A model of parton multiple scattering in a dense and expanding medium is
described. The simulated results reproduce the general features of the data. In
particular, in the intermediate trigger momentum region there is a dip-bump
structure, while at higher trigger momentum the double bumps merge into a
central peak. Also, a new measure is proposed to quantify the azimuthal
distribution with the virtue that it suppresses the statistical fluctuations
event-by-event, while enhancing the even-structure of the signal.Comment: 4 pages including 7 figures. Talk presented at Hard Probes 200