Thu·Aug 7, 2014Thursday·August 7, 2014

1. 01*

   Beam energy dependence of the expansion dynamics in relativistic heavy ion collisions: Indications for the critical end point?

   Roy A. Lacey (Depts. of Chemistry and Physics, Stony Brook University)🇺🇸

   The flow harmonic $v_n$ and the emission source radii $R_{\text{out}}$, $R_{\text{side}}$ and $R_{\text{long}}$ are studied for a broad range of centrality selections and beam collision energies in Au+Au ($\sqrt{s_{NN}}=7.7-200$ GeV) and Pb+Pb ($\sqrt{s_{NN}}=2.76$ TeV) collisions at RHIC and the LHC respectively. They validate the acoustic scaling patterns expected for hydrodynamic-like expansion over the entire range of beam energies studied. The combined data sets allow estimates for the \sqsn\ dependence of the mean expansion speed $⟨c_s⟩$, emission duration $⟨\Delta \tau ⟩$ and the viscous coefficients $⟨{\beta }^{\prime \prime }⟩$ that encode the magnitude of the specific shear viscosity $⟨\eta /s⟩$. The estimates indicate initial-state model independent values of $⟨\eta /s⟩$ which are larger for the plasma produced at 2.76 TeV (LHC) compared to that produced at 200 GeV (RHIC) (${⟨4\pi \eta /s⟩}_{\text{LHC}}=2.2\pm 0.2$ and ${⟨4\pi \eta /s⟩}_{\text{RHIC}}=1.3\pm 0.2$). They also show a non-monotonic \sqsn\ dependence for $⟨{\beta }^{\prime \prime }⟩$, $⟨c_s⟩$ and $⟨\Delta \tau ⟩$, with minima for $⟨{\beta }^{\prime \prime }⟩$ and $⟨c_s⟩$, and a complimentary maximum for $⟨\Delta \tau ⟩$. These dependencies signal a significant change in reaction dynamics in a narrow span of $\sqrt{s_{NN}}$, which may be linked to reaction trajectories close to the critical end point (CEP) in the phase diagram for nuclear matter.

   nucl-exNPA(2014)·8 citations
2. 02*

   Coulomb effect in Au+Au and Pb+Pb collisions as a function of collision energy

   D. Cebra🇺🇸 · S.G. Brovko🇺🇸 · C.E. Flores🇺🇸 · B.A. Haag🇺🇸 · J.L. Klay🇺🇸

   The subtle differences between positive and negative pion spectra can used be used to study the nature of the nuclear interaction region in heavy-ion collisions. Several large acceptance heavy ion experiments at facilities ranging from SIS, the AGS, the SPS, to RHIC have measured mid-rapidity ${\pi }^{+}$ and ${\pi }^{-}$ spectra for central Au+Au or Pb+Pb collisions. From these spectra one can create pion ratios as a function of $m_t-m_0$, which are used to determine the Coulomb potential, $V_C$, and the initial pion ratio, $R_i$, across a range of collision energies from 1 to 158 AGeV. The implications of the $V_C$ and $R_i$ trends with collision energy will be discussed.

   nucl-exnucl-th19 citations
3. 03*

   Probing the non-equilibrium dynamics of hot and dense QCD with dileptons

   Gojko Vujanovic🇨🇦 · Jean-Francois Paquet🇨🇦 · Gabriel S. Denicol🇨🇦 · Matthew Luzum🇨🇦 · Bjoern Schenke🇺🇸 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

   It is argued that, in heavy ion collisions, thermal dileptons are good probes of the transport properties of the medium created in such events, and also of its early-time dynamics, usually inaccessible to hadronic observables. In this work we show that electromagnetic azimuthal momentum anisotropies do not only display a sensitivity to the shear relaxation time and to the initial shear-stress tensor profile, but also to the temperature dependence of the shear viscosity coefficient.

   ↳ nucl-thhep-phnucl-exNPA(2014)·10 citations
4. 04*

   Exclusive ${\rm Y}$ photoproduction in hadronic collisions at CERN LHC energies

   V. P. Goncalves🇧🇷 · B. D. Moreira🇧🇷 · F. S. Navarra🇧🇷

   The exclusive ${\rm Y}$ photoproduction in proton-proton and proton - nucleus collisions at LHC energies is investigated using the color dipole formalism and considering different models for the ${\rm Y}$ wave function and forward dipole - target scattering amplitude. Our goal is to update the color dipole predictions and estimate the theoretical uncertainty present in these predictions. We present predictions for the kinematical ranges probed by the ALICE, CMS and LHCb Collaborations.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2015)·72 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.