Energy and system size dependence of chemical freeze-out in relativistic nuclear collisions

AbstractWe introduce a novel approach based on elastic and inelastic scattering rates to extract the hyper-surface of the chemical freeze-out from a hadronic transport model in the energy range from E$$_\mathrm {lab}=1.23$$ lab = 1.23 AGeV to $$\sqrt{s_\mathrm {NN}}=62.4$$ s NN = 62.4 GeV. For this study, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model combined with a coarse-graining method is employed. The chemical freeze-out distribution is reconstructed from the pions through several decay and re-formation chains involving resonances and taking into account inelastic, pseudo-elastic and string excitation reactions. The extracted average temperature and baryon chemical potential are then compared to statistical model analysis. Finally we investigate various freeze-out criteria suggested in the literature. We confirm within this microscopic dynamical simulation, that the chemical freeze-out at all energies coincides with $$\langle E\rangle /\langle N\rangle \approx 1$$ ⟨ E ⟩ / ⟨ N ⟩ ≈ 1 GeV, while other criteria, like $$s/T^3=7$$ s / T 3 = 7 and $$n_\mathrm {B}+n_{\bar{\mathrm {B}}}\approx 0.12$$ n B + n B ¯ ≈ 0.12 fm$$^{-3}$$ - 3 are limited to higher collision energies.

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Strangeness freeze-out: role of system size and missing resonances

EPJ Web of Conferences ◽

10.1051/epjconf/201817114002 ◽

2018 ◽

Vol 171 ◽

pp. 14002

Author(s):

Sandeep Chatterjee ◽

Sabita Das ◽

Ajay Kumar Dash ◽

Debadeepti Mishra ◽

Bedangadas Mohanty ◽

...

Keyword(s):

Size Dependence ◽

System Size ◽

Conventional Approach ◽

Strangeness Production ◽

Additional Parameter ◽

Theoretical Approaches ◽

Missing Resonances ◽

Freeze Out

The conventional approach to treat strangeness freezeout has been to consider a unified freezeout scheme where strangeness freezes out along with the nonstrange hadrons (1CFO), with or without an additional parameter accounting for out-of-equilibrium strangeness production (γS). Several alternate scenarios have been formulated lately. Here, we will focus on flavor dependent freezeout with early freezeout of strangeness (2CFO) in comparison to 1CFO and its variants with respect to the roles played by the system size and missing resonances predicted by different theoretical approaches but yet to be seen in experiments. In contrast to the performance of 1CFO with/without γS that is insensitive to system size, 2CFO exhibits a clear system size dependence-while for Pb+Pb the χ2/NDF is around 0-2, for smaller system size in p+Pb and p+p, the χ2/NDF> 5 and larger than 1CFO+γS. This clearly shows a system size dependence of the preference for the freezeout scheme, while 2CFO is preferred in Pb+Pb, 1CFO+γS is preferred in p+Pb and p+p. We have further investigated the role of the missing resonances on strangeness freezeout across SPS to LHC beam energies.

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Hadronization and hadronic freeze-out in relativistic nuclear collisions

Physical Review C ◽

10.1103/physrevc.85.044921 ◽

2012 ◽

Vol 85 (4) ◽

Cited By ~ 45

Author(s):

Francesco Becattini ◽

Marcus Bleicher ◽

Thorsten Kollegger ◽

Michael Mitrovski ◽

Tim Schuster ◽

...

Keyword(s):

Nuclear Collisions ◽

Relativistic Nuclear Collisions ◽

Freeze Out

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Using local nuclear scaling of initial condition parameters to improve the system size dependence of transport model descriptions of nuclear collisions

Physical Review C ◽

10.1103/physrevc.104.014908 ◽

2021 ◽

Vol 104 (1) ◽

Author(s):

Chao Zhang ◽

Liang Zheng ◽

Shusu Shi ◽

Zi-Wei Lin

Keyword(s):

Size Dependence ◽

Transport Model ◽

System Size ◽

Initial Condition ◽

Nuclear Collisions

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

International Journal of Modern Physics E ◽

10.1142/s0218301320500068 ◽

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.

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Chemical freeze-out of light nuclei in high energy nuclear collisions and resolution of the hyper-triton chemical freeze-out puzzle

Journal of Physics Conference Series ◽

10.1088/1742-6596/1690/1/012123 ◽

2020 ◽

Vol 1690 ◽

pp. 012123

Author(s):

K A Bugaev ◽

O V Vitiuk ◽

B E Grinyuk ◽

N S Yakovenko ◽

E S Zherebtsova ◽

...

Keyword(s):

High Energy ◽

Light Nuclei ◽

Nuclear Collisions ◽

Chemical Freeze ◽

Freeze Out

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System size dependence of the non-monotonous pion freeze-out volume excitation function

Open Physics ◽

10.2478/s11534-012-0093-0 ◽

2012 ◽

Vol 10 (5) ◽

Cited By ~ 1

Author(s):

Qingfeng Li ◽

Caiwan Shen ◽

Marcus Bleicher

Keyword(s):

Excitation Function ◽

Local Minimum ◽

Particle Production ◽

Size Dependence ◽

Transport Model ◽

System Size ◽

Charged Pions ◽

String Formation ◽

Hbt Correlation ◽

Freeze Out

AbstractHanburry-Brown-Twiss (HBT) correlation functions and radii of negatively charged pions from C+C, Si+Si, Cu+Cu, and In+In at lower RHIC/SPS energies are calculated with the UrQMD transport model and the CRAB analyzing program. We find a minimum in the excitation function of the pion freeze-out volume at low transverse momenta and around E lab ∼ 20–30AGeV which can be related to the change from initial string emission to bulk emission from the created resonance matter. For small systems, we predict a local minimum in the excitation function of the HBT (freeze-out) volume which is explained by the competition of two mechanisms of the particle production, namely resonance decays and string formation/fragmentation.

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Resolving the hyper-triton yield description puzzle in high energy nuclear collisions

The European Physical Journal A ◽

10.1140/epja/s10050-021-00370-6 ◽

2021 ◽

Vol 57 (2) ◽

Author(s):

O. V. Vitiuk ◽

K. A. Bugaev ◽

E. S. Zherebtsova ◽

D. B. Blaschke ◽

L. V. Bravina ◽

...

Keyword(s):

Collision Energy ◽

Hard Core ◽

Star Collaboration ◽

High Energy ◽

Nuclear Collisions ◽

Cluster Data ◽

New Strategy ◽

Nuclear Cluster ◽

Chemical Freeze ◽

Freeze Out

AbstractThe recently developed hadron resonance gas model with multicomponent hard-core repulsion is used to address and resolve the long standing problem to describe the light nuclear cluster multiplicities including the hyper-triton measured by the STAR Collaboration, known as the hyper-triton chemical freeze-out puzzle. An improved description for the hadronic and light nuclear cluster data measured by STAR at the collision energy $$\sqrt{s_{NN}} =200$$ s NN = 200 GeV and by ALICE at $$\sqrt{s_{NN}} =2.76$$ s NN = 2.76 TeV is obtained. This is achieved by applying a new strategy of analyzing the light nuclear cluster data and by using the value for the hard-core radius of the (anti-)$$\varLambda $$ Λ hyperons found in earlier work. One of the most striking results of the present work is that for the most probable scenario of chemical freeze-out for the STAR energy the obtained parameters allow to simultaneously reproduce the values of the experimental ratios $$S_3$$ S 3 and $${\overline{S}}_3$$ S ¯ 3 which were not included in the fit.

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