Dear JH, others, Nice work, JH. This will really help with making the reduction more automated! I have, in the past couple of days, reduced around 1000seq. from various settings, but used the 'default' drift velocities for TPM1 and TPM2. If someone (Peter???) could put these vdrift in the data base (or teach me how to do it) I can quickly redo the reductions that I have done. Also, as far as I know, the proper vdrift has been the only thing keeping us from a 'final' (ok, maybe semi-final) reduction pass, that is, one in which all the local tracking is done. As soon as we have a set of Vdrift in the data base, I will get this effort going. One question: how do we do this for runs before the fibers were put in? Is it possible to correlate the Vdrift you measure with the results from the DVM? If these are correlated (and one imagines they should differ at most by a constant factor) then we could use the DVM runs to do a Vdrift calibration for the entire run. Again, JH, thanks for the nice resuslts! Ian PS: the reduced data can be found at /brahms/data01/igb/RXXXX/seq/ XXXX=run number. You should check the date on the root files (run00XXXXseqNNN.root),if they were produced after the 10.th of December, they include the nice calibrations Peter has done for the TPCs, including vdrift for T1 and T2. I think that they also contain the latest greatest DC calibrations, but I need to check with Pawel to be sure. -----Original Message----- From: owner-brahms-l@bnl.gov [mailto:owner-brahms-l@bnl.gov]On Behalf Of J.H. Lee Sent: 13. december 2001 00:25 To: brahms-l@bnl.gov Subject: Drift Velocty Variations of TPM Hi, During the data taking, drift velocities for TPC's varied due to some changes in gas flows, atmospheric pressure, temperature and possibly some unknown factors. As we know, it's important to calibrate the variations since the drift velocity is directly proportional to the y positions of the tracks. Even though y information is not used for the momentum calculations, it's still important to know it accurately because it's used for - Selecting tracks from the vertex (<y> - y, and BB vertex - y), - Selecting matched tracks (front track y : back track y), - Time of flight matching (projected y : tof y) and Path length, and also used for - Normalization/acceptance corrections (delta y). Here are some plots illustrating how much the velocities vary in time. - Attached 1: y positions of Fibers on the Front of TPM2 "seen" by TPM2 tracks overlaid by y positions of TPM1 tracks projected to beam plane as a function of the run number. - Attached 2: y positions of Fibers on the Back of TPM2 "seen" by TPM2 tracks overlaid by y positions of TPM1 tracks projected to beam plane as a function of the run number. - Attached 3: "y vs. x (cm)" of Front and Back Fibers seen by TPM2 tracks. They are from almost all "high-pt runs" we took at the end of the run. (from runs 5853 (Nov. 16) - 5983 (Nov. 25): MRS 90 degree 6KG B) For some earlier note about the Fibers and the analysis, please see http://pii3.brahms.bnl.gov/~jhlee/brahms/analysis/mrs/fiber.html These are some of information we've learned from the data about the variations. - It confirms that the drift velocity we are using for TPM2, 1.6, is reasonable. - Drift velocities has strong correlations with path of gas flow (see the anti-correlation between back and front in the attached figure 3). - Drift velocities change up to 10%. - The changes for the drift velocities are due to a common source (environmental changes and/or gas flow...) at least for TPM1 and TPM2. To reflect the variations on the analysis, run-by-run y cuts (vertex, track matching, tof matching) need to be used. And, for more accurate tracking/identification/yield calculations the dependence of velocities on positions ( x and y) of TPC's need to be taken into account in the analysis. JH
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