Flavio Gatti, PSI, 11 February , 2004 1
Genova/Pavia/Roma
Timing Counter: status @ january 2004
Flavio Gatti, PSI, 11 February , 2004 2
Genova/Pavia/Roma
Timing Counter Activities
• Timing resolution (Ge-Pv-Rm)• PMs characteristics in magnetic field(Ge-Pv) • APD for the counter (Ge)
• MC simulation activities(Pv-Rm)• Helium(Ge-Pv)
Flavio Gatti, PSI, 11 February , 2004 3
Genova/Pavia/Roma
Timing resolutionThe spread of the time distribution of the positron impact,T0, is
evaluated as: (T0) (TL- TR)]/2
where (TL- TR)] is the delay spread between the L and R PM------------------------------------------------------------------------- T0 =(TL+TR)/2 +L/(2Veff) (T0) [(TL+TR)/2] ; [(TL+TR)]= [(TL-TR)]
TLTR
T0
Flavio Gatti, PSI, 11 February , 2004 4
Genova/Pavia/Roma
Timing resolution Main parameters to be evaluated and matched in the TC:
1. Scintillation time, attenuation length, PM coupling2.PM’s Transit Time Spread, Quantum Efficiency, Gain3. Signal Slew Rate, Bandwidth and Noise4.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
R7761-70(1.5”) 350 ps 470 ps
R5924 (2”) 440 ps 650 ps
XP2020 UR (2”) 350 ps 350 ps
Flavio Gatti, PSI, 11 February , 2004 5
Genova/Pavia/Roma
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 (tL- tR)]/2= 124 ps FWHM
Scintillator
Light guide
248 ps FWHM(tL- tR)
Low Thr.
High Thr.
Delaycoinc
PM
Flavio Gatti, PSI, 11 February , 2004 6
Genova/Pavia/Roma
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 : x=2mm y=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
APD
Scint. Fiber Spot SizeTime spread ~25ps
Flavio Gatti, PSI, 11 February , 2004 7
Genova/Pavia/Roma
Timing resolution measurements• BC404 and BC408 (2X5x80 cm3) directly coupled to 1.5” and
2” Hamamatsu Fine Mesh PMs• Digital electronic readout (CAMAC)
Beam
Approx. Beam Focus Position
APD Cross and Preamplifier
TC
BTF Beam line
Flavio Gatti, PSI, 11 February , 2004 8
Genova/Pavia/Roma
Timing resolution measurements1. 1,2,3 electron events are resolved in the charge spectrum2. (tL- tR) is selected in the 1e peak Our Best Results :
2.35x (tL- tR)]/2= 1042ps FWHM
1e2e
3e
Flavio Gatti, PSI, 11 February , 2004 9
Genova/Pavia/Roma
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, PSI, 11 February , 2004 10
Genova/Pavia/Roma
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 (
di s
tan
ce f
rom
ce
nte
r ) [
c m]
Flavio Gatti, PSI, 11 February , 2004 11
Genova/Pavia/Roma
2” PM in Magnetic Field (Data presented in July 03)
2” PM 2” PM
Transit time spread respect to B=0
Magnetic field [ T ]Magnetic field [ T ]
Gain respect to B=0
0º
10º
20º
Note: no charge/amplitude corrected
Flavio Gatti, PSI, 11 February , 2004 12
Genova/Pavia/Roma
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
50x20 mm
39x30 mm
Flavio Gatti, PSI, 11 February , 2004 13
Genova/Pavia/Roma
Guideline for Operation in Magnetic FieldImpact angles: 60º in the orthogonal
plane, 40º in the longitudinal plane
Magn. Field at radius 29<R<31 in figure.
Minimal CrossSection 39x30 mm 60º
PM section
PM activediameter
20º 20º8.5º
From COBRA center
105 cm
10º
25 cm
BB0.75 T 1.05 T
Reductio factor
Ext. PM Int. PM
Gain 12 @ 8.5º 5 @ 20º
35 @ 10º15 @ 20º
TTS 1.2* @ 8.5º1.2* @ 20º
1.8* @ 10º1.6* @ 20º
Expected Positron Path-Length: ~7cm (factor ~ 1.4)Geom. Matching Improv.: ~ 1.5Total increase of light yield:~ 2.1Better situation @ 30º PM tilt angleMC comparison of different config.
(Rotated Slab, ..) under study for further impr. (coincidence….)
*Note: data not corrected for time-walk effect
Flavio Gatti, PSI, 11 February , 2004 14
Genova/Pavia/Roma
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, PSI, 11 February , 2004 15
Genova/Pavia/Roma
- 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, PSI, 11 February , 2004 16
Genova/Pavia/Roma
- 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.
FromHamamatsu
from CMSselection
Flavio Gatti, PSI, 11 February , 2004 17
Genova/Pavia/Roma
Schedule
Beam Test
2002 2003 2004 2005
Test MilestoneAssemblyDesign Manufactoring
Design
Assembly
PMT Evaluation PMT procur.
Procur & Manuf.
2” Fine Mesh 19 dyn. R5924
APD Evaluation APD test APD procur.
5x5 mm APD Hmamatsu