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

Malte Backhaus - FE-I4 testing, 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

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

Malte Backhaus - FE-I4 testing, 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]

Malte Backhaus - FE-I4 testing, 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]

Malte Backhaus - FE-I4 testing, 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 / 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…

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

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

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

Malte Backhaus - FE-I4 testing, Tb E γ : keV and keV Expected #e-h pairs: and 14030

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

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

Malte Backhaus - FE-I4 testing, Quick result Calibration constant correction factor: K = 1 / slope of fit = 1 / = 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…

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

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

Malte Backhaus - FE-I4 testing, 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...