Advanced Timing Counter Activities & Resolution Study

1. Timing Counter: status @ january 2004

2. Timing Counter Activities • Timing resolution (Ge-Pv-Rm) • PMs characteristics in magnetic field(Ge-Pv) • APD for the F counter (Ge) • MC simulation activities(Pv-Rm) • Helium(Ge-Pv)

3. T0 TR TL 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)]

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.

5. Low Thr. High Thr. coinc Delay Scintillator 248 ps FWHM Light guide 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 PM (tL- tR)

6. APD Scint. Fiber beam APD Timing resolution measurements • Last test (LNF-Frascati-Beam Test Facility –BTF-) January 04: Energy Range 25-800 MeV e- 25-550 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. Spot Size Time spread ~25ps

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

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

9. TDC Thr. ADC off-line selection 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.

10. 2x(distance from center) [cm] 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)

11. 2” PM in Magnetic Field (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 0º 10º Magnetic field [ T ] Magnetic field [ T ]

12. 50x20 mm 39x30 mm Timing resolution measurements • Conclusions: • 2” PMs allow to obtain the target resolution • We are still 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) • In these tests there is no evidence of limits due to the electronics (slew rate, noise, …) • No evidence of differences between BC404 and BC408 • To be done: • Geometrical arrangement that provide the same efficiency of positron collection and same timing resolution in Magn. Field (see exe. in figures ->) - Selection of 2” PMs with respect the Q.E. and gain may be needed. • Improvements & fine tuning will be done in the next beam times • Finalize the design of TC from now

13. PM active diameter Minimal Cross Section 39x30 mm 60º PM section From COBRA center 105 cm 25 cm 8.5º 20º 20º 10º B B Guideline for Operation in Magnetic Field Impact angles: 60º in the orthogonal plane, 40º in the longitudinal plane Magn. Field at radius 29<R<31 in figure. *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 situation @ 30º PM tilt angle MC comparison of different config. (Rotated Slab, ..) under study for further impr. (coincidence….) 0.75 T 1.05 T

14. 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.

15. - detector (triggering) • We found good APDs with high S/N ratio that we tested at PSI and LNF (Frascati) e- beam Pure e-beam

16. - 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

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