Neutral Pions with Large Transverse Momentum in pp, dAu and AuAu Collisions
measured with the PHENIX Experiment

The suppression of high pT neutral pions in central Au+Au collisions
relative to the binary scaled p+p results has been one of the most
significant observations at RHIC. The observed suppression may be
interpreted as the effect of energy loss of the initially hard-scattered
partons as they traverse the hot and dense matter produced in central Au+Au
collisions. However, other theoretical studies interpret the suppression as
an initial state effect, such as due to gluon saturation. In d+Au
collisions, where no hot and dense matter is produced in the final state,
the hard-scattered partons propagate and fragment in QCD vacuum. Initial
state effects, however, are equally present in both d+A and A+A collisions,
allowing the d+Au neutral pion results to provide a baseline measurement to
separate initial and final state effects. We discuss the PHENIX results on
neutral pion production in p+p, d+Au and Au+Au collisions. Recent results at
62.4 GeV will be presented in this context.