1. Malte Backhaus - FE-I4 testing, 07.02.20111 Calibration Constant Measurements Malte Backhaus, University of Bonn

2. Malte Backhaus - FE-I4 testing, 07.02.20112 Problem Problem: can not measure C_inj Idea: use known input charge from γ in sensor: #e = Eγ / 3.61 and compare with measured threshold How to do this? Vth EγEγ #e-h = E γ/3.61 Vcal C_inj

3. Malte Backhaus - FE-I4 testing, 07.02.20113 Idea Measure hit rate in dependency of threshold. Expected result: Rate threshold At „50%-value“: Threshold [e] = E γ / 3.61 [e]

4. Malte Backhaus - FE-I4 testing, 07.02.20114 Idea Measure hit rate in dependency of threshold. Expected result: Example measurement: Am241  how to know „50%-value“? Rate threshold At „50%-value“: Threshold [e] = E γ / 3.61 [e]

5. Malte Backhaus - FE-I4 testing, 07.02.20115 Idea Measure hit rate in dependency of threshold. Expected result: Example measurement: Am241  how to know „50%-value“? Derivative of rate is spectrum! Rate threshold At „50%-value“: Threshold [e] = E γ / 3.61 [e]

6. Malte Backhaus - FE-I4 testing, 07.02.20116 Measurement plan Use variable x-ray source to have different E γ with known energies. Iterative process for four energies: - Search for „peak energy [VthinDAC]“ with untuned chip. - Set peak VthinDAC, measure „mean threshold“. - Tune chip to „mean threshold“. - Measure „peak energy [VthinDAC]“ with tuned chip. - Peak position [VthinDAC] moved (dominated by some pixels)  need to retune chip… - Set (new) peak VthinDAC, measure „mean threshold“. - Tune chip to „mean threshold“. - finally measure peak position [VthinDAC]. - Measure threshold [e] with this settings, compare with expected #e = E γ / 3.61. Calculate correction for calibration constant… Problems: Measurement loop implemented in USBpixTest, but USBpixTest can not tune the chip / load a tuning  need to run Stcontrol and USBpixTest in parallel, which is dangerous… Only „final“ measurements for Mo, Ag, Ba and Tb are shown in next slides…

7. Malte Backhaus - FE-I4 testing, 07.02.20117 Mo E γ : 17.44 keV and 19.63 keV Expected #e-h pairs: 4831 and 5438

8. Malte Backhaus - FE-I4 testing, 07.02.20118 Ag E γ : 22.1 keV and 24.99 keV Expected #e-h pairs: 6122 and 6922

9. Malte Backhaus - FE-I4 testing, 07.02.20119 Ba E γ : 32.06 keV and 36.55 keV Expected #e-h pairs: 8881 and 10125

10. Malte Backhaus - FE-I4 testing, 07.02.201110 Tb E γ : 44.23 keV and 50.65 keV Expected #e-h pairs: 12252 and 14030

11. Malte Backhaus - FE-I4 testing, 07.02.201111 #e-h-pairs vs. VthinDAC

12. Malte Backhaus - FE-I4 testing, 07.02.201112 Threshold vs. #e-h-pairs

13. Malte Backhaus - FE-I4 testing, 07.02.201113 Quick result Calibration constant correction factor: K = 1 / slope of fit = 1 / 0.6443 = 1.55 # e_injected = (V_cal * C_inj) * 1.55 = ((PulserDAC * slope + offset) * C_inj) * 1.55 slope of PulserDAC can be measured (was assumed to be 1.5 mV/DAC)  Thresholds measured using Stcontrol have to be multiplied with 1.55  Noise: ~90e * 1.55 = ~140 e, close to expected noise value with sensor… Test this correction factor with K β- peak…

14. Malte Backhaus - FE-I4 testing, 07.02.201114 Threshold vs. #e-h-pairs

15. Malte Backhaus - FE-I4 testing, 07.02.201115 PulserDAC calibration Vcal [mV] = PulserDAC [DAC] * 2.06 [mV/DAC]  K splits to K_plsr and K_inj

16. Malte Backhaus - FE-I4 testing, 07.02.201116 Result + Outview K_plsr = slope_measured / slope_assumed = 2.06 / 1.5 = 1.37 K = K_plsr * K_inj  K_inj = K / K_plsr = 1.55 / 1.37 = 1.13  C_inj = C_assumed * K_inj = 5.9 fF * 1.13 = 6.7 fF Still to do: - Think carefully about uncertainties: does splitting charge cloud lower rate? (Remark from Maurice...) width of photo-peak in Si, Threshold,... - Redo this procedure with second pixel flavour (result should be the same...) - Redo this procedure with CAP0 and CAP1 independendly  value of CAP0 and CAP1 - Crosscheck result with 2 nd method...