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The procedure for CAL gain intercalibration at PS and SPS uses the [CalTuple|http://www.slac.stanford.edu/exp/glast/ground/software/status/documentation/EngineeringModel/latest/CalXtalResponse/latest/] of all 4-range readout runs taken at different scanning positions. *It is based on the signal (in MeV) stored in the CalXtalFaceSignalAllRange\[tower\]\[layer\]\[column\]\[side\]\[range\] 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 at PS. We also calibrated tower 1 for which LEX1/HEX8 was not well calibrated at PS. |
To intercalibrate gains of each given log end, we summed almost (see below) all runs available (to maximize the statistics) and fitted the profile histogram of R_i (signal for gain #i) vs R_i+1 (signal for gain #i+1) to get the slope. This profile is limited to the events where 1/ a) R_i does not saturate 2/ b) R_i+1 < saturation value of R_i and 3/ c) the ratio R_i/R_i+1 is close to 1 within 30%(within a band parallel to and centered on the y=x line).
In addition, for the logs at the center of a module, we 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) in each energy range (R_0=LEX8, R_1=LEX1, R_2=HEX8, R_3=HEX1) while the 6 plots at the bottom are R_i vs R_i+1 (scatter plot on the left, superimposed on the linear fit of the profile histogram in red) and R_0i/R_i+1 (distribution on the right). Two populations are clearly visible in the R_1/R_2 ratio plot (with a difference of ~7% in ratio). The "bad" population 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 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
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- , except for a very few runs which were then rejected (e.g. run 700001796 for T2-L6-X5-S0 or run 700001795 for T2-L4-X6-S1).
This procedure yielded a list of selected runs for each log end ratio and better results, see e.g. T2-L6-X5-S0. It was applied to all log end ends 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 (one per log end) show the same kind of plots as those described above, and the 3 last pages show the graphs and distributions of the slope, chisquare and the crossing value of the linear fit of the 96x3 profile histograms (the crossing value is in MeV and the range of the plots is +-1% of the R_i+1 spectrum maximum). These results that tower 2 is correctly calibrated. In tower 3, Y logs are correctly calibrated as well, while 2 outliers (T3-L2-X7-S1-R_1/R_2 slope, T3-L6-X4-S0-R_2/R_3 slope) are observed as underflows in the slope distributions of X logs, also visible in the crossing value distribution graph as points with large errors; the individual plots show that the second outlier is due to poor statistics, while the first one should be looked at in much detail (actually we assumed that the calibration is fine here, like for all other logs in tower 3...). Finally in tower 1, X logs calibration constants are reliably obtained (1st and 3rd slopes very close to 1, and 2nd slope R_1/R_2 ~1.087 with a RMS of ~0.03), except in layer 0 for the R_2/R_3 slope slopes (not used anyway in data analysis anyway...) in layer 0 due to poor statistics at high energy since showers start deeper in the CAL in the absence of TKR in front of the 1st CAL module; as for the Y logs in tower 1, calibration constants are also reliably obtained, except T1-L7-X11-S0 which exhibits a strange behaviour (R_1/R_2 and R_2/R_3 slopes , were forced to 1 in the absence of any explanation...).
In conclusion, only R_1/R_2 (LEX1/HEX8) slopes for tower 1 were propagated in the DB by modifying the HEX8 MeV/DAC (see below).
Update of CAL calibration constants in DB (Aug 7th) pdf resumé
- A new CAL pedestals (700000953) has been recorded. Zach produced a set of xml files (see $LATCalibRoot/CAL/CU06):
cidac2adc.digitization-latte-v1r030603p2_700000446_digi_DIGI.xml
muonAsym.digitization-latte-v1r030603p2_700000276_digi_DIGI.FLIGHT_GAIN.xml
muonMPD.digitization-latte-v1r030603p2_700000276_digi_DIGI.FLIGHT_GAIN.xml
muonPeds.digitization-latte-v1r030603p4_700000953_digi_DIGI.FLIGHT_GAIN.xml
tholdci.CU06.FLIGHT_GAIN.08022006.xml
- After intercalibration of LEX1 and HEX8 (from runs 700000700 to 700000750) the asymmetry and MevPerDac files have been updated:
muonAsym.digitization-latte-v1r030603p2_700000276_digi_DIGI.FLIGHT_GAIN_correct_v2.xml
muonMPD.digitization-latte-v1r030603p2_700000276_digi_DIGI.FLIGHT_GAIN_correct_v2.xml
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