These processes represents the production of a Z boson and 2 jets, including also the effect of a virtual photon (nproc=44 only). The Z∕γ^{*} decays to an e^{+}e^{-} pair (nproc=44) or into three species of neutrino (nproc=46). Virtual amplitudes are taken from ref. [1]. For more details on this calculation, please see Refs. [2, 3].
The calculation may be performed up to NLO. For Z + 2 jet production the next-to-leading order matrix elements are particularly complex and so they have been divided into two groups. The division is according to the lowest order diagrams from which they originate:
Diagrams involving two external quark lines and two external gluons, the “Gflag” contribution. The real diagrams in this case thus involve three external gluons.
Diagrams where all four external lines are quarks, the “Qflag” contribution. The real diagrams in this case involve only one gluon.
By specifying Gflag and Qflag in the file input.ini one may select one of these options at a time. The full result may be obtained by straightforward addition of the two individual pieces, with no meaning attached to either piece separately. The default is that both of these are set to .true. simultaneously.
When removebr is true, the Z boson does not decay.
nplotter_Zjets.f is the default plotting routine.
[1] Z. Bern, L.J. Dixon and D.A. Kosower, One loop amplitudes for e+ e- to four partons, Nucl. Phys. B513 (1998) 3 [hep-ph/9708239].
[2] J.M. Campbell and R.K. Ellis, Next-to-Leading Order Corrections to W^{+} 2 jet and Z^{+} 2 Jet Production at Hadron Colliders, Phys. Rev. D 65 (2002) 113007 [hep-ph/0202176].
[3] J.M. Campbell, R.K. Ellis and D.L. Rainwater, Next-to-leading order QCD predictions for W + 2 jet and Z + 2 jet production at the CERN LHC, Phys. Rev. D 68 (2003) 094021 [hep-ph/0308195].