Study of $⟨p_{\mathrm{T}}⟩$ and its higher moments, and extraction of the speed of sound in Pb-Pb collisions with ALICE

Abstract

Ultrarelativistic heavy-ion collisions produce a state of hot and dense strongly interacting QCD matter called quark--gluon plasma (QGP). On an event-by-event basis, the volume of the QGP in ultracentral collisions is mostly constant, while its total entropy can vary significantly due to quantum fluctuations, leading to variations in the temperature of the system. Exploiting this unique feature of ultracentral collisions allows for the interpretation of the correlation of the mean transverse momentum of produced charged hadrons and the number of charged hadrons as a measure for the speed of sound. It is determined by fitting the relative increase in transverse momentum with respect to the relative change in the average charged-particle density measured at midrapidity. This study reports the event-average transverse momentum of charged particles as well as the self-normalized variance, skewness, and kurtosis of the event-by-event transverse momentum distribution in ultracentral Pb-Pb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair using the ALICE detector. Different centrality estimators based on charged-particle multiplicity or the transverse energy of the event are used to select ultracentral collisions. By ensuring a pseudorapidity gap between the region used to define the centrality and the region used to perform the measurement, the influence of biases on the rise of the mean transverse momentum is tested. The measured values are found to strongly depend on the exploited centrality estimator. The variance shows a steep decrease towards ultracentral collisions, while the skewness variables show a maximum, followed by a fast decrease. These non-Gaussian features are understood in terms of the vanishing of the impact-parameter fluctuations contributing to the event-to-event transverse momentum distribution.

arXiv comment35 pages, 10 captioned figures, 2 tables, authors from page 29, figures at http://alice-publications.web.cern.ch/node/12592

References in corpus (28)

• Thermal phenomenology of hadrons from 200 AGeV S+S collisions
• Performance of the ALICE Experiment at the CERN LHC
• Heavy Ion Collisions: The Big Picture, and the Big Questions
• The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events
• Interpretation of the nonextensitivity parameter $q$ in some applications of Tsallis statistics and Lévy distributions
• Alternative ansatz to wounded nucleon and binary collision scaling in high-energy nuclear collisions
• Performance of the ALICE VZERO system
• Alignment of the ALICE Inner Tracking System with cosmic-ray tracks
• Particle production and equilibrium properties within a new hadron transport approach for heavy-ion collisions
• Properties of hot and dense matter from relativistic heavy ion collisions
• Bayesian analysis of heavy ion collisions with the heavy ion computational framework Trajectum
• Relativistic hydrodynamics for heavy-ion collisions
• Thermodynamics of hot strong-interaction matter from ultrarelativistic nuclear collisions
• The First fm/c of Heavy-Ion Collisions
• Effect of the QCD equation of state and strange hadronic resonances on multiparticle correlations in heavy ion collisions
• Transverse-momentum fluctuations in relativistic heavy-ion collisions from event-by-event viscous hydrodynamics
• Size fluctuations of the initial source and the event-by-event transverse momentum fluctuations in relativistic heavy-ion collisions
• Relating centrality to impact parameter in nucleus-nucleus collisions
• The mean transverse momentum of ultracentral heavy-ion collisions: A new probe of hydrodynamics
• Transverse momentum fluctuations in ultrarelativistic Pb+Pb and p+Pb collisions with wounded quarks
• Fast resonance decays in nuclear collisions
• Skewness of mean transverse momentum fluctuations in heavy-ion collisions
• Heavy Ion physics with the ALICE experiment at the CERN LHC
• Extracting the speed of sound in quark-gluon plasma with ultrarelativistic lead-lead collisions at the LHC
• Higher-order transverse momentum fluctuations in heavy-ion collisions
• Non-Gaussian transverse momentum fluctuations from impact parameter fluctuations
• Accessing the speed of sound in relativistic ultracentral nucleus-nucleus collisions using the mean transverse momentum
• Pseudorapidity profile of transverse momentum fluctuations in heavy ion collisions

Cited by in corpus (1)

• The size of the quark-gluon plasma in ultracentral collisions: impact of initial density fluctuations on the average transverse momentum