PROJET: Jet cross sections in deeply inelastic electron proton scattering. Version 4.1 Original Research Article

PROJET is a parton level Monte Carlo program for the calculation of jet cross sections in deeply inelastic electron proton scattering. In its present version it contains the Born level diagrams for the production of (1 + 1), (2 + 1) and (3 + 1) jets and the next-to-leading order corrections for the production cross sections of (1 + 1) and (2 + 1) jets for all polarisations of the exchanged virtual photon. In particular, the full angular correlations between the lepton and jet momenta are implemented. The program permits the application of acceptance cuts on all external momenta. For this purpose, the program creates an event record accessible to the user program with all momenta in the laboratory frame and in the center of momentum frame of the proton and the virtual photon. This option is indispensable for phenomenological studies because of the strong dependence of cross sections on phase space restrictions and the large uncertainty of fragmentation corrections in the proton direction. Since PROJET uses the Monte Carlo integration method for the evaluation of phase space integrals, the weights of the generated events can be used to produce distributions of observables related to jet momenta.