Transverse energy from minijets in ultrarelativistic nuclear collisions: a next-to-leading order analysis

We compute in next-to-leading order (NLO) perturbative QCD the amount of transverse energy produced into a rapidity region $\Delta Y$ of a nuclear collision from partons created in the few-GeV subcollisions. The NLO formulation assumes collinear factorization and is based on the subtraction method. We first study the results as a function of the minimum transverse momentum scale and define and determine the associated $K$-factors. The dependence of the NLO results on the scale choice and on the size of $\Delta Y$ is also studied. The calculations are performed for GRV94 and CTEQ5 sets of parton distributions. Also the effect of nuclear shadowing to the NLO results is investigated. The main results are that the NLO results are stable relative to the leading-order (LO) ones even in the few-GeV domain and that there exists a new kinematical region not present in the LO, which is responsible for the magnitude of the $K$-factors. The dependence on the size of $\Delta Y$ is found to be practically linear within two central units of rapidity, and the scale dependence present at RHIC energies is seen to vanish at the LHC energies. Finally, the effect of NLO corrections to the determination of transverse energies and multiplicities in nuclear collisions is discussed within the framework of parton saturation.

K.J. Eskola, K. Tuominen · 2000