Alexander Somov wrote: > Hello Richard, > > I have a couple of quick questions > (I am estimating rates for a Level-1 trigger now and > want to be sure that I am using the latest geometry): > > 1. Could you please check that a beamline geometry > (BeamLine_HDDS.xml file attached to this mail) is the > latest one (versio 2.0, 2006-11-25) ? > Yes, that is the current one according to my records. > 2. When I look on z coordinates of the conversion of > 'primary' gammas, I see a peak around z ~ -95 cm. Do you > have an idea what it could be (is it DET 7 ?). I am attaching a ps > file with the z-coordinates of the converted gammas > (and also a plot of x%y coordinates for -100 < z < -95 cm) > > To obtain these plots I simply require > ISTAK == 0, IPART ==1, and LMEC(NMEC) == 6 Those spikes at -1400cm and -100cm appear to come from the entrance and exit mylar foils that terminate the photon beam vacuum pipe. There is a vacuum pipe from the second sweep magnet in the collimator cave down to just before the target. Those mylar foils are called "CAP1" and "CAP2" if you want to look for them in the geometry tree. They are 0.5 mm thick each. DET7 is just 2cm of air. There will be some conversions in that too, but most of what you see there seems to be coming from the mylar. > 3. In BeamLine_HDDS.xml file, what is the position, XYZ, of a composition > "beamPipe" (as far as I understood it starts at XYZ = 0) > > <composition name="beamPipe"> > <posXYZ volume="DET4" X_Y_Z=" 0.0 0.0 -1400.0"/> > <posXYZ volume="DET5" X_Y_Z=" 0.0 0.0 1400.0"/> > <posXYZ volume="DET6" X_Y_Z=" 0.0 600.0 0.0"/> > <posXYZ volume="DET7" X_Y_Z=" 0.0 0.0 -591.0"/> > <posXYZ volume="HallPipe" X_Y_Z="150.0 -350.0 -1046.0"/> > </composition> > (so that the position of DET7 is -5.91 m)? You have to be careful about what coordinate system you are dealing with. The comments in BeamLine_HDDS.xml state that "the origin of beamPipe is the center of the Hall". This is different from the detector origin or the target position. So when you say DET7 is at -5.91m do you mean relative to the GlueX detector origin or the Hall geometric center? Answers are no and yes, respectively. The CSG volumes used by Geant have local origins at their geometric centers; this is not a convention that I invented. The target center is at (150, -300, -500) in hall-centric coordinates. So relative to the detector origin, the DET7 placement is at z = -91cm, as you suspected. Richard Jones
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