Constituent quarks and systematic errors in mid-rapidity charged multiplicity $dN_{\rm ch}/d\eta$ distributions

TL;DR

This paper discusses how systematic uncertainties in centrality determination in heavy-ion collisions affect measurements of charged particle multiplicity, emphasizing the importance of accounting for constituent quark participants to avoid mistaken conclusions.

Contribution

It highlights the impact of trigger efficiency uncertainties on centrality measures and the resulting charged multiplicity comparisons between different collision systems.

Findings

Systematic errors reduce with more central collisions.

Misaccounted uncertainties can lead to incorrect conclusions about particle production.

Proper correction is essential for accurate comparison between A+A and p+p collisions.

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 ($50\pm 5\%$ for PHENIX at RHIC). In A$+$A collisions where centrality is measured by the number of nucleon collisions, $N_{\rm coll}$, or the number of nucleon participants, $N_{\rm part}$, or the number of constituent quark participants, $N_{\rm qp}$, 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 $N_{\rm part}$, $N_{\rm coll}$ or $N_{\rm qp}$ 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 $({dN_{\rm ch}/d\eta})/{N_{\rm qp}}$ in Au$+$Au at RHIC was the same as the value in p$+$p collisions.