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

V Workshop on RPCs and related detectors Outline Introduction Characteristics of the prototype Description of the testbeam setup Results Conclusion 28/10/99 V Workshop on RPCs and related detectors

Introduction: LHCb experiment Muon Station M2 Angular coverage ~ 10 mrad to 300 mrad 28/10/99 V Workshop on RPCs and related detectors

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 ~ 1.6 -4 kHz/cm2 for 2 -5x1032 cm-2s-1 (q > 150 mrad) 28/10/99 V Workshop on RPCs and related detectors

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 10 12 W cm Gas mixture : 96 % C2H2F4 / 3%iso-C4H10 / 1%SF6 0.7 mm gas gaps 28/10/99 V Workshop on RPCs and related detectors

Experimental Set-up at CERN PS and SPS 1.0 cm pitch Hodoscope (8x8) Scintillator 20x20 cm2 Scintillator 15x15 cm2 MRPC Prototype 28/10/99 V Workshop on RPCs and related detectors

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 28/10/99 V Workshop on RPCs and related detectors

Efficiency vs SPS burst time 120 GeV/c p - beam Two effects : rate variation relaxation time 28/10/99 V Workshop on RPCs and related detectors

Gamma Irradiation Facility 108 cm 28/10/99 V Workshop on RPCs and related detectors

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 28/10/99 V Workshop on RPCs and related detectors

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 28/10/99 V Workshop on RPCs and related detectors

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 28/10/99 V Workshop on RPCs and related detectors

V Workshop on RPCs and related detectors 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 28/10/99 V Workshop on RPCs and related detectors

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 97 % 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 28/10/99 V Workshop on RPCs and related detectors

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 10 32 cm-2s-1 additional safety factor of 2.5 4 kHz/cm2 @ 5 x 10 32 cm-2s-1 1x10-5/cm2/interaction 28/10/99 V Workshop on RPCs and related detectors

V Workshop on RPCs and related detectors Big Prototype 28/10/99 V Workshop on RPCs and related detectors

V Workshop on RPCs and related detectors Sensitive Area : 1.2x2.2 m2 28/10/99 V Workshop on RPCs and related detectors

V Workshop on RPCs and related detectors MRPC Prototype: 24x24 cm2 28/10/99 V Workshop on RPCs and related detectors