How can I apply radiative corrections to electrons and positrons?

MaskRadPhotons is a masking class that removes radiated photons from the particle iterator and corrects the momentum of electrons and positrons that radiated these photons. This is applied in Create_xx.C with:

   FS->MaskParticles(new MaskRadPhotons(30,0.7,1));

The first argument of MaskRadPhotons is the minimal PCAL distance [cm] between the radiated particle and the electron/positron which is required to avoid correcting with calorimeter split offs (another masking class allows to mask split offs, more information on this is found here). The second argument is the maximal Theta angular difference [degrees] between the radiated particle and the electron/positron, which should be close to 0. Diagnostic plots are outputted in the output directory specified in Run_xx.C and should be used to choose these parameters. The final argument allows to correct (1) or not (0) the momentum of the electrons/positrons by adding the momentum of the photon to that of the electron. Note, if you want to access this corrected momentum in your final state or in a particle data class you mustn't use the momentum information from the corresponding clas12 hipo bank but should instead use the momentum from the four vector (P4) of the chanser particle object itself.

The Phi angular difference between the photons and electrons denotes where the photon has been radiated. The detector variable of the electrons/positrons keeps track of this and is set to 20 for a Phi difference less than 1.5 degrees, 21 between 1.5 and 10 degrees (or -1.5 and -10 degrees for the inbending field setting) and 22 for any other value.

The correction is also applied to photons that are misidentified by the event builder as neutrons. In this case, the momentum of the photon is recalculated from the calorimeter sampling fraction parametrisation before being added to the electron/positron momentum. To denote this the detector variable is set to 30/31/32 depending on the Phi difference.

In Create_xx.C you can choose different combitorial algorithms that use either the Event Builder PID (ALL) or charge (NONE) to loop over particles. When using ALL the correction will only be applied to electrons/positrons. When using NONE the correction is applied to any negatively or positively charged particle.