Collective flows of protons andπ−mesons in2H+C,Ta and He+C, Ta collisions at 3.4 GeV/nucleon

Abstract

Collective flows of protons and negative pions have been studied in ${}^{2}$H $+$ C, Ta and He $+$ C, Ta collisions at an energy of 3.4 GeV/nucleon. The data have been obtained by the 2-m Propane Bubble Chamber (PBC-500) at JINR. It is found that the directed flow of protons and \ensuremath{\pi}${}^{\ensuremath{-}}$ mesons characterized by $d\ensuremath{\langle}{P}_{x}\ensuremath{\rangle}/d(y)$ increases with increase of the mass numbers of colliding nucleus pairs; the elliptic proton flow points out of the reaction plane and also strengthens as the system mass increases; the negative pion directed flow is in the same reaction plane as the proton flow for the lighter (${}^{2}$H $+$ C, He $+$ C) systems and in the opposite direction for the heavier (${}^{2}$H $+$ Ta, He $+$ Ta) systems. In ${}^{2}$H $+$ C, He $+$ C, C $+$ C, C $+$ Ne, ${}^{2}$H $+$ Ta, He $+$ Ta, C $+$ Cu, and C $+$ Ta collisions, the linear dependence of directed and elliptic flow parameters from mass numbers of projectile and target nuclei, (${A}_{P}$\ifmmode\cdot\else\textperiodcentered\fi{}${A}_{T}$)${}^{1/2}$, is similar for protons while for \ensuremath{\pi}${}^{\ensuremath{-}}$mesons the dependence of directed flow parameters is stronger. The ultrarelativistic quantum molecular dynamical model (URQMD) enlarged by the statistical multifragmentation model (SMM) satisfactorily describes the obtained experimental results for all pairs of nuclei. The data for such asymmetric nuclear collisions are obtained, to the best of our knowledge, for the first time.