About BCM calibration

• The goals are:
• to provide a general knowledge of BCM calibration constants for HAPPEX-III and PVDIS;
• to determine the linearity of BCMs for PVDIS, and its effect on the rate-scan method of the deadtime;
• If the BCm linearity determined from previous data turn out to be not good enough for the deadtime measurement, *think* about the problem and come up with a solution.
• Some background:
• There are two "boxes" in the counting house middle room, one contains amplifiers and V2Fs that are sent to the HRS scalers (u1, d1, u3, d3, u10, d10), the other (Bob called it "the old box") processes the signals and send them to HAPPEX ADCs.  This means the copies sent to the HAPPEX crate are completely different from those to the HRS scalers, and they are subjected to different sources of non-linearities;
• From HAPPEX/PAN data, we can get the "HAPPEX-ADC" copies of the BCM. And if we send some of the "HRS V2F" copies to the PVDIS scaler, we will have those copies too. Right now the d10 copy is already in the PVDIS scalers (TDC ch61 or scaler7_29). For productions this fall should also send the u1,d1,u3,d3 and u10.
• During previous HAPPEX experiments (presumable we are talking about the HAPPEX-ADC copies here. Information from Kent):
• BCMs were cross-compared with the Unser and the RF BCMs. The linearity was determined to a 1-3% level. See HAPLOG entries 608 and 836;  This is the method similar to the usual BCM calibration done by all other Hall A experiments;
• Also did a final correction to BCm based on comparison of BCM asymmetries with detector asymmetries (this should mean the HAPPEX detector), essentially    [A(det) - A(BCM1)]  versus A(BCM2), which should be flat if the detector and BCM1 are both perfectly linear. A correlation would imply that the detector and/or the BCM are not linear. Haplog 969 explains some of that work.
• For all Hall A experiments, "regular" BCM calibration was done by cross-comparing BCM readings (the HRS-V2F copies) to the Injector reading (OLO2, which is further calibrated with the injector Faraday cup). Latest Hall A BCM calibration that went up to 100uA was done in 2007:
• halog entries and other data records: 
1. For calibrating Hall A scalers with injector (typically OLO2)
1. runs 3219 and 3220, with bcm log 127: entry 201210 on 5/7/2007;
2. runs 3893 and 3894, with bcm log 128 and 129: entry 203697 on 5/30/2007;
3. Alexandre's calibration work:
1. data (root files): saved in  /work/halla/e04018/disk1/camsonne/bcm/
2. halog entry 203739 on 5/30/2007;
3. the wiki page report (contains root commands used to do the calibration).
2. For calibrating injector OLO2 with injector faraday cup:
1. copies of all bcm logger files can be found here, (the format is in README).
• An earlier report by Mark Jones on BCM calibrations from 2002 data can be found here. Also here is a report by Vince on the beam charge calculation for E97-110.
• We should write root macros for the calibration and to determine an upper limit on the non-linearity of all scaler copies (u1, d1, u3, d3, u10, d10). Or better yet, determine how to get the absolute current from these scalers with the nonlinearity included.