Nucleon-gold collisions at 200A GeV using tagged d + Au interactions in the PHOBOS detector

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 √s[subscript 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[subscript 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 p + [bar over 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 midrapidity. These studies augment recent results from experiments at the CERN Large Hadron Collider and BNL Relativistic Heavy Ion Collider 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.