These processes describe t production including semi-leptonic decays for both the top and the anti-top. Since version 6.2 we have updated this to use the one-loop amplitudes of ref. [1]. The code for the virtual amplitudes now runs about three times faster than earlier versions where the virtual amplitudes of ref. [2] were used. Switching zerowidth from .true. to .false. only affects the W bosons from the top quark decay, because our method of including spin correlations requires the top quark to be on shell.
Process 141 includes all corrections, i.e. both radiative corrections to the decay and to the production. This process is therefore the basic process for the description of top production where both quarks decay semi-leptonically. When removebr is true in process 141, the top quarks do not decay. When one wishes to calculate observables related to the decay of the top quark, removebr should be false in process 141. The LO calculation proceeds as normal. At NLO, there are two options:
part=virt, real or tota : final state radiation is included in the production stage only
part = todk : radiation is included in the decay of the top quark also and the final result corresponds to the sum of real and virtual diagrams. Note that these runs automatically perform an extra integration, so will take a little longer.
Process 142 includes only the corrections in the semileptonic decay of the top quark. Thus it is of primary interest for theoretical studies rather than for physics applications. Because of the method that we have used to include the radiation in the decay, the inclusion of the corrections in the decay does not change the total cross section. This feature is explained in section 6 of ref. [3].
In the case of process 145, there are no spin correlations in the decay of the top quarks. The calculation is performed by multiplying the spin summed top production cross section, by the decay matrix element for the decay of the t and the . These processes may be used as a diagnostic test for the importance of the spin correlation.
nplotter_ttbar.f is the default plotting routine.
[1] S. Badger, R. Sattler and V. Yundin, One-Loop Helicity Amplitudes for t Production at Hadron Colliders, Phys. Rev. D83 (2011) 074020 [1101.5947].
[2] J.G. Korner and Z. Merebashvili, One loop corrections to four point functions with two external massive fermions and two external massless partons, Phys. Rev. D66 (2002) 054023 [hep-ph/0207054].
[3] J.M. Campbell and R.K. Ellis, Top-Quark Processes at NLO in Production and Decay, J. Phys. G42 (2015) 015005 [1204.1513].