The recent single-tag two-photon experiments at petra and the issue of quark charges

Abstract

The data of recent single-tag two-photon experiments indicating noticeable excess in (R^~_γγ)^jet over fractionally charged quark-parton model-predictions is studied from the point of view of its implications on the gauge integer charge quark model. Focusing attention on the region of pT exceeding about 3 GeV, where higher order QCD and non-perturbative effects might be expected to be small, it is noted that this excess and its Q2 dependence can be attributed to the presence of a colour component in the electromagnetic current provided the effective mass of the gluon lies between about 150 to 350 MeV. Accurate measurements of (R^~_γγ in the high p_T region (p_T ≳ 5 GeV) are crucial for an unambiguous distinction between fcq and gauge-icq models.