Scientists from the Joint Institute for Nuclear Research, in cooperation with Mexican colleagues from the National Autonomous University of Mexico (UNAM), the University of Colima, and the Autonomous University of Sinaloa, determined the relaxation time for the alignment between quark spin and angular velocity in a rotating quantum chromodynamics (QCD) medium. The paper was issued in Physical Review D.

Relaxation times were computed for massive quarks and antiquarks to align their spins with the angular velocity in a rigidly rotating medium at finite temperature and baryon density. The rotation effects were implemented using a fermion propagator immersed in a cylindrical rotating environment. The relaxation time was computed as the inverse of the interaction rate to produce an asymmetry between the quark (antiquark) spin components along and opposite to the angular velocity. For conditions resembling heavy-ion collisions, the relaxation times for quarks are smaller than for antiquarks.

For semicentral collisions, the relaxation time for quarks is within the possible lifetime of the QGP for all collision energies. However, for antiquarks, this happens only for collision energies √^sNN ≳ 50 GeV. The results were quantified in terms of the intrinsic quark and antiquark polarisations, namely, the probability to build the spin asymmetry as a function of time.

The research results show that these intrinsic polarizations tend to 1 with time at different rates given by the relaxation times with quarks reaching a sizable asymmetry at a faster pace. These are key results to further elucidate the mechanisms of hyperon polarisation in relativistic heavy-ion collisions.

For more information about the paper entitled “Relaxation time for the alignment between quark spin and angular velocity in a rotating QCD medium”, please refer to the link. A researcher at the Laboratory of High Energy Physics at JINR Ivonne Maldonado is among the authors.