Relaxation time for the alignment between the spin of a finite-mass quark or antiquark and the thermal vorticity in relativistic heavy-ion collisions

Abstract

We study the relaxation time required for the alignment between the spin of a finite-mass quark or antiquark and the thermal vorticity, at finite temperature and baryon chemical potential, in the context of relativistic heavy-ion collisions. The relaxation time is computed as the inverse of the total reaction rate that in turn is obtained from the imaginary part of the quark or antiquark self-energy. We model the interaction between spin and thermal vorticity within the medium by means of a vertex coupling quarks and thermal gluons that, for a uniform temperature, is proportional to the global angular velocity and inversely proportional to the temperature. We use realistic estimates for the angular velocities for different collision energies and show that the effect of the quark mass is to reduce the relaxation times as compared to the massless quark case. Using these relaxation times we estimate the intrinsic quark and antiquark polarizations produced by the thermal vorticity. We conclude by pointing out that, although the intrinsic global polarization of the s-quark turns out to be larger than that of thes-quark, there is room to explain recent STAR results which show that the global polarization ofΛ is larger than that of Λ when considering that these hyperons can be produced from different density regions in a core-corona model.

Global spin polarization of multistrange hyperons and feed-down effect in heavy-ion collisions

“…Nevertheless, how spin of particles reaches the thermal equilibrium in a strongly interacting quark-gluon plasma so that Eq. ( 1) can apply is still an open question which is under intense investigation [26][27][28][29][30][31][32][33]. Therefore, more theoretical and experimental results of the global polarization are essential to verify the current vorticity interpretation.…”

Relativistic second-order dissipative spin hydrodynamics from the method of moments

“…We note that spin relaxation time has been studied using perturbative QCD techniques [85][86][87][88], the Nambu-Jona-Lasinio model [89], and an effective vertex for the interaction with the thermal vorticity [90,91]. In Ref.…”

Rise and fall of $Λ$ and $\barΛ$ global polarization in semi-central heavy-ion collisions at HADES, NICA and RHIC energies from the core-corona model

“…Equations (11) assume that the 𝑠 and s quark polarizations translate into the Λ and Λ polarization, respectively, during the hadronization process. The relaxation times 𝜏 and τ can be computed as the inverse of the interaction rate for the spin alignment of a massive quark or antiquark with energy 𝑝 0 with the angular velocity with magnitude 𝜔 as [58] Γ…”

“…𝐶 𝑖 , 𝑖 = 𝑇, 𝐿 are the result of the trace calculation after contraction of the transverse and longitudinal projection operatorsthat come together with the gluon spectral functions 𝜌 𝑖 - with the quark propagator and the vertices, after summing over the Matsubara frequencies (see Ref. [58] for further details). The total interaction rate is obtained integrating Eq.…”