Abstract
We present empirical features of parton energy loss in nucleus–nucleus collisions at RHIC through studies of the spectra and nuclear modification factors ( R A A ) for charged hadrons, neutral pions ( π 0 ) and non-photonic electrons. The flat distribution of R A A at high transverse momentum ( p T ) for a given collision centrality is consistent with a scenario where parton energy loss Δ p T is proportional to p T . The centrality dependence of the parton energy loss indicates the absence of path length dependence in the magnitude of energy loss. The lack of strong path length dependence suggests a dynamical picture where the dense partonic medium undergoes rapid expansion and the density of the medium falls rapidly in the first a few Fermi interval, which may be much shorter than the full path length. Implications of the empirical constraints on the parton energy loss will also be discussed.
Highlights
Nucleus-nucleus collisions at RHIC produce a hot and dense medium
Particle production in the higher pT region is consistent with features of parton fragmentations, and may be used to study parton energy loss in the hot and dense medium
Experimental measurements at RHIC have shown a strong suppression of high pT particles with respect to the expectation of binary nucleon-nucleon collision scaling for charged hadrons [3], for neutral pions [4, 5] and for non-photonic electrons [6]
Summary
Both approximately proportional to the cube root number of participants (Npart), the energy loss goes with Np2a/r3t as observed for π0 by the experimentally measured dN dy. If the collision system S, and L by dN g
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