1. SiPM linearization status update
Arjan Heering, Anton Karneyeu, Iouri Musienko, Mitchell Wayne
HCAL Upgrade / 19 January 2017

2. SiPM SiPM is an array of small cells connected in parallel
Cell release constant charge on hit
Cells operate (“fire”) independently
A cell needs time to recover the charge after “fire” (cell is ~not sensitive to new incoming photons until the end of recovery) – the source of non-linearity
The output signal is a sum of signals produced by individual cells
SiPM linearity is determined by its total number of cells

3. Setup
Light source and path: - commercial LED pulser - Y11 scintillation fiber - clear fiber
Photodetectors: - Production HCAL RM module (marked “RM1 not for P5”) with SiPM/QIE11 readout (QIE11 is not calibrated in this module) – non linear - Old RM module with HPD/QIE8 for light reference – linear
Measured correction factor is: K = (HPD_charge / SiPM_pixels) vs. SiPM_pixels
The setup is an update of light mixer measurements setup: - shorter LED pulse - HPD instead of APD for linear reference

4. Correction form
Proposed correction form: K = p0 + p1*x + p2*x*x A = K * x x – SiPM pixels fired K – correction factor A – linearized output
Previous talks:

5. Dataset #1: 1 and 4 fiber, 2.8 and 3.3 mm: RAW
- Ref. counts is HPD charge in fC
- Sum of 10 time samples
- Pedestal is subtracted

6. CORRECTION Spread < 4% up to ~300 GeV
Plot is relevant up to 11k pixels
4-fiber channels get more light and go to higher number of pixels
10k pixels is approximately 300 GeV (in one depth segment)
3.3mm devices have 38k pixels total
2.8mm devices have 27k pixels total
Spread < 4% up to ~300 GeV

7. CORRECTION: zoom to low light region
Outliers: effect of QIE11 (un)calibration?

8. CORRECTION, no outliers
Plot is relevant up to 11k pixels
Spread < 2% up to ~300 GeV
Statistics (number of curves) is low -> additional 1-fiber dataset with higher statistics

9. Dataset #2: 1 fiber, 2.8 and 3.3 mm: RAW

10. CORRECTION Spread < 3% up to ~300 GeV Relevant up to 14k pixels
Outliers is same channels as dataset #1

11. CORRECTION, no outliers
Relevant up to 14k pixels
Spread < 1.5% up to ~300 GeV

12. CORRECTION, no outliers, global fit
Correction curve is almost linear

13. Global fit: 2.8 mm devices Spread < 1.4% up to ~300 GeV
Relevant up to 14k pixels
NO. NAME VALUE ERROR
1 p e fixed
2 p e e-08
3 p e e-12
Spread < 1.4% up to ~300 GeV

14. Global fit: 3.3 mm devices Spread < 1.4% up to ~300 GeV
Relevant up to 14k pixels
NO. NAME VALUE ERROR
1 p e fixed
2 p e e-08
3 p e e-12
Spread < 1.4% up to ~300 GeV

15. Correction curves
Old correction is based on light mixer measurements data
Correction factor
SiPM pixels

16. Conclusion and plans
Presented corrections are SiPM+QIE11, not only SiPM
Correction form is almost linear
The spread of correction curves < 2% up to ~300 GeV
Plans:
Measurements with calibrated RM/QIE11
Testbeam measurements

17. Backup

18. LED pulse shape

19. QIE11 calibration issue? A drop by ~4% on switch to subrange 2
point 3 / shunt=11.5
~88pC/10.9 = 8.1pC
range 3, subrange 1
point 0 / shunt=1
~52pC
range 4, subrange 1
point 2 / shunt=1
~92pC
range 4, subrange 2
point 1 / shunt=1
~76pC
range 4, subrange 2
A drop by ~4% on switch to subrange 2