Tue·May 26, 2020Tuesday·May 26, 2020

1. 01*

   Unveiling the strong interaction among hadrons at the LHC

   ALICE Collaboration

   One of the key challenges for nuclear physics today is to understand from first principles the effective interaction between hadrons with different quark content. First successes have been achieved using techniques that solve the dynamics of quarks and gluons on discrete space-time lattices. Experimentally, the dynamics of the strong interaction have been studied by scattering hadrons off each other. Such scattering experiments are difficult or impossible for unstable hadrons and so high-quality measurements exist only for hadrons containing up and down quarks. Here we demonstrate that measuring correlations in the momentum space between hadron pairs produced in ultrarelativistic proton-proton collisions at the CERN Large Hadron Collider (LHC) provides a precise method with which to obtain the missing information on the interaction dynamics between any pair of unstable hadrons. Specifically, we discuss the case of the interaction of baryons containing strange quarks (hyperons). We demonstrate how, using precision measurements of p-omega baryon correlations, the effect of the strong interaction for this hadron-hadron pair can be studied with precision similar to, and compared with, predictions from lattice calculations. The large number of hyperons identified in proton-proton collisions at the LHC, together with an accurate modelling of the small (approximately one femtometre) inter-particle distance and exact predictions for the correlation functions, enables a detailed determination of the short-range part of the nucleon-hyperon interaction.

   nucl-exhep-exNature(2020)·248 citations
2. 02*

   Dielectron production in proton-proton and proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The first measurements of dielectron production at midrapidity ($|{\eta }_{\mathrm{e}}|<0.8$) in proton-proton and proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass $m_{\mathrm{ee}}$ and the pair transverse momentum $p_{\mathrm{T},\mathrm{ee}}$ in the ranges $m_{\mathrm{ee}}$ < 3.5 GeV/$c^2$ and $p_{\mathrm{T},\mathrm{ee}}$ < 8.0 GeV/$c^2$, in both collision systems. In proton-proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at $\sqrt{s}$ = 7 and 13 TeV. The slope of the $\sqrt{s}$ dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton-lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton-lead and proton-proton collisions are directly compared at the same $\sqrt{s_{\mathrm{NN}}}$ via the dielectron nuclear modification factor $R_{\mathrm{pPb}}$. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.

   nucl-exhep-exPhys. Rev. C 102 (2020) 055204; Phys. Rev…
3. 03*

   Directed, elliptic and higher order flow harmonics of protons, deuterons and tritons in Au+Au collisions at $\sqrt{s_{NN}}=2.4$ GeV

   HADES collaboration: J. Adamczewski-Musch🇩🇪 · O. Arnold🇩🇪 · C. Behnke🇩🇪 · A. Belounnas🇫🇷 · A. Belyaev🇷🇺 · J. C. Berger-Chen🇩🇪 · A. Blanco🇵🇹 · C. Blume🇩🇪 · M. Böhmer🇩🇪 · P. Bordalo🇵🇹 · S. Chernenko🇷🇺 · L. Chlad🇨🇿 and 113 other authors

   Flow coefficients $v_n$ of the orders $n=1-6$ are measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI for protons, deuterons and tritons as a function of centrality, transverse momentum and rapidity in Au+Au collisions at $\sqrt{s_{NN}}=2.4$ GeV. Combining the information from the flow coefficients of all orders allows to construct for the first time, at collision energies of a few GeV, a multi-differential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation-of-state of dense baryonic matter.

   nucl-exPRL(2020)·113 citations
4. 04*

   Isovector parton distribution functions of the proton on a superfine lattice

   Zhouyou Fan🇺🇸 · Xiang Gao🇺🇸 · Ruizi Li🇺🇸 · Huey-Wen Lin🇺🇸 · Nikhil Karthik🇺🇸 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸 · Sergey Syritsyn🇺🇸 · Yi-Bo Yang🇨🇳 · Rui Zhang🇺🇸

   We study isovector unpolarized and helicity parton distribution functions (PDF) of the proton within the framework of Large Momentum Effective Theory. We use a gauge ensemble, generated by the MILC Collaboration, with a superfine lattice spacing of $0.042$ fm and a pion mass of $310$ MeV, enabling us to simultaneously reach sub-fermi spatial separations and larger nucleon momenta. We compare the spatial dependence of quasi-PDF matrix elements in different renormalization schemes with the corresponding results of the global fits, obtained using 1-loop perturbative matching. We present determinations of the first four moments of the unpolarized and helicity PDFs of proton from the Ioffe-time dependence of the isovector matrix elements, obtained by employing a ratio-based renormalization scheme.

   ↳ hep-lathep-phnucl-exnucl-thPRD(2020)·83 citations
5. 05*

   Characterizing Proton-Proton Collisions at the Large Hadron Collider with Thermal Properties

   Dushmanta Sahu🇮🇳 · Raghunath Sahoo🇮🇳

   High-multiplicity proton-proton (pp) collisions at the Large Hadron Collider (LHC) energies have created a new domain of research to look for a possible formation of quark-gluon plasma in these events. In this paper, we estimate various thermal properties of the matter formed in pp collisions at the LHC energies, such as mean free path, isobaric expansivity, thermal pressure, and heat capacity using a thermodynamically consistent Tsallis distribution function. Particle species-dependent mean free path and isobaric expansivity are studied as functions of final state charged particle multiplicity for pp collisions at the center-of-mass energy $\sqrt{s}$ = 7 TeV. The effects of degree of non-extensivity, baryochemical potential, and temperature on these thermal properties are studied. The findings are compared with the theoretical expectations.

   ↳ hep-phhep-exnucl-exnucl-thMDPI Physics(2021)·8 citations
6. 06*

   Progress of Quantum Molecular Dynamics model and its applications in Heavy Ion Collisions

   Yingxun Zhang🇨🇳 · Ning Wang🇨🇳 · Qingfeng Li🇨🇳 · Li Ou🇨🇳 · Junlong Tian🇨🇳 · Min Liu🇨🇳 · Kai Zhao🇨🇳 · Xizhen Wu🇨🇳 · Zhuxia Li🇨🇳

   In this review article, we first briefly introduce the transport theory and quantum molecular dynamics model applied in the study of the heavy ion collisions from low to intermediate energies. The developments of improved quantum molecular dynamics model (ImQMD) and ultra-relativistic quantum molecular dynamics model (UrQMD), are reviewed. The reaction mechanism and phenomena related to the fusion, multinucleon transfer, fragmentation, collective flow and particle production are reviewed and discussed within the framework of the two models. The constraints on the isospin asymmetric nuclear equation of state and in-medium nucleon-nucleon cross sections by comparing the heavy ion collision data with transport models calculations in last decades are also discussed, and the uncertainties of these constraints are analyzed as well. Finally, we discuss the future direction of the development of the transport models for improving the understanding of the reaction mechanism, the descriptions of various observables, the constraint on the nuclear equation of state, as well as for the constraint on in-medium nucleon-nucleon cross sections.

   ↳ nucl-thnucl-exFront.Phys.(Beijing)(2020)·57 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.