1. Timing Counter status @ Sept. 2004
CSN I, Assisi 2004
Giorgio Cecchet

2. Timing Counter Activities
Timing resolution: 100 ps FWHM have been achieved.
PM’s characterised in the COBRA magnet for gain and timing.
Full characterisation of single TC’s counter is started
Final design and integration with DC is started
Ф-detector : APD directly from Hamamatsu
CSN I, Assisi 2004
Giorgio Cecchet

3. Timing resolution measurements
Low Thr.
High Thr.
Delay
coinc
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
248 ps FWHM
Scintillator
Light guide PM
(tL- tR)
CSN I, Assisi 2004
Giorgio Cecchet

4. Timing resolution measurements
Last test (LNF-Frascati-Beam Test Facility) January 04:
Energy Range MeV e MeV e+
Max. Repetition Rate 50 Hz
Pulse Duration 1-10 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
Scint. Fiber
Spot Size
Time spread ~25ps
CSN I, Assisi 2004
Giorgio Cecchet

5. 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
CSN I, Assisi 2004
Giorgio Cecchet

6. Characterisation in MagField
CSN I, Assisi 2004
Giorgio Cecchet

7. CSN I, Assisi 2004
Giorgio Cecchet

8. CSN I, Assisi 2004
Giorgio Cecchet

9. 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 T and 27.5º at V.
Unallowable increase of biasing voltage are needed at 0º.
CSN I, Assisi 2004
Giorgio Cecchet

10. Gain Vs Bias at several angles
+10º
Max gain curve
in magn. field
Same gain
+10º
CSN I, Assisi 2004
Giorgio Cecchet

11. RMS timing resolution vs p.e.
attenuator
60ps pulsed
blue Laser
100um Fiber
Laser beam
illuminates the
whole photocatode PM
CSN I, Assisi 2004
Giorgio Cecchet

12. CSN I, Assisi 2004
Giorgio Cecchet

13. ExpectedReduction factor
Ext. PM
Int. PM
Gain
8.5º
20º
10º
20º
TTS
8.5º
20º
10º
20º
☺ Increase Positron Path-Length ~ 5 cm
☺ Improve Geom. Matching Scint.-PMT
☺ Tilt the ~ 30º respect Magn. Field
→ Rotated Scint. Slab improves response uniformity and timing performance due to coincidences.
CSN I, Assisi 2004
Giorgio Cecchet

14. TC key features 30º 8.5º 105 cm 10º 25 cm B 0.75 T 1.05 T 70º
Scintillator Cross
Section 39x39 mm
PM active
diameter
70º
PM section
30º
8.5º
From COBRA
center
105 cm
10º
25 cm B
0.75 T
1.05 T
CSN I, Assisi 2004
Giorgio Cecchet

15. Conclusions: To be done: 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 recovers the timing resolution.
2” PMs can supply 100uA -maximum- current ( 10uA for 1.5” PMs)
2” PMs lifetime 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:
First systematic tests of single element of TC started in the run (May, 31 – June, 12) and will continue in the Frascati BTF
Finalize the design of TC and integration with DC
50x39 mm
39x39 mm
CSN I, Assisi 2004
Giorgio Cecchet

16. CSN I, Assisi 2004
Giorgio Cecchet

17. Single Counter Response Study
CSN I, Assisi 2004
Giorgio Cecchet

18. Single Counter Response Study
39x39 slab in rotated configuration simulating a positron 40.5° along z and 70°in radial plane
Very Preliminary
Position (mm)
Time Resolution FWHM (ps)
BC408
BC404
CSN I, Assisi 2004
Giorgio Cecchet

19. Mechanical design
CSN I, Assisi 2004
Giorgio Cecchet

20. 30º 8.5º 105 cm 10º 25 cm B From COBRA center CSN I, Assisi 2004
Giorgio Cecchet

21. CSN I, Assisi 2004
Giorgio Cecchet

22. 3D view of TC
CSN I, Assisi 2004
Giorgio Cecchet

23. Transverse Timing Counter
CSN I, Assisi 2004
Giorgio Cecchet

24. Curved detector (triggering)
The design of the curved detectors has been modified in order to match the budget limits for procurement of virgin APD form Hamamatsu (159 Euro/each).
~ 80 scintillating fibers and 160 APD per each TC.
Procurement preliminary procedure started
APD
Scint. Fibers
5 x 10 mm
CSN I, Assisi 2004
Giorgio Cecchet

25. Timing Counter Schedule
2002
2003
2004
2005
COBRA Test
Beam Test
Design
Assembly
PMT Evaluation
PMT procur.
Procur & Manuf.
APD Evaluation
APD test
APD procur.
Mechanical
matching BG
test
New APDs
Full
installation
Test
Milestone
Assembly
Design
Manufactoring
CSN I, Assisi 2004
Giorgio Cecchet

26. - detector (triggering)
We found good APDs with high S/N ratio that we tested at PSI and LNF (Frascati)
e- beam
Pure e-beam
CSN I, Assisi 2004
Giorgio Cecchet

27. - 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
CSN I, Assisi 2004
Giorgio Cecchet

28. 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 bench in Genoa
About 10% can be accepted
CSN I, Assisi 2004
Giorgio Cecchet