Abstract
We present an implementation of the vector boson pair production processes ZZ, W+W- and WZ within the POWHEG BOX V2. This implementation, derived from the POWHEG BOX version, has several improvements over the old one, among which the inclusion of all decay modes of the vector bosons, the possibility to generate different decay modes in the same run, speed optimization and phase space improvements in the handling of interference and singly resonant contributions.
Highlights
The treatment of the phase space, especially when handling processes with interference, has been changed with respect to the original version. We compute both the amplitudes A and Aexch, where Aexch is the amplitude with the final state identical particles exchanged
Noticing that both factors are symmetric for the exchange of the momenta of the identical particles, and that |A|2 and |Aexch|2 go into each other by this exchange, we can as well use the expression
The code has been written in such a way that the selection of decay modes can be carried out by the user by editing the subroutine alloweddec in the init_processes.f file
Summary
The treatment of the phase space, especially when handling processes with interference, has been changed with respect to the original version. This had the disadvantage that the regions for the importance sampling of the resonances were mixed up, and had to be handled with care [1]. The ambiguity in the assignment is only present in the small interference term, and no particular importance sampling tricks are needed to handle it. A further improvement was given by generating the partonic s variable in the underlying Born configuration with Lorenzian importance sampling over the possible singleresonant contribution. This leads to a better description of the single-resonant region
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
