Transcript A new m e g experimet at PSI

Genova/Pavia/Roma
Timing Counter:
progress report
Flavio Gatti, CSNI, May 17th , 2004
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Genova/Pavia/Roma
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
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Genova/Pavia/Roma
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)]
T
0
TL
Flavio Gatti, CSNI, May 17th , 2004
TR
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Timing resolution
Main parameters to be evaluated and matched in the TC:
1. Scintillation time, attenuation length, PM coupling
2.PM’s Transit Time Spread, Quantum Efficiency, Gain
3. Signal Slew Rate, Bandwidth and Noise
4.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, CSNI, May 17th , 2004
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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
Scintillator
PM
(tL- tR)
248 ps FWHM
Light guide
Flavio Gatti, CSNI, May 17th , 2004
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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 : 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.
5x5 mmScint.
Fiber
APD
Spot Size
Time Spread ~25ps
beam
Flavio Gatti, CSNI, May 17th , 2004
APD
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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)
Approx. Beam Focus Position
BTF Beam line
TC
Beam
APD Cross and Preamplifier
Flavio Gatti, CSNI, May 17th , 2004
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Timing resolution measurements
1. 1,2,3 electron events are resolved in the charge spectrum
2. (tL- tR) is selected in the 1e peak
Our Best Results :
2.35x s[(tL- tR)]/2= 1042ps FWHM
1e
2e
3e
Flavio Gatti, CSNI, May 17th , 2004
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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 7s (rms
noise level) from the baseline.
TDC Thr.
ADC off-line
selection
Flavio Gatti, CSNI, May 17th , 2004
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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)
Flavio Gatti, CSNI, May 17th , 2004
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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
20º
2” PM
10º
0º
Magnetic field [ T ]
Flavio Gatti, CSNI, May 17th , 2004
Magnetic field [ T ]
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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.
Reductio
factor
Ext. PM
Int. PM
Gain
12 @ 8.5º
5 @ 20º
35 @ 10º
15 @ 20º
TTS
1.2* @ 8.5º
1.2* @ 20º
1.8* @ 10º
1.6* @ 20º
*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….)
Flavio Gatti, CSNI, May 17th , 2004
Scintillator Cross
Section 39x30 mm
or 39x50 mm
PM active
diameter
60º
PM section
From
COBRA
center
105 cm
8.5º
30º
B
25 cm
30º
10º
0.75 T
B 1.05 T
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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
Flavio Gatti, CSNI, May 17th , 2004
COBRA
Magnet
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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 2100 V.
Unallowable increase of biasing voltage are needed at 0º.
Flavio Gatti, CSNI, May 17th , 2004
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Gain Vs Bias at several angles
+10º
Max gain curve
in magn. field
Same gain
+10º
Flavio Gatti, CSNI, May 17th , 2004
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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
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Conclusions
•
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 50kHz @ 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
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TC inside the COBRA
Flavio Gatti, CSNI, May 17th , 2004
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3D view of TC
Flavio Gatti, CSNI, May 17th , 2004
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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
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- detector (triggering)
• We found good APDs with high S/N ratio that we tested at PSI and
LNF (Frascati)
e- beam
Flavio Gatti, CSNI, May 17th , 2004
Pure e-beam
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- 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
Flavio Gatti, CSNI, May 17th , 2004
From
Hamamatsu
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Genova/Pavia/Roma
Status of test and procurements of APD
APD
Copper
block
Splitters
APD test banch in Genoa
Pulsed
Laser
Peltier Cell
Integrating
Calibrated
Photometer
Fast
Photodiode
1/1000
attenuator
Photomultiplier
peak-to-noise ratio @ 250 photons signal
30.00
20.00
About 10% can be accepted
S/N ratio
10.00
0.00
1
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2002
2003
Schedule
2004
2005
2” Fine Mesh 19 dyn. R5924
PMT Evaluation
Beam Test
APD Evaluation APD procur.
5x5 mm APD Hmamatsu
COBRA test
PMT procur.
APD test
Design
Procur & Manuf.
Assembly
Design
Flavio Gatti, CSNI, May 17th , 2004
Manufactoring
Assembly
Test
Milestone
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