Wed·Jul 19, 2017Wednesday·July 19, 2017

1. 01*

   Searches for transverse momentum dependent flow vector fluctuations in Pb-Pb and p-Pb collisions at the LHC

   ALICE Collaboration

   The measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region $|\eta |<0.8$ as a function of centrality and transverse momentum $p_{\mathrm{T}}$ using two observables, to search for evidence of $p_{\mathrm{T}}$-dependent flow vector fluctuations. For Pb-Pb collisions at 2.76 TeV, the measurements indicate that $p_{\mathrm{T}}$-dependent fluctuations are only present for the second order flow vector. Similar results have been found for p-Pb collisions at 5.02 TeV. These measurements are compared to hydrodynamic model calculations with event-by-event geometry fluctuations in the initial state to constrain the initial conditions and transport properties of the matter created in Pb-Pb and p-Pb collisions.

   nucl-exhep-exJHEP(2017)·48 citations
2. 02*

   Estimating the Charm Quark Diffusion Coefficient and thermalization time from D meson spectra at RHIC and LHC

   Francesco Scardina🇮🇹 · Santosh K. Das🇮🇹 · Vincenzo Minissale🇮🇹 · Salvatore Plumari🇮🇹 · Vincenzo Greco🇮🇹

   We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of a Boltzmann transport approach. Non-perturbative interaction between heavy quarks and light quarks have been taken into account through a quasi-particle approach in which light partons are dressed with thermal masses tuned to lQCD thermodynamics. Such a model is able to describe the main feature of the non-perturbative dynamics: the enhancement of the interaction strength near $T_c$. We show that the resulting charm in-medium evolution is able to correctly predict simultaneously the nuclear suppression factor, $R_{AA}$, and the elliptic flow, $v_2$, at both RHIC and LHC energies and at different centralities. The hadronization of charm quarks is described by mean of an hybrid model of fragmentation plus coalescence and plays a key role toward the agreeement with experimental data. We also performed calculations within the Langevin approach which can lead to very similar $R_{AA}(p_T)$ as Boltzmann, but the charm drag coefficient as to be reduced by about a $30\%$ and also generates an elliptic flow $v_2(p_T)$ is about a $15\%$ smaller. We finally compare the space diffusion coefficient $2\pi T{D}_s$ extracted by our phenomenological approach to lattice QCD results, finding a satisfying agreement within the present systematic uncertainties. Our analysis implies a charm thermalization time, in the $p\to 0$ limit, of about $4-6fm/c$ which is smaller than the QGP lifetime at LHC energy.

   ↳ nucl-thhep-phnucl-exPRC(2017)·199 citations
3. 03*

   Pion transverse-momentum spectrum and elliptic anisotropy of partially coherent source

   Peng Ru🇨🇳 · Ghulam Bary🇨🇳 · Wei-Ning Zhang🇨🇳

   In this letter, we study the pion momentum distribution of a coherent source and investigate the influences of coherent emission on the pion transverse-momentum ($p_T$) spectrum and elliptic anisotropy. With a partially coherent source, constructed by a conventional viscous hydrodynamics model (chaotic part) and a parameterized expanding coherent source model, we reproduce the pion $p_T$ spectrum and elliptic anisotropy coefficient $v_2(p_T)$ in the peripheral Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. It is found that the influences of coherent emission on the pion $p_T$ spectrum and $v_2(p_T)$ are related to the initial size and shape of the coherent source, largely due to the interference effect. However, the effect of source dynamical evolution on coherent emission is relatively small. The results of the partially coherent source with 33% coherent emission and 67% chaotic emission are consistent with the experimental measurements of the pion $p_T$ spectrum, $v_2(p_T)$, and especially four-pion Bose-Einstein correlations.

   ↳ nucl-thhep-phnucl-exPLB(2018)·6 citations
4. 04*

   Probing short-range correlations in asymmetric nuclei with quasi-free pair knockout reactions

   Sam Stevens🇧🇪 · Jan Ryckebusch🇧🇪 · Wim Cosyn🇧🇪 · Andreas Waets

   Short-range correlations (SRC) in asymmetric nuclei with an unusual neutron-to-proton ratio can be studied with quasi-free two-nucleon knockout processes following the collision between accelerated ions and a proton target. We derive an approximate factorized cross section for those SRC-driven $p(A,p^{\prime }{N}_1{N}_2)$ reactions. Our reaction model hinges on the factorization properties of SRC-driven $A(e,e^{\prime }{N}_1{N}_2)$ reactions for which strong indications are found in theory-experiment comparisons. In order to put our model to the test we compare its predictions with results of ${}^{12}\text{C}(p,p^{\prime }pn)$ measurements conducted at Brookhaven National Laboratory (BNL) and find a fair agreement. The model can also reproduce characteristic features of SRC-driven two-nucleon knockout reactions, like back-to-back emission of the correlated nucleons. We study the asymmetry dependence of nuclear SRC by providing predictions for the ratio of proton-proton to proton-neutron knockout cross sections for the carbon isotopes ${}^{9-15}$C thereby covering neutron excess values $(N-Z)/Z$ between -0.5 and +0.5.

   ↳ nucl-thnucl-exPLB(2018)·13 citations
5. 05*

   Study of the d$E$/d$x$ resolution of a GEM Readout Chamber prototype for the upgrade of the ALICE TPC

   Andreas Mathis (on behalf of the ALICE collaboration)🇩🇪

   The ALICE Collaboration is planning a major upgrade of its central barrel detectors to be able to cope with the increased LHC luminosity beyond 2020. For the TPC, this implies a replacement of the currently used gated MWPCs (Multi-Wire Proportional Chamber) by GEM (Gas Electron Multiplier) based readout chambers. In order to prove, that the present particle identification capabilities via measurement of the specific energy loss are retained after the upgrade, a prototype of the ALICE IROC (Inner Readout Chamber) has been evaluated in a test beam campaign at the CERN PS. The d$E$/d$x$ resolution of the prototype has been proven to be fully compatible with the current MWPCs.

   ↳ physics.ins-detnucl-exEPJ Web Conf.(2018)·4 citations
6. 06*

   Upgrade of compact neutron spectrometer for high flux environments

   M. Osipenko🇮🇹 · A. Bellucci · V. Ceriale🇮🇹 · D. Corsini🇮🇹 · G. Gariano🇮🇹 · F. Gatti🇮🇹 · M. Girolami🇬🇧 · S. Minutoli🇮🇹 · F. Panza · M. Pillon · M. Ripani🇮🇹 · D.M. Trucchi🇮🇹

   In this paper a new version of Li6-based neutron spectrometer for high flux environments is described. The new spectrometer was built with commercial single crystal Chemical Vapour Deposition diamonds of electronic grade. These crystals feature better charge collection as well as higher radiation hardness. Ohmic metal contacts were deposited on the diamonds suppressing build-up of space charge observed in the previous prototypes. New passive preamplification of signal at detector side was implemented to improve the resolution. This preamplification is based on RF transformer not sensitive to high neutron flux. Compact mechanical design allowed to reduce detector size to a tube of 1 cm diameter and 13 cm long. The spectrometer was tested in thermal column of TRIGA reactor and at DD neutron generator. The test results indicate an energy resolution of 72 keV (RMS) and coincidence timing resolution of 68 ps (RMS). The measured data are in agreement with Geant4 simulations except for larger energy loss tail presumably related to imperfections of metal contacts and glue expansion.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2018)·2 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.