A Comparison of Particles Recoiling from High PT Direct Photons and π0's at the ISR

We have studied the distribution of charged particles recoilingfrom high pT (> 3.5 GeV/c) direct photons and neutral pions in pp collisions at ? s= 63GeV. One expects a different mixture of quark and gluon initiated jets in the two cases, with predominantly u-quark jets recoilingfrom direct photons. No significant differences are observed in our momentum range apart from the charge composition, with a larger positive to negative ratio for particles with pT > 1 GeV/c opposite direct photons than opposite ?0.