Problem 896

Summary:	abnormal proton-nucleus scattering in Bertini cascade model
Product:	Geant4	Reporter:	zhemchugov
Component:	processes/hadronic	Assignee:	aatos.heikkinen
Status:	RESOLVED FIXED
Severity:	major	CC:	dennis.herbert.wright, zhemchugov
Priority:	P2
Version:	8.1
Hardware:	PC
OS:	Linux
URL:	http://cern.ch/jemtchou/g4bug/index.html

Description zhemchugov 2006-10-04 11:50:11 CEST

An incident proton with momentum 4 GeV/c has been simulated interacting with
Berillium target (thickness 60 mm), using Bertini cascade model for hadronic
interactions (QGSP_BERT). Final state with two outgoing protons has been
selected. Distribution of invariant mass, calculated for these protons, has
abnormally high peak at 3 GeV (which corresponds to proton-proton elastic
scattering). Distribution of polar angles of protons, corresponding to the peak,
also shows strange correlation: one of protons always has polar angle equal to
20 degrees, and another one - to about 45 degrees.
Change of momentum of initial proton does not change the picture qualitatively,
as well as change of target material. The same simulation using Binary cascade
model (QGSP_BIC) shows significantly different  behavior.
Illustrating plots can be found at http://cern.ch/jemtchou/g4bug/index.html

Comment 1 zhemchugov 2008-02-11 10:46:18 CET

Seems to disappear in 4.9.1

Comment 2 dennis.herbert.wright 2008-03-06 05:33:00 CET

Confirmed that this was fixed by removing a bug in nucleon-nucleon scattering
angular distribution.   In version 9.1, angular distribution was changed from
nearly isotropic to exp(t).