<HTML dir="ltr"><HEAD><TITLE>[Clas12_software] GEMC and particles.</TITLE>
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<DIV dir="ltr"><FONT face="Arial" size="2" color="#000000">Dear Maurik,</FONT></DIV>
<DIV dir="ltr"><FONT face="Arial" size="2">Concerning the pid number, here is the (Geant4?) convention Maurizio uses:</FONT></DIV>
<DIV dir="ltr"><FONT face="Arial" size="2"> // Nuclear codes are given as 10-digit numbers +-100ZZZAAAI.<BR> //For a nucleus consisting of np protons and nn neutrons<BR> // A = np + nn and Z = np.<BR> // I gives the isomer level, with I = 0 corresponding<BR> // to the ground state and I >0 to excitations<BR>According to this, your 1000020040 appears to be an alpha.</FONT></DIV>
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<DIV dir="ltr"><FONT face="Arial" size="2">Cheers,</FONT></DIV>
<DIV dir="ltr"><FONT face="Arial" size="2">Sébastien.</FONT></DIV></DIV>
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<FONT face="Tahoma" size="2"><B>De:</B> clas12_software-bounces@jlab.org de la part de Maurik Holtrop<BR><B>Date:</B> jeu. 28/10/2010 22:50<BR><B>À:</B> Maurizio Ungaro<BR><B>Cc:</B> Clas12 Software<BR><B>Objet :</B> [Clas12_software] GEMC and particles.<BR></FONT><BR></DIV>
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<P><FONT size="2">Hello Maurizio,<BR><BR>I have been spending some time looking into the internals of GEANT4 and the different particle models that it uses, particularly in the context of electro-production processes. I have the following observations that are probably relevant to the wider gemc community:<BR><BR>Method: send of order 3E9 electrons through a thin (0.25% X0) tungsten target and look at the particles produced by GEANT4.<BR>Note: It is difficult and time consuming to check the actual cross sections of the particles produced. I am interested in very small angle scattering, where there is little data, even for e+ and gamma production.<BR><BR><BR>1) The standard choice of physics model "QGSC_BERT" does fairly well scattering electrons and producing gammas and positrons, but does not produce anywhere near the correct amount of pions, and no kaons at all. I do see protons and neutrons.<BR><BR>2) The build-in list called "gemc", does the same level of bremsstrahlung, but does not produce any pions or kaons, and too few protons and neutrons. I am surprised about this, since the class HadronPhysics does invoke the G4ElectronNeuclearReacion class. This appears to be a bug?<BR><BR>3) The "LHEP_BERT_HP" appears to give more realistic pion and kaon production. I need to check the actual cross sections though, which is on my "to do" list. The "LHEP_BERT" list also suffers from insufficient pion production. The HP part (high precision neutron tracking) seems to do more than just do a better job with the neutrons.<BR><BR>I am starting up some QGSP_BERT_HP jobs to see if these improve pion production similarly as for the LHEP list.<BR><BR>For ALL the physics options, I get a not insignificant number of particles with pids larger than 1E10, most of the time this pid=1000020040, sometimes other values around it. This is quite outside the range of the permitted pids. I have no clue yet what is going on there and need to spend some debugging time there.<BR><BR><BR>Any comments on this, especially some additional insight, would be greatly appreciated.<BR><BR>Cheers,<BR> Maurik<BR><BR></FONT></P></DIV></BODY></HTML>