Improved timing

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  • Work in progress - intended more as a logbook than presentation of results*

CDC prototype cosmics data

  • 50/50 mixed Ar, CO2
  • Recalibrated MFCs
  • Outer plenum added to CDC prototype to prevent leaks
  • New pre-production HVB
  • 2050V
  • Modified preamp4 (terminating resistors removed)
  • Prototype tilted at 30o to enclosing scintillators (scints trigger the daq)


Fed scintillator signals post-discriminator and coincidence signal through then level converter to ECL, then attenuator, into fADC. Took threshold as half peak value (also tried 1/4 and 3/4 peak but these broadened the timing spectra). Used interpolation algo. (The DAQ is triggered by the coinc signal.) The time offset in the first set is equal to the (uninterpolated threshold crossing bin - 10) x 8 ns.

Interpolated signals for many events, ADC value vs time, time in ns after an offset
Histogram of threshold crossing time
Scintillator threshold crossing time
Histogram of threshold crossing time - coincidence time for scintillators and 2D plot

Drift time histogram (for all straws) and expanded about t0

Drift times
Drift times

T0 was taken as the x-intercept of a straight line fitted to the leading edge over 10% to 90% of the maximum value. Here (hit threshold=5sigma) this value is 91.3ns.


Drift time vs fitted drift distance using Garfield calculations for 50/50 Ar/CO2 (left) and 49/51 (right).

50/50 Ar/CO2 gas mix
49/51 Ar/CO2 gas mix


Resolution (difference between fitted track radius including and excluding that hit from the fit) for ch 20 (straw close to center of prototype)

50/50 Ar/CO2 gas mix
49/51 Ar/CO2 gas mix

Resolution for various time increment (offset) dt added to fitted t0, ie t0 = 91.3 + dt, ignoring events before t0
Optimum is offset dt=11ns for 49/51 (14ns for 50/50 has slightly worse resolution)
Check how the mean varies with drift dist around optimum dt

50/50 Ar/CO2 gas mix z-min=159
49/51 Ar/CO2 gas mix z-min=151
48/52 Ar/CO2 gas mix z-min=158
50/50 Ar/CO2 gas mix Resolution for fitted track radius > 1mm z-min=149
49/51 Ar/CO2 gas mix Resolution for fitted track radius > 1mm z-min=140
48/52 Ar/CO2 gas mix Resolution for fitted track radius > 1mm z-min=147
50/50 Ar/CO2 gas mix Resolution for fitted track radius > 2mm z-min=134
49/51 Ar/CO2 gas mix Resolution for fitted track radius > 2mm z-min=126
48/52 Ar/CO2 gas mix Resolution for fitted track radius > 2mm z-min=133



Use dt=14ns for 50/50 mix, 11ns for 49/51 mix

50/50 Ar/CO2 gas mix Resolution dt=14ns
49/51 Ar/CO2 gas mix Resolution dt=11ns
50/50 Ar/CO2 gas mix Resolution vs drift time dt=14ns
49/51 Ar/CO2 gas mix Resolution vs drift time dt=11ns
50/50 Ar/CO2 gas mix Resolution vs fitted drift distance dt=14ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance dt=11ns

Re-assign events with time < t0 to a range of early times >= t0

50/50 Ar/CO2 gas mix Resolution, early events reassigned to fixed drift time (y-axis)
49/51 Ar/CO2 gas mix Resolution, early events reassigned to fixed drift time (y-axis)
50/50 Ar/CO2 gas mix Resolution for fitted track radius > 1mm, early events reassigned to fixed drift time (y-axis)
49/51 Ar/CO2 gas mix Resolution for fitted track radius > 1mm, early events reassigned to fixed drift time (y-axis)
50/50 Ar/CO2 gas mix Resolution for fitted track radius > 2mm, early events reassigned to fixed drift time (y-axis)
49/51 Ar/CO2 gas mix Resolution for fitted track radius > 2mm, early events reassigned to fixed drift time (y-axis)

Assign early events to t0+1ns

50/50 Ar/CO2 gas mix Resolution dt=14ns
49/51 Ar/CO2 gas mix Resolution dt=11ns
50/50 Ar/CO2 gas mix Resolution vs drift time dt=14ns
49/51 Ar/CO2 gas mix Resolution vs drift time dt=11ns
50/50 Ar/CO2 gas mix Resolution vs fitted drift distance dt=14ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance dt=11ns

Resolution with drift distance for 49/51 mix, dt=11ns, early events assigned to t0 + 1ns

49/51 Ar/CO2 gas mix Resolution vs fitted drift distance dt=11ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance dt=11ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance dt=11ns

Earlier run with same timing setup but larger lower scintillator with angled light-guide gave very slightly worse resolution (optimal for dt=15 ns, early events assigned to t0)

49/51 Ar/CO2 gas mix Resolution with larger lower scintillator dt=15ns
Old scintillator timing

Varied hit threshold. Resolution fitted with 1 gaussian has smallest width for thr=4sigma (previously 5 sigma) dt=10ns tfix=1ns but shows slight curve when plotted vs drift time or distance.

49/51 Ar/CO2 gas mix Resolution ch 20, Hit threshold varied (n x pedestal sigma) , dt=tz
49/51 Ar/CO2 gas mix Resolution ch 20, Hit threshold=4sigma

Hit count for tracked hits in ch20:
for thr=4 is 8% 5 hits, 79% 6 hits, 13% 7 hits
for thr=8 is 17% 5 hits, 77% 6 hits, 6% 7 hits


Resolution with drift distance for 49/51 mix, hit threshold 4sigma, dt=10ns, early events assigned to t0 + 1ns

49/51 Ar/CO2 gas mix Resolution thr=4sigma dt=10ns tfix=1ns
49/51 Ar/CO2 gas mix Resolution vs drift time thr=4sigma dt=10ns tfix=1ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance thr=4sigma dt=10ns tfix=1ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=10ns tfix=1ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=10ns tfix=1ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=10ns tfix=1ns
49/51 Ar/CO2 gas mix Fit residuals vs max amplitude ch 20, hit thr=4sigma dt=10ns tfix=1ns


More....
resolution vs drift is slightly curved
resolution does fit better with 2 gaussians but does not help to find minimum, one works well enough
find an easy way to estimate t0 offset dt
does this change with HV?



2100V Drift time histogram (for all straws) and expanded about t0

Drift times
Drift times

T0 was taken as the x-intercept of a straight line fitted to the leading edge over 10% to 90% of the maximum value. Here this value is 89.1ns. With hit threshold=4sigma the fitted t0 is 88.1ns.

2100V Resolution with drift distance for 49/51 mix, hit threshold 4sigma, dt=9ns, early events assigned to t0

49/51 Ar/CO2 gas mix Resolution thr=4sigma dt=9ns tfix=0ns
49/51 Ar/CO2 gas mix Resolution vs drift time thr=4sigma dt=9ns tfix=0ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance thr=4sigma dt=9ns tfix=0ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=9ns tfix=0ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=9ns tfix=0ns
49/51 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=9ns tfix=0ns




Resolutions for ch20 ignoring hits before tzero, using 50/50 mix in Garfield and wire diameter of 17.8um instead of 20um, 2100V (left) and 2050V (right).

50/50 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=7ns hits before tzero ignored
50/50 Ar/CO2 gas mix Resolution vs fitted drift distance, hit thr=4sigma dt=10ns hits before tzero ignored