1. Correction of saturation effect of ICCD
Institute of High Energy Physics, CAS

2. Data analysis for HERD beam test
The energy reconstruction procedure includes following steps:
Crosstalk correction;
Saturation correction;
Calibration of all 250 cells by using MIP;
Event selection by removing pile-up events and impurities (hadron component in electron beam, etc).

3. Saturation effect
With limited charge capacity, saturation and blooming could easily happen in the CCD pixels if energy deposition in the crystal is too large.
Because of large noise and bad performances of the CCD, the data of the high range ICCD could not be direct used.
Calibration of low range ICCD
By using high range ICCD
By using measured energy response matrix (RMF)

4. Calibration by using high range ICCD
Though statistic error of high range ICCD is larger than expected, linearity is still reliable.

5. Calibration by using measured RMF
Two laser diodes, simulating the scintillation photons from the crystals, are used to inject on the lateral surface of WLS fibers.
Relative (not absolute) amplitude of the input light is known.

6. RMF of low range fibers
The maximum Gray Scale for one fiber that we get from the beam test is about 180 k, where the GS of the facula goes far beyond linearity.
Saturation occurs at a GS of about 25k.
Deviation from linearity response:
1-GSreal/GSvis

7. Correction of saturation
Piecewise fitting of RMF
Discontinuous
Interpolation of RMF
Sawtooth

8. Discussion
Correction of saturation is necessary especially for future HERD calorimeter, because of limited DR performances of possible devices.
For the HERD beam test in 2015, saturation correction may not work well. Possible reasons are:
The two laser diodes does not simulate the LYSO very well in timing sequence.
RMF measurement method may cause much larger accumulated error with larger amplitude of input sources.
Coupling between fibers and ICCD has changed after beam test.
Temperature environment at H4 hall and in lab are not the same.
Next work
To optimize the method of RMF measurement
To refine correction procedure by using RMF data
To use events in electron runs to perform MIP calibration and calibration of low range ICCD by using high range ICCD.

9. Some results (to be updated)
Detailed calibration and correction is needed.