Systematic study of photon production at forward rapidity in STAR

Abstract

We present the measurement of multiplicity and pseudorapidity distributions of photons production at forward rapidity (−2.3 ≤ η ≤ −3.8) for Cu + Cu collisions at \( \sqrt {S_{NN} } \) = 62.4 and 200 GeV. Photons are measured using the Photon Multiplicity Detector (PMD) in STAR experiment at RHIC. The distributions of (η−ηbeam), where ηbeam is beam rapidity is presented. Pseudorapidity distributions of photons at forward rapidities, when ob-served in the frame of one of the colliding particles show the signature of energy independent scaling at forward rapidities known as Limiting Fragmentation. Measurement of inclusive photons reflect the distribution for π0 as most of the photons come from π0 decay. Gluon saturation at initial conditions of the collisions is one of the possible explanations for this scaling. Study of system-size and incident energy dependence of this phenomenon help us understand the mechanisms better. The system-size and energy dependence of the widths of scaling in pseudorapidity and comparison with model predictions are presented.