Hi Flemming, thanks for the explanation regarding the phi angle. I have a few questions though: > 1) The official coordinate system has Z along the beam axis pointing 'north' along the FS. Y point towards the heavens > and X toward the MRS spectrometer. This is what is used by BRAG (GEANT) and thus for > FS it implies that for track > y> 0 -> phi is in range 180-190 > y< 0 -> phi is in range 170-190 I thought that if phi is measured from the positive X-axis, and Y being upward, y> 0 -> phi is in range 170-180 y< 0 -> phi is in range 180-190 assuming the FS is symmetric about the XZ plane. > > 2) The tracking code calculates phi,theta from the vector connecting the vertex and the entrance to D1, but has implemented this using atan.. rather than atan2 and thus resulting > y>0 -> phi in range of -10-0 (negative) > y<0 -> phi ~ -10-0 > thus phi(reco) = pi-phi(geant) should this be phi(reco) = phi(geant) - pi so that phi(geant) = phi(reco) + pi This seems to be the case looking at my phi distributions before and after reconstruction Selemon, > > > ---------------------------------------------------------------- > Flemming Videbaek > Physics Department > Brookhaven National Laboratory > > e-mail: videbaek@bnl.gov > phone: 631-344-4106 _______________________________________________ Brahms-dev-l mailing list Brahms-dev-l@lists.bnl.gov http://lists.bnl.gov/mailman/listinfo/brahms-dev-lReceived on Thu Dec 23 12:07:52 2004
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