Latest approach to hit finding is as follows:
- Find a hit channel and filter events
- Calculate mean pedestal Pm & s.d. (σ) for first 100 samples in 100 events (trigger is approx sample 200)
- Set a threshold Pm + Tpm (Tpm ~ 3.5 σ) for further investigation, select events & channels where adc value exceeds this
- Calculate event pedestal
- Calculate event pedestal Pevt for current event & channel, as mean of 100 samples ending 10 samples before trigger time
- Use event pedestal to find high threshold time and new local pedestal
- Upsample data from samples 150 to 350 (max drift time + trigger time is approx sample 290)
- Select events where adc value goes over a high threshold Pevt + Tpe at point x (Tpe ~ 5sigma))
- Find a local pedestal Ploc as adc value at Np upsampled points (minisamples) before x (eg Np=15)
- Use local pedestal to find high and low threshold times
- Search forward from x-Np to find point x1 where data goes over a slightly less high threshold Ploc + Th where Th ~ 4 σ
- Search backward from x1 to find point x2 where data goes below low threshold Ploc + Tl where Tl ~ σ
To find where to take local pedestal:
Distribution of ADC values after subtracting pedestal at different Np
20 minisamples before threshold crossing
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15 minisamples before threshold crossing
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12 minisamples before threshold crossing
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10 minisamples before threshold crossing
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5 minisamples before threshold crossing
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ADC values after subtracting pedestal at different Np
20 minisamples before threshold crossing
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15 minisamples before threshold crossing
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12 minisamples before threshold crossing
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10 minisamples before threshold crossing
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5 minisamples before threshold crossing
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Resolution after subtracting pedestal at different Np for Th1 5sigma, Th = 4sigma, Tl = 1sigma
20 minisamples before threshold crossing (tz=8)
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15 minisamples before threshold crossing (tz=7)
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12 minisamples before threshold crossing (tz=6)
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10 minisamples before threshold crossing (tz=6)
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Optimised thresholds and Np, best combination for this data is Th1 5sigma, Th = 4sigma, Tl = 1sigma and Np = 13 or 14 with dt=6ns.
Drift-time=Tl crossing time; Th1 5sigma, Th = 4sigma, Tl = 1sigma, Np=14, dt=6
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Resolution with drift distance ch20
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Resolution with drift distance ch20
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Resolution with drift distance ch20
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Drift-time=Projection from Th through Tl to Ploc; Th1 5sigma, Th = 4sigma, Tl = 1sigma, Np=13, dt=6
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Resolution with drift distance ch20
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Resolution with drift distance ch20
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Resolution with drift distance ch20
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Drift-time=Intercept of straight line fit of crossing-points of Th Tl and their midpoint with Ploc; Th1 5sigma, Th = 4sigma, Tl = 1sigma, Np=13, dt=6
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Resolution with drift distance ch20
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Resolution with drift distance ch20
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Resolution with drift distance ch20
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