Tue·Apr 9, 2019Tuesday·April 9, 2019

1. 01*

   Energy dependence study of directed flow in Au+Au collisions using an improved coalescence in AMPT model

   Kishora Nayak🇨🇳 · Shusu Shi🇨🇳 · Nu Xu🇨🇳 · Zi-Wei Lin🇺🇸

   The rapidity-odd component of directed flow ($v_1$) of identified hardons (${\pi }^{\pm }$, $K^{\pm }$, $K_S^0$, $p$, $\bar{p}$, $\varphi$, $\Xi$, $\bar{\Xi }$, $\Lambda$, $\bar{\Lambda }$) and partons ($u$, $\bar{u}$, $d$, $\bar{d}$, $s$, $\bar{s}$) in Au+Au collisions at various beam energies ($\sqrt{s_{\mathrm{NN}}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, 200 GeV) using a multi-phase transport model is analyzed. A data driven approach (inspired from the experimental analysis) is performed here to distinguish the transported and produced quarks which are found to have different directed flow values at various collision beam energies. The coalescence sum rule (Number of Constituent Quark scaling) violation is observed at lower energies where hadronic matters dominate. The strange quark ($s$) and $\varphi$ meson slope (d$v_1$/d$y$) show a double sign change around 14.5 GeV, unlike other partons and hadrons. It suggests that strange quark is more sensitive to the softening of Equation of State (EoS).

   nucl-exPRC(2019)·24 citations
2. 02*

   Observation of light-by-light scattering in ultraperipheral Pb+Pb collisions with the ATLAS detector

   ATLAS Collaboration

   This letter describes the observation of the light-by-light scattering process, $\gamma \gamma \to \gamma \gamma$, in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. The analysis is conducted using a data sample corresponding to an integrated luminosity of 1.73 nb${}^{-1}$, collected in November 2018 by the ATLAS experiment at the LHC. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy $E_{\text{T}}^{\gamma }>3$ GeV and pseudorapidity $|{\eta }_{\gamma }|<2.37$, diphoton invariant mass above 6 GeV, and small diphoton transverse momentum and acoplanarity. After applying all selection criteria, 59 candidate events are observed for a background expectation of 12 $\pm$ 3 events. The observed excess of events over the expected background has a significance of 8.2 standard deviations. The measured fiducial cross section is 78 $\pm$ 13 (stat.) $\pm$ 7 (syst.) $\pm$ 3 (lumi.) nb.

   ↳ hep-exnucl-exPRL(2019)·269 citations
3. 03*

   Charge asymmetry dependence of the elliptic flow splitting in relativistic heavy-ion collisions

   Zhang-Zhu Han🇨🇳 · Jun Xu🇨🇳

   The elliptic flow splitting $\Delta v_2$ between $\bar{u}$ and $u$ quarks as well as between ${\pi }^{-}$ and ${\pi }^{+}$ in midcentral Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV has been studied, based on the framework of an extended multiphase transport model with the partonic evolution described by the chiral kinetic equations of motion. Within the available statistics, the slope of $\Delta v_2$ between $\bar{u}$ and $u$ quarks with respect to the electric charge asymmetry $A_{ch}$ from the linear fit is found to be negative, due to the correlation between the velocity and the coordinate in the initial parton phase-space distribution. Simulations with the magnetic field in QGP overestimate the splitting of the spin polarization between $\Lambda$ and $\bar{\Lambda }$ observed experimentally, with the latter more consistent with results under the magnetic field in vacuum. Considering the uncertainties from the magnetic field, the quark-antiquark vector interaction, and the hadronization, as well as the hadronic evolution, our study shows that the experimentally observed positive slope of $\Delta v_2$ with respect to $A_{ch}$ is not likely due to the chiral magnetic wave.

   ↳ nucl-thhep-exnucl-exPRC(2019)·10 citations
4. 04*

   Pulse-shape discrimination potential of new scintillator material: La-GPS:Ce

   Keita Mizukoshi🇯🇵 · Takashi Iida🇯🇵 · Izumi Ogawa🇯🇵 · Kensei Shimizu🇯🇵 · Shunsuke Kurosawa🇯🇵 · Kei Kamada🇯🇵 · Masao Yoshino🇯🇵 · Akira Yoshikawa🇯🇵

   (Gd,La)${}_2$Si${}_2$O${}_7$:Ce (La-GPS:Ce) is a new scintillator material with high light output, high energy resolution, and fast decay time. Moreover, the scintillator has a good light output even at high temperature (up to 150${}^{\circ }$C) and is non-hygroscopic in nature; thus, it is especially suitable for underground resource exploration. Particle identification greatly expands the possible applications of scintillator. For resource exploration, the particle identification should be completed in a single pulse only. The pulse-shape discrimination of the scintillator was confirmed. We compared two methods; a double gate method and a digital filter method. Using digital filter method (shape indicator), F-measure to evaluate a separation between $\alpha$ and $\gamma$ particles was obtained to be 0.92 at 0.66 MeVee.

   ↳ physics.ins-dethep-exnucl-exJINST(2019)·2 citations
5. 05*

   Results on heavy ion physics at LHCb

   Giacomo Graziani🇮🇹

   In the last years, the \lhcb experiment established itself as an important contributor to heavy ion physics by exploiting some of its specific features. Production of particles, notably heavy flavour states, can be studied in p-p, p-Pb and Pb-Pb collisions at LHC energies in the forward rapidity region (pseudorapidity between 2 and 5), providing measurements which are highly complementary to the other LHC experiments. Moreover, owing to its forward geometry, the detector is also well suited to study fixed-target collisions, obtained by impinging the LHC beams on gas targets with different mass numbers. In this configuration, p-A collisions can be studied at the relatively unexplored scale of sqrt(sNN) ~ 100 GeV, also providing valuable inputs to cosmic ray physics. An overview of the measurements obtained so far by the LHCb ion program is presented.

   ↳ hep-exnucl-exJ.Phys.Conf.Ser.(2019)·8 citations
6. 06*

   Investigating the 10Li continuum through 9Li(d,p)10Li reactions

   A.M. Moro🇪🇸 · J. Casal🇪🇸 · M. Gómez-Ramos🇪🇸

   The continuum structure of the unbound system ${}^{10}$Li, inferred from the ${}^9$Li$(d,p{)}^{10}$Li transfer reaction, is reexamined. Experimental data for this reaction, measured at two different energies, are analyzed with the same reaction framework and structure models. It is shown that the seemingly different features observed in the measured excitation energy spectra can be understood as due to the different incident energy and angular range covered by the two experiments. The present results support the persistence of the $N=7$ parity inversion beyond the neutron dripline as well as the splitting of the well-known low-lying $p$-wave resonance. Furthermore, they provide indirect evidence that most of the $\ell =2$ single-particle strength, including possible $d_{5/2}$ resonances, lies at relatively high excitations energies.

   ↳ nucl-thnucl-exPLB(2019)·12 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.