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Hello, Today I talked with the Geant4 collaboration spokesperson about the issues we have with the EM physics. He suggested the following actions for us to try and resolve these issues: 1) Verify that the same problems occur with the current version of Geant4 which is the 10.00.p01 release. It was claimed that there have been many fixes to multiple scattering in the past several releases, and these may have corrected the distribution tails. 2) Post details of our results as a comment on the EM forum of the Geant4 Hypernews, which is read by the developers. http://hypernews.slac.stanford.edu/HyperNews/geant4/get/emprocess.html 3) Open a report on their bug tracker including all the relevant details. http://bugzilla-geant4.kek.jp/ 4) Communicate directly with the EM working group coordinator: [log in to unmask]<mailto:[log in to unmask]> The details of the original issues are summarized below from an email Takashi sent me: -- Multiple scattering: http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/PhysicsReferenceManual/html/node34.html In Eq. (7.49) the power "d" should be exactly 2. "d=2" should solve the multiple scattering problem. Although it is possible to use single Coulomb scattering model, it is very slow. Bremsstrahlung and Pair production: Polar angle of the final state particle is sampled from an approximated function Eq. (8.39) in Bremsstrahlung and Eq. (6.36) in pair production. Correct angular distribution by Tsai (shown above Eq. (8.39)) should be used. Bremsstrahlung: http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/PhysicsReferenceManual/html/node42.html Pair production: http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/PhysicsReferenceManual/html/node27.html#SECTION04232000000000000000 —Jeremy ######################################################################## Use REPLY-ALL to reply to list To unsubscribe from the HPS-SOFTWARE list, click the following link: https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=HPS-SOFTWARE&A=1