Process 287 represents the production of three real photons. The cross section diverges when one of the photons is very soft or in the direction of the beam. Thus in order to produce sensible results, the input file must supply values for both ptmin_photon and etamax_photon. This will ensure that the cross section is well-defined.
The calculation of process 285 may be performed at NLO using either the Frixione algorithm [1] or standard cone isolation. The production of a photon via parton fragmentation is included at NLO and can be run separately by using the frag option in part. This option includes the contributions from the integrated photon dipole subtraction terms and the LO QCD matrix element multiplied by the fragmentation function. The phase space cuts for the final state photons are defined in input.ini, for multiple photon processes such as 285 - 287 the pT’s of the individual photons (hardest, next-to hardest and softest) can be controlled independently. The remaining cut on Rγj, ηγ etc. are applied universally to all photons. Users wishing to alter this feature should edit the file photon_cuts.f in the directory src/User.
The calculation is described in Ref. [2].
Process 287 represents the production of three real photons. The cross section diverges when one of the photons is very soft or in the direction of the beam. Thus in order to produce sensible results, the input file must supply values for both gammptmin and gammrapmax. This will ensure that the cross section is well-defined.
The calculation of process 285 may be performed at NLO using either the Frixione algorithm [1] or standard cone isolation. The production of a photon via parton fragmentation is included at NLO and can be run separately by using the frag option in part. This option includes the contributions from the integrated photon dipole subtraction terms and the LO QCD matrix element multiplied by the fragmentation function. The phase space cuts for the final state photons are defined in input.ini, for multiple photon processes such as 285 - 287 the pT’s of the individual photons (hardest, next-to hardest and softest) can be controlled independently. The remaining cut on Rγj, ηγ etc. are applied universally to all photons. Users wishing to alter this feature should edit the file photon_cuts.f in the directory src/User.
nplotter_trigam.f is the default plotting routine.
[1] S. Frixione, Isolated photons in perturbative QCD, Phys. Lett. B429 (1998) 369 [hep-ph/9801442].
[2] J.M. Campbell and C. Williams, Triphoton production at hadron colliders, Phys. Rev. D 89 (2014) 113001 [1403.2641].