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J. Cleymans

Publications and source records attributed to J. Cleymans.

At least 19 recordsLinked to original sources
arXiv2021

Tsallis Statistics in High Energy Physics: Chemical and Thermal Freeze-Outs

We present an overview of a proposal in relativistic proton-proton ($pp$) collisions emphasizing the thermal or kinetic freeze-out stage in the framework of the Tsallis distribution. In this paper we take into account the chemical potential present in the Tsallis distribution by following a two step procedure. In the first step we used the redundancy present in the variables such as the system temperature, $T$, volume, $V$, Tsallis exponent, $q$, chemical potential, $μ$, and performed all fits by effectively setting to zero the chemical potential. In the second step the value $q$ is kept fixed at the value determined in the first step. This way the complete set of variables $T, q, V$ and $μ$ can be determined. The final results show a weak energy dependence in $pp$ collisions at the centre-of-mass energy $\sqrt{s}= 6$ GeV to 13 TeV. The chemical potential $μ$ at kinetic freeze-out shows an increase with beam energy. This simplifies the description of the thermal freeze-out stage in $pp$ collisions as the values of $T$ and of the freeze-out radius $R$ vary only mildly over a wide range of beam energies.

hep-ph↗
arXiv2020

Determination of the chemical potential in the Tsallis distribution at LHC energies

The transverse momentum distributions measured in $p-p$ collisions at the LHC determine the kinetic freeze-out stage of the collision. The parameters deduced from these distributions differ from those determined at chemical freeze-out. The present investigation focuses on the chemical potentials at kinetic freeze-out, these are not necessarily zero as they are at chemical freeze-out, the only constraint is that they should be equal for particles and antiparticles at LHC energies. The thermodynamic variables are determined in the framework of the Tsallis distribution. The chemical potentials in the Tsallis distribution analysis of $p-p$ collisions at four different LHC energies have correctly been taken into account. This leads to a much more satisfactory analysis of the various parameters and confirms the usefulness of the Tsallis distribution in high-energy collisions. In particular we find that the temperature $T$ and the volume $V$ at each beam energy are the same for all particle types considered (pions, kaons and protons). The chemical potentials for these particles are however very different. Hence we conclude that there is evidence for thermal equilibrium at kinetic freeze-out, albeit in the sense of the Tsallis distribution and there is no evidence for chemical equilibrium at the final stage of the collision.

hep-ph↗
arXiv2020

Energy density at kinetic freeze-out in Pb-Pb collisions at the LHC using the Tsallis distribution

The thermodynamic parameters like energy density, pressure, entropy density, temperature and particle density are determined from the transverse momentum distributions of charged particles in Pb-Pb collisions at the LHC. The results show a clear increase with the centrality and the beam energy in all parameters. It is determined that in the final freeze-out stage the energy density reaches a value of about 0.039 GeV/fm$^3$ for the most central collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. This is less than that at chemical freeze-out where the energy density is about 0.36 GeV/fm$^3$. This decrease approximately follows a $T^4$ law. The results for the pressure and entropy density are also presented for each centrality class at $\sqrt{s_{NN}}$ = 2.76 and 5.02 TeV.

hep-ph↗
arXiv2018

Non-extensivity of the QCD pT spectra

We try to establish a connection between the hadronic distributions, in proton-proton collisions at very high transverse momentum $p_{\mathrm{T}}$, obtained via perturbative QCD and the Tsallis non extensive statistics. Our motivation is that while the former is expected to be valid at extremely high momentum, due to asymptotic freedom, the latter has been very successful in describing experimental spectra over a wide range of momentum. Matching the non extensive statistics with the asymptotic $p_{\mathrm{T}}$ behaviour expected from QCD leads to the value of $q=1.25$.

hep-ph↗
arXiv2018

On the precise determination of the Tsallis parameters in proton - proton collisions at LHC energies

A detailed analysis is presented of the precise values of the Tsallis parameters obtained in $p-p$ collisions for identified particles, pions, kaons and protons at the LHC at three beam energies $\sqrt{s} = 0.9, 2.76$ and $7$ TeV. Interpolated data at $\sqrt{s} = $ 5.02 TeV have also been included. It is shown that the Tsallis formula provides reasonably good fits to the $p_T$ distributions in $p-p$ collisions at the LHC using three parameters $dN/dy$, $T$ and $q$. However, the parameters $T$ and $q$ depend on the particle species and are different for pions, kaons and protons. As a consequence there is no $m_T$ scaling and also no universality of the parameters for different particle species.

hep-ph↗
arXiv2017

The Physics Case for the $\sqrt{s_{NN}} \approx 10$ GeV Energy Region

There are indications that the beam energy region $\sqrt{s_{NN}} \approx 10$ GeV for heavy-ion collisions is an interesting one. The final state has the highest net baryon density at this beam energy. A transition from a baryon dominated to a meson dominated final state takes place around this beam energy. Ratios of strange particles to mesons show clear and pronounced maxima around this beam energy. The theoretical interpretation can be clarified by covering fully this energy region. In particular the strangeness content needs to be determined, data covering the full phase space ($4 π$) would be helpful to establish the properties of this energy region.

hep-ph↗
arXiv2017

Systematic Comparison of Tsallis Statistics for Charged Pions Produced In $pp$ Collisions

The energy dependence of Tsallis statistics parameters is presented for charged pions produced at beam energies ranging between 6.3 GeV and 7 TeV. It is found that deviations from Boltzmann statistics are monotonically growing with beam energy. This may be attributed to the dominance of low $x$ at higher energies leading to the power-like NLO QCD spectra for which Tsallis statistics may serve as effective theory. At the same time, for larger $x$ at lower beam energies the Gaussian falloff of transverse-momentum-dependent distributions is crucial and correspondent effective description is provided by the Boltzmann distribution.

nucl-th↗
arXiv2017

Thermal Model Description of Collisions of Small Nuclei

The dependence of particle production on the size of the colliding nuclei is analysed in terms of the thermal model using the canonical ensemble. The concept of strangeness correlation in clusters of sub-volume $V_c$ is used to account for the suppression of strangeness. A systematic analysis is presented of the predictions of the thermal model for particle production in collisions of small nuclei. The pattern of the maxima of strange-particles-to-pion ratios as a function of beam energy is quite special, as they do not occur at the same beam energy and are sensitive to system size. In particular, the $Λ/π^+$ ratio shows a clear maximum even for small systems while the maximum in the K$^+/π^+$ ratio is less pronounced

hep-ph↗
arXiv2016

Separate chemical freeze-outs of strange and non-strange hadrons and problem of residual chemical non-equilibrium of strangeness in relativistic heavy ion collisions

We present an elaborate version of the hadron resonance gas model with the combined treatment of separate chemical freeze-outs for strange and non-strange hadrons and with an additional $γ_{s}$ factor which accounts for the remaining strange particle non-equilibration. Within suggested approach the parameters of two chemical freeze-outs are connected by the conservation laws of entropy, baryonic charge, third isospin projection and strangeness. The developed model enables us to perform a high-quality fit of the hadron multiplicity ratios measured at AGS, SPS and RHIC with $χ^2/dof \simeq 0.93$. A special attention is paid to a successful description of the Strangeness Horn. The well-known problem of selective suppression of $\bar Λ$ and $\bar Ξ$ hyperons is also discussed. The main result is that for all collision energies the $γ_{s}$ factor is about 1 within the error bars, except for the center of mass collision energy 7.6 GeV at which we find about 20\% enhancement of strangeness. Also we confirm an existence of strong jumps in pressure, temperature and effective number of degrees of freedom at the stage of strange particle chemical freeze-out, when the center of mass collision energy changes from 4.3 to 4.9 GeV. We argue that these irregularities may signal about the quark-hadron phase transition.

nucl-th↗
arXiv2016

Collisions of Small Nuclei in the Thermal Model

An analysis is presented of the expectations of the thermal model for particle production in collisions of small nuclei. The maxima observed in particle ratios of strange particles to pions as a function of beam energy in heavy ion collisions, are reduced when considering smaller nuclei. Of particular interest is the $Λ/π^+$ ratio shows the strongest maximum which survives even in collisions of small nuclei.

nucl-th↗
arXiv2016

On the Use of the Tsallis Distribution at LHC Energies

Numerous papers have appeared recently showing fits to transverse momentum ($p_T$) spectra measured at the Large Hadron Collider (LHC) in proton - proton collisions.This talk focuses on the fits extending to very large values of the transverse momentum with $p_T$ values up to 200 GeV/c as measured by the ATLAS and CMS collaborations at $\sqrt{s}$ = 0.9 and 7 TeV. A thermodynamically consistent form of the Tsallis distribution is used for fitting the transverse momentum spectra at mid-rapidity. The fits based on the proposed distribution provide an excellent description over 14 orders of magnitude. Despite this success, an ambiguity is noted concerning the determination of the parameters in the Tsallis distribution. This prevents drawing firm conclusions as to the universality of the parameters appearing in the Tsallis distribution.

hep-ph↗
arXiv2016

Indication of Differential Kinetic Freeze-out at RHIC and LHC Energies

The transverse momentum spectra at RHIC and LHC for A+A and p+p collisions are studied with Tsallis distributions in different approaches i.e. with and without radial flow. The information on the freeze-out surface in terms of freeze-out volume, temperature, chemical potential and radial flow velocities for different particle species are obtained. These parameters are found to show a systematic behavior with mass dependence. It is observed that the heavier particles freeze-out early as compared to lighter particles and freeze-out surfaces are different for different particles, which is a direct signature of mass dependent differential freeze-out. Further, we observe that the radial flow velocity decreases with increasing mass. This confirms the mass ordering behavior in collectivity observed in heavy-ion collisions. It is also observed that the systems created in peripheral heavy-ion collisions and in proton-proton collisions are of similar thermodynamic nature.

hep-ph↗
arXiv2016

Exploring high-density baryonic matter: Maximum freeze-out density

The hadronic freeze-out line is calculated in terms of the net baryon density and the energy density instead of the usual T and mu_B. This analysis makes it apparent that the freeze-out density exhibits a maximum as the collision energy is decreased. This maximum freeze-out density is well within the parameters of the proposed NICA accelerator.

nucl-th↗
arXiv2015

Large Transverse Momenta and Tsallis Thermodynamics

The charged particle transverse momentum ($p_T$) spectra measured by the ATLAS and CMS collaborations in proton - proton collisions at sqrt(s) = 0.9 and 7 TeV have been studied using Tsallis thermodynamics. A thermodynamically consistent form of the Tsallis distribution is used for fitting the transverse momentum spectra at mid-rapidity. It is found that the fits based on the proposed distribution provide an excellent description over 14 orders of magnitude with $p_T$ values up to 200 GeV/c.

hep-ph↗
arXiv2015

The Tsallis Distribution at Large Transverse Momenta

Fits to the transverse momentum distributions of charged particles produced in p - p collisions at LHC energies based on the Tsallis distribution have been shown to work over 14 orders of magnitude. Two versions of the Tsallis distribution are compared and discussed, the thermodynamically consistent version leads to a temperature of T = 74 +/- 13 MeV at the highest beam energy, a result which is in agreement with previous analyses done with lower transverse momentum data.

hep-ph↗
arXiv2015

Description of High-Energy pp Collisions Using Tsallis Thermodynamics: Transverse Momentum and Rapidity Distributions

A systematic analysis of transverse momentum and rapidity distributions measured in high-energy proton - proton (pp) collisions for energies ranging from 53 GeV to 7 TeV using Tsallis thermodynamics is presented. The excellent description of all transverse momentum spectra obtained in earlier analyses is confirmed and extended. All energies can be described by a single Tsallis temperature of 68 +/- 5 MeV at all beam energies and particle types investigated (43 in total). The value of the entropic index, q, shows a wider spread but is always close to q approx 1.146. These values are then used to describe the rapidity distributions using a superposition of two Tsallis fireballs along the rapidity axis. It is concluded that the hadronic system created in high-energy p - p collisions between 53 GeV and 7 TeV can be seen as obeying Tsallis thermodynamics.

hep-ph↗
arXiv2014

Transverse Momentum Distributions in proton - proton Collisions at LHC Energies and Tsallis Thermodynamics

A detailed study of the transverse momentum distributions of charged particles produced in proton - proton collisions at LHC energies is presented. This is done using a thermodynamically consistent form of the Tsallis distribution. All variables used are thermodynamical and in particular, the temperature $T$ follows from the standard thermodynamic definition as being the derivative of the energy with respect to the (Tsallis) entropy. The momentum distribution of the final state particles obtained describe the transverse momentum distributions very well. The values of the parameters are determined from measurements by the ALICE, ATLAS and CMS collaborations and are discussed in detail. In particular, the Tsallis parameter, $q$ is found with consistent values for all the transverse momentum distributions despite large differences in kinematic regions and shows a slight increase with beam energy, reaching a value of 1.15 at 7 TeV. It is concluded that the hadronic system created in high-energy p - p collisions can be seen as obeying Tsallis thermodynamics.

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