It has been observed that the yield of neutral pions at high transverse
momentum (pT > 5 GeV/c) region is strongly suppressed in central Au+Au
collisions at Relativistic Heavy Ion Collider (RHIC), compared to the one
expected in p+p collisions. This suppression may be due to an energy loss of
hard scattered partons in the medium (jet quenching), that results in a
decrease of the yield at a given pT. The magnitude of the suppression would
depend on the path length of scattering partons in the medium, and therefore is
associated with azimuthal angle from reaction plane in non-central collisions.
Studying the path length dependence of energy loss would give additional
information on understanding the energy loss mechanism. We discuss the parton
energy loss mechanism using the nuclear modification factor (RAAβ) of
neutral pion with respect to reaction plane. A new reaction plane detector was
installed in the PHENIX detector in RHIC Year-7 run, and improved the reaction
plane resolution. More precise measurement of the hadron suppression with
respect to path length is expected using the detector. I will report about
analysis status of neutral pion production in Au+Au collisions at
sNNββ=200 GeV.Comment: 4 pages, 5 figures, Proceedings of the 20th International Conference
on Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008",
Jaipur, India, February 4-10, 200