Response curve measurement of the SiPM

Transcription

1 Response curve measurement of the SiPM The theoritical formula : N Fired = N pix. (1 (1 1/N pix ) Npe ) does not hold because: 1) crosstalk and afterpulses increases N Fired (by a factor 1 / (1 ε) for N pix = ) 2) illumination is not uniform 3) pixels can trigger several times Spatial distribution of photons on the SiPM surface (From Lesya's simulation) Satoru Uozumi, Study and Development of Multi Pixel Photon Counter for the GLD Calorimeter Readout, International workshop on new photon-detectors PD07

2 Setup to measure the SiPM response curve LED emitting at 450nm (λ scintillator = 425nm) Pulse width 5 ns SiPM reading the WLS fiber WLS fiber (green) embeded in a piece of scintillator PMT (XP2020Q) N pe = Q PMT x n / (Q PMT for n fired pixels on the SiPM ) (Where n ~ 50) N Fired = Q SiPM / Q SiPM for 1 pe

3 How big is the recovery effect on the SiPM response curve? Remark: The number of photo electrons coted on the X axis is N pe, including crosstalk and afterpulses. (N pe / (1 ε), with ε = 0.22 at U=2.5 V)

4 How optimize the linearity? Spread the light on all the pixels Make the illumination homogeneuous Spread the light in time (slow scintillator: 230 ns decay time)

5 Insertion of a diffusor (tracing paper) between the fiber and the SiPM

6 SiPM response curve for a full illumination With a long recovery time, the SiPM should saturate at : 3136 fired pixels (without afterpulses) Remark: The number of photo electrons coted on the X axis is N pe, including crosstalk and afterpulses. (N pe / (1 ε), with ε = 0.22 at U=2.5 V)

7 Dependence of the response curve on the temperature A strong dependence of the recovery time on the temperature has been mentionned (*) : at 0 C, 190 µs and at 22 C, 98 µs. The reason was the increase of the resistivity of the polysilicon quenching resistors. With our SiPM, no significant dependence on the temperature is observed (*) I. Britvitch, D. Renker, Measurements of the recovery time of Geiger-mode avalance photodiodes, NIMA, vol 567 (2006), p260

8 Dependence of the response curve on the position SiPM 6, 42, 78 cm LED Aluminium mirror Small dependence on the position Duration for back and forth travel: T = d / v = 2 x 0.8m / (3 x 10 8 x 1.6) = 8 ns

9 Proposal Readout on both sides (preferably with VA64: peaking time max ~400 ns and only 1 gain) Slow scintillator to make linear the response up to 2000 pe Use thicker scintillator plate: 5 mm instead of 3 mm to compensate for the lower LY of the slow scintillator (30% less). Three calibration methods: MIP + momentum info from the tracker + beam

10 Proposal for the injection of light Eventualy, the light could be monitored with an APD? LED Plexiglas to distribute the light

11 Annex

12 convolution Shape of the light pulse reaching the SiPM surface Light production with Scintillator or LED + Emission of the WLS fiber: decay time of 8.8 ns (*) Illumination with LED should well reproduce the illumination produced by a shower (*) The WLS Fiber Time Properties Study, LHCb HCAL

13 Extraction of the shape of the LED light pulse PMT response for 1 pe (fitted with a Landau) PMT response for a direct LED illumination (For both fit, there are two free parameters for time delay and amplitude) Gaussian shape for the LED light pulse shows good agreement with the measurement From the fit : FWHM = 4 ns

14 Extraction of the WLS fiber decay time from the PMT response to the fiber readout E - t / τ + + Gaussian LED emission WLS fiber PMT response for 1 pe Free parameters for the fit are: WLS decay time, time delay, amplitude WLS decay time = 5.7 ns (The decay time measured in (*) is 8.8 ns (*) The WLS Fiber Time Properties Study, LHCb HCAL

15 Photo peaks spectrum Calibration of the Spiroc 11 ADC ch / pe

16 Response curve of the SiPM (measured with the Spiroc) (Spiroc saturation occurs at ~2200 fired cells.) A possible interpretation if we neglect the pixel recovery: The response curve have two contributions 1) from pixels strongly illuminated (a ring?) ----> N Fired = N pix. (1 (1 1/N pix ) Npe ) 2) from pixels lightly illuminated ---> linear response (22 % of the light is spread in this lightly illuminated region)