Mid-rapidity Region Research Articles

Search for baryon junctions in photonuclear processes and isobar collisions at RHIC

During the early development of quantum chromodynamics, it was proposed that baryon number could be carried by a non-perturbative Y-shaped topology of gluon fields, called the gluon junction, rather than by the valence quarks as in the QCD standard model. A puzzling feature of ultra-relativistic nucleus-nucleus collisions is the apparent substantial baryon excess in the mid-rapidity region that could not be adequately accounted for in most conventional models of quark and diquark transport. The transport of baryonic gluon junctions is predicted to lead to a characteristic exponential distribution of net-baryon density with rapidity and could resolve the puzzle. In this context we point out that the rapidity density of net-baryons near mid-rapidity indeed follows an exponential distribution with a slope of -0.61±0.03\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-0.61\\pm 0.03$$\\end{document} as a function of beam rapidity in the existing global data from A+A collisions at AGS, SPS and RHIC energies. To further test if quarks or gluon junctions carry the baryon quantum number, we propose to study the absolute magnitude of the baryon vs. charge stopping in isobar collisions at RHIC. We also argue that semi-inclusive photon-induced processes (γ+p\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma +p$$\\end{document}/A) at RHIC kinematics provide an opportunity to search for the signatures of the baryon junction and to shed light onto the mechanisms of observed baryon excess in the mid-rapidity region in ultra-relativistic nucleus-nucleus collisions. Such measurements can be further validated in A+A collisions at the LHC and e+p\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e+p$$\\end{document}/A collisions at the EIC.

Observation of abnormal suppression of f0(980) production in p–Pb collisions at [formula omitted] = 5.02 TeV

The dependence of f0(980) production on the final-state charged-particle multiplicity in p–Pb collisions at sNN=5.02 TeV is reported. The production of f0(980) is measured with the ALICE detector via the f0(980)→π+π− decay channel in a midrapidity region of −0.5<y<0. Particle yield ratios of f0(980) to π and K⁎(892)0 are found to be decreasing with increasing charged-particle multiplicity. The magnitude of the suppression of the f0(980)/π and f0(980)/K⁎(892)0 yield ratios is found to be dependent on the transverse momentum pT, suggesting different mechanisms responsible for the measured effects. Furthermore, the nuclear modification factor QpPb of f0(980) is measured in various multiplicity ranges. The QpPb shows a strong suppression of the f0(980) production in the pT region up to about 4 GeV/c. The results on the particle yield ratios and QpPb for f0(980) may help to understand the late hadronic phase in p–Pb collisions and the nature of the internal structure of f0(980) particle.

Extracting the hyperon-nucleon interaction via collective flows in heavy-ion collisions

The 2-body hyperon-nucleon interaction softens the equation of state of neutron star matter and leads to the maximum mass of neutron star to be 1.3-1.6M⊙, which deviates from the recent observation with the masses of PSR J0348+0432 (2.01±0.04M⊙) and J0740+6620 (2.14−0.09+0.10M⊙). One attempt is to introduce the more repulsive hyperon-nucleon interaction above the saturation density. A phenomenological Λ potential by fitting the 3-body ΛNN results of chiral effective field theory is implemented into the quantum molecular dynamics transport model to solve the ‘hyperon puzzle’ in neutron stars. It is found that the directed and elliptic flows are sensitive to the high-density hyperon-nucleon potentials in collisions of 197Au + 197Au and 124Sn + 124Sn. The influence of the phenomenological potential on the Λ yields, rapidity distributions and transverse momentum spectra is negligible in comparison with the ones calculated by the well-known relativistic mean-field model. The inclusion of the ΛN, ΣN and ΞN potentials leads to the reduction of hyperon production in the midrapidity region. The Λ directed flows and the slope in the midrapidity region are enhanced with the phenomenological potential and more consistent with the STAR data in collisions of 197Au + 197Au at sNN=3 GeV.

Energy dependence of J/ψ production in pp collisions from the PACIAE model

In this work we investigate the J/ψ production in proton-proton collisions at the center-of-mass energy (s) equal to 2.76, 5.02, 7, 8, and 13 TeV with the parton and hadron cascade model PACIAE 2.2a. It is based on PYTHIA but extended considering the partonic and hadronic rescatterings before and after hadronization, respectively. In the PYTHIA sector the J/ψ production quantum chromodynamics processes are selected specially and a bias factor is proposed correspondingly. The calculated total cross sections, the transverse momentum differential, and the rapidity differential cross sections of J/ψ in the forward rapidity region reproduce the corresponding experimental measurements reasonably well. In the mid-rapidity region, the double-differential cross sections at s=5.02, 7, and 13 TeV are also in a good agreement with the experimental data. Moreover, we interpolate the double-differential cross section as well as the total cross section of J/ψ in the mid-rapidity region at s=8 TeV, which could be validated if the experimental data are available. Published by the American Physical Society 2024

Suppression of spin polarization as an indicator of QCD critical point

We study the impact of the QCD critical point (CP) on the spin polarization of Lambda -hyperon generated by the thermal vorticity in viscous quark gluon plasma (QGP). The equations of the relativistic causal viscous hydrodynamics have been solved numerically in (3+1) dimensions to evaluate the thermal vorticity. The effects of the CP have been incorporated through the equation of state (EoS) and the scaling behavior of the transport coefficients. We observe a significant suppression of the spin polarization around mid-rapidity region induced by the CP and propose that such changed behaviour of the spin polarization can be used to detect the CP. To the best of our knowledge this is the first study on the effects of critical point on the spin polarization in QCD matter.

Light-nuclei production in pp and pA collisions in the baryon canonical ensemble approach

The increase in yields of light nuclei with charged particle multiplicity, as reported by the ALICE collaboration at CERN in p-p and p-Pb collisions at the LHC energy is investigated in the thermal hadron resonance gas model. The model is extended to account for exact baryon number conservation. The focus is on the production of protons, deuterons, $^3$He, and $^3_\Lambda$H. A very good description of proton and deuteron yields is obtained as a function of charged particle multiplicity in the mid-rapidity region using the same fixed temperature as in central Pb-Pb collisions. The yields of light nuclei $^3$He and $^3_\Lambda$H though qualitatively explained as a function of multiplicity, are lower than the model expectation. One of the possible reasons could be that for $^{3}$He and $^{3}_{\Lambda}$H, the chemical equilibrium is not yet reached at small multiplicities.

Λ Polarization and Vortex Rings in Heavy-Ion Collisions at NICA Energies

We review recent studies of vortical motion and the resulting polarization of Λ hyperons in heavy-ion collisions at NICA energies, in particular, within the model of three-fluid dynamics (3FD). This includes predictions of the global Λ polarization and ring structures that appear in Au+Au collisions. The global Λ polarization in Au+Au collisions is calculated, including its rapidity and centrality dependence. The contributions of the thermal vorticity and meson-field term (proposed by Csernai, Kapusta, and Welle) to the global polarization are considered. The results are compared with data from recent STAR and HADES experiments. It is predicted that the polarization maximum is reached at sNN≈ 3 GeV if the measurements are performed with the same acceptance. It is demonstrated that a pair of vortex rings are formed, one at forward rapidities and another at backward rapidities, in ultra-central Au+Au collisions at sNN&gt; 4 GeV. The vortex rings carry information about the early stage of the collision, in particular, the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable RΛ, even in the midrapidity region at sNN= 5–20 GeV. At forward/backward rapidities, the RΛ signal is expected to be stronger. The possibility of observing the vortex-ring signal against the background of non-collective transverse polarization is discussed.

MT scaling approach to study the identical spectral shape and similar suppression patterns of π0 and η mesons at RHIC and LHC energies

We present a systematic study of the transverse mass ([Formula: see text]) spectra of [Formula: see text] and [Formula: see text] mesons in [Formula: see text] collisions at [Formula: see text][Formula: see text]GeV, [Formula: see text] collisions at [Formula: see text][Formula: see text]GeV, [Formula: see text] collisions at [Formula: see text][Formula: see text]TeV and [Formula: see text] collisions at [Formula: see text][Formula: see text]TeV. The published data of invariant yields of [Formula: see text] and [Formula: see text] mesons as a function of [Formula: see text] are taken from PHENIX and from ALICE collaborations in the mid-rapidity region for different centrality cases. The primary object is to check the similar suppression patterns and identical spectral shapes of [Formula: see text] and [Formula: see text] mesons at different center-of-mass energies in different collision systems. We employ [Formula: see text] scaling approach to study the spectral shapes of [Formula: see text] meson from the given pion ([Formula: see text]) spectra. For this purpose, we use the modified Hagedorn function as a fit function. We obtain [Formula: see text] scaled [Formula: see text] ratio to study the spectral shape and suppression pattern of [Formula: see text] and [Formula: see text] mesons. This ratio is useful to obtain the decay contribution of [Formula: see text] and [Formula: see text] mesons in photonic and leptonic channels but also points to the quantitative changes in the dynamics of the heavy ion collisions.

Elliptic flow splitting of charged pions in relativistic heavy-ion collisions

Relativistic heavy-ion collisions are an important experimental way of studying the new state of matter as well as the phase diagram of the quantum chromodynamics (QCD) under extremely high temperatures and high densities. In recent years, the beam-energy scan program has been carried out on the relativistic heavy-ion collider at Brookhaven National Laboratory in USA, and the STAR collaboration at relativistic heavy ion collision (RHIC) has measured the difference in the elliptic flow &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$v_2$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; between &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$\pi^-$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$\pi^+$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; on an event-by-event basis, and found a linear dependence on the charge asymmetry &lt;i&gt;A&lt;/i&gt;&lt;sub&gt;ch&lt;/sub&gt; of the collision system, which is considered as a possible signal of the chiral magnetic wave. Based on the extended multi-phase transport model (AMPT), this paper uses a 3 flavor Nambu-Jona-Lasinio (NJL) model to study the quark isospin Mean-field potential, which provides a new idea for explaining the experimental phenomenon of the linear relationship between the pion elliptic flow splitting &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$\Delta v_2=v_2(\pi^-)- $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;&lt;inline-formula&gt;&lt;tex-math id="M8-1"&gt;\begin{document}$ v_2(\pi^+)$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M8-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and charge asymmetry &lt;i&gt;A&lt;/i&gt;&lt;sub&gt;ch&lt;/sub&gt;. Our results show that isovector interaction can cause a splitting of the isospin asymmetric quark matter mean-field potential, manifesting as &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$d(\bar{u})$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; quarks experiencing a mean-field potential greater than &lt;inline-formula&gt;&lt;tex-math id="M10"&gt;\begin{document}$u(\bar{d})$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M10.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M10.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; quarks. Therefore, &lt;inline-formula&gt;&lt;tex-math id="M11"&gt;\begin{document}$d(\bar{u})$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M11.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M11.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; quarks experience more repulsion than &lt;inline-formula&gt;&lt;tex-math id="M12"&gt;\begin{document}$u(\bar{d})$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M12.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M12.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; quarks in collision processes, resulting in a small increase in the elliptic flow of the partial subflow &lt;inline-formula&gt;&lt;tex-math id="M13"&gt;\begin{document}$v_2(d)$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M13.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M13.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M14"&gt;\begin{document}$v_2(\bar{u})$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M14.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M14.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, while &lt;inline-formula&gt;&lt;tex-math id="M15"&gt;\begin{document}$v_2(u)$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M15.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M15.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M16"&gt;\begin{document}$v_2(\bar{d})$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M16.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M16.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; decrease slightly. In the hadronization process, the &lt;inline-formula&gt;&lt;tex-math id="M17"&gt;\begin{document}$\pi$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M17.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M17.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; elliptic flow splitting occurs due to the split of &lt;inline-formula&gt;&lt;tex-math id="M18"&gt;\begin{document}$d$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M18.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M18.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M19"&gt;\begin{document}$u$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M19.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M19.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; elliptic flows combined with the split of &lt;inline-formula&gt;&lt;tex-math id="M20"&gt;\begin{document}$\bar{u}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M20.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M20.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M21"&gt;\begin{document}$\bar{d}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M21.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M21.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; elliptic flows. We also found a linear correlation between charge asymmetry and isospin asymmetry at mid-rapidity region from our transport model, and thus explained the experimental phenomenon of the linear relationship between the pion elliptic flow splitting &lt;inline-formula&gt;&lt;tex-math id="M22"&gt;\begin{document}$\Delta v_2$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M22.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230454_M22.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and charge asymmetry &lt;i&gt;A&lt;/i&gt;&lt;sub&gt;ch&lt;/sub&gt; by using the isospin mean-field potential of quark matter. Further, isospin properties of quark matter also provide a theoretical basis for isobar collisions and the equation of state of compact star matter.

Probing neutron-skin thickness with free spectator neutrons in ultracentral high-energy isobaric collisions

We show that the yield ratio of free spectator neutrons produced in high-energy 96Zr+96Zr to 96Ru+96Ru collisions is a clean probe of the neutron-skin thickness of colliding nuclei and the slope parameter L of the symmetry energy. The idea is demonstrated based on the proton and neutron density distributions via a state-of-the-art Skyrme-Hartree-Fock-Bogolyubov calculation. Among spectator nucleons given by the Glauber model, free spectator neutrons include those from direct production that survive from clusterization as well as those from deexcitation of heavy clusters described by the popular GEMINI model. More free neutrons are produced in collisions of 96Zr nucleus due to its larger neutron skin, compared to those produced in collisions of 96Ru nucleus with a smaller neutron skin. The difference of the free spectator neutron yield is further increased with the increasing difference of the neutron-skin thickness between 96Zr and 96Ru with a larger L value, and the increase in ultracentral collisions is particularly insensitive to model details and experimental uncertainties. Since the production of free spectator neutrons is not affected by the complicated dynamics in the mid-rapidity region, the ratio of their multiplicities in ultracentral isobaric collisions is a robust observable for constraining the neutron skin and L value.

Charge-dependent directed flows in heavy-ion collisions by Boltzmann-Maxwell equations

We have calculated the directed flow ${v}_{1}$ and charge-dependent directed flow $\mathrm{\ensuremath{\Delta}}{v}_{1}$ of pions and protons in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=200$ GeV by solving the coupled Boltzmann-Maxwell equations self-consistently. Our numerical results show that ${v}_{1}$ for pions and protons are all negative in the positive midrapidity region and have similar behavior and magnitude. In contrast we find a quite different behavior in $\mathrm{\ensuremath{\Delta}}{v}_{1}$ for pions and protons. The difference lies in that $\mathrm{\ensuremath{\Delta}}{v}_{1}$ for protons mainly comes from pressure gradients of the medium, while the dominant contribution to $\mathrm{\ensuremath{\Delta}}{v}_{1}$ for pions is from electromagnetic fields. Our results indicate that the effect of the electric field will slightly exceed that of the magnetic field and lead to a small negative slope of $\mathrm{\ensuremath{\Delta}}{v}_{1}$ for pions.

On the Ambiguity of the Definition of Shear and Spin-Hall Contributions to the Λ Polarization in Heavy-Ion Collisions

Recently proposed thermal-shear and spin-Hall contributions to the particle polarization in heavy-ion collisions are discussed. Alternative definitions of the thermal-shear contribution, i.e., those of Becattini–Buzzegoli–Palermo on the one hand and Liu–Yin on the other, are very similar in the midrapidity region while quite different at forward-backward rapidities, which are measured in fixed-target experiments. It is shown that the thermal-shear contribution to the global polarization with momentum averaging extended to all momenta is very different within these alternative definitions. The spin-Hall contribution to the global polarization, defined similarly to the Liu–Yin shear one, is identically zero, if averaging runs over all momenta. Only application of restrictive momentum acceptance and the boost (to Λ rest frame) correction result in nonzero global spin-Hall polarization. If the spin-Hall contribution were defined similarly to Becattini–Buzzegoli–Palermo shear one, the global spin-Hall polarization would be nonzero even without any acceptance and the boost correction.

Measurements of electrons from heavy-flavor hadron decays in 27, 54.4, and 200 GeV Au+Au collisions in STAR

In these proceedings, we present the measurements of nuclear modification factors for electrons from open charm (c→e) and bottom hadron decays (b→e) at mid-rapidity region in Au+Au collisions at √SNN = 200 GeV. The significance of the difference in nuclear modification factors between b→e and c→e is ≥ 3σ. We also present the measurements of the elliptic flow (v2) of inclusive heavy-flavor hadron decayed electrons (HFE) in Au+Au collisions at √SNN = 27 and 54.4 GeV. The results show non-zero HFE v2 in 54.4 GeV Au+Au collisions and a hint of smaller HFE v2 in 27 GeV Au+Au collisions than those at 54.4 and 200 GeV.

Recent J/ψ results in p+p and Au+Au collisions from STAR

In these proceedings, we present the measurements of inclusive J/ψ production at mid-rapidity region (|y| &lt; 1.0) in Au+Au collisions at √SNN = 54.4 GeV by the STAR experiment. The dependences of nuclear modification factor (RAA) on centrality and transverse momentum (pT) are presented and compared to model calculations. No significant energy dependence of RAA is found within uncertainties. We also report the distribution of z(J/&lt;) = pTJ/&lt;/pTjet and the fraction of J/ψ produced within a charged jet at mid-pseudorapidity (|η| &lt; 0.6) with kinematic cuts of pTjet &gt; 10 GeV/c and pTJ/&lt; &gt; 5 GeV/c in p+p collisions at √S = 500 GeV. Comparisons to model calculations are presented and physics implications are discussed.

Theoretical analysis of pT spectra of light-flavor hadrons in p + p collisions at s = 7 TeV under differential and single freeze-out scenarios

We present the published data of ALICE at mid-rapidity region ([Formula: see text]) to study the [Formula: see text] spectra of light-flavor hadrons in different charged-particle multiplicities ([Formula: see text]) for [Formula: see text] collisions at [Formula: see text] TeV. We parametrize the [Formula: see text] spectra of different hadrons such as pion ([Formula: see text]), kaon ([Formula: see text]), [Formula: see text], [Formula: see text] ([Formula: see text]), [Formula: see text], proton ([Formula: see text]), lambda ([Formula: see text]), cascade ([Formula: see text]) and omega ([Formula: see text]) using Tsallis distribution. We perform this analysis by considering both differential and single freeze-out scenarios. In the differential freeze-out scenario, both the Tsallis parameters [Formula: see text] and [Formula: see text] increase with charged multiplicities for most of the particles. This implies that the multipartonic interactions increase the multiplicities in [Formula: see text] collisions and it brings the system towards thermal equilibrium. Here we observe that both [Formula: see text] and [Formula: see text] have different trends with different masses of particles. The parameters [Formula: see text] and [Formula: see text] are higher for massive particles (except for multistrange baryons) in comparison to lighter ones, which supports the differential freeze-out scenario and suggests that massive particles freeze-out earlier from the system. In the case of single freeze-out scenario, the value of parameter [Formula: see text] has a little variation with multiplicity and the parameter [Formula: see text] increases with multiplicity. This implies that the degree of thermalization remains similar for the events of different multiplicity classes.

Multiplicity dependence of (multi)strange baryons in the canonical ensemble with phase shift corrections

The increase in strangeness production with charged particle multiplicity, as seen by the ALICE collaboration at CERN in $p\text{\ensuremath{-}}p$, $p$-Pb, and Pb-Pb collisions, is investigated in the hadron resonance gas model taking into account interactions among hadrons using $S$-matrix corrections based on known phase shift analyses. Strangeness conservation is taken into account in the framework of the canonical strangeness ensemble. A very good description is obtained for the variation of the strangeness content in the final state as a function of the number of charged hadrons in the midrapidity region using the same fixed temperature value as obtained in the most central Pb-Pb collisions and with a fixed strangeness suppression factor ${\ensuremath{\gamma}}_{s}=1$. It is shown that the number of charged hadrons is linearly proportional to the volume of the system. For small multiplicities the canonical ensemble with local strangeness conservation restricted to midrapidity leads to a stronger suppression of (multi)strange baryons than seen in the data. This is compensated by introducing a global conservation of strangeness in the whole phase-space which is parametrized by the canonical correlation volume larger than the fireball volume at the midrapidity. The results on comparing the hadron resonance gas model with and without S-matrix corrections, are presented in detail. It is shown that the interactions introduced by the phase shift analysis via the $S$-matrix formalism are essential for a better description of the yields data.

Isospin equilibration phenomenon and mid-rapidity IMF emission in the 48Ca +27 Al 40 MeV/nucleon collision

It is discussed the dynamics of Isospin equilibration in reactions involving the production of Intermediate Mass Fragment (IMF) in the mid-rapidity region. The investigation proceeds through the measurements of the reduced value of the total dipolar signal obtained from the measured velocities and charges of all fragments produced in the collision 48 Ca +27 Al at 40 MeV/nucleon. Preliminary experimental results, along with the comparison with CoMD-III model calculations for different density functionals related to the symmetry energy, are presented.

Correlation between global polarization, angular momentum, and flow in heavy-ion collisions

Possible correlations of the global polarization of $\Lambda$ hyperons with the angular momentum and transverse flow in the central region of colliding nuclei are studied based on refined estimate of the global polarization. Simulations of Au+Au collisions at collision energies $\sqrt{s_{NN}}=$ 6-40 GeV are performed within the model of the three-fluid dynamics. Within the crossover and first-order-phase-transition scenarios this refined estimate quite satisfactorily reproduces the experimental STAR data. Hadronic scenario fails at high collision energies, $\sqrt{s_{NN}}>$ 10 GeV, and even predicts opposite sign of the global polarization. It is found that the global polarization correlates with neither the angular momentum accumulated in the central region nor with directed and elliptic flow. At the same time we observed correlation between the angular momentum and directed flow in both their time and collision-energy dependence. These results suggest that, although initially the angular momentum is the driving force for the vortex generation, later the angular momentum and vortex motion become decorrelated in the midrapidity region. Then the midrapidity angular momentum is determined by the pattern of the directed flow and even becomes negative when the antiflow occurs. At the freeze-out stage, the dominant part of the participant angular momentum is accumulated in the fragmentation regions.

Long-Range Correlations between Observables in a Model with Translational Invariance in Rapidity

We estimate the impact of the fixation of the total number of sources (quark–gluon strings) on the long-range rapidity correlations between different observables. In our approach this condition models the fixation of the collision centrality class, what is the usual practice in modern collider experiments, like Relativistic Heavy Ion Collider (RHIC), Large Hadron Collider (LHC) and so on. The estimates are obtained under the assumption of the translational invariance in rapidity, which is usually assumed in mid-rapidity region at high energies. Based on these assumptions, we are developing a technique for the analytical calculation of various average values of extensive and intense variables at high string densities on the transverse lattice, taking into account the effects of string fusion, leading to the formation of string clusters. Using this technique we calculate the asymptotes of the correlations coefficients both between the multiplicities and between the multiplicity and the event-mean transverse momentum of particles in two separated rapidity intervals. As a result, we found that fixing the total number of strings has a significant effect on the behavior of both types of correlations, especially in the case of a uniform distribution of strings in the transverse plane.

Intermittency Study of Charged Particles Generated in Pb-Pb Collisions at sNN=2.76 TeV Using EPOS3

Charged particle multiplicity fluctuations in Pb-Pb collisions are studied for the central events generated using EPOS3 (hydro and hydro+cascade) at sNN=2.76 TeV. Intermittency analysis is performed in the midrapidity region in two-dimensional (η, ϕ) phase space within the narrow transverse momentum (pT) bins in the low pT region (pT≤1.0 GeV/c). Power-law scaling of the normalized factorial moments with the number of bins is not observed to be significant in any of the pT bins. Scaling exponent ν, deduced for a few pT bins, is greater than that of the value 1.304, predicted for the second-order phase transition by the Ginzburg-Landau theory. The link in the notions of fractality is also studied. Generalized fractal dimensions, Dq, are observed to decrease with the order of the moment q suggesting the multifractal nature of the particle generation in EPOS3.