DESY BT analysis- MPPC Saturation Correction -

S. UozumiFeb-21 2008 Sci-ECAL meeting

1. MPPC Gain Measurement (with LED data)2. Inter-calibration of readout electronics gain (with LED data)3. MPPC response curves with 3 configurations4. MPPC saturation correction to beam data

MPPC Gain Measurement• Gain of the MPPC has been measured with LED system during

no-beam period.• LED run data were taken with high gain mode, by adjusting

amount of light from LED by hand.• 116 of fiber-readout strips, and 16 of extruded strips have

been measured.• No LED data with direct readout strips, since accelerator

worked quite well and LED run takes much time.• The data are fitted by 4 Gaussians with following constraints.

– Width of 4 Gaussians must be same, and distances between successive peaks have to be same

– Eventually there are 7 free parameters (d-value, pedestal position, Gaussian sigma, heights of 4 peaks)

Relatively good fits Moderate OK but not very nice

d-value

Result of the Gain (d-value) Measurement• For fiber readout module :

- d = 144.9 with +-4.4 % variation.- Vbias = V0 + 2.9 (V) (assumed)

• For extruded module :- d = 182.8 with +- 2.8 % variation.- Vbias = V0 + 3.7 (V) (assumed)

•d/Vbias = 47.375 [ADC counts / V] . For direct readout module (Vbias = V0 + 3.2 V) d = 144.9 + d/Vbias x (3.2 – 2.9) = 159.1• It would be conservative to attach uncertainty of +- 4.4% to the d-values for all the configurations.

Those d-values are used in later analysis :• d = 144.9 +- 6.4 for fiber readout module• d = 159.1 +- 7.0 for direct readout module• d = 182.8 +- 8.0 for extruded module

Electronics Gain Inter-calibrationThere are two modes with AHCAL electronics :

• High-gain mode (Calibration mode)– used to see 1 p.e peaks for SiPM gain monitoring.– LED runs were taken with this mode.

• Low-gain mode (Physics mode)– Have lower gain to enhance ADC upper range– Beam data were taken with this mode.

• We have measured d-values with the high gain mode.• To convert d-values for the low-gain mode, we need to know ratio of

gains in two modes (inter-calibration factor = high gain / low gain).• Since the inter-calibration factor may be changed with pulse shape

etc, we had to measure it with our detector.

• Inter-calibration run : just put LED light into a strip with appropriate strength, and compare response both with low and high gain mode.

Electronics Gain Inter-calibration

Signal for LED lightLow gain mode

High gain mode

• Inter-calib factor Cinter = 10.08 +- 0.95 .• No difference between results with fiber and extruded modules.

Strip type dependence?Red … fiber readoutBlue … extruded

Maybe not.

• Now we can calculate d-values and its uncertainties in low gain mode : dlow-gain [ADC counts] = dhigh-gain / Cinter

= 14.4 +- 1.5 for fiber readout module 15.8 +- 1.6 for direct readout module 18.1 +- 1.9 for fiber readout module,• With this value, we can convert unit of MPPC output

from ADC counts to number of fired pixels.

Measurement of MPPC response curve

• At the end of the DESY BT, we have measured the response curve with 3 types of single scintillators.• Data are also taken with some different bias voltages values.• Inter-calibration and runs to know d-value are also performed.

Inter-calibrationwith the MPPC response curve measurement

• Inter-calib factor ~ 13.8 !(was 10.08 with LED runs between beam runs.)• Maybe DAQ setting of low/high-gain mode has

been changed, because d/V also increases about x 1.5 …• Anyway this set of d and inter-calib factor may

be usable for the response curve measurement.

Vbias = 76.75 Vd = 206.9

Vbias = 78.25 Vd = 324.2

d/V= (324.2 – 206.9)/1.5= 78.2(was 47.4 in LED runs)

Observed response curveFiber readoutVbias = 78.25 VNpix = 2080.0 +- 3.8s = 4.578 +- 0.003

Npix … “effective” number of pixelss = Np.e. / ADCPMT… scale factor of x-axis

Analysis is still ongoing, may need an another couple of days.– Look at shape of response curve with different bias

voltages, different strip types.– Apply correction for MPPC response curve.