Problem 494

Summary:	mu - scattering with different cut values
Product:	Geant4	Reporter:	Markus.Hauger
Component:	processes/electromagnetic	Assignee:	Michel.Maire
Status:	RESOLVED REMIND
Severity:	normal
Priority:	P2
Version:	5.0
Hardware:	PC
OS:	Linux

Description Markus.Hauger 2003-05-28 09:06:41 CEST

I scattered 10 GeV muons off lead with different thicknesses (1 to 30 mm).
I am looking for scattered muons with transverse momentum bigger than 200 MeV/c
or 250 MeV/c resp.. For a "defaultCutValue" of 1 mm, i get a non linear rate as
a function of the thickness of the lead. Decreasing the "defaultCutValue" the
rate becomes more and more linear, which is fine. But the rate becomes smaller
and smaller, the higher the Cut Value is; much below the experimental values.

Due to single muon scattering the behaviour should be linear for large angles
(large transverse momentum), but why is the rate so sensitive to the Cut Values?
Why does the rate not converge for small Cut Values?

Comment 1 Michel.Maire 2003-06-17 08:13:59 CEST

With low production threshold, the emission of d-rays and bremsstrahlung
in the absorber guarantees several steps.
With high cut, there is only 1 step, and the multiple scattering occurs
only once, when
the particle exits the absorber. Then the tail of the theta distribution
is contreversal.
There is a way to force a stepMax 'by hand', in order to have several
steps in the
absorber, via G4UserLimits.
I ran few test jobs with a program derived from our
examples/extended/electromagnetic.
I attach the code and the results.txt : when using a stepMax, the
results are more stable
against the production cuts.

It is foreseen to implement an algorithm to force the multiple
scattering to do automatically
at least few steps in any layers. But this is still under study.