1. 1 VCI, 21. 2. 2001 1Werner Riegler RPCs and Wire Chambers for the LHCb Muon System  Overview  Principles  Performance Comparison: Timing, Efficiency, Crosstalk  Conclusion Werner Riegler, CERN

2. 2 VCI, 21. 2. 2001 2Werner Riegler The LHCb Experiment  A muon trigger is given by a coincidence of all 5 muon stations within 25ns  >99% efficiency/station in 20ns time window  Time resolution <3ns  Up to 100kHz/cm 2  50% Wire Chambers(MWPCs) 50% RPCs (<1kHz/cm 2 )  1 Station: 4 MWPC Layers or 2 RPC Layers

3. 3 VCI, 21. 2. 2001 3Werner Riegler Geometry and Materials  2mm gas gap  2mm Bakelite  = 9x10 9  cm  Linseed oil  Carbon 100 k  /square  Readout pads on 200  m PET  5mm gas gap  30  m wire  1.5mm wire pitch  Readout pads on 1.6mm G10 RPCMWPC

4. 4 VCI, 21. 2. 2001 4Werner Riegler Segmentation RPCMWPC 140-150cm 29-31cm

5. 5 VCI, 21. 2. 2001 5Werner Riegler Simulation Tools  Garfield (Rob Veenhof) electric fields, particle drift, induced signals….  Magboltz (Steve Biagi) transport properties of gas mixtures Townsend coefficient and gas gain from data  Heed (Igor Smirnov) charge deposit of fast particles in gas mixtures  Maxwell (Ansoft) weighting fields, capacitances, inductances

6. 6 VCI, 21. 2. 2001 6Werner Riegler Operating Parameters  C 2 H 2 F 4 /i-C 4 H 10 /SF 6 95/4/1  10kV on carbon  50kV/cm in gas gap  Ar/CO 2 /CF 4 40/50/10  3150V on wire  8kV/cm on cathode, 260kV/cm on wire RPCMWPC

7. 7 VCI, 21. 2. 2001 7Werner Riegler Primary Ionization, Drift, Gain  20.2 clusters in 2mm for 10 GeV muon (Heed)  v  100  m/ns (50kV/cm,assumed)  Limited space charge mode -not included in simulation  Average total charge induced by electrons =1.5pC (  eff  95cm -1 )  Total avalanche charge=37pC  21.4 clusters in 5mm for 10 GeV muon (Heed)  v  90  m/ns (8kV/cm, Magboltz)  Proportional mode  Average total charge induced on cathode = 0.37pC (gain=10 5 )  total avalanche charge=0.74pC RPCMWPC

8. 8 VCI, 21. 2. 2001 8Werner Riegler Signal Characteristics RPCMWPC Induced signals mA AA

9. 9 VCI, 21. 2. 2001 9Werner Riegler Signal Characteristics  Only electron signal visible  Maximum signal duration < d/v  20ns  Ions take  2  s to Bakelite  Electron+ion signal visible t 0  1.5ns  Signal length  50ns (after electronics shaping)  Ions take  20  s to the cathode RPCMWPC

10. 10 VCI, 21. 2. 2001 10Werner Riegler Charge Spectra RPCMWPC Saturation neglected

11. 11 VCI, 21. 2. 2001 11Werner Riegler Intrinsic Timing Time r.m.s. EfficiencyEfficiency in 20ns RPCMWPC Time r.m.s.

12. 12 VCI, 21. 2. 2001 12Werner Riegler Electronics Electronics  Intrinsic timing is of order of 3ns r.m.s.  Longer integration time in order to collect a few clusters  ATLAS GaAs chip: 160MHz Bandwidth  CMS RPC chip: few ns rise-time  ‘Amplifier should have the same rise-time as the RPC signal in order to fully exploit the intrinsic timing of the detector’ RPCMWPC

13. 13 VCI, 21. 2. 2001 13Werner Riegler Electronics Time r.m.s. for different preamp peaking times RPCMWPC

14. 14 VCI, 21. 2. 2001 14Werner Riegler Direct Induction Crosstalk  For a 2.5cm strip the cluster size is  1.2 from direct induction (at our working point) RPCMWPC

15. 15 VCI, 21. 2. 2001 15Werner Riegler Electrical Crosstalk  Inhomogeneous lossless N-conductor transmission line  Completely defined by capacitance and inductance matrix (NxN) which can be calculated with MAXWELL RPCMWPC

16. 16 VCI, 21. 2. 2001 16Werner Riegler Electrical Crosstalk  N different velocities (modal dispersion)  For termination we theoretically need 0.5N(N+1) termination resistors  Crosstalk depends on distance of the signal from preamp  For long strips crosstalk is smaller for slow amplifiers

17. 17 VCI, 21. 2. 2001 17Werner Riegler Electrical Crosstalk Far end: Ideal termination Preamp End: Crosstalk is minimal for R in = 0 You do NOT want to terminate there !

18. 18 VCI, 21. 2. 2001 18Werner Riegler Rates+Ageing   1kHz/cm 2   100 Gray in 10 LHC years  Carbon layer ?  Bakelite resistivity ?  Surface effects ?  up to 100kHz/cm 2 (space charge effects expected only at 1MHz/cm 2 )   0.7C/cm wire in 10 LHC years RPCMWPC  Tests are ongoing

19. 19 VCI, 21. 2. 2001 19Werner Riegler Measured Performance Measured Performance RPC EfficiencyMWPC efficiency

20. 20 VCI, 21. 2. 2001 20Werner Riegler Conclusion  Single Gap RPCs and MWPCs for the LHCb muon system have been studied in detail.  The intrinsic time resolution is  1.2ns for 2mm RPCs and  3ns for 5mm MPWCs (1.5mm wire pitch).  For high threshold, RPCs lose their efficiency due to small pulses while MWPCs lose their efficiency due to decreasing time resolution.  Apart from avalanche saturation effects the detectors can be simulated very well in every detail (gas, signals, crosstalk …)  Measurements and simulations agree well on the 10-20% level - we have a ‘clue’ what we are doing.  Double RPC layers and 4xMWPC layers fulfill the requirements for the LHCb muon system.  The crucial issue will be the long term stability of the system ….