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