Mon·May 16, 2016Monday·May 16, 2016

1. 01*

   Heavy-ion physics at the LHC: Review of Run I results

   Renu Bala🇮🇳 · Irais Bautista🇲🇽 · Jana Bielcikova🇨🇿 · Antonio Ortiz🇲🇽

   In this work we review what we consider are, some of the most relevant results of heavy-ion physics at the LHC. This paper is not intended to cover all the many important results of the experiments, instead we present a brief overview of the current status on the characterization of the hot and dense QCD medium produced in the heavy-ion collisions. Recent exciting results which are still under debate are discussed too, leading to intriguing questions like whether we have a real or fake QGP formation in small systems.

   ↳ hep-exnucl-exIJMPE(2016)·31 citations
2. 02*

   Applying Bayesian parameter estimation to relativistic heavy-ion collisions: simultaneous characterization of the initial state and quark-gluon plasma medium

   Jonah E. Bernhard🇺🇸 · J. Scott Moreland🇺🇸 · Steffen A. Bass🇺🇸 · Jia Liu🇺🇸 · Ulrich Heinz🇺🇸

   We quantitatively estimate properties of the quark-gluon plasma created in ultra-relativistic heavy-ion collisions utilizing Bayesian statistics and a multi-parameter model-to-data comparison. The study is performed using a recently developed parametric initial condition model, TRENTO, which interpolates among a general class of particle production schemes, and a modern hybrid model which couples viscous hydrodynamics to a hadronic cascade. We calibrate the model to multiplicity, transverse momentum, and flow data and report constraints on the parametrized initial conditions and the temperature-dependent transport coefficients of the quark-gluon plasma. We show that initial entropy deposition is consistent with a saturation-based picture, extract a relation between the minimum value and slope of the temperature-dependent specific shear viscosity, and find a clear signal for a nonzero bulk viscosity.

   ↳ nucl-thhep-phnucl-exPRC(2016)·595 citations
3. 03*

   Background Rejection of n${}^{+}$ Surface Events in GERDA Phase II

   Björn Lehnert (for the GERDA Collaboration)🇩🇪

   The GERDA experiment searches for neutrinoless double beta ($0\nu \beta \beta$) decay in ${}^{76}$Ge using an array of high purity germanium (HPGe) detectors immersed in liquid argon (LAr). Phase II of the experiment uses 30 new broad energy germanium (BEGe) detectors with superior pulse shape discrimination capabilities compared to the previously used semi-coaxial detector design. By far the largest background component for BEGe detectors in GERDA are n${}^{+}$-surface events from ${}^{42}$K $\beta$ decays which are intrinsic in LAr. The $\beta$ particles with up to 3.5 MeV can traverse the 0.5 to 0.9 mm thick electrode and deposit energy within the region of interest for the $0\nu \beta \beta$ decay. However, those events have particular pulse shape features allowing for a strong discrimination. The understanding and simulation of this background, showing a reduction by up to a factor 145 with pulse shape discrimination alone, is presented in this work.

   ↳ physics.ins-detnucl-exJ.Phys.Conf.Ser.(2016)·5 citations
4. 04*

   Vortical fluid and $\Lambda$ spin correlations in high-energy heavy-ion collisions

   Long-Gang Pang (FIAS)🇩🇪 · Hannah Petersen (FIAS and ITP)🇩🇪 · Qun Wang (USTC)🇨🇳 · Xin-Nian Wang (CCNU and LBNL)🇨🇳

   Fermions become polarized in a vortical fluid due to spin-vorticity coupling. The spin polarization density is proportional to the local fluid vorticity at the next-to-leading order of a gradient expansion in a quantum kinetic theory. Spin correlations of two $\Lambda$-hyperons can therefore reveal the vortical structure of the dense matter in high-energy heavy-ion collisions. We employ a (3+1)D viscous hydrodynamic model with event-by-event fluctuating initial conditions from A MultiPhase Transport (AMPT) model to calculate the vorticity distributions and $\Lambda$ spin correlations. The azimuthal correlation of the transverse spin is shown to have a cosine form plus an offset due to a circular structure of the transverse vorticity around the beam direction and global spin polarization. The longitudinal spin correlation shows a structure of vortex-pairing in the transverse plane due to the convective flow of hot spots in the radial direction. The dependence on colliding energy, rapidity, centrality and sensitivity to the shear viscosity are also investigated.

   ↳ hep-phnucl-exnucl-thPRL(2016)·230 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.