- General descriptions

Inter-Calibration Factor is a ratio of a High Gain (HG) and a Low Gain (LG) amplifiers on SPIROC series. The amplitude of the preamplifier is defined by the ratio of capacitance between input capacitor and feedback capacitor. For the SPIROC2b, the capacitance of the feedback capacitors on HG and LG preamplifiers are controlled at the same time and then the IC factor is defined by the ratio of input capacitors. On the other hand, the SPIROC2e has a capability to set a capacitance for each preamplifier. IC factor of the SPIROC2b is ~10 which is calculate from the design of the input capacitors. IC factor of the SPIROC2e is depend on users. We set the IC factor of SPIRROC2e to ~20 for the testbeam campaign in 2018.

IC factor plays a important role for the energy reconstruction. When we reconstruct an event, we use MIP calibration parameter which is extracted from muon runs with ATAG mode and then the unit of MIP is ADC tick of HG output. Physics runs are taken with the ATAG mode and LG output is recorded when the response from a channel is larger than a threshold of AG. For the LG output, we have to apply IC factor to calibrate the output correctly. After applied the IC factor to the LG output, hit energy distribution of a channel should be a smooth curve.

There are several ideas to extract IC factor.

- LED runs with ETIC or ATIC mode
- take a slope of (HG output) vs (LG output)
- take a ratio of difference of light yield of consecutive runs

- Muon (electron and pion) runs with ATIC mode
- take a MPV or Mean of HG and LG output
- take a ratio of a higher side of an edge on HG output and a lower side of of an edge on LG output

- Event by event IC extraction from LED or physics data with ATIC or ETIC mode

The method 1 is a stable and reliable than the method 2 and 3. Because pedestal instabilities are better handled than the other 2 methods. In AT mode, LG pedestal position with hit is not trivial value. For example, MPV position of LG output with ATIC mode locate almost same as pedestal position and then the method 2 is not available for the IC extraction. In principle, event by event IC calculation is possible but it depends on pedestal fluctuation and the fluctuation is not negligible. We then have to select a pedestal independent or less affected method. the method 1 is employed from this point of view.

- Slope of HG output vs LG output

- get HG and LG pedestal for each memory cell
- make a (HG output) vs (LG output) for each channel
- fit the graph by linear function
- the slope of the linear function is the first iteration of IC factor
- get higher order correction of the slope to compensate a pedestal shift caused by large input of charge in a chip
- apply the higher order correction and get the final IC factor

Link to the macros for IC factor extraction by the slope method: /nfs/dust/ilc/user/sudoyuji/misc/ICFactor/ICSlope

- delta Light Yield (dLY) method

- calculate dLY of consecutive runs for HG and LG output for each memory cell
- IC factor = dLY_HG/dLY_LG
- make a histogram with IC factor memory by memory cell for each channel and take a mean of the histogram
- make a histogram from a result of all the consecutive runs for each channel and take a mean of the histogram

Link to the macros for IC factor extraction by the dLY method: /nfs/dust/ilc/user/sudoyuji/misc/ICFactor/ICdLY