MC@NLO for Heavy Quarks in Photoproduction

MC@NLO [2, 3] is a generator for calculating next-to-leading order matrix elements, combined with a Monte Carlo event generator. When constructing an MC@NLO one needs to match the NLO matrix element with the parton shower of the generator. If wrongfully done, some of the configurations produced by the real gluon emissions in the matrix element may also be produced by the first branching in the parton shower. Therefore, to avoid to doubly count these configurations the first branching in the parton shower is subtracted from the real emission part of the matrix element. This method is called ’modified subtraction’, since it is based on the subtraction method of performing NLO calculations. The terms being subtracted are called ’Monte Carlo subtraction terms’. These terms are dependent upon which process is being calculated as well as on the parton shower itself. MC@NLO has previously been constructed for many processes, all in hadron-hadron collisions. In the following will be presented an MC@NLO for heavy quarks in photo production which is the first MC@NLO to be constructed for lepton-hadron collisions. The NLO calculation is taken from FMNR [4] and the parton shower from the HERWIG event generator [5] . For the NLO matrix element in this process, there are three kinds of contributions, namely the Born term, the real emissions, and the virtual corrections. The total NLO rate is schematically calculated as