Hi All, I've spent some time trying to understand the deviation of the momentum measurement by D3 and D4 magnets. Attached file MomPuzzle.ps shows mean values of P_D4 - P_D3 distribution scaled to Bfs momentum (=0.5*(P_D3+P_D4)) versus absolute value of the Bfs momentum. The runs and field settings are indicated in the legend on the plot. Same marker's color refer to the same field setting. From figure one clearly see that deviation between D4 and D3 momenta depends on the field settings and is about 7% for 1/8 field and ~3% for 1/2 field. The Deviations are the same for A and B polarities. Figure Fit5662.ps shows an example of how the mean values where extracted from the gaussian fit to data from run 6662 (1/8B). I found that we can remove all this deviation (for each of the field settings simultaneously) assuming that the relation between "real" current on D4, I, and current requested during measurement, I_set, is: I = b + a*I_set; where b=24.83 and a=1.0107. Of course, it was done assuming that fields on the D3 are OK, just to show that a simple re-definition of the current can remove the relative deviations in momentum measurements. Our conclusion is that we don't know what is a relation between real current and I_set and because of this we have to measure B versus I_set (at least for one FS magnet and probably for D5). Any other ideas for explanation of what is seen in MomPuzzle.ps are welcome. Regards Pawel. -- ---------------------------------------------------------------------- | Pawel Staszel | | Niels Bohr Institute Tb 8 email: staszel@nbi.dk | | Blegdamsvej 17 phone: (+45) 35 32 53 51 | | København Ø FAX: (+45) 35 32 50 16 | | Danmark | ----------------------------------------------------------------------
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