Polarization transfer in hyperon decays and its effect in relativistic nuclear collisions

Abstract

We calculate the contribution to the polarization of Λ hyperons in relativistic nuclear collisions at high energy from the decays of Σ * (1385) and Σ 0 , which are the predominant sources of Λ production besides the primary component, as a function of the Λ momentum. Particularly, we estimate the longitudinal component of the mean spin vector as a function of the azimuthal angle in the transverse plane, assuming that primary Σ * and Σ 0 polarization follow the predictions of local thermodynamic equilibrium in a relativistic fluid. Provided that the rapidity dependence around midrapidity of polarization is negligible, we find that this component of the overall spin vector has a very similar pattern to the primary one. Therefore, we conclude that the secondary decays cannot account for the discrepancy in sign between experimental data and hydrodynamic model predictions of the longitudinal polarization of Λ hyperons recently measured by the STAR experiment at RHIC.

Unruh effect universality: emergent conical geometry from density operator

“…where the integrals I 0 and I 1 are of the form The integrals (5.12), can be found 13) and, thus, the energy density for fermions in the order m 2 takes the following form…”

“…Various quantum-field effects associated with acceleration and vorticity have been discovered: the chiral vortical effect (CVE) [1][2][3][4][5], the Unruh effect [6], phase transitions due to rotation [7] and acceleration [8][9][10] of the medium. These effects are now also the subject of an experimental search in heavy ion collisions and quark-gluon plasma, in particular, vorticity, or more precisely the thermal vorticity tensor, can lead to polarization of hadrons [11][12][13][14], and acceleration is considered as a possible source of thermalization and hadronization [15,16].…”

Quantum kinetic theory of spin polarization of massive quarks in perturbative QCD: Leading log

“…Some of the spin polarization of quarks and gluons in this phase can be transferred to that of hadrons after hadronization, which may affect the experimentally observed spin polarization of hadrons. Whether this effect survives hadronic phase dynamics depends on the relaxation dynamics of spin polarization in hadronic phase, as well as many other realistic conditions of heavy-ion collisions [18,19]. As a first step, a reliable tracking of time-evolution of spin polarization of quarks and gluons within the de-confined phase itself would be a prerequisite in any quantitative theory prediction of spin polarization of observed hadrons.…”

Local spin polarization in high energy heavy ion collisions

“…Although one model based on the chiral kinetic theory can explain the sign of the data [69], it cannot reproduce the magnitude of the data. Recent studies showed that the feed-down effects cannot resolve the sign difference [70,71].…”