Freeze-out scenarios in small systems at RHIC and LHC energies

2020 ◽  
Vol 29 (02) ◽  
pp. 2050006
Author(s):  
Susil Kumar Panda ◽  
Subhasis Samanta ◽  
Ajay Kumar Dash ◽  
Ranbir Singh ◽  
Rita Paikaray ◽  
...  
Keyword(s):  
System Size ◽  
Particle Multiplicity ◽  
Charged Particle Multiplicity ◽  
Suppression Factor ◽  
Increase With Increase ◽  
Multiplicity Formula ◽  
Charge Multiplicity ◽  
System Volume ◽  
Chemical Freeze ◽  
Freeze Out

We study the hadronic yields produced in two small collision systems [Formula: see text] at [Formula: see text][Formula: see text]TeV and [Formula: see text] at [Formula: see text][Formula: see text]TeV, and extracted the chemical freeze-out (CFO) parameters. The CFO parameters are obtained using a hadron resonance gas (HRG) model and in this study present the system size dependence of the parameters. We observe that with the strangeness suppression factor [Formula: see text] included in the model, a single freeze-out scenario can describe hadronic yields for all the centralities of [Formula: see text] collision at [Formula: see text][Formula: see text]TeV, indicating that the strange hadrons have not reached full equilibrium. On the other hand, for small average charged particle multiplicity ([Formula: see text]) bins of [Formula: see text] collision at [Formula: see text][Formula: see text]TeV strangeness is not fully equilibrated whereas strangeness equilibration seems to be reached in large [Formula: see text]. For both the collision systems, no significant system volume dependence of the temperature has been observed. However, in comparable [Formula: see text] values, temperatures are 10–20[Formula: see text]MeV larger for [Formula: see text] collision compared to [Formula: see text] collision. We observe that the volume of the system at the CFO increases with increase of charge multiplicity for both the collisions. The increase is much steeper in [Formula: see text] collision at [Formula: see text][Formula: see text]TeV than [Formula: see text] collision at [Formula: see text][Formula: see text]TeV. Further, we analyze the transverse momentum ([Formula: see text]) spectra of different hadrons produced in [Formula: see text] collision at [Formula: see text][Formula: see text]TeV in a combined freeze-out scenario. We show the [Formula: see text] dependence of freeze-out parameters. It is observed that with [Formula: see text] included in the model, a single freeze-out scheme can describe the [Formula: see text] spectra. For similar [Formula: see text] values, [Formula: see text] in both the collision systems are close to each other and overall values of [Formula: see text] increase with increase of [Formula: see text]. Unlike CFO scenario using the produced hadron yields only, freeze-out temperature in combined scenario of chemical and kinetic freeze-out, obtained from [Formula: see text] spectra, increases with increase of [Formula: see text]. For smaller [Formula: see text] values, the temperature in [Formula: see text] collision at [Formula: see text][Formula: see text]TeV is similar to that of [Formula: see text] collision at [Formula: see text][Formula: see text]TeV. However, temperatures are larger in [Formula: see text] collision than [Formula: see text] collision at larger [Formula: see text] values.

scholarly journals Freeze-Out Parameters in Heavy-Ion Collisions at AGS, SPS, RHIC, and LHC Energies

2015 ◽  
Vol 2015 ◽  
pp. 1-20 ◽  
Author(s):  
Sandeep Chatterjee ◽  
Sabita Das ◽  
Lokesh Kumar ◽  
D. Mishra ◽  
Bedangadas Mohanty ◽  
...  
Keyword(s):  
Transverse Momentum ◽  
Heavy Ion Collisions ◽  
Heavy Ion ◽  
High Energy ◽  
Particle Multiplicity ◽  
Charged Particle Multiplicity ◽  
Ion Collisions ◽  
Momentum Distributions ◽  
Chemical Freeze ◽  
Freeze Out

We review the chemical and kinetic freeze-out conditions in high energy heavy-ion collisions for AGS, SPS, RHIC, and LHC energies. Chemical freeze-out parameters are obtained using produced particle yields in central collisions while the corresponding kinetic freeze-out parameters are obtained using transverse momentum distributions of produced particles. For chemical freeze-out, different freeze-out scenarios are discussed such as single and double/flavor dependent freeze-out surfaces. Kinetic freeze-out parameters are obtained by doing hydrodynamic inspired blast wave fit to the transverse momentum distributions. The beam energy and centrality dependence of transverse energy per charged particle multiplicity are studied to address the constant energy per particle freeze-out criteria in heavy-ion collisions.

scholarly journals Inferring freeze-out parameters from pion measurements at RHIC and LHC

2015 ◽  
Vol 24 (06) ◽  
pp. 1550046 ◽  
Author(s):  
Priyanka Sett ◽  
Prashant Shukla
Keyword(s):  
Transverse Momentum ◽  
System Size ◽  
Transverse Flow ◽  
Particle Multiplicity ◽  
Charged Particle Multiplicity ◽  
Momentum Range ◽  
Momentum Spectra ◽  
Transverse Momentum Spectra ◽  
Tsallis Distribution ◽  
Freeze Out

We analyze the transverse momentum spectra of charged pions measured in Au + Au collisions at [Formula: see text] and in Pb + Pb collisions at [Formula: see text] using the Tsallis distribution modified to include transverse flow. All the spectra are well described by the modified Tsallis distribution in an extended transverse momentum range upto 6 GeV/c. The kinetic freeze-out temperature (T), average transverse flow (β) and degree of nonthermalization (q) are obtained as a function of system size for both the energies. With increasing system size β shows increasing trend whereas T remains constant. While the systems at RHIC and LHC energies show similar β and q, the parameter T is higher at LHC as compared to RHIC. The kinetic freeze-out temperature is also extracted using the measured charged particle multiplicity and HBT volume of the system as a function of system size and collision energies.

scholarly journals A Baseline Study of the Event-Shape and Multiplicity Dependence of Chemical Freeze-Out Parameters in Proton-Proton Collisions at \( {\sqrt{s}} \) = 13 TeV Using PYTHIA8

Physics ◽  
2020 ◽  
Vol 2 (4) ◽  
pp. 679-694
Author(s):  
Rutuparna Rath ◽  
Arvind Khuntia ◽  
Sushanta Tripathy ◽  
Raghunath Sahoo
Keyword(s):  
High Energy ◽  
Monte Carlo Event ◽  
Event Generator ◽  
Particle Multiplicity ◽  
Event Shape ◽  
Charged Particle Multiplicity ◽  
Pp Collisions ◽  
Proton Proton ◽  
Chemical Freeze ◽  
Freeze Out

The event-shape and multiplicity dependence of the chemical freeze-out temperature (Tch), freeze-out radius (R), and strangeness saturation factor (γs) are obtained by studying the particle yields from the PYTHIA8 Monte Carlo event generator in proton-proton (pp) collisions at the centre-of-mass s = 13 TeV. Spherocity is one of the transverse event-shape techniques to distinguish jetty and isotropic events in high-energy collisions and helps in looking into various observables in a more differential manner. In this study, spherocity classes are divided into three categories, namely (i) spherocity integrated, (ii) isotropic, and (iii) jetty. The chemical freeze-out parameters are extracted using a statistical thermal model as a function of the spherocity class and charged particle multiplicity in the canonical, strangeness canonical, and grand canonical ensembles. A clear observation of the multiplicity and spherocity class dependence of Tch, R, and γs is observed. A final state multiplicity, Nch≥ 30 in the forward multiplicity acceptance of the ALICE detector appears to be a thermodynamic limit, where the freeze-out parameters become almost independent of the ensembles. This study plays an important role in understanding the particle production mechanism in high-multiplicity pp collisions at the Large Hadron Collider (LHC) energies in view of a finite hadronic phase lifetime in small systems.

scholarly journals IDENTICAL MESON INTERFEROMETRY IN STAR EXPERIMENT

2007 ◽  
Vol 16 (07n08) ◽  
pp. 1883-1889 ◽  
Author(s):  
◽  
DEBASISH DAS
Keyword(s):  
Particle Production ◽  
Star Collaboration ◽  
Heavy Ion ◽  
Relativistic Heavy Ion Collisions ◽  
Transverse Mass ◽  
Particle Multiplicity ◽  
Charged Particle Multiplicity ◽  
Time Dynamics ◽  
Ion Collisions ◽  
Freeze Out

The influence of Bose–Einstein statistics on multi-particle production characterized for various systems and energies by the STAR collaboration provides interesting information about the space-time dynamics of relativistic heavy-ion collisions at RHIC. We present the centrality and transverse mass dependence measurements of the two-pion interferometry in Au + Au collisions at [Formula: see text] and Cu + Cu collisions at [Formula: see text] and 200 GeV. We compare the new data with previous STAR measurements from p + p , d + Au and Au + Au collisions at [Formula: see text]. In all systems and centralities, HBT radii decrease with transverse mass in a similar manner, which is qualitatively consistent with collective flow. The scaling of the apparent freeze-out volume with the number of participants and charged particle multiplicity is studied. Measurements of Au + Au collisions at same centralities and different energies yield different freeze-out volumes, which mean that N part is not a suitable scaling variable. The multiplicity scaling of the measured HBT radii is found to be independent of colliding system and collision energy.

scholarly journals Separate freeze-out of strange particles and the quark-hadron phase transition

2018 ◽  
Vol 182 ◽  
pp. 02057
Author(s):  
K. Bugaev ◽  
V. Sagun ◽  
A. Ivanytskyi ◽  
E. Nikonov ◽  
J. Cleymans ◽  
...  
Keyword(s):  
Collision Energy ◽  
Center Of Mass ◽  
Suppression Factor ◽  
Hadron Phase ◽  
Hadron Multiplicity ◽  
Strange Particles ◽  
The One ◽  
Baryonic Charge ◽  
Chemical Freeze ◽  
Freeze Out

The scenario of the independent chemical freeze-outs for strange and nonstrange particles is discussed. Within such a scenario an apparent in-equilibrium of strangeness is naturally explained by a separation of chemical freeze-out of strange hadrons from the one of non-strange hadrons, which, nevertheless, are connected by the conservation laws of entropy, baryonic charge and third isospin projection. An interplay between the separate freeze-out of strangeness and its residual non-equilibrium is studied within an elaborate version of the hadron resonance gas model. The developed model enables us to perform a high-quality fit of the hadron multiplicity ratios measured at AGS, SPS and RHIC with an overall fit quality ϰ2/dof = 0:93. A special attention is paid to a description of the Strangeness Horn and to the well-known problem of selective suppression of Δ- and ж hyperons. It is remarkable that for all collision energies the strangeness suppression factor γs is about 1 within the error bars. The only exception is found in the vicinity of the center-of-mass collision energy 7.6 GeV, at which a residual enhancement of strangeness of about 20 % is observed.

Hadron resonance gas model and high multiplicities in p–p, p–Pb and Pb–Pb collisions at the LHC

2019 ◽  
Vol 28 (09) ◽  
pp. 1940002 ◽  
Author(s):  
Jean Cleymans ◽  
Boris Hippolyte ◽  
Masimba W. Paradza ◽  
Natasha Sharma
Keyword(s):  
Charged Particle ◽  
Recent Work ◽  
Thermal Model ◽  
Particle Multiplicity ◽  
Charged Particle Multiplicity ◽  
Final State ◽  
Proton Proton ◽  
Particle Composition ◽  
Rapidity Interval ◽  
Multiplicity Formula

Recent work on the particle composition (hadrochemistry) of the final state in proton–proton (p–p), proton–lead (p–Pb) and lead–lead (Pb–Pb) collisions as a function of the charged particle multiplicity ([Formula: see text]) is reviewed. It is argued that for high multiplicities (at least about 20 charged hadrons in the mid-rapidity interval), consistent results are obtained in the thermal model.

scholarly journals On the Higher Moments of Particle Multiplicity, Chemical Freeze-Out, and QCD Critical Endpoint

2013 ◽  
Vol 2013 ◽  
pp. 1-22 ◽  
Author(s):  
A. Tawfik
Keyword(s):  
Lower Order ◽  
Thermal Evolution ◽  
Order Moment ◽  
Particle Multiplicity ◽  
Higher Moments ◽  
Third Order ◽  
Chemical Potentials ◽  
Dynamical Fluctuation ◽  
Chemical Freeze ◽  
Freeze Out

We calculate the first six nonnormalized moments of particle multiplicity within the framework of the hadron resonance gas model. In terms of the lower order moments and corresponding correlation functions, general expressions of higher order moments are derived. Thermal evolution of the first four normalized moments and their products (ratios) are studied at different chemical potentials, so that it is possible to evaluate them at chemical freeze-out curve. It is found that a nonmonotonic behaviour reflecting the dynamical fluctuation and strong correlation of particles starts to appear from the normalized third order moment. We introduce novel conditions for describing the chemical freeze-out curve. Although the hadron resonance gas model does not contain any information on the criticality related to the chiral dynamics and singularity in the physical observables, we are able to find out the location of the QCD critical endpoint atμ~350 MeV and temperatureT~162 MeV.

scholarly journals (Anti-)(hyper-)nuclei production in Pb–Pb collisions with ALICE at the Large Hadron Collider

2020 ◽  
Vol 1643 (1) ◽  
pp. 012017
Author(s):  
Stefano Trogolo
Keyword(s):  
Hadron Collider ◽  
System Size ◽  
Heavy Ion ◽  
Particle Identification ◽  
Relativistic Heavy Ion Collisions ◽  
Particle Multiplicity ◽  
Charged Particle Multiplicity ◽  
Alice Experiment ◽  
Ion Collisions ◽  
Theoretical Predictions

Abstract In ultra-relativistic heavy-ion collisions a great variety of (anti-)(hyper-)nuclei are produced, namely deuteron, triton, 3He, 4He, hypertriton ( Λ 3 H ) and their antiparticles. The ALICE experiment is the most suited to investigate the production of (hyper-)nuclei at the LHC, thanks to an excellent particle identification and low-material budget detectors. Recent results on (hyper-)nuclei production as a function of transverse momentum (pT) and charged particle multiplicity (dN ch/d η ) in Pb–Pb collisions are presented. The evolution of the production yields with the system size is also shown, via comparison to the results obtained in small collision systems, like pp and p–Pb. The results on the production of (hyper-)nuclei are also compared with the predictions based on a naive coalescence approach and the statistical hadronization models. Furthermore, the latest and currently most precise measurement of the hypertriton lifetime is presented. It is compared with results obtained by different experimental techniques and with theoretical predictions.

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