I have committed classes to the VLE package which allow inverse beta decay events to be generated using the standard gEvGen.exe.
Before they can be used, some of the global configuration files must be editted (in order to add the IBD Event Generator). I want to check with Constantinos before committing these. I will add a comment to this entry when the configurations have been committed to CVS.
The only other outstanding issue is that there is a hard-coded cutoff on the minimum neutrino energy of 10 MeV when GENIE makes the cross section splines. This issue is being discussed with Costas and will be resolved soon(ish).
Eliminating this cutoff at 10 MeV produces very nice results. Here are some plots, where I've used the neutrino flux given in Eqn 26 of Strumia, with the supernova distance and total energy corresponding to SN1987A (D=51.4 kpc, Etot=3e53 ergs).
Here is the positron energy distribution (compare to Fig 2a of Strumia):
Here is the positron angular distribution (compare to Fig 2b of Strumia):
As a sanity check, the following plot shows the initial state neutrino energy distribution in green (arbitrary units). This is compared to the neutrino flux (in blue, the functional form from Strumia, and in black circles, the histogrammed flux used internally by GENIE) as well as to the IBD cross section.
And the longitudinal positron momentum as a function of the neutrino energy:
These results can be compared to those coming from the default GENIE with the 10 MeV cut in place:
Finally, the cross section spline file including the IBD can be obtained here:
This contains 200 knots over the of 1 to 400 MeV for both IBD and the inverse reaction.
These splines can be viewed in the following plots. Note that the default quasi-elastic cross section which was already in GENIE already did quite a good job at calculating the cross section! The trick will be getting the neutrino - nucleus xsec's...