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The procedure for CAL gain intercalibration at PS and SPS is based on uses the CalTuplefor the of all 4-range readout runs taken at different scanning positions. It is based on the signal (in MeV) stored in the CalXtalFaceSignalAllRangetowerlayercolumnsiderange array. At SPS we checked the constants obtained at PS (towers 2 and 3), especially for HEX8 for which the lever arm in energy deposit was not so large. We also calibrated tower 1 for which LEX1/HEX8 was not well calibrated at PS.
To intercalibrate gains of each given log end, we sum summed almost (see below) all runs available and fit (to maximize the statistics) and fitted the profile histogram of sR_i (signal for gain #i) vs sR_i+1 (signal for gain #i+1) to get the slope. This profile is limited to the events where 1/ sR_i does not saturate 2/ sR_i+1 < saturation value of sR_i and 3/ the ratio sR_i/sR_i+1 is close to 1 within 30%.
In addition, for the logs at the center of a module, we don't keep first ignored the runs corresponding to scan positions near their end to avoid direct illumination of the diodes due to beam and shower spread (in that case the scatter plots are a mess...). Despite these criteria, some weird features were observed, e.g. for the log end T2-L6-X5-S0 (i.e. tower 2, layer 6, column 5, side 0): in this file the 4 plots
at the top are the R_i spectra (summed over all runs) for in each energy range (R0R_0=LEX8, R1R_1=LEX1, R2R_2=HEX8, R3R_3=HEX1) while the 6 plots at the bottom are R0 vs R1 R_0 vs R_1 (scatter
plot on the left, with superimposed on the linear fit of the profile histogram in red) and R0/R1 R_0/R_1 (distribution on the right), R1 vs R2 and R1/R2, R2 vs R3 and R2/R3. 2 R_1 vs R_2 and R_1/R_2, R_2 vs R_3 and R_2/R_3. Two populations are clearly visible in the R1 vs R2 plots R_1/R_2 plot (with a difference of ~7% in ratio), the . The "bad" population coming was found to arise from one specific scanning position. Since other similar cases were found, new runs were taken at the same scanning positions, but the effect remains ( and could not be attributed to a Thus we decided to In the following, we investigated these discrepancies by looking is still not understood. However, we removed it using the following run selection:
- we decided to use only the runs taken in the X (resp. Y) scan to calibrate the Y (resp. X) logs;
- we looked at the dependency of the slope (from the linear fit of the profile histogram) of each log end ratio as a function of run number: in all cases the slope did not change from run to run for a given log end ratio, except for a very few runs which were rejected (e.g. run 700001796 for T2-L6-X5-S0 or run 700001795 for T2-L4-X6-S1).
This procedure yielded , and the runs far from the mean were rejected, yielding a list of selected runs for each log end ratio and better results, see e.g. T2-L6-X5-S0. This procedure It was applied to each all log end and the results were stored in the following files:
tower 1, X logs
tower 1, Y logs
tower 2, X logs
tower 2, Y logs
tower 3, X logs
tower 3, Y logs
In these files the 96 first pages are the same plots as those described above, for each log end, and the 3 last pages show the distributions of the slope, chi^2 and the crossing value of the linear fit of the profile histograms (the crossing value is in MeV and the range of the plots is +-1% of the R_i+1 spectrum maximum.
From these files tower 2 appears to be perfectly calibrated. In tower
as you can see in page 10 which gives the fitted slope value
for each channel (left column, points in red): the plot on the left in the
middle show that LEX1/HEX8 slope is close to 1 (a bit less), somtimes as low as
~0.95 or even 0.93 for a few logs.
Update of CAL calibration constants in DB (Aug 7th) pdf resumé
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