By the usual definition of theta_y (angle of elevation from the xz plane), the direction cosine cos(b) (where b is the angle of inclination from the y-axis) exactly equals sin(theta_y). What I meant to say is that in small angle, sin(theta_y)~=theta_y. The relation sin(theta)sin(phi)=sin(theta_y) is exact. On Fri, 13 May 2016, Bradley T Yale wrote: > Even if theta is a small angle, it is multiplied by sin(phi), where phi is not. > ________________________________________ > From: [log in to unmask] <[log in to unmask]> on behalf of Sho Uemura <[log in to unmask]> > Sent: Friday, May 13, 2016 11:00:46 AM > To: Maurik Holtrop > Cc: Bradley T Yale; [log in to unmask]; HPS Software; Valeri Koubarovski; Norman A. Graf > Subject: Re: [Hps-analysis] Moller Generator Fixed! (again) > > I don't understand - I thought this cut was intended as a theta_y cut (>10 > mrad above or below the beam plane,so we only keep particles that might > hit a detector), and does v(np) not correctly describe theta_y? > > So I buy that this explains the difference in the envelope of your MC > truth distribution from theory (the U shape) but not that this has > anything to do with the gap, or any data-MC discrepancy seen after > readout. > > On Fri, 13 May 2016, Maurik Holtrop wrote: > >> Hi Bradley, >> >> That is great investigative work. You should now indeed check the other EGS5 generators for similar issues. As we discussed yesterday, there may be an issue with the background events for tridents. >> >> Can you please mention (advertise) this new result at the analysis meeting today? >> >> Best, >> Maurik >> >> >>> On May 13, 2016, at 3:25 AM, Bradley T Yale <[log in to unmask]> wrote: >>> >>> I think I found the real problem with how the Moller generator was initially set up. >>> This one affects the generated distribution a LOT more than the RNG precision probably did, and explains the remaining strangeness in the generated distribution. >>> >>> Looking at the egs5 Moller procedure, the angular cut was defined as: >>> >>> abs(v(np)) > 0.010 radians >>> >>> where v(np) is supposed to be theta. >>> However, the variables u, v, and w in egs are actually directional cosines, p_x = p*u, p_y = p*v, and p_z = p*w. >>> >>> So this means that in reality, the generator was saving Moller events such that >>> abs [ sin(theta)*sin(phi) ] > 0.010 >>> >>> which has a periodic nature to it. Plot this equation for some value of phi (or just think about it) and you'll see what was likely making these strange hills and gaps in the energy distribution - full-wave rectified Mollers! >>> >>> The scattered beam simulation does correctly define theta though: >>> sqrt[ u^2 + v^2 ] >>> >>> I made a moller_v3 procedure with this correction (still with a >10 mrad cut), and the comparison between before and after is shown. >>> The generated events now agree with the calculated cross section (XS curve is shown on the 'bad' plot), and no apparent missing events. >>> >>> These will be run through recon to see if we can finally get good Moller agreement with data. >>> I'm also going to try changing the scattered beam energy cut shown in the software meeting to see if it fixes Tim's phi vs. energy discrepancy. >>> -Brad >>> <BadMollers.png><2pt3_mol_v3_moller_E.png>_______________________________________________ >>> Hps-analysis mailing list >>> [log in to unmask] <mailto:[log in to unmask]> >>> https://mailman.jlab.org/mailman/listinfo/hps-analysis <https://mailman.jlab.org/mailman/listinfo/hps-analysis> >> > > ######################################################################## > 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 > > ######################################################################## > 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 > ######################################################################## 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