1. Calorimeter calibrations with Flight Software.
Gamma-ray Large Area Space Telescope
Calorimeter calibrations with Flight Software.
Alexandre Chekhtman
NRL/GMU

2. Pedestals
Previously pedestals were extracted from B13 runs with 4 range readout and zero suppression OFF
With flight software we expected to get pedestals from standard configuration using events with 10 Hz periodic trigger
Special trigger engine allows to read periodic triggers with 4 range readout and zero suppression OFF
Now, due to some problem in FSW, periodic trigger is disabled
Expected to be fixed in near future
We use now another source of pedestals: run pedestal_ci_CPT
This run collects 9000 events using solicited trigger with no charge injection for 9 different gain settings (1000 events per gain setting)
Pedestal position and noise depend on gain setting
Settings for low energy diode and high energy diode are different
pedestals for ranges 0 and 1 (LE diode) - from events
Pedestals for ranges 2 and 3 (HE diode)
For LAT71x (muon gain) - from events
For LAT701 (flight gain) – from events
For the moment pedestals from pedestal_ci_CPT were defined using IDL function and then merged manually
May be we need to implement this procedure in calibGenCAL ?

3. Pedestal difference
Difference of pedestals defined from B13 run (Jan 14,2006) and from pedestal_ci_CPT run (Apr 11,2006)
Pedestal difference in range 0 is ~3 adc unit = 0.1 MeV

4. Charge injection calibration
Charge injection calibration with flight software works much slower (by factor of ~5)
Standard columnwise charge injection run takes now 2 hours
We decided to use broadcast charge injection
pulse all calorimeter channels simultaneously
This decreases the time and file size by factor 12
We should verify that the result of calibration stays unchanged
Even with 100 Hz pulsing rate we afraid of missing events
We have no information in the digi root file on the moment when DAC setting (injected charge) changes
we just count events (50 events per DAC setting)
If some events are lost, we have to use another way to separate events corresponding to different DAC settings
Find peaks on ADC histogram ?

5. Missing events – run
Plot of Adc signal vs event number shows that the change of DAC setting happens exactly as expected at event =50*N
So, there is NO missing events

6. Columnwise vs broadcast
Difference between columnwise and broadcast charge injection calibration is less than 0.5%
This plot produced by IDL without any protection against outpiers
Peaks at some points are due to coincidence with scintillation in some events
Should be suppressed by existing outlier protection in calibGenCAL

7. To be done next
Modify calibGenCAL to work with broadcast charge injection files
Zach has done it but not tested yet
Process LAT71x files to get muon calibration (asym, MeVperDAC)
Implement in calibGenCAL the processing of flight gain charge injection files, to get correct calibration for flight gains.
Take into account LE to HE crosstalk