1. Performance of a Multigap RPC prototype for the LHCb Muon System
LAPE
IF - UFRJ
Performance of a Multigap RPC prototype for the LHCb Muon System
E. Polycarpo
On behalf of LHCb MRPC Working Group
CERN/LAPE
28/10/99
V Workshop on RPCs and related detectors

2. V Workshop on RPCs and related detectors
Outline
Introduction
Characteristics of the prototype
Description of the testbeam setup
Results
Conclusion
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3. Introduction: LHCb experiment
Muon Station M2
Angular coverage ~ 10 mrad to 300 mrad
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4. Introduction : LHCb Muon System
Provides :
Muon identification
L0 trigger
Requires:
reasonable momentum resolution
good time resolution
correct bunch-crossing identification
good performance at high rate
~ kHz/cm2 for 2 -5x1032 cm-2s-1 (q > 150 mrad)
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5. Characteristics of the MRPC prototype
Ground plane (copper foil)
Honeycomb
HV plane
(graphite layer)
Readout Strips  1.3 cm wide and 24 cm long (1.5 cm readout pitch)
connected to ASD8-B chip
0.7 mm thick Melamine-Phenolic-Melamine plates
r = 4x W cm
Gas mixture : % C2H2F4 / 3%iso-C4H10 / 1%SF6
0.7 mm gas gaps
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V Workshop on RPCs and related detectors

6. Experimental Set-up at CERN PS and SPS
1.0 cm pitch
Hodoscope (8x8)
Scintillator 20x20 cm2
Scintillator 15x15 cm2
MRPC Prototype
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V Workshop on RPCs and related detectors

7. Results - Efficiency at CERN PS
~ 3 GeV/c p - beam
Shift of the knee of the plateau:
voltage drop across the plates
Spill duration : ~ 400 ms
Relaxation time t ~re0er ~ O (1 s)
Overestimation of efficiency
at high rates
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8. Efficiency vs SPS burst time
120 GeV/c p - beam
Two effects :
rate variation
relaxation time
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9. Gamma Irradiation Facility
108 cm
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10. Measurement of Rate Effective rate (ER): Fit of Dt distribution
Photon Rate:
Rg = 740 GBq x 0.85 x 0.5 x (1/4pd2) x eg x 1/AF
Measured Photon Rate:
R’g = ER (AF) - ER(without source)
Fit of R’g to Rg :
eg ~ 1/200 ~ #gaps/800
AF =100
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11. V Workshop on RPCs and related detectors
GIF Rate Capability
Efficiency corrected for probability of spurious hit in the time window of 15 ns
(~ .01 %)
97% efficiency at 18 kV for ~ 1.9 kHz/cm2
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V Workshop on RPCs and related detectors

12. V Workshop on RPCs and related detectors
Timing Properties
Time walk: ~ 1 ns/kHz/cm2
Time resolution (sigma of gaussian fit) : 1.5 ns to 1.9 ns
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Cross-talk and Noise
1.2 kHz/cm2
Cluster size at operating voltages ~ 1.2 strips small cross-talk
High noise rate ~ 60 Hz/cm2
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14. Summary and Conclusions
Measurements at three CERN facilities have been performed, with emphasis on rate capability
The description of the efficiency drop within the SPS burst must take into account the significant variation in the rate.
In spite of high resistivity of the plates, the chamber reaches % efficiency for 1.9 kHz/cm2 in GIF
Small cross-talk (1.2 strips/cluster), but high noise rate (60 Hz/cm2)
Timing properties match the LHCb requirements
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V Workshop on RPCs and related detectors

15. Rate capability requirement
Background estimation in the LHCb muon stations:
PYTHIA as event generator
pathlength/volume as rate definition
MARS as simulation package
luminosity up to 5 x cm-2s-1
additional safety factor of 2.5
4 5 x cm-2s-1
1x10-5/cm2/interaction
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Big Prototype
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Sensitive Area : 1.2x2.2 m2
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18. V Workshop on RPCs and related detectors
MRPC Prototype: 24x24 cm2
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V Workshop on RPCs and related detectors