Quark parton model with large partonk T

Abstract

The quark-parton model is generalized to allow for large partonk T subject to mass shell restrictions. Since it is expected that <k T > will rise withQ 2 in (highly virtual) photon mediated processes, this generalization is necessary to restore the applicability of the quark-parton model. By treatingk T as an essential kinematical variable, we have been led to the introduction of a new scaling variablez. Together with Bjorken'sx variable, we give a unified kinematical description of the four distribution functions: hadron structure functions and jet decay functions for spacelike and timelike photons. Possibility of a simple interpolating universal function is considered. Phenomenological determination of that function is examined in detail. Predictions onR, parton <k T >, hadron <p T > in jets, etc., are made with the dimuon <q T > being used as an input. The usual relation $$\left\langle {q_T } \right\rangle = \sqrt 2 \left\langle {k_T } \right\rangle$$ is shown to be false in the region wherek T is not small compared tok L , a situation which prevails in the production of dileptons recently measured. Thek T distributions for timelike and spacelike cases are shown to be not identical. The model is consistent with nearly all relevant data on virtual photon processes.