Hi Flemming, others TPCers, Thanks for the info. I suggest we use these numbers for a first reduction, and then if they change appreciably, we redo the reduction. Since one of the primary uses of this reduction is to get data for TOF calibrations, we will not be too adversly impacted by small changes in geo, vdrift, etc. That is, we may wish to re reduce for analysis, but we may not have to recalibrate. Any comments? As for the vdrift... I think that the relative drift velocity seems (and note, I said 'seems', I didn't say 'has been proven beyond the shadow of a doubt') to fairly stable. Now that we have the fibers, we can check this quite easily and will do so. Still, does anyone have a good feeling for how much the vdrift must change to impact any measured physics variables? I think that by requiring FFS tracks with a valid tof, one effectively makes a fiducial cut in the D2 magnet, which is what the y position would be used for. I would, of course, appreciate any criticizism to the forgoing. Finally, to what extent can we use the DVM to monitor changes in the drift velocity? Ian -----Original Message----- From: owner-brahms-dev-l@bnl.gov [mailto:owner-brahms-dev-l@bnl.gov]On Behalf Of Flemming Videbaek Sent: Thursday, October 18, 2001 9:58 PM To: brahms-tpc-l@bnl.gov Cc: brahms-dev-l@bnl.gov Subject: tpc geometries The currently recommended values for tpc tracking (in particular for TPM1 and TPM2) have been deduced looking at several zero-file runs, and field runs at different angles, and revisiting the survey and complementing measurements. Additionaly they have been compared to the rudimentary survey done before the run, as well as performing measuremnts on TPC timing etc, looking at positions of clusters within TPCs etc. Some of the information is also pertinent to the forward TPCs. a) The TPM1,TPM2 values are for 90 degrees b) The small tpm2 rotation is consistent with the survey value (of -.4 deg) c) The heights are derived from the survey top's and internal geometries. (design drawings + later checks). All TPCs d) The timing offsets for the SCA readout start are from a measurement of T1. It is estimated the other TPCs at most can deviate by 50 nsec. e) Drift velocities have been found for tpm1 as the 'best value' the consistently -- get the track projection near Ty~0 -- the bottom cluster y (in local coordinates between -10 to -9 cm) [physical constraint] -- reasonable matching with TPM2 -- matching with Tpm2 tracks. f ) TPM2 average velocities from projection and matching with fibres and tof calibration slats. g) It is apparent the changes in Vdrift has occured over the running period even within hours, and calibrations will have to be done. Also for at least Tpm2 there are x,y dependent effects in the tracking that eventually has to be taken care of. This should also be investigated to wehat degree this is present in T1,T2 now with the fibres avaliable. h) The quoted values for Vdrift for T1 and T2 are speculations The 1.6 from the presently used values. The larger value comes if one assumes that the lowest y-values comes from near the bottom cathode plane (at -10 cm). The other T1, T2 values should be used. i) There are several effects NOT understood for the MRS tracking as the mentioned x,y variations (as observed by track projection with fibres), the change of matching angle vs track angle.So the present geometry though reasonable and consistent is not the final word on this story. Eun-Joo, JHLee and FV -------------------------------------------------------------------------- ------- TPM1 geo x (90) 0 y(90) 1.8 +-0.1 z(90) 94.6 angle 90 params fTimeOffset 1030 +-50 fTimeBase 12 +-.2 fDrift 1.7 +-0.05 Time dependent? TPM2 geo x (90) 0 y(90) 2.05 +-0.1 z(90) 286.6 angle 89.75 +-0.05 params fTimeOffset 1030 +-50 fTimeBase 11.8 +-.1 fDrift 1.6 +-0.05 Time dependent? T1 geo x (90) y(90) 0.8 +-0.1 z(90) angle 1.95 params fTimeOffset 1030 +-20 fTimeBase 11.8 +-.1 fDrift 1.6-1.9 +-0.05 Time dependent? T2 geo x (90) y(90) 0.8 +-0.1 z(90) angle params fTimeOffset 1030 +-50 fTimeBase 11.8 +-.1 fDrift 1.6-1.9 +-0.05 Time dependent? ------------------------------------------------------ Flemming Videbaek Physics Department Brookhaven National Laboratory tlf: 631-344-4106 fax 631-344-1334 e-mail: videbaek@bnl.gov
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