Dear Collaborators, I have a problem with which I hope at least one of you can help. The (very) short story is this: If I determine the momentum from T1-D2-T2, I get some momentum which I call p2. Similarly, I can obtain p3 (from T2-D3-T4) and p4 (from T4-D4-T5). The problem is that p3!=p2, p4!=p2, and p4!=p3. In addition, I suspect (and can almost prove) that p2 is slightly lower than the 'real' momentum of the track. I suspect this because the masssquare measure in the FFS is slightly low (of course, some of this difference could be due to improper offset in the TOF calibration). The alignment of the various tracking chambers has been checked thoroughly (thanks to Pawel's hard work!) using runs in which the magnetic field(s) were off. So, it seems unlikely that the problem is due to the geometry of the tracking detectors. If I compare the field (By) calculated in BRAT from the magnet current from the RUNDB, to the field measured by the Hall Probes, I find that for D1: Hall probe says 2.582, BRAT says 2.492 D2: Hall probe says 3.347, BRAT says 3.322 D3: Hall probe says 2.895, BRAT says 2.433 D4: Hall probe says 3.951, BRAT says 2.373 I have spent some time trying to guess what could be wrong, and so far the only thing that I can think of is that the current which get written to the DB is incorrect, and gets more incorrect as one goes from D2 to D3 to D4. I would appreciate very much any information/ideas any you have which could help shed light on this problem. In fact, I would appreciate it so much that I will give the person who has the solution one (1) 12 pack of Carlsberg at the next collaboration meeting. -Ian
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