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Update from the Hall: Why is the MIP not distinct?

Update from the Hall: Why is the MIP not distinct?. Thomas K Hemmick. Classical Signal Conditioning. Charge-Sensitive pre-amp Charge collected increases like an ascending staircase. V=Q/C with RC decay applied. Derivative of V(pre) shows spikes at each charge injection.

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Update from the Hall: Why is the MIP not distinct?

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  1. Update from the Hall:Why is the MIP not distinct? Thomas K Hemmick

  2. Classical Signal Conditioning • Charge-Sensitive pre-amp • Charge collected increaseslike an ascending staircase. • V=Q/C with RC decay applied. • Derivative of V(pre) showsspikes at each charge injection. • Shaper uses time-weightingfunction to produce pulse. • Mathematically:

  3. WaveForm Analysis • We do not have a shaper. • We digitize (sample) waveformof the V(preamp) directly. • Simple Access to things you want to know: • “Post”-“Pre” = Charge. • Centroid = Pulse Time • RMS = Rise Time. • Analysis presently does allthree of these. • Minor trouble from previouspulses interfering…

  4. Previous Pulses • Probability: • 200 kHz of BBC LL1. • 400 kHz of interactions. • 10 MHz of crossings • 4% chance of collision. • Latency: • Pre-amp crosses zero at 2 msec. • Pre-amp crosses after 20 crossings. • Probability of a prior event: • These MOSTLY have decayed away but not all. • For now cut away when Sample[0]!=0 Pulses from prior Crossings clearly visible Decay of pulse duringdigitization interval can be significant

  5. Samples of Pulse Analysis • “Derivative” showsclear peak in slide 4. • Centroid of peak quite tight for big pulses. • RMS narrow for big pulses.

  6. What do you call signal? • Sample[i] is a plot of charge vs. time. • S[i+n]-S[i] is a plot of current vs time. • I believe that CHARGE is our signal. • Note some simple math: • If you integrate back overthe differences, you eliminatesamples in the middle. • Is the signal current: • MAX(Di) as a single sample. • Amplitude to fit (e.g. Gauss)to get peak current? • Or is the signal charge: • Post – Pre.

  7. Summary of Progress: • We see a large difference in yield of big pulses with a difference in the grid bias. • The yield in forward bias SHOULD be MIPs. • No efforts have yet resulted in a narrow MIP peak: • Single pad same as “allpads”. • Sorted into columns same. • Increased drift field same. • Oscilloscope spectrum same. • Confusion reigns supreme… • Will having a tag of which pad to lookat help? • If MIP is not distinct, why should blobbe tight distribution. • Why was (is?) 55Fe a tight peak? • Optimist: • Please someone tell me how to be optimistic.

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