Directed flow in asymmetric nucleus-nucleus collisions and the inverse Landau-Pomeranchuk-Migdal effect

摘要

It is proposed to identify a strong electric field—created during relativistic collisions of asymmetric nuclei— via the observation of pseudorapidity and transverse momentum distributions of hadrons with the same mass but opposite charge. The results of detailed calculations within the parton-hadron string dynamics (PHSD) approach for the charge-dependent directed flow v1 are presented for semicentral Cu+Au collision at s_(NN)~(1/2) =200 GeV incorporating the inverse Landau-Pomeranchuk-Migdal (iLPM) effect, which accounts for a delay in the electromagnetic interaction with the charged degrees of freedom. By including the iLPM effect, we achieve a reasonable agreement of the PHSD results for the charge splitting in ν_1(p_T) in line with the recent measurements by the STAR Collaboration for Cu+Au collisions at s_(NN)~(1/2) = 200 GeV while an instant appearance and coupling of electric charges at the hard collision vertex overestimates the splitting by about a factor of 10. We predict that the iLPM effect should practically disappear at energies of s_(NN)~(1/2) ≈ 9 GeV, which should lead to a significantly larger charge splitting of ν_1 at the future FAIR/NICA facilities.