Changes between Version 8 and Version 9 of perWeight

Timestamp:

Jun 25, 2018, 12:49:19 PM (6 years ago)

Author:

mosel

Comment:

--

perWeight

@@ -1 @@
-= 'perturbative' and 'real' particles; the perturbative weigth =
+= 'perturbative' and 'real' particles; the perturbative weight =
 
 == 'perturbative' and 'real' particles ==
@@ -38 +38 @@
 ''The weights can also be negative''. This happens, e.g., in the case of pion production on nucleons. In this case the cross section is determined by the square of a coherent sum of resonance and background amplitudes and as such is positive. In the code the resonance contribution is separated out as the square of the resonance amplitude and as such is positive as well. The remainder, i.e. the sum of the square of the background amplitude and the interference term of resonance and background amplitudes, can be negative, however. This latter contribution is just the event type labeled 32 and 33 in the code that describes the 1pi bg plus interference.
 
+== How to compute cross sections from the perturbative weights ==
+The output file FinalEvents.dat contains all the events generated. Per event all the four-momenta of final state particles are listed together with the incoming neutrino energy and various other useful properties (see documentation for FinalEvents.dat). As an example we consider here the calculation of the differential cross section dsigma/dE for the outgoing lepton. In FinalEvents.dat the lines with the particle number 902 contain all the muon kinematics as well as the perweight. In order to produce a spectrum one first has to bin the muon energies into energy bins. This binning process must preserve the connection between energy and perweight. Then all the perweights in a given energy bin are summed and divided by the bin width to obtain the differential cross section. If the GiBUU run used - for better statistics - a nonzero number of runs at the same energies, then this number of runs has to be divided out to obtain the final differential cross section.
+
+All cross sections in GiBUU, both the precomputed ones and the reconstructed ones, are given per nucleon. The units are 10^{-38} cm^2 for neutrinos and 10^{-33} cm^2 for electrons.