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Timing Counter
Report of Feb 20th, 2008F.Gatti
Final Construction Phase of TC
TC with fibers exposed TC upside down for Fiber APD gluing
High reflectance polymer foil coating
TC before insertion in COBRA Cables and pipes of TC in COBRA before final positioning
TC/Bag final positioning
TC
COBRA BORE
+15 mm from nominal position
Bag SS inner edge
COBA inner step
DCH supports
Bag SS inner cap
Bag EVAL inner sidebackside illuminated
PM at the final position inside bag
Fibers detector Fibers detector “turned on” The analog output achieved a good S/N level that has
been tested channel by channel. A selected event of a CR that hits at least 3 fibers is
shown as example8 Channelsanalog sum
8 Channelsanalog sum
Signal of 8+8 Interleaved fibers
8 Channelsanalog sum
Timing Analysis Use positrons runs with TRIGGER on TC only (2 or 3 contiguous
bars in coincidence). Reference data: 250k triggers belonging to #8378-#8408 runs Measure bar average time Tk
First method: (Tk-Tk+1) ≈ (s/cT Second method: (Tk+Tk+2 )/2 - Tk+1≈ (0+T
BCA
e+
A
T TA TB
2 TC
Tk t0k t1k
2s
No cuts timing analysis: 3 bars example
Higher order effects
Correction for the first two bars used
TCTWcorr TA
TWcorr
(T) (TC
TWcorr TATWcorr )
275ps
No cuts timing analysis: all bars
Bar1–Bar0
Bar2–Bar1
upstreamdownstream
Different chip
Searching the intrinsec timing resolutions
The methods give z-dependent results low z cuts give better resolution not fully explained by MC and presently under study
Time reconstruction from digitized pulse are affected by the electronics/algorithm intrinsic jitter evaluation of this time jitter has been done in a dedicated run.
Double Threshold Discriminator pulse is available to overcome the elctr./alg. jitter
Z-cuts Timing Analysis with DTD and PMT pulses
Bar3 - Bar2
Bar3 - Bar2
PMT
DTD Time resolution = 52 ps
DTD
Bar3 - Bar2
Cuts: 0.1V<pulse height<0.3V (Landau peak) Reconstructed z on first bar < 55 cm
PMT Time resolution = 62 ps
Intrinsic electronics/algorithm jitter in PMT signal Dedicated positron runs: one PM
signal feeds the two input channels of the corresponding bar:
same signal to the two electronics chains of the bar.
Time distribution only affected by electronics/algorithm jitter
It has been measured T1-T2)= 2 (T1+T2/2))
Average jitter value= 54 ps
Final PMT timing resolution after elect/algor. jitter subtraction 55 ps rms 129 ps FWHM
DTD analysis gives 120 ps FWM without jitter correction.
Latest preliminary resultsLatest preliminary results on DTD after jitter correction: 108 ps FWHM
Runs 9362-9363
Runs 9337-9344
First comments on time analysis DTD pulse analysis method shows better performance in the first
analysis (not all correction applied as in PMT signal analysis). PMT and DTD give us good redundancy for the timing of a single
event. Corrections for the time-walk, hit position, electr./algorithm jitter,
systematic of the timing resolution analysis methods, are under study.
Z dependence of T resolution under study (MC vs data comparison): the effect suggests a dependence of the chosen timing method on track inclination (low Z low impulse z projection).
Finally the TC intrinsic time resolution in operating conditions is now evaluated to be 120 ps FWMH120 ps FWMH (20% excess respect to the proposal),
Latest preliminary results show 108 ps FWHM108 ps FWHM jitter corrected DTD signal.
We are confident that there is room for the fine tuning of the timing analysis and a further assessment of the of the timing resolution
PMT equalization ( CR and CW data)
Black: CR runBlack: CR runRed: B runRed: B runGreen: LiF runGreen: LiF run
Charge Analysis Veff:
measurement of positron impact time on the bar, T
measurement of z can be made, in principle, from the width of the t1-t0 distribution
Measurement of z with the charge, once that eff is known
need (veff)/veff ~1% to achieve the desired T resolution
eff: independent measurement of z can
be measured from: - ln(Q1/Q0) vs z determined with
time once that veff is known - ln(Q1/Q0) using z measurement
from fibers
effv
LttT
2201
2
)( 10 ttvz eff
eff
z
G
G
Q
Q
2
ln)ln(0
1
0
1
eff. and Veff. Significant differences among
bars, consistent with results at BTF.
Data suggests not uniform losses in the internal reflection: - residual surface roughness
(measured value lower than 0.2 m RA)
- plastic enclosure residual reflectivity
Effective velocity: 14.5+/-0.2
cm/n
Black: CR runBlack: CR runRed: B runRed: B runGreen: LiF runGreen: LiF run
eff
Laser for 532 and 266 nm monitoring pulse The system delivered during the run. Now under test with the optical fiber
distributor Power stability at 48 MHz, 1064 nm, within 0.3% over a week of monitoring Timing pulse distributed via optical fiber and detected on TC DS at 50 Hz free
running repetition rate
3m cavity 48 MHz, 1064nmDiode pumped Nd:YVO
Acustic-optical pulse selectors
50 Hz
2 stages pulse amplifier
50Hz @ 532nm
256 nm
To fast APDfor power and int.pulse sync
To opt. fiberand fast APDfor trig. Out.
Laser Status Laser assembly and table under integration before
transportation at PSI
Preparation for the run08
Completion of the commissioning of the digital hit map for the fibers with CR (Mostly done last weekMostly done last week)
Works on TC: change of PMTs with unexplained low gain, close light leak in the APD fibers detector, change not working APD boards, improve S/N and noise immunity of the APD analog output
Improvement of the S/N will allow to decrease the threshold level in trigger algorithm recover some delay (20-30 ns ?) in the trigger latency
Rebuild N2 Bags Integrate the Laser for TC and XEC
Question of shaping time of APD electronics The 160 ns shaping time (10-90%) + the latency of the
trigger APD algorithm prevented the use of the in the on line trigger selection in the run07
An anticipation of about 60 ns of the formed trigger signal from APD should be enough ton solve the problem
Improvement of the S/N will allow to decrease the threshold recover some delay (20-30 ns?)
From the trigger side it is possible to reduce the processing time of the algorithm.
APD online in the trigger for Run08 Alternative possibility of reducing shaping time for 512
channels is not a trivial task and requires 7 weeks of with 6 people. This could be done eventually at the end of the run 08
Last on PMT life
The measurement lasted 290 days for a total current of 2130 Coulomb on a new PMT
The average current produced by the PMT over the period has been 88,2 microA
Data presented has been already corrected by the laser power variation with the photocell values
Previous measurements on old PM
Drift region of the old1-1/2” PM
life G/G(0)
0.2 90%
2.0 77%
3.3 70%
5.0 65%1 2 3 5
New measurements: 6.6 x life without changes
1 2 3 4 5 6
Schedule
End of slides
backup
MC
T-data
backup
Backup T1= t0 + x/c T2= t0 + (L-x)/c T1+T2= 2 t0 + L/c TA=(T1+T2)/2= t0 + L/2c TB=t0+s/c+ L/2c TA-TB = s/c s/2 TA+TB=2t0+s/c+(L/c) TC=t0+s/2c+L/2c (TA+TB)/2-TC= t0+s/2c+L/2c-t0-s/2c+L/2c=0
A C B
s/2