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The procedure for CAL gain intercalibration at PS and SPS is based on the
we've been looking at the calibration runs 700001789-700001863 using the cal
tuples, to check the constants obtained at PS (towers 2 and 3), especially for
HEX8 for which the lever arm in energy deposit was not so large (for the moment
let's forget about tower 1 for which LEX1/HEX8 was not calibrated at PS).
To intercalibrate gains of each given log end, we sum almost (see below) all
runs available and fit the profile histogram of s_i (signal for gain #i) vs
s_i+1 (signal for gain #i+1) to get the slope. This profile is limited to the
events where 1/ s_i does not saturate 2/ s_i+1 < saturation value of s_i and 3/
the ratio s_i/s_i+1 is close to 1 within 30%. In addition, for the logs at the
center of a module, we don't keep 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.
Let's indeed take the example of tower 2 and the 4+4=8 logs at the center in X
and Y direction (columns 4 to 7): for those we only keep the scan positions 5 to
8 (the scan position range from 1 to 12). Please have a look at pages 4 to 10
of the file in attachment:
- page 4 shows the plots for layer 6, col 5 and side 1 (L6-X5-S1). The 4 plots
at the top are the spectra (summed over all runs) for each range (R0=LEX8, ...
R3=HEX1). The 6 plots at the bottom are R0 vs R1 (scatter plot on the left) and
R0/R1 (distribution on the right), R1 vs R2 and R1/R2, R2 vs R3 and R2/R3. Here
all plots are fine.
- page 5: same plots for the other end of the log (I'll finish this asap - Fred)
L6-X5-S0): here 2 populations
are clearly visible in the R1 vs R2 plots
- page 6: L6-X5-S0 w/ Y scan runs only; still the same problem
- page 7: L6-X5-S0 w/o the Y scan position number 7 (run 700001796); now it's ok
- page 8: L6-X5-S0 for run 700001796 only: here is the 2nd population
We have found some other cases like this one. Note that the effect is of the
order of a few %, 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.
I am investigating these small discrepancies by looking at the dependency of
each slope as a function of run number, however I dont see anything else that
such a systematic study to delimit them (this effect which is not geometric and
only seen on a few log ends like L6-X5-S0). Would you have any other idea ?
Update of CAL calibration constants in DB Update of CAL calibrations (Aug 7th) pdf resumé
- A new CAL pedestals (700000953) has been recorded. Zach produced a set of xml files (see $LATCalibRoot/CAL/CU06):
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