Tue·Dec 29, 2015Tuesday·December 29, 2015

1. 01*

   Longitudinal Asymmetry and its Measurable Effects in Pb-Pb Collisions at 2.76 TeV

   Rashmi Raniwala🇮🇳

   Collisions of identical nuclei at finite impact parameter have an unequal number of participating nucleons from each nucleus due to fluctuations. The event-by-event fluctuations have been estimated by measuring the difference of energy in the zero-degree calorimeters on either side of interaction vertex. The fluctuations affect the global variables such as the rapidity distributions, and the effect has been correlated with a measure of these fluctuations.

   nucl-exNPA(2016)·3 citations
2. 02*

   PHENIX Measurements of Single Electrons from Charm and Bottom Decays at Midrapidity in Au+Au Collisions

   D. McGlinchey (for the PHENIX Collaboration)🇺🇸

   Heavy quarks are an ideal probe of the quark gluon plasma created in heavy ion collisions. They are produced in the initial hard scattering and therefore experience the full evolution of the medium. PHENIX has previously measured the modification of heavy quark production in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV via electrons from semileptonic decays, which indicated substantial modifications of the parent hadron momentum distribution. The PHENIX barrel silicon vertex detector (VTX), installed in 2011, allows for the separation of electrons from charm and bottom hadron decays through the use of displaced vertex measurements. These proceedings present the results of the completed analysis of the 2011 data set using the VTX.

   nucl-exNPA(2016)·0 citations
3. 03*

   Surprisingly large uncertainties in temperature extraction from thermal fits to hadron yield data at LHC

   Volodymyr Vovchenko🇩🇪 · Horst Stoecker🇩🇪

   The conventional hadron-resonance gas (HRG) model with the Particle Data Group (PDG) hadron input, full chemical equilibrium, and the hadron type dependent eigenvolume interactions is employed to fit the hadron mid-rapidity yield data of ALICE Collaboration for the most central Pb+Pb collisions. For the case of point-like hadrons the well-known fit result $T=154\pm 2$ MeV is reproduced. However, the situation changes if hadrons have different eigenvolumes. In the case when all mesons are point-like while all baryons have an effective hard-core radius of 0.3 fm the ${\chi }^2$ temperature dependence of the ${\chi }^2$ has a broad minimum in the temperature range of $155-210$ MeV, with fit quality comparable to the $T\sim 155$ MeV minimum in the point-particle case. Very similar result is obtained when only baryon-baryon eigenvolume interactions are considered, with eigenvolume parameter taken from previous fit to ground state of nuclear matter. Finally, when we apply the eigenvolume corrections with mass-proportional eigenvolume $v_i\sim m_i$, fixed to particular proton hard-core radius $r_p$, we observe a second minimum in the temperature dependence of the ${\chi }^2$, located at the significantly higher temperatures. For instance, at $r_p=0.5$ fm the fit quality is better than in the point-particle HRG case in a very wide temperature range of $170-320$ MeV, which gives an uncertainty in the temperature determination from the fit to the data of 150 MeV. These results show that thermal fits to the heavy-ion hadron yield data are very sensitive to the modeling of the short-range repulsion eigenvolume between hadrons, and that chemical freeze-out temperature can be extracted from the LHC hadron yield data only with sizable uncertainty.

   ↳ hep-phhep-exhep-latnucl-ex+1J.Phys.G(2017)·47 citations
4. 04*

   Origins of the di-jet asymmetry in heavy ion collisions

   José Guilherme Milhano🇵🇹 · Korinna Christine Zapp🇨🇭

   The di-jet asymmetry --- the measure of the momentum imbalance in a di-jet system --- is a key jet quenching observable. Using the event generator \jewel we show that the di-jet asymmetry is dominated by fluctuations both in proton-proton and in heavy ion collisions. We discuss how in proton-proton collisions the asymmetry is generated through recoil and out-of-cone radiation. In heavy ion collisions two additional sources contribute to the asymmetry, namely energy loss fluctuations and differences in path length. The latter is shown to be a sub-leading effect. We discuss the implications of our results for the interpretation of this observable.

   ↳ hep-phnucl-exnucl-thEPJC(2016)·130 citations
5. 05*

   Isoscalar dipole transition as a probe for asymmetric clustering

   Y. Chiba · M. Kimura🇯🇵 · Y. Taniguchi

   Background: The sharp $1^{-}$ resonances with enhanced isoscalar dipole transition strengths are observed in many light nuclei at relatively small excitation energies, but their nature was unclear. Purpose: We show those resonances can be attributed to the cluster states with asymmetric configurations such as $\alpha$+${}^{16}\mathrm{O}$. We explain why asymmetric cluster states are strongly excited by the isoscalar dipole transition. We also provide a theoretical prediction of the isoscalar dipole transitions in ${}^{20}\mathrm{Ne}$ and ${}^{44}\mathrm{Ti}$. Method: The transition matrix is analytically derived to clarify the excitation mechanism. The nuclear model calculations by Brink-Bloch wave function and antisymmetrized molecular dynamics are also performed to provide a theoretical prediction for ${}^{20}\mathrm{Ne}$ and ${}^{44}\mathrm{Ti}$. Results: It is shown that the transition matrix is as large as the Weisskopf estimate even though the ground state is an ideal shell model state. Furthermore, it is considerably amplified if the ground state has cluster correlation. The nuclear model calculations predict large transition matrix to the $\alpha$+${}^{16}\mathrm{O}$ and $\alpha$+${}^{40}\mathrm{Ca}$ cluster states comparable with or larger than the Weisskopf estimate. Conclusion: We conclude that the asymmetric cluster states are strongly excited by the isoscalar dipole transition. Combined with the isoscalar monopole transition that populates the $0^{+}$ cluster states, the isoscalar transitions are promising probe for asymmetric clusters.

   ↳ nucl-thnucl-exPRC(2016)·57 citations
6. 06*

   New insights from 3D simulations of heavy ion collisions

   Gabriel Denicol🇺🇸 · Akihiko Monnai🇺🇸 · Sangwook Ryu🇨🇦 · Bjoern Schenke🇺🇸

   Viscous relativistic hydrodynamics in 3+1 dimensions is applied to describe heavy ion collisions at RHIC and LHC. We present calculations of observables that are sensitive to the longitudinal structure of the created system. In particular we present pseudo-rapidity correlations and demonstrate their dependence on both the initial state and short range correlations introduced via a microscopic transport description. We further demonstrate the effect of a varying temperature dependence of the shear viscosity to entropy density ratio on rapidity dependent flow harmonics.

   ↳ nucl-thhep-phnucl-exNPA(2016)·11 citations
7. 07*

   Pre-equilibrium dynamics and heavy-ion observables

   Ulrich W. Heinz🇺🇸 · Jia Liu (Ohio State University)🇺🇸

   To bracket the importance of the pre-equilibrium stage on relativistic heavy-ion collision observables, we compare simulations where it is modeled by either free-streaming partons or fluid dynamics. These cases implement the assumptions of extremely weak vs. extremely strong coupling in the initial collision stage. Accounting for flow generated in the pre-equilibrium stage, we study the sensitivity of radial, elliptic and triangular flow on the switching time when the hydrodynamic description becomes valid. Using the hybrid code iEBE-VISHNU we perform a multi-parameter search, constrained by particle ratios, integrated elliptic and triangular charged hadron flow, the mean transverse momenta of pions, kaons and protons, and the second moment $⟨p_T^2⟩$ of the proton transverse momentum spectrum, to identify optimized values for the switching time ${\tau }_s$ from pre-equilibrium to hydrodynamics, the specific shear viscosity $\eta /s$, the normalization factor of the temperature-dependent specific bulk viscosity $(\zeta /s)(T)$, and the switching temperature $T_{\mathrm{sw}}$ from viscous hydrodynamics to the hadron cascade UrQMD. With the optimized parameters, we predict and compare with experiment the $p_T$-distributions of $\pi$, $K$, $p$, $\Lambda$, $\Xi$ and $\Omega$ yields and their elliptic flow coefficients, focusing specifically on the mass-ordering of the elliptic flow for protons and Lambda hyperons which is incorrectly described by VISHNU without pre-equilibrium flow.

   ↳ nucl-thhep-phnucl-exNPA(2016)·27 citations
8. 08*

   Fission life-time calculation using a complex absorbing potential

   Guillaume Scamps🇫🇷 · Kouichi Hagino🇯🇵

   A comparison between the semi-classical approximation and the full quantum calculation with a complex absorbing potential is made with a model of the fission of 258Fm. The potential barrier is obtained with the constrained Skyrme HF+BCS theory. The life-time obtained by the two calculations agree with each other the difference being only by 25%.

   ↳ nucl-thnucl-exEPJ Web Conf.(2016)·0 citations
9. 09*

   Large Acceptance Spectrometers for Invariant Mass Spectroscopy of Exotic Nuclei and Future Development

   T. Nakamura🇯🇵 · Y. Kondo🇯🇵

   Large acceptance spectrometers at in-flight RI separators have played significant roles in investigating the structure of exotic nuclei. Such spectrometers are in particular useful for probing unbound states of exotic nuclei, using invariant mass spectroscopy with reactions at intermediate and high energies. We discuss here the key characteristic features of such spectrometers, by introducing the recently commissioned SAMURAI facility at the RIBF, RIKEN. We also explore the issue of cross talk in the detection of multiple neutrons, which has become crucial for exploring further unbound states and nuclei beyond the neutron drip line. Finally we discuss future perspectives for large acceptance spectrometers at the new-generation RI-beam facilities.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.B(2016)·54 citations
10. 10*

    The Middle of the Spectrum

    Larry Zamick🇺🇸

    There has been a great deal of attention to the low lying energy spectum in a nucleus becuse of the abundance of experimetal data. Likewise ,perhaps to a lesser extent but still significant the high end for a given configuratiion has been examined. Here ,using single j shell calculations as a guide we examine the middle part of the spectum resulting form single j shell calculations.Seniority arguments are used to partially explain the midshell behaviours even though in general seniority is not a good quantum number for mixed systems of neutrons and protons.

    ↳ nucl-thnucl-exPhys. Rev. C93. 034327 (2016)·0 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.