1. Timing Counter: progress report
Flavio Gatti, CSNI, May 17th , 2004

2. Timing Counter Activities
Timing resolution: 100 ps FWHM have been achieved.
PM’s characteristics in the COBRA magnet: gain and timing.
TC – Design: first engineering design.
APD: measurement and status of procurement
Flavio Gatti, CSNI, May 17th , 2004

3. Timing resolution
The spread s of the time distribution of the positron impact,T0, is evaluated as:
s(T0)  s[(TL- TR)]/2
where s[(TL- TR)] is the delay spread between the L and R PM
T0 =(TL+TR)/2 +L/(2Veff)
s2(T0)  s2[(TL+TR)/2] ; s2[(TL+TR)]= s2[(TL-TR)] TL TR T0
Flavio Gatti, CSNI, May 17th , 2004

4. Timing resolution
Main parameters to be evaluated and matched in the TC:
Scintillation time, attenuation length, PM coupling
PM’s Transit Time Spread, Quantum Efficiency, Gain
Signal Slew Rate, Bandwidth and Noise
Particle trajectory length(=light output) and its spread
High Luminosity Event, High Quantum Efficiency and PM Collecting Area, High Slew Rate Signal (dV/dt), High S/N ratio, High Bandwidth. PM
TTS (FWHM) Typ.
TTS Measured
R (1.5”)
350 ps
470 ps
R5924 (2”)
440 ps
650 ps
XP2020 UR (2”)
Flavio Gatti, CSNI, May 17th , 2004

5. Timing resolution measurements
First test(PSI-E5)- may 03:
-BC404 (1X5x80 cm3) – light guides and 1”1/2 and 2” Hamamatsu Fine Mesh PMs
-passive beam collimation (6mm diameter)
-5 cm positron path length.
-Analogic electronics - Double Threshold Discriminator-MCA
 2.35x s[(tL- tR)]/2= 124 ps FWHM
Low Thr.
High Thr.
Delay
coinc
248 ps FWHM
Scintillator
Light guide PM
(tL- tR)
Flavio Gatti, CSNI, May 17th , 2004

6. Timing resolution measurements
Last test (LNF-Frascati-Beam Test Facility –BTF-) January 04:
Energy Range MeV e MeV e+
Max. Repetition Rate 50 Hz
Pulse Duration: ~ ns
Current/pulse 1 to 1010 particles (Allowed Current 103 particles/second)
Beam spot : sx=2mm sy=4mm (in the focus)
Further geometrical selection of 5mmx5mm spot by two scintillating fibers with APD read-out. Time spread due to the spot size ~25ps.
Coincidence with “APD cross” and the LINAC trigger allow to reject most of the bck. events.
beam
APD
5x5 mmScint. Fiber
Spot Size
Time Spread ~25ps
Flavio Gatti, CSNI, May 17th , 2004

7. Timing resolution measurements
BC404 and BC408 (2X5x80 cm3) directly coupled to 1.5” and 2” Hamamatsu Fine Mesh PMs
Digital electronic readout (CAMAC)
Approx. Beam Focus Position
BTF Beam line TC
Beam
APD Cross and Preamplifier
Flavio Gatti, CSNI, May 17th , 2004

8. Timing resolution measurements
1,2,3 electron events are resolved in the charge spectrum
(tL- tR) is selected in the 1e peak
Our Best Results :
2.35x s[(tL- tR)]/2= 1042ps FWHM 2e 1e 3e
Flavio Gatti, CSNI, May 17th , 2004

9. Timing resolution measurements
We don’t see walk-effect (time/amplitude correlation).
The thresholds have been set to 0.5% of the average pulse height (3 V) at about 7 (rms noise level) from the baseline.
TDC Thr.
ADC off-line selection
Flavio Gatti, CSNI, May 17th , 2004

10. Timing resolution measurements
The plastic slab acts as a light guide with Veff=12.6 cm/ns
The time resolution is proportional to the inverse of the sqrt(path length)
2x(distance from center) [cm]
Flavio Gatti, CSNI, May 17th , 2004

11. 2” PM in Magnetic Field 2” PM 2” PM Gain respect to B=0
(Data presented in July 03)
Gain respect to B=0
Transit time spread respect to B=0
Note: no charge/amplitude corrected
2” PM
2” PM
20º
10º 0º
Magnetic field [ T ]
Magnetic field [ T ]
Flavio Gatti, CSNI, May 17th , 2004

12. Guideline for Operation in Magnetic Field
Scintillator Cross
Section 39x30 mm
or 39x50 mm
60º
PM section
PM active
diameter
Impact angles: 60º in the orthogonal plane, 40º in the longitudinal plane
Magn. Field at radius 29<R<31 in figure.
Reductio factor
Ext. PM
Int. PM
Gain
8.5º
20º
10º
20º
TTS
8.5º
20º
10º
20º
30º
8.5º
From COBRA
center
105 cm
10º
25 cm B
*Note: data not corrected for time-walk effect
Expected Positron Path-Length:
~7cm (factor ~ 1.4)
Geom. Matching Improv.: ~ 1.5
Total increase of light yield:~ 2.1
Better 30º PM tilt angle
MC comparison of different config. (Rotated Slab, ..) under study for further impr. (coincidence….)
0.75 T
1.05 T
Flavio Gatti, CSNI, May 17th , 2004

13. Gain and TTS in the COBRA Magnet (April 04)
Test of PM’s gain and timing resolution
in the final operating conditions PM
Drift Chamber
assembly
Scintillator slab
COBRA
Magnet
Flavio Gatti, CSNI, May 17th , 2004

14. Unallowable increase of biasing voltage are needed at 0º.
Gain vs Rate
Zero field
1.05 T
27.5º
The Gain vs Rate at 1500 V in zero field is fully recovered at 1.05 and 27.5º at V.
Unallowable increase of biasing voltage are needed at 0º.
Flavio Gatti, CSNI, May 17th , 2004

15. Gain Vs Bias at several angles
Max gain curve
in magn. field
+10º
Same gain
+10º
Flavio Gatti, CSNI, May 17th , 2004

16. RMS timing resolution vs p.e.
attenuator
60ps pulsed
blue Laser
100um Fiber
Laser beam
illuminates the
whole photocatode PM
Flavio Gatti, CSNI, May 17th , 2004

17. Conclusions 50x39 mm 39x30 mm Conclusions:
2” PMs allow to obtain the target resolution
At first order, the resolution is limited by the number of photoelectrons (light output from scintillator, quantum efficiency of PM, coupling scintillator-PM[2”], which has 39 mm dia. active area)
At second order, the slew rate could be used to improve the resolution in small signal regime: we have demonstrated that amplification improves timing resolution.
2” PMs can supply 100uA -maximum- current ( 10uA for 1.5” PMs)
2” PMs Lifetime=100uAx100h which correspond to 2.3 years at the event rate of gain of 6x105. An increase of a factor 2 can be easily obtained.
To be done:
Systematic tests of single element of TC are foreseen in the next run (May, 26 – June, 16)
Define the final shape and sizes of scintillators
Finalize the design of TC
50x39 mm
39x30 mm
Flavio Gatti, CSNI, May 17th , 2004

18. TC inside the COBRA
Flavio Gatti, CSNI, May 17th , 2004

19. 3D view of TC
Flavio Gatti, CSNI, May 17th , 2004

20. Curved detector (triggering)
Problem: curved thin scintillators orthogonal to the field
Proposal: 5mmx5mm scintillating fibers coupled with APD.
*APD high efficiency 95%
*Optimal Matching of fibers/detectors
*No relevant results published result on fast scintillator results ( 0.5 ns claimed)
*Preliminary results in which we observed light pulses in plastic with Advanced Photonics and Hamamatsu APDs are obtained in the last summer.
November 03: received first batch of APDs selected for CMS
We made our selection, which is based on static parameters measurements (I-dark and Gain vs Vbias, Vbkd…), in order to calculate the expected Signal/Noise at the working point.
Flavio Gatti, CSNI, May 17th , 2004

21. - detector (triggering)
We found good APDs with high S/N ratio that we tested at PSI and LNF (Frascati)
e- beam
Pure e-beam
Flavio Gatti, CSNI, May 17th , 2004

22. - detector (triggering)
But, only about 10% of the selected APDs are good enough
Huge spread in dynamic parameters not predictable from static parameters [left figure]
The CMS selection and conditioning of the first batch of APDs is not applicable to MEG (we are working at few Volts from Vbkd – high gain- and we are interested to high slew rate and high S/N for timing purpose)
For comparison new APDs from Hamamatsu have similar response[right figure]
More work is needed to better understand the correlation between static and dynamic parameters of CMS APDs.
from CMS
selection
From
Hamamatsu
Flavio Gatti, CSNI, May 17th , 2004

23. Status of test and procurements of APD
Pulsed Laser
Integrating
Calibrated
Photometer
Fast Photodiode
Photomultiplier
1/1000 attenuator
Splitters
APD
Copper block
Peltier Cell
APD test banch in Genoa
About 10% can be accepted
Flavio Gatti, CSNI, May 17th , 2004

24. Schedule 2002 2003 2004 2005 Flavio Gatti, CSNI, May 17th , 2004
2” Fine Mesh 19 dyn. R5924
PMT Evaluation
Beam Test
COBRA test
PMT procur.
APD Evaluation
APD procur.
APD test
Design
Procur & Manuf.
5x5 mm APD Hmamatsu
Assembly
Test
Milestone
Assembly
Design
Manufactoring
Flavio Gatti, CSNI, May 17th , 2004