Tue·Oct 15, 2019Tuesday·October 15, 2019

1. 01*

   Time-based Reconstruction of Hyperons at PANDA at FAIR

   Jenny Regina🇸🇪 · Walter Ikegami Andersson🇸🇪

   The upcoming PANDA (anti-Proton ANnihilation at DArmstadt) experiment at FAIR (Facility for Anti-proton and Ion Research) offers unique possibilities for performing hyperon physics such as extraction of spin observables. Due to their relatively long-lived nature, the displaced decay vertices of hyperons impose a particular challenge on the track reconstruction and event building. The foreseen high luminosity and beam momenta at PANDA requires new advanced tracking algorithms for successfully identifying the hyperon events. The purely software based event selection of PANDA puts high demands on the online reconstruction. A fast, versatile, modular and dynamic approach to track reconstruction and event building is required. This text addresses the reconstruction algorithms used in the scheme such as the Cellular Automaton. A method for obtaining the z-component of the particle momentum is described as well as methods for merging the information from different track reconstruction detectors.

   nucl-exphysics.ins-det1 citation
2. 02*

   The JETSCAPE framework: p+p results

   A. Kumar🇺🇸 · Y. Tachibana🇺🇸 · D. Pablos🇺🇸 · C. Sirimanna🇺🇸 · R. J. Fries🇺🇸 · A. Angerami🇺🇸 · S. A. Bass🇺🇸 · S. Cao🇺🇸 · Y. Chen🇺🇸 · J. Coleman🇺🇸 · L. Cunqueiro🇺🇸 · T. Dai🇺🇸 and 34 other authors

   The JETSCAPE framework is a modular and versatile Monte Carlo software package for the simulation of high energy nuclear collisions. In this work we present a new tune of JETSCAPE, called PP19, and validate it by comparison to jet-based measurements in $p+p$ collisions, including inclusive single jet cross sections, jet shape observables, fragmentation functions, charged hadron cross sections, and dijet mass cross sections. These observables in $p+p$ collisions provide the baseline for their counterparts in nuclear collisions. Quantifying the level of agreement of JETSCAPE results with $p+p$ data is thus necessary for meaningful applications of JETSCAPE to A+A collisions. The calculations use the JETSCAPE PP19 tune, defined in this paper, based on version 1.0 of the JETSCAPE framework. For the observables discussed in this work calculations using JETSCAPE PP19 agree with data over a wide range of collision energies at a level comparable to standard Monte Carlo codes. These results demonstrate the physics capabilities of the JETSCAPE framework and provide benchmarks for JETSCAPE users.

   ↳ nucl-thhep-exnucl-exPRC(2020)·62 citations
3. 03*

   Precision Measurements of Fundamental Interactions with (Anti)Neutrinos

   R. Petti🇺🇸

   We discuss the main limitations of past neutrino scattering experiments and possible ways to address them in a next-generation program of precision measurements of fundamental interactions with (anti)neutrinos. A reduction of the longstanding precision gap with respect to electron scattering experiments could provide interesting synergies with the existing efforts in the fixed-target, collider, and nuclear physics communities.

   ↳ hep-exhep-phnucl-exnucl-th13 citations
4. 04*

   Probing the neutron skin with ultrarelativistic isobaric collisions

   Hanlin Li🇨🇳 · Hao-jie Xu🇨🇳 · Ying Zhou🇨🇳 · Xiaobao Wang🇨🇳 · Jie Zhao🇺🇸 · Lie-Wen Chen🇨🇳 · Fuqiang Wang🇺🇸

   Particle production in ultrarelativistic heavy ion collisions depends on the details of the nucleon density distributions in the colliding nuclei. We demonstrate that the charged hadron multiplicity distributions in isobaric collisions at ultrarelativistic energies provide a novel approach to determine the poorly known neutron density distributions and thus the neutron skin thickness in finite nuclei, which can in turn put stringent constraints on the nuclear symmetry energy.

   ↳ nucl-thnucl-exPRL(2020)·97 citations
5. 05*

   Two-Photon-Exchange effects in $ep\to en{\pi }^{+}$ and their corrections to separated cross sections ${\sigma }_{\text{L,T,LT,TT}}$ at small $-t$

   Hui-Yun Cao🇨🇳 · Hai-Qing Zhou🇨🇳

   In this work, the two-photon-exchange (TPE) effects in $ep\to en{\pi }^{+}$ at small $-t$ are discussed within a hadronic model. Under the pion dominance approximation the TPE contribution to the amplitude can be described by a scalar function in the limit $m_e\to 0$. The TPE contributions to the amplitude and the unpolarized differential cross section are both estimated when only the elastic intermediate state is considered. We find that the TPE corrections to the unpolarized differential cross section are about from $-4\%$ to $-20\%$ at $Q^2=1$--$1.6$ GeV${}^2$. After considering the TPE corrections to the experimental data sets of unpolarized differential cross section, we analyze the TPE corrections to the separated cross sections ${\sigma }_{\text{L,T,LT,TT}}$. We find that the TPE corrections (at $Q^2=1$--$1.6$ GeV${}^2$) to ${\sigma }_{\text{L}}$ are about from $-10\%$ to $-30\%$, to ${\sigma }_{\text{T}}$ are about $20\%$, and to ${\sigma }_{\text{LT,TT}}$ are much larger. By these analysis, we conclude that the TPE contributions in $ep\to en{\pi }^{+}$ at small $-t$ are important to extract the separated cross sections ${\sigma }_{\text{L,T,LT,TT}}$ and the electromagnetic magnetic form factor of ${\pi }^{+}$ in the experimental analysis.

   ↳ hep-phnucl-exnucl-thPRC(2020)·5 citations
6. 06*

   Different space-time freeze-out picture -- an explanation of different $\Lambda$ and $\bar{\Lambda }$ polarization?

   O. Vitiuk🇺🇦 · L. Bravina🇳🇴 · E. Zabrodin🇳🇴

   Thermal vorticity in non-central Au+Au collisions at energies $7.7\le \sqrt{s}\le 62.4$ GeV is calculated within the UrQMD transport model. Tracing the $\Lambda$ and $\bar{\Lambda }$ hyperons back to their last interaction point we were able to obtain the temperature and the chemical potentials at the time of emission by fitting the extracted bulk characteristics of hot and dense medium to statistical model of ideal hadron gas. Then the polarization of both hyperons was calculated. The polarization of $\Lambda$ and $\bar{\Lambda }$ increases with decreasing energy of nuclear collisions. The stronger polarization of $\bar{\Lambda }$ is explained by the different space-time distributions of $\Lambda$ and $\bar{\Lambda }$ and by different freeze-out conditions of both hyperons.

   ↳ hep-phnucl-exnucl-thPLB(2020)·81 citations
7. 07*

   Shear viscosity in microscopic calculations of A+A collisions at energies of Nuclotron-based Ion Collider fAcility (NICA)

   M. Teslyk🇳🇴 · L. Bravina🇳🇴 · O. Panova🇳🇴 · O. Vitiuk🇳🇴 · E. Zabrodin🇳🇴

   Time evolution of shear viscosity $\eta$, entropy density $s$, and their ratio $\eta /s$ in the central area of central gold-gold collisions at NICA energy range is studied within the UrQMD transport model. The extracted values of energy density, net baryon density and net strangeness density are used as input to (i) statistical model of ideal hadron gas to define temperature, baryo-chemical potential and strangeness chemical potential, and to (ii) UrQMD box with periodic boundary conditions to study the relaxation process of highly excited matter. During the relaxation stage, the shear viscosity is determined in the framework of Green-Kubo approach. The procedure is performed for each of 20 time slices, corresponding to conditions in the central area of the fireball at times from 1~fm/$c$ to 20~fm/$c$. For all tested energies the ratio $\eta /s$ reaches minimum, ${\left(\eta /s\right)}_{min}\approx 0.3$ at $t\approx 5$~fm/$c$. Then it increases up to the late stages of the system evolution. This rise is accompanied by the drop of both, temperature and strangeness chemical potential, and increase of baryo-chemical potential.

   ↳ nucl-thhep-phnucl-exPRC(2020)·13 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.