Multiplicity dependence for the production of strange hadrons and charged particles in proton-proton collisions

In this contribution, the production rates and the transverse momentum distributions of strange hadrons are reported as a function of charged particle multiplicity. In this analysis, the data collected in proton-proton collisions at $\sqrt{s}$ = 13 TeV with the ALICE detector at the LHC are used. It is found that the production rate of $K_{S}^{0}$, $\Lambda$, $\Xi^{\pm}$, and $\Omega$ increases with multiplicity faster than that for charged particles. The higher the strangeness content of the hadron, the more pronounced is the increase. Moreover, the energy and multiplicity dependence of charged particle production in pp collisions are presented and the results are compared to predictions from Monte Carlo (MC) event generators. It turns out that the average multiplicity density increases steeply with center-of-mass energy for high multiplicity classes.Comment: Proceedings of XXV Cracow EPIPHANY Conference on Advances in Heavy Ion Physics conference, 8-11 January 201

Evolution of strange and multi-strange hadron production with relative transverse multiplicity activity in underlying event

In this work, relative Underlying Event (UE) transverse multiplicity activity classifier ($R_{\rm {T}}$) is used to study the strange and multi-strange hadron production in proton-proton collisions. Our study with $R_{\rm {T}}$ would allow to disentangle these particles which are originating from the soft and hard QCD processes. We have used the PYTHIA 8 MC with different implementation of color reconnection and rope hydronisation models to demonstrate the proton-proton collisions data at $\sqrt{s}$ = 13 TeV. The relative production of strange and multi-strange hadrons are discussed extensively in low and high transverse activity region. In this contribution, the relative strange hadron production is enhanced with increasing $R_{\rm {T}}$. This enhancement is significant for strange baryons as compared to mesons. In addition, the particle ratios as a function of $R_{\rm {T}}$ confirms the baryon enhancement in newCR, whereas Rope model confirms the baryon enhancement only with strange quark content. An experimental confirmation of such results will provide more insight into the soft physics in the transverse region which will be useful to investigate various tunes based on hadronization and color reconnection schemes

Dynamics of Hot QCD Matter -- Current Status and Developments

The discovery and characterization of hot and dense QCD matter, known as Quark Gluon Plasma (QGP), remains the most international collaborative effort and synergy between theorists and experimentalists in modern nuclear physics to date. The experimentalists around the world not only collect an unprecedented amount of data in heavy-ion collisions, at Relativistic Heavy Ion Collider (RHIC), at Brookhaven National Laboratory (BNL) in New York, USA, and the Large Hadron Collider (LHC), at CERN in Geneva, Switzerland but also analyze these data to unravel the mystery of this new phase of matter that filled a few microseconds old universe, just after the Big Bang. In the meantime, advancements in theoretical works and computing capability extend our wisdom about the hot-dense QCD matter and its dynamics through mathematical equations. The exchange of ideas between experimentalists and theoreticians is crucial for the progress of our knowledge. The motivation of this first conference named "HOT QCD Matter 2022" is to bring the community together to have a discourse on this topic. In this article, there are 36 sections discussing various topics in the field of relativistic heavy-ion collisions and related phenomena that cover a snapshot of the current experimental observations and theoretical progress. This article begins with the theoretical overview of relativistic spin-hydrodynamics in the presence of the external magnetic field, followed by the Lattice QCD results on heavy quarks in QGP, and finally, it ends with an overview of experiment results.Comment: Compilation of the contributions (148 pages) as presented in the `Hot QCD Matter 2022 conference', held from May 12 to 14, 2022, jointly organized by IIT Goa & Goa University, Goa, Indi

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Measurements of Dileptons and Photon Pairs from Two-photon Scattering in Ultra-Peripheral and Hadronic Pb+Pb Collisions with ATLAS Detector

In ultra-relativistic heavy-ion collisions, one expects copious rates of γ + γ processes through the interaction of the large electromagnetic fields of the nuclei, which can produce new particles (e.g. leptons) or even lead to light-by-light scattering via loop diagrams. The latter process is a notable prediction of QED and was only recently observed by ATLAS using the full 2018 dataset. In ultra-peripheral collisions (UPCs), characterized by large impact parameter between the nuclei, the outgoing leptons and photons are produced exclusively, and exhibit a strong back-to-back momentum correlation, with long tails induced by higher-order QED effects. This talk presents measurements of dilepton production and light-by-light scattering performed by the ATLAS collaboration. The angular correlations as well as differential production cross sections in UPCs are measured and compared to theoretical models, including final state QED radiation. The role of forward neutron production in disentangling pure QED and dissociative processes will also be discussed. Finally, limits on axion-like particle production, from the observed light-by-light cross sections, will be discussed. Muon pairs produced the same two-photon scattering process in hadronic Pb+Pb collisions also potentially provide a sensitive probe of the quark gluon plasma. First measurements by ATLAS and STAR of dileptons produced via two-photon scattering in non-ultra-peripheral (non-UPC) nucleus-nucleus collisions showed an unexpected centrality-dependent broadening of the angular correlation between the two leptons and/or of the two-lepton pT distribution. ATLAS has recently measured dimuons produced via two-photon scattering in non-UPC Pb+Pb collisions at √sNN = 5.02 TeV using data collected during the 2018 Pb+Pb run at the LHC corresponding to an integrated luminosity of 1.73 nb−1. This data set represents a factor of ~4 increase in statistics over the 2015 data set used for the first ATLAS measurement. The increased statistics allow new features to be observed in the data, as well as differential studies of the dependence of the pair-distribution on the transverse-momentum and pseudorapidity of the two muons. The results of the new measurement and the possible physics implications will be discussed

Measurements of dileptons and photon pairs from two-photon scattering in ultra-peripheral and hadronic Pb+Pb collisions with the ATLAS detector

In ultra-relativistic heavy ion collisions, one expects copious rates of $\gamma + \gamma$ processes through the interaction of the large electromagnetic fields of the nuclei, which can produce new particles (e.g. leptons) or even lead to light-by-light scattering via loop diagrams. The latter process is a notable prediction of QED and was only recently observed by ATLAS using the full 2018 dataset. In ultra-peripheral collisions (UPCs), characterized by large impact parameter between the nuclei, the outgoing leptons and photons are produced exclusively, and exhibit a strong back-to-back momentum correlation, with long tails induced by higher-order QED effects. This work presents measurements of dilepton production and light-by-light scattering performed by the ATLAS collaboration. The angular correlations as well as differential production cross sections in UPCs are measured and compared to theoretical models, including final state QED radiation. Muon pairs produced the same two-photon scattering process in hadronic Pb+Pb collisions also potentially provide a sensitive probe of the quark gluon plasma. First measurements by ATLAS and STAR of dileptons produced via two-photon scattering in non-ultra-peripheral (non-UPC) nucleus-nucleus collisions showed an unexpected centrality-dependent broadening of the angular correlation between the two leptons and/or of the two-lepton pT distribution. ATLAS has recently measured dimuons produced via two-photon scattering in non-UPC Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV using data collected during the 2018 Pb+Pb run at the LHC corresponding to an integrated luminosity of 1.73 nb$^{-1}$. This data set represents a factor of 4 increase in statistics over the 2015 data set used for the first ATLAS measurement. The increased statistics allow new features to be observed in the data, as well as differential studies of the dependence of the pair-distribution on the transverse-momentum and pseudorapidity of the two muons. The results of the new measurement and the possible physics implications will be discussed

Measurements of dileptons and photon pairs from two-photon scattering in ultra-peripheral and hadronic Pb plus Pb collisions

In ultra-relativistic heavy ion collisions, one expects copious rates of $\gamma + \gamma$ processes through the interaction of the large electromagnetic fields of the nuclei, which can produce new particles (e.g. leptons) or even lead to light-by-light scattering via loop diagrams. The latter process is a notable prediction of QED and was only recently observed by ATLAS using the full 2018 dataset. In ultra-peripheral collisions (UPCs), characterized by large impact parameter between the nuclei, the outgoing leptons and photons are produced exclusively, and exhibit a strong back-to-back momentum correlation, with long tails induced by higher-order QED effects. This work presents measurements of dilepton production and light-by-light scattering performed by the ATLAS collaboration. The angular correlations as well as differential production cross sections in UPCs are measured and compared to theoretical models, including final state QED radiation. Muon pairs produced the same two-photon scattering process in hadronic Pb+Pb collisions also potentially provide a sensitive probe of the quark gluon plasma. First measurements by ATLAS and STAR of dileptons produced via two-photon scattering in non-ultra-peripheral (non-UPC) nucleus-nucleus collisions showed an unexpected centrality-dependent broadening of the angular correlation between the two leptons and/or of the two-lepton pT distribution. ATLAS has recently measured dimuons produced via two-photon scattering in non-UPC Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV using data collected during the 2018 Pb+Pb run at the LHC corresponding to an integrated luminosity of 1.73 nb$^{-1}$. This data set represents a factor of 4 increase in statistics over the 2015 data set used for the first ATLAS measurement. The increased statistics allow new features to be observed in the data, as well as differential studies of the dependence of the pair-distribution on the transverse-momentum and pseudorapidity of the two muons. The results of the new measurement and the possible physics implications will be discussed