Torqued fireballs in relativistic heavy-ion collisions

Abstract

We show that the fluctuations in the wounded-nucleon model of the initial stage of relativistic heavy-ion collisions, together with the natural assumption that the forward (backward) moving wounded nucleons emit particles preferably in the forward (backward) direction, lead to an eventby-event torqued fireball. The principal axes associated with the transverse shape are rotated in the forward region in the opposite direction than in the backward region. On the average, the standard deviation of the relative torque angle between the forward and backward rapidity regions is about 20• for the central and 10• for the mid-peripheral collisions. The hydrodynamic expansion of a torqued fireball leads to a torqued collective flow, yielding, in turn, torqued principal axes of the transverse-momentum distributions at different rapidities. We propose experimental measures, based on cumulants involving particles in different rapidity regions, which should allow for a quantitative determination of the effect from the data. To estimate the non-flow contributions from resonance decays we run Monte Carlo simulations with THERMINATOR. If the event-by-event torque effect is found in the data, it will support the assumptions concerning the fluctuations in the early stage of the fireball formation, as well as the hypothesis of the asymmetric rapidity shape of the emission functions of the moving sources in the nucleus-nucleus collisions.PACS numbers: 25.75Gz, 25.75.Ld

Longitudinal decorrelation of anisotropic flows in heavy-ion collisions at the CERN Large Hadron Collider

“…Such a twist in the AMPT model is caused by different contributions to the initial particle production from projectile and target participant nucleons and the difference in the initial participant angles in the forward and backward rapidity regions [64]. It should also be partially responsible for the long-range longitudinal decorrelations observed in this study.…”

Charge-dependent directed flow in asymmetric nuclear collisions

“…One should note that the observed differences between the directed flow of protons and antiprotons could give information also on the different rate of baryon stopping on the Cu and Au side of the fireball. Moreover, the reaction plane correlations in the fireball are modified in asymmetric collisions with stronger correlations between odd and even order event planes [41,42]. The notation is the same as in Fig.…”

Initial state fluctuations and final state correlations in relativistic heavy-ion collisions

“…Theoretical calculations by Bozek et al [150], Petersen et al [151] and Pang et al [111] demonstrate that longitudinal fluctuations may result in non-trival pseudorapidity dependencies of the triangular flow event plane and two-particle correlations. In some calculations, one can even find that the v 3 flow vector is anticorrelated between the far forward and backward regions [152].…”