta mass. We find that 10^{-3}-10^{-2} solar masses are ejected, which is enough for mergers to be the main source of heavy (A > 140) galactic r-nuclei for merger rates of some 10^{-5} per year. While asymmetric mergers eject 2-3 times more mass than symmetric ones, the exact amount depends weakly on whether the NSs have radii of ~15 km for a "stiff" nuclear equation of state (EOS) or ~12 km for a "soft" EOS. R-process nucleosynthesis during the decompression becomes largely insensitive to the detailed conditions because of efficient fission recycling, producing a composition that closely follows the solar r-abundance distribution for nuclei with mass numbers A > 140. Estimating the light curve powered by the radioactive decay heating of r-process nuclei with an approximative model, we expect high emission in the B-V-R bands for 1-2 days with potentially observable longer duration in the case of asymmetric mergers because of the larger ejecta mass.

   ↳ astro-ph.SRnucl-exnucl-thApJL(2011)·403 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.