Nucleon-Gold Collisions at 200 AGeV Using Tagged d+Au Interactions in PHOBOS

TL;DR

This paper investigates charged hadron production in d+Au, p+Au, and n+Au collisions at 200 GeV using forward calorimetry in the PHOBOS detector, providing insights into particle production mechanisms and isospin effects.

Contribution

It introduces a method to identify p+Au and n+Au collisions using forward calorimeters and constructs an improved reference system for Au+Au collisions, enhancing understanding of particle production.

Findings

Charged particle yields in d+Au match the combined p+Au and n+Au yields.

Transverse momentum distributions smoothly extrapolate from p+p to d+Au.

No significant charge asymmetry observed at mid-rapidity.

Abstract

Forward calorimetry in the PHOBOS detector has been used to study charged hadron production in d+Au, p+Au and n+Au collisions at sqrt(s_nn) = 200 GeV. The forward proton calorimeter detectors are described and a procedure for determining collision centrality with these detectors is detailed. The deposition of energy by deuteron spectator nucleons in the forward calorimeters is used to identify p+Au and n+Au collisions in the data. A weighted combination of the yield of p+Au and n+Au is constructed to build a reference for Au+Au collisions that better matches the isospin composition of the gold nucleus. The p_T and centrality dependence of the yield of this improved reference system is found to match that of d+Au. The shape of the charged particle transverse momentum distribution is observed to extrapolate smoothly from pbar+p to central d+Au as a function of the charged particle pseudorapidity density. The asymmetry of positively- and negatively-charged hadron production in p+Au is compared to that of n+Au. No significant asymmetry is observed at mid-rapidity. These studies augment recent results from experiments at the LHC and RHIC facilities to give a more complete description of particle production in p+A and d+A collisions, essential for the understanding the medium produced in high energy nucleus-nucleus collisions.