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Hi Alex, If I remember correctly 1 and 13 were put into a different tdc "grouping" as they were not part of the trigger since they see such little energy or events. It is quite possible that they were reversed. -Blake George Lolos wrote: 467B5E9F020000250004B53B@gw004.cc.uregina.ca">Hi Alex: Interesting observation. Since the was no reason to manipulate any of the BCAL cables for the cosmic ray runs, were the TDC cables also reversed for the photon runs? GeorgeAlex Dzierba <dzierba@indiana.edu> 06/22/07 4:53 AM >>>Dear Friends In the note that I sent out yesterday titled "BCAL Test Module - Studies with Cosmic Rays" - referring to Fig 5, we noted that the North-South TDC difference spectra showed multiple peaks. For the cosmic runs where the trigger paddles were located at z .ne. 0 there is a primary peak at the 'right' TDC difference and a secondary peak with the opposite sign. The 'right' answer is dt=2*z/c where c is the effective speed of light in the module, about 16 cm/ns. For runs at z = -50 and -150 cm there are smaller additional peaks. The secondary peaks for all the z .ne. 0 runs appear to have a trivial explanation -- the cables for segments 1 and 13 must have been reversed going into the TDC's. I determined this by looking at TDC differences for modules separately for events in which more than 90% of the energy is contained in a single layer. Segments 1 and 13 are the top and bottom segments in the first layer (as seen by the photon beam). In the plots of Figure 5, the ratio of events in the primary to secondary peaks is approximately 9 to 1 -- consistent with this conclusion as there are 18 entries per event - corresponding to the 18 segments. I am in the process of trying to track down the other smaller peaks for the z = -50 and -150 cm runs. Cheers Alex |