CERN Program Library Long Writeup W5013 - CERNLIB ...

where:
Γ = kα
2π
[
ɛ =
W
E
1
1 − ɛ
1+2 Q2 + ν 2
Q 2 tan 2 θ 2 ]
Q 2 and ν are the normal scaling variables expressed by:
Q 2 = −q 2 =2(EW −|p||p ′ | cos θ − m 2 −µ) and ν = E − W
here σ T and σ S are the photo-absorption cross-sections for transverse and longitudinal photons respectively
for which the relation used is:
(
σ S =0.3 1 − 1 )
1.868 Q2 ν σ T
and σ T is assumed to be constant σ T =0.12 mb. For the incident flux K of the photons Gillman’s convention
is used:
K = ν + Q 2 /2ν
A three-dimensional importance sampling in the variables E, W and θ is performed each time an interaction
has to occur.
This set of routines only works if GUPHAD calls GPGHEI and GUHADR calls GHEISH. The hadrons are generated
in an approximate way. The virtual photon is replaced by a real pion of random charge with the same kinetic
energy. Then the GUHADR routine is called to generate a π-nucleus inelastic scattering. While the final state
generated this way gives a good approximation for calorimetric purposes, the kinematics of the final state
may be a rather poor approximation of reality. The muon-nucleus interactions are activated by the MUNU
data record of GEANT. After a muon-nucleus interaction the muon will still be the current particle. If MUNU 1
has been specified, secondaries coming from the interaction of the virtual photon with the nucleus will be in
the GEANT temporary stack. If MUNU 2 has been specified, then the secondary particles will not be generated
and the energy lost by the muon will be added to DESTEP. For each material a table of muon-nucleus crosssections
is stored at initialisation time. See material bank structure for details.
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