Mon·Jul 23, 2018Monday·July 23, 2018

1. 01*

   Collision system and beam energy dependence of anisotropic flow fluctuations

   Niseem Magdy (for the STAR collaboration)🇺🇸

   New measurements of two- and four-particle elliptic flow are used to investigate flow fluctuations in collisions of U+U at $\sqrt{s_{NN}}$ = 193~GeV, Cu+Au at $\sqrt{s_{NN}}$ = 200~GeV and Au+Au at several beam energies. These measurements highlight the dependence of these fluctuations on the event-shape, system-size and beam energy and indicate a dominant role for initial-state-driven fluctuations. These measurements could provide further constraints for initial-state models, as well as for precision extraction of the temperature-dependent specific shear viscosity $\frac{\eta }{s}(T)$.

   nucl-exNPA(2019)·23 citations
2. 02*

   Extracting Nuclear Symmetry Energies at High Densities from Observations of Neutron Stars and Gravitational Waves

   Nai-Bo Zhang🇨🇳 · Bao-An Li🇺🇸

   By numerically inverting the Tolman-Oppenheimer-Volkov (TOV) equation using an explicitly isospin-dependent parametric Equation of State (EOS) of dense neutron-rich nucleonic matter, a restricted EOS parameter space is established using observational constraints on the radius, maximum mass, tidal polarizability and causality condition of neutron stars (NSs). The constraining band obtained for the pressure as a function of energy (baryon) density is in good agreement with that extracted recently by the LIGO+Virgo Collaborations from their improved analyses of the NS tidal polarizability in GW170817. Rather robust upper and lower boundaries on nuclear symmetry energies are extracted from the observational constraints up to about twice the saturation density ${\rho }_0$ of nuclear matter. More quantitatively, the symmetry energy at $2{\rho }_0$ is constrained to $E_{\mathrm{sym}}(2{\rho }_0)=46.9\pm 10.1$ MeV excluding many existing theoretical predictions scattered between $E_{\mathrm{sym}}(2{\rho }_0)=15$ and 100 MeV. Moreover, by studying variations of the causality surface where the speed of sound equals that of light at central densities of the most massive neutron stars within the restricted EOS parameter space, the absolutely maximum mass of neutron stars is found to be 2.40 M${}_{\odot }$ approximately independent of the EOSs used. This limiting mass is consistent with findings of several recent analyses and numerical general relativity simulations about the maximum mass of the possible super-massive remanent produced in the immediate aftermath of GW170817.

   ↳ nucl-thastro-ph.HEastro-ph.SRgr-qc+1EPJA(2019)·126 citations
3. 03*

   Upgrade of the ALICE central barrel tracking detectors: ITS and TPC

   P. Gasik fo the ALICE Collaboration🇩🇪

   The ALICE Collaboration will undertake a major upgrade of the detector apparatus during the second LHC Long Shutdown LS2 (2019-2020) in view of the Runs 3 and 4 (2021-2029). The objective of the upgrade is two-fold: i) an improvement of the tracking precision and efficiency, in particular in the low-momentum range; ii) an improvement of the readout capabilities of the experiment, in order to fully exploit the luminosity for heavy ions envisaged after LS2. The first goal will be achieved by replacing the Inner Tracking System with a new tracker, composed of seven layers of silicon pixel detectors. The new tracker will be made up of about 25000 Monolithic Active Pixel Sensors with fast readout, resulting in a material thickness reduced to 0.3% (inner layers) - 1% (outer layers) of the radiation length and a granularity of $28\times 28$ $\mu$m${}^2$. The second goal will be achieved, among other measures, by replacing the readout chambers of the 90 m${}^3$ Time Projection Chamber with Micro Pattern Gaseous Detectors. In particular, the new readout chambers will consist of stacks of 4 Gas Electron Multiplier foils combining different hole pitches. The upgraded detector will operate continuously without the use of a triggered gating grid. It will thus be able to record all Pb--Pb collisions at the LHC interaction rate of 50 kHz.

   ↳ physics.ins-detnucl-exNPA(2019)·5 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.