Constituent quarks and systematic errors in mid-rapidity charged multiplicity dNch/dη distributions

Abstract

Centrality definition in A + A collisions at colliders such as RHIC and LHC suffers from a correlated systematic uncertainty caused by the efficiency of detecting a p + p collision ([Formula: see text] for PHENIX at RHIC). In A + A collisions where centrality is measured by the number of nucleon collisions, [Formula: see text], or the number of nucleon participants, [Formula: see text], or the number of constituent quark participants, [Formula: see text], the error in the efficiency of the primary interaction trigger (Beam–Beam Counters) for a p + p collision leads to a correlated systematic uncertainty in [Formula: see text], [Formula: see text] or [Formula: see text] which reduces binomially as the A + A collisions become more central. If this is not correctly accounted for in projections of A + A to p + p collisions, then mistaken conclusions can result. A recent example is presented in whether the mid-rapidity charged multiplicity per constituent quark participant [Formula: see text] in Au + Au at RHIC was the same as the value in p + p collisions.