Difference between revisions of "CDC 60 40"
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|[[Image:run_31824_tz7_npmulti.png|thumb|x250px|10, 15, and 20 points (1.6ns each) before hit threshold]] | |[[Image:run_31824_tz7_npmulti.png|thumb|x250px|10, 15, and 20 points (1.6ns each) before hit threshold]] | ||
|[[Image:run_31824_tz7_npmulti3.png|thumb|x250px|15, 16, and 17 points (1.6ns each) before hit threshold]] | |[[Image:run_31824_tz7_npmulti3.png|thumb|x250px|15, 16, and 17 points (1.6ns each) before hit threshold]] | ||
+ | |} | ||
+ | |||
+ | |||
+ | {| border="0" cellpadding="2" | ||
+ | |+ Resolution for 1975V, 58.5/41.5 Garfield, hit thresholds 5sigma, timing thresholds 4sigma, 1sigma, pedestal at t(t4sig)-16, tz_add=7ns, tfix=1000 | ||
+ | |[[Image:run_31842_585_415_thr5_np16_tz7_tfix1000_res20.png|thumb|x250px|1975V, resolution ch 20]] | ||
+ | |[[Image:run_31842_585_415_thr5_np16_tz7_tfix1000_resx20.png|thumb|x250px|1975V, resolution vs hit radius]] | ||
+ | |} | ||
+ | |||
+ | Now include previously ignored hits which arrived before tzero+tz_add, assign these to a fixed drift time | ||
+ | {| border="0" cellpadding="2" | ||
+ | |+ 1975V 58.5/41.5 Garfield etc Resolution for np=16, tz_add=7ns, early hits assigned to 0ns, 1ns, 2ns | ||
+ | |[[Image:run_31824_tz7_tfixmulti.png|thumb|x250px|tfix = 0, 1, 2ns]] | ||
+ | |} | ||
+ | |||
+ | |||
+ | {| border="0" cellpadding="2" | ||
+ | |+ Resolution for 1975V, 58.5/41.5 Garfield, hit thresholds 5sigma, timing thresholds 4sigma, 1sigma, pedestal at t(t4sig)-16, tz_add=7ns, tfix=1ns | ||
+ | |[[Image:run_31842_585_415_thr5_np16_tz7_tfix1_res20.png|thumb|x250px|1975V, resolution ch 20]] | ||
+ | |[[Image:run_31842_585_415_thr5_np16_tz7_tfix1_resx20.png|thumb|x250px|1975V, resolution vs hit radius]] | ||
|} | |} |
Revision as of 15:07, 1 October 2012
60/40 Ar/CO2 and cosmics, prototype horizontal
HV | Fit MPV | Fit sigma (FWHM/4) | MPV/sigma | 99% point | 4045/MPV |
---|---|---|---|---|---|
1950 | 185 | 50 | 3.7 | 79 | 22 |
1975 | 226 | 67 | 3.4 | 84 | 18 |
2000 | 285 | 87 | 3.3 | 101 | 14 |
This does not look nearly as good as 50/50 gas mix. Resolution is calculated as fitted drift distance - measured (interpolated) distance, so it is positive when the measured drift time and distance are too small. In this case they are slightly too small at small drift distance but too large at large drift distance. This could be a problem with the gas mix. For reference, plot res vs distance for tz=5,7,and 0.
Increasing tz_add to 8ns shifts the resolution up at earlier times but it hardly moves at later times. This would probably have been obvious from the tz=0 data (below) where all the measured drift distances are too large. "Measured" drift distances are actually interpolated from a table of distance calculated for a given gas mix and a range of time measurements. So for this data I should use Garfield tables for a gas mix with slower drift velocity, ie less Ar.
Suspect total flow of 60sccm might be too low for the CO2 MFC. Increase to 80sccm and repeat. Also try Garfield for different gas mixes and look at tmax.
Fitted Tmax was 573, edge is from 560 to 600ns. Garfield calcs give 560ns for 60/40, 573ns (ta-daa!) for 59/41, 588ns for 28/42 and 610ns for 57/43.
It's easiest to look at resolution far from the wire to find the best gas mix model.
Now look at timing. Where to take local pedestal. These are plots of change in ADC value vs time relative to the threshold crossing time. Nothing to do with Garfield or tz_add but already have a good default in place (take pedestal at np=13 minisamples before threshold crossing) so small changes here are a fine tuning.
Mean goes through 0.5 and 1 at -16.4 and -13.7 for thr=5sigma, -17.6 and -14.9 for thr=6sigma
Now include previously ignored hits which arrived before tzero+tz_add, assign these to a fixed drift time