Kinetics of an expanding pion gas

Gerber, P.; Leutwyler, H.; Goity, J. L.

doi:10.1016/0370-2693(90)90640-r

Cited by 65 publications

(51 citation statements)

References 25 publications

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“…The cross sections for inelastic, particle-number-changing processes are known to be smaller than those of elastic, resonance-forming processes at lower temperatures [12,13]. Final hadron abundance ratios also seem to favor a chemical freeze-out temperature of about T ch ≈ 160 − 175 MeV [14,15], while the slopes of spectra prefer a lower kinetic freeze-out temperature [16].…”

Section: Hadron Gas and Anisotropic Flowmentioning

confidence: 99%

“…To estimate the sensitivity, we multiply the local shear stress tensor at each point on the conversion hypersurface by a constant factor κ in order to mimic a change in specific shear viscosity η/s → κη/s. In the Navier-Stokes approximation (13), this is reasonable because viscous corrections to flow gradients are generally small [27,28]. We then capture the difference in particlization models empirically via adjusting κ.…”

Section: Uncertainty In Shear Viscosity Extractionmentioning

confidence: 99%

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Flow harmonics from self-consistent particlization of a viscous fluid

Wolff

Molnár

2017

Phys. Rev. C

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The quantitative extraction of quark-gluon plasma (QGP) properties from heavy-ion data, such as its specific shear viscosity η/s, typically requires comparison to viscous hydrodynamic or "hybrid" hydrodynamics+transport simulations. In either case, one has to convert the fluid to hadrons, yet without additional theory input the conversion is ambiguous for dissipative fluids. Here, shear viscous phase-space corrections calculated using linearized transport theory are applied in CooperFrye freezeout to quantify the effects on anisotropic flow coefficients vn(pT ) at both RHIC and LHC energies. Expanding upon our previous flow harmonics studies [1,2], we calculate pion and proton v2(pT ), v4(pT ), and v6(pT ), but here we incorporate a hadron gas that is chemically frozen below a temperature of 175 MeV and use hypersurfaces from realistic viscous hydrodynamic simulations. For additive quark model cross sections and relative phase-space corrections with p 3/2 momentum dependence rather than the quadratic Grad form, we find at moderately high transverse momentum noticeably higher v4(pT ) and v6(pT ) for protons than for pions. In addition, the value of η/s deduced from elliptic flow data differs by nearly 50% from the value extracted using the naive "democratic Grad" form of freeze-out distributions. To facilitate the use of the self-consistent viscous corrections calculated here in hydrodynamic and hybrid calculations, we also present convenient parameterizations of the corrections for the various hadron species (cf. Table I).

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Section: Hadron Gas and Anisotropic Flowmentioning

confidence: 99%

Section: Uncertainty In Shear Viscosity Extractionmentioning

confidence: 99%

Flow harmonics from self-consistent particlization of a viscous fluid

Wolff

Molnár

2017

Phys. Rev. C

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“…A consistent description of pion scattering processes in the vacuum and at low temperatures can be obtained within chiral perturbation theory [18][19][20][21][22][23]. However, the expansion breaks down in the chiral crossover region where nonperturbative effects become essential.…”

Section: Introductionmentioning

confidence: 99%

Chiral restoration effects on the shear viscosity of a pion gas

2012

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We investigate the shear viscosity of a pion gas in relativistic kinetic theory, using the Nambu-JonaLasinio model to construct the pion mass and the ππ-interaction at finite temperature. Whereas at low temperatures the scattering properties and, hence, the viscosity are in agreement with lowestorder chiral perturbation theory, we find strong medium modifications in the crossover region. Here the system is strongly coupled and the scattering lengths diverge, similarly as for ultra-cold Fermi gases at a Feshbach resonance. As a consequence, the ratio η/s is found to be strongly reduced as compared to calculations without medium-modified masses and scattering amplitudes. However, the quantitative results are very sensitive to the details of the applied approximations.

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“…The pion chemical potential was introduced to explain the early data at the SPS [39], and was similarly justified by partial thermalization [40], and also by pion condensation [41][42][43]. However, the update of the resonance list gave the same effect [5], and pion BEC was abandoned.…”

Section: Introductionmentioning

confidence: 99%

Fluctuations as a test of chemical nonequilibrium at energies available at the CERN Large Hadron Collider

Begun

2016

Phys. Rev. C

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It is shown that large chemical potential leads to the significant increase of multiplicity fluctuations for bosons, and makes the fluctuations infinite in the case of Bose-Einstein condensation. It allows to distinguish between the models that explain the anomalous proton to pion ratio and the low transverse momentum enhancement of pion spectra in Pb+Pb collisions at the LHC within chemical equilibrium or non-equilibrium models. The effects of resonance decays, finite size of the system, requirements to the event statistics, different momentum cuts, and limited detector acceptance are considered. The obtained results show the possibility to observe a substantial increase of the normalized kurtosis for positively or negatively charged pions in the case of non-equilibrium or partial pion condensation using currently measured data.

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Kinetics of an expanding pion gas

Cited by 65 publications

References 25 publications

Flow harmonics from self-consistent particlization of a viscous fluid

Flow harmonics from self-consistent particlization of a viscous fluid

Chiral restoration effects on the shear viscosity of a pion gas

Fluctuations as a test of chemical nonequilibrium at energies available at the CERN Large Hadron Collider

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