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

Abstract

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.

Pion Condensation by Rotation in a Magnetic Field

“…In this letter, we show that the combined effects of magnetism plus a rotation can induce a pion superfluid phase in off-central heavy ion collision. This superfluid phase maybe at the origin of the large multi-pion correlations reported by ALICE [13], as also suggested by a recent non-equilibrium study [14].…”

“…Assuming that at chemical freeze-out, R ∼ 10 fm with still eB ∼ m 2 π , this would translates to a LL degeneracy N = eBR 2 /2 ∼ (m π × 10 fm) 2 ∼ 100/4 and a rotational chemical potential µ N = N Ω ∼ 1.25 m π . From the hadro-chemistry analysis, the pion chemical potentials at freeze-out are typically µ f ∼ 0.5 m π at RHIC, and µ f ∼ 0.86 m π at the LHC [14]. With the rotation at finite B, they would translate to µ π = µ N + 2µ f ∼ 1.96 m π and 2.98 m π respectively.…”

“…Consider the metric for a rotating frame in 1+3dimensions with mostly negative signature (+, −, −, −) ds 2 = (1 − Ω 2 ρ 2 )dt 2 + 2yΩdxdt − 2xΩdydt − dr 2 (14)…”

Resonances in a sudden chemical freeze-out model

“…It may also indicate that the non-equilibrium, as implemented in [3,4], may effectively include the re-scattering, because γ q and γ s are equivalent to non-equilibrium chemical potentials for each particle, see [3,4]. It is important to differentiate between the equilibrium with the re-scattering, and the single sudden freeze-out in the non-equilibrium, because the nonequilibrium also leads to pion condensation [6,7].…”

“…[8]. The parameters obtained in the fit to the 2.76 TeV Pb+Pb LHC data in equilibrium (EQ), non-equilibrium (NEQ) [3,4], and nonequilibrium with the possibility of pion Bose-Einstein condensation (BEC) on the ground state [6,7] in hadron-resonance gas, using correspondingly modified SHARE [9] and THERMINATOR [2] codes, are shown in Fig. 1.…”