1. VCI 2004Gaia Lanfranchi-LNF/INFN1 Time resolution performances and aging properties of the MWPC and RPC for the LHCb muon system Gaia Lanfranchi – INFN/LNF on behalf of the LHCb muon group on behalf of the LHCb muon group Overview Overview MWPC design; MWPC design; Time resolution performances; Time resolution performances; Aging properties; Aging properties; RPC aging results. RPC aging results. Conclusions. Conclusions.

2. VCI 2004Gaia Lanfranchi-LNF/INFN2  5 muon stations, one in front (M1), 4 behind (M2-M5) the calorimeters.  Muon detector must provide high-pt L0 muon trigger through a coincidence of hits in all five stations within the bunch crossing time of 25 ns.  The muon momentum must be measured with δp t /p t ~ 20% accuracy. The LHCb Muon Detector M1 M2 M5 M3 M4 R4 R3 R2 R1

3. VCI 2004Gaia Lanfranchi-LNF/INFN3 Requirements:  High (> 99%) efficiency per station in a 20 ns time window:  good time resolution  Good rate capability: up to ~200 kHz/cm 2 @ L = 510 32 cm –2 s -1 in hottest region;  fast  Aging resistant: up to integrated charge ~ 1 C/cm for safe operation in 10 years @ = 210 32 cm –2 s -1.

4. VCI 2004Gaia Lanfranchi-LNF/INFN4Options: M4M5 M1 M2 M3 MWPC GEM RPC ~48% RPC ~ 52% MWPC ~ 0.1% GEM : M1R1, rate ~ 500 kHz/cm 2. ~ 99.9 % MWPC ~435 m 2, 1380 chambers

5. VCI 2004Gaia Lanfranchi-LNF/INFN5 MWPC design  4 wire layers ( for time resolution and redundancy);  5 mm gas gap;  2 mm wire pitch ( gold plated tungsten wires, 30 μm diameter ). Cathode PCB Structural Panel (poliuretanic foam) 2 layers are OR-ed in one FE channel 2 FE channels OR-ed on FE board HV 4 separate HV supplies the anode wires Gold plated cathode pads

6. VCI 20046 MWPC operating parameters:  Gas mixture: Ar/C0 2 /CF 4 (40:40:20);  Working point: Gain~ 510 4, total avalanche charge per mip ~ 0.4 pC  Field on wires: 212 kV/cm, field on cathodes: ~ 5 kV/cm. Drift velocity almost saturated at ~ 90-100 μm/ns For 6 GeV muons we expect about: ~ 45 clusters/cm, 53 e-/gap. clusters/cm Drift velocity: 6 GeV

7. VCI 2004Gaia Lanfranchi-LNF/INFN7 Different readouts and detector capacitances pose special requirements to the FE-chip. MWPC readout schemes: R4: wire pad readout R3: cathode pad readout R1/R2-M2/M3: mixed readout Wire pad, cathode pad and mixed (wires+cathode pads) readout schemes depending on the granularity requested from trigger and offline and on the particle rates. Granularity goes from (1x2.5)cm 2 to (25x30) cm 2 MWPC dimensions from (20x48)cm 2 to (149x31)cm 2

8. VCI 2004Gaia Lanfranchi-LNF/INFN8 A small MWPC prototype: panel Gold plated cathode pads 4 gaps Lateral bars of FR4

9. VCI 2004Gaia Lanfranchi-LNF/INFN9 Photos M2R4 – wire readout M3R3 – cathode readout M2R1 prototype (mixed readout) ~ 15 prototypes built and tested with (almost) final front-end electronics at T11 test beam area at CERN.

10. The Front-End Electronics: the CARIOCA chip Specifications important for time resolution and rate capability:  short peaking time: tp ~ 10 ns for Cdet = (40  220) pF  low noise: ENC ~ 2000+40 e-/pF  high rate capability:  pulse width ~ 50 ns, signal tail cancellation and baseline restoration circuits. Carioca is the Amplifier-Shaper-Discriminator front-end chip developed for MWPC of LHCb. (documentation in: http://www.cern.ch/riegler)

11. VCI 200411 Time resolution: rms = 3.5 ns rms = 4.3 ns rms = 7.4 ns 20 ns time window  ε (quadrigap station) > 99% in 20 ns time window;  ε (double gap)  95% in 20 ns time window  time rms for double gap < 5 ns Double Gap Time Resolution: Double Gap Time Spectra: Cathode pad readout 5 ns

12. VCI 2004Gaia Lanfranchi-LNF/INFN12 Time resolution and efficiency ε(double gap)  95% in 20 ns  rms (double gap)  5 ns:  HV(95%) = 2.45 kV for wires readout;  HV(95%) = 2.55 kV for cathodes/mixed readout; Double gap efficiency for cathode readout Working Point = 2.6 kV

13. VCI 200413 Time Resolution and Efficiency Uniformity: Example of uniformity measurements on a M3R3 prototype with cathode pad readout: > 99% pads are inside the specifications Time resolution:Double Gap Efficiency in 20 ns: 5 ns 95 % Pad number Time rms = (4.3  0.2) ns ε (HV=2.6 kV) = (96.7 ±0.1) %

14. VCI 2004Gaia Lanfranchi-LNF/INFN14 High Rate behavior Time resolution stable (no space charge effects) Small Efficiency drop due to signal pile-up Test @ GIF up to 500 kHz/FEE channel: ~ 2%

15. VCI 2004Gaia Lanfranchi-LNF/INFN15 Aging Test of MWPCs - Q < 10 mC/cm for 76% of area. - 10 mC/cm <Q < 100 mC/cm for 19% of area. - 100 mC/cm < Q < 1 C/cm for 5% of area. - Particle rates are from LHCb-Muon TDR2001. - Safety factors of have been included to take into account the deposited charge of low energy background hits. Integrated charges in 10 years @ 210 32 cm -2 s -1

16. VCI 2004Gaia Lanfranchi-LNF/INFN16 Aging tests @ ENEA Casaccia Calliope Facility:  Source 60 Co (~ 10 15 Bq), ~ 1.25 MeV.  3 MWPC irradiated with dose rates up to ~ 0.3 Gy/hr and different gas flows (vented and re- circulating gas system).  Standard mixture: Ar:C0 2 :CF 4 =40:40:20  Gas gain ~ (1  1.5) 10 5 (~double wrt to the nominal one). LNF,CERN1, CERN2 PC Co 60 HV CONTROL ROOM 4.5 m P T window ~0.3 Gy/hr

17. VCI 200417 Gas System: Chambers materials: LNF chamber: Adekit 140 for chamber closing. CERN chambers: Natural rubber O-rings. Kapton foils to protect HV-traces and glued with epoxy. Low temperature soldering, carbon film resistors and SMD capacitors. CERN CHAMBERS Common Materials: Gold plated 30 μm tungsten wires. Gold plated cathode pads. Adekit 145/450 epoxy for wire glueing.  One bottle of each gas (Ar, CO 2, CF 4 ).  Mass flowmeter with ORing in Viton.  Total gas flow: 40/40/20 cc/min = 6 l/hr to mixer.  Typical flows: Open Mode ~ 4.8 l/hr (~2 volumes/hr of LNF) Closed Loop: fresh gas ~1.35 l/hr, circulating gas:~ 5.2 l/hr  All pipes in Copper except 10 cm connections to chambers in Rilsan + brass connectors. (with final components)

18. VCI 2004Gaia Lanfranchi-LNF/INFN18 Aging tests @ ENEA Casaccia Calliope Facility  32 days of tests.  Integrated charge per cm of wire: Q ~ (440  480) mC/cm  (5  10) years depending on the rate evaluation.  Typical current density: I ~ (1÷1.4) µA/cm 2 (active areas = 500÷1200 cm 2 );  In each chamber, one gap (out of 4) was switched on only for short periods to be used as reference. Integrated Charge: Reference gap test gaps

19. VCI 200419 Aging tests @ ENEA Casaccia Calliope Facility  We normalized the currents of tested gaps respect to the reference gap in order to remove T and P dependence and accidental gas mixture changes.  Current ratios are constant within ~10% for all chambers. Current ratios – vented mode Current ratios - closed loop ~ 4% ~ 8% Malter currents: The self-sustaining rest currents were measured following the source off, using current monitors with a resolution of 1 nA.  All gaps of all chambers draw currents of the order of few tens of nA or smaller with a decreasing trend.

20. VCI 2004Gaia Lanfranchi-LNF/INFN20 Photo 0 SEM Analysis of Wires Wires are clean

21. VCI 2004Gaia Lanfranchi-LNF/INFN21 Photo 1 Boundary of FR4 etching Etching of the FR4 frame: The FR4 is etched also where there is no electric field. This effect is visible also in the reference gap :  due to ionized gas fluorine etching.

22. VCI 2004Gaia Lanfranchi-LNF/INFN22 The etching of the FR4 frame goes with the gas flow : B1 gap, “gas in”side B2 gap, “gas in” B2 gap, “gas out”A2 gap, “gas in” No etching…. …No etching…. …No etching yet…...Etching starts… …FR4 etched....FR4 etched!! A2 gap, “gas out” B1 gap, “gas out” Photo 2 Gas flow direction: B1  B2  A2  A1, B1=reference gap

23. VCI 2004Gaia Lanfranchi-LNF/INFN23 Photo 3 “Bumps” under the guard strips of the cathode pads (not found in the reference gap)

24. VCI 2004Gaia Lanfranchi-LNF/INFN24 Conclusions on the MWPC aging test  In 32 days we integrated up to Q~480 mC/cm corresponding to 5  10 years (depending on the rates foreseen) of LHCb @ 2 10 32 cm -2 s -1.  Materials exposed to CF 4 under irradiation show a surface etching BUT no drop in gas gain observed within 10%:  we decided do not change chamber design and materials.

25. VCI 2004Gaia Lanfranchi-LNF/INFN25 RPC for LHCB Muon System M1M2M3M4M5 R1 R2 R3 0.75 1.1 0.65 1.0 R4 0.25 0.4 0.23 0.3 RPC Historical review 1998: RPC were proposed for LHCb Muon detector in regions with rates < 1 kHz/cm 2. 1999: 2 prototypes built with identical characteristics: - bakelite electrodes (ρ ~ 10 10 Ω cm); - linseed oil; - graphite ( 100 kΩ/) ; - 50 x 50 cm 2 area. - 2 mm gas gap (C 2 H 2 F 4 : iC 4 H 10 : SF 6 = 95:4:1) - avalanche mode (HV ~10.6 kV). 2000: rate capability was measured to be  3 kHz/cm 2 (NIM A 456 (2000) 95.) 2001: an extensive test for study the aging properties started at GIF… Rates (kHz/cm 2 ) and integrated charge (C/cm 2 ) for L = 510 32 cm -2 s -1

26. VCI 2004Gaia Lanfranchi-LNF/INFN26 Aging test in 2001 @ GIF  RPC A irradiated at GIF during 7 months up to Q~ 0.4 C/cm 2.  RPC B not irradiated, used as reference.  I, V 0 and T continuously monitored.  Bakelite resistivity ρ extracted from (I,V 0 ) curve using a model for RPC operating under high flux conditions ( NIMA 498 (2003) 135) and corrected for T dependence. RPC A (high flux):Q A ~0.4 C/cm 2 RPC B (low flux): Q B ~ 0.05 C/cm 2 GIF test setup

27. VCI 2004Gaia Lanfranchi-LNF/INFN27 Aging test in 2001 @ GIF: RPC A results Integrated charge (mC/cm 2 ) ρ (T=20°) (10 10 Ωcm) jan01 aug01 dec01 mar01 month Q ~ 420 mC/cm 2 ρ ~ 40 10 10 Ωcm irradiation ρ ~ 6 10 10 Ωcm Observed a steady increase of ρ with and without irradiation. no irradiation ρ ~ 70 10 10 Ωcm

28. VCI 2004Gaia Lanfranchi-LNF/INFN28 Aging test in 2002 @ GIF  Both detectors slowly irradiated ( Q~0.05 C/cm 2 accumulated charge ).  Resistivity continuously measured during ~ 350 days.  Observed a steady increase of ρ with time for both deterctors probably due to drying up of bakelite.  Addition of 1.2% of H 2 O vapor to the nominal gas mixture produced a decrease of resistivity. This effect in any case disappeared as soon as dry gas was flowed. ρ ~ 200 10 10 Ωcm RPCARPCB ρ ~ 220 10 10 Ωcm ρ ~ 10 10 10 Ωcm ρ ~ 70 10 10 Ωcm H 2 O vapor

29. VCI 200429 RPC Rate capability T=25.0 o C T=24.5 o C  HV HV  August 2001: ρ = 4010 10 Ωcm (T=20°)July 2002: ρ = 11010 10 Ωcm (T=20°) Rate capability ~ 640 Hz/cm 2 @ 20 o C Rate capability ~ 200 Hz/cm 2 @ 20 o C These results brought the LHCb Collaboration to abandon the RPC technology for the Muon Detector.

30. VCI 2004Gaia Lanfranchi-LNF/INFN30 Conclusions  Three years of extensive tests showed that our design of MWPCs operating with CF 4 based gas mixture satisfies all the requirements for the LHCb Muon System.  We built a fast detector, with good time resolution and aging resistant.  It will cover ~ 435 m 2 area with ~ 1380 chambers and ~126000 readout channels.  The production is started and the detector should be ready for the 1st LHC beams.

31. VCI 2004Gaia Lanfranchi-LNF/INFN31 Spares:

32. VCI 200432 Gas System:  One bottle of each gas (Ar, CO 2, CF 4 ).  Mass flowmeter with ORing in Viton.  Total gas flow: 40/40/20 cc/min = 6 l/hr to mixer.  Typical flows: Open Mode ~ 4.8 l/hr (~2 volumes/hr of LNF) Closed Loop: fresh gas ~1.35 l/hr, circulating gas:~ 5.2 l/hr  All pipes in Copper except 10 cm connections to chambers in Rilsan + brass connectors. Ar GAS SYSTEM CO2 CF4 REF(A,B)LNFCERN 2 REF(C,D)CERN 1 Fresh gas Circulating gas CLOSED LOOP OPEN MODE Exhaust ( with final components)

33. VCI 2004Gaia Lanfranchi-LNF/INFN33 Mechanical Tolerances:  The specifications for a single gap were defined such as the gas gain is within : - 0.8*G 0 and 1.25*G 0 in 95% of the chamber area; - G 0 /1.5 and 1.5*G 0 in 5% of the chamber area.  What chamber imperfections are allowed in order to keep the gain within specifications? SPECIFICATIONS: Gap: 95% in  90 µm 5% in  180 µm Wire pitch: 95% in  50 µm 5% in  100 µm Wire y-offset: 95% in  100 µm 5% in  200 µm Wire plane y-offset: 95% in  100 µm 5% in  200 µm  The most critical parameter for our chambers is the gap dimension !!

34. VCI 2004Gaia Lanfranchi-LNF/INFN34 Measurement of gain uniformity: A:B: C: D: good ~ good very good ~ good -We scan each gap using a radioactive source ( 137 Cs, 40 mCi, 0.66 MeV photons). -The current drawn by group of wires is measured by a nano-amperometer with 1 nA resolution. 137 Cs source Lead case 137 Cs source Lead case MWPC

35. VCI 2004Gaia Lanfranchi-LNF/INFN35 M1M2M3M4M5 R1 460 GEM 37.5 mixed r/o 10 mixed r/o 6.5 cathode r/o 4.4 cathode r/o R2 186 GEM or MWPC 26.5 mixed r/o 3.3 mixed r/o 2.2 cathode r/o 1.8 cathode r/o R3 80 cathode r/o 6.5 cathode r/o 1.0 cathode r/o 0.75 cathode r/o 0.65 cathode r/o R4 25 wires r/o 1.2 wires r/o 0.4 wires r/o 0.25 wires r/o 0.23 wires r/o Rates and Readout

36. VCI 2004Gaia Lanfranchi-LNF/INFN36 Average rates and Integrated Charges: - Rates (TDR2000) and integrated charges in 10 equivalent (~ 10 8 s) years for average luminosity = 2 10 32 cm -2 s -1, - Safety factors (2 in M1 and 5 in M2-M5) are included. M1M2M3M4M5 R1 184 GEM 15 132 MWPC 4 35 MWPC 2.6 46 MWPC 1.76 31 MWPC R2 74.4 328 GEM or MWPC 10.6 185 MWPC 1.32 25 MWPC 0.88 16 MWPC 0.72 13 MWPC R3 32 141 MWPC 2.6 46 MWPC 0.4 7 MWPC 0.3 6 MWPC 0.26 5 MWPC R4 10 44 MWPC 0.48 4.3 MWPC 0.17 1.5 MWPC 0.1 1 MWPC 0.09 0.8 MWPC kHz/cm 2 mC/cm

37. VCI 2004Gaia Lanfranchi-LNF/INFN37 MWPC readout schemes: rates + granularity M1M2M3M4M5 R1 460 1x2.5 GEM 37.5 0.6x3.1 mixed r/o 10 0.67x3.4 mixed r/o 6.5 2.9x3.6 cathode r/o 4.4 3.1x3.9 cathode r/o R2 186 2x2.5 GEM 26.5 1.3x6.3 mixed r/o 3.3 1.35x3.4 mixed r/o 2.2 5.8x7.3 cathode r/o 1.8 6.2x7.7 cathode r/o R3 80 4x10 cathode r/o 6.5 2.5x12.5 cathode r/o 1.0 2.7x13.5 cathode r/o 0.75 11.6x14.5 cathode r/o 0.65 12.4x15.5 cathode r/o R4 25 8x20 wires r/o 1.2 5x25 wires r/o 0.4 5.4x27 wires r/o 0.25 13.1x29 wires r/o 0.23 24.8x30.9 wires r/o

38. VCI 2004Gaia Lanfranchi-LNF/INFN38 Comparison with simulations  Comparison with simulations has been done by plotting double gap efficiency and time resolution as a function of threshold.  The threshold is expressed as a fraction of the average signal in order to be independent from the gain.  Full simulation: - primary ionization (HEED); - drift, diffusion (MAGBOLTZ); - induced signals (GARFIELD). Good agreement between data and simulations

39. VCI 2004Gaia Lanfranchi-LNF/INFN39 Efficiency and crosstalk Crosstalk: probability of firing the neighboring pad Pt accuracy measurement requires: Crosstalk < 5% Main source is the pad-to-pad capacitive coupling (crosstalk ~ s Rin Cpp) ~4% 2.6 kV Crosstalk in 20 ns TW Efficiency in 20 ns

40. VCI 2004Gaia Lanfranchi-LNF/INFN40 The ATLAS Cathode Strip Chambers are intended for position resolution. Amplifier peaking time 80ns, bipolar shaping, ‘crosstalk intended’ on cathode strips for center of gravity. The CMS Cathode Strip Chambers are intended for position resolution (cathodes strips) and timing (wires). Cathode amplifier peaking time 100ns, wire amplifier peaking time 30ns. The LHCb MWPCs are intended for highly efficient timing within a certain spatial granularity at the LVL0 trigger. Amplifier peaking time of 10ns, pulse width<50ns, unipolar shaping, low crosstalk. Since crosstalk is   R in C pp and since  (  20 MHz) is high we have to minimize the pad-pad capacitance C pp and amplifier input impedance R in. Because we want unipolar shaping we need a baseline restorer in the front end. Comparison with ATLAS/CMS

41. VCI 2004Gaia Lanfranchi-LNF/INFN41 Principle of RPC operation qiqi ---- ------- +++++++ ++++ q=Gq i V0V0 gas Electrodes d,S,  particle G~10 6 -10 7 ; G  1 for V 0 < V T Due to space-charge effects (especially with SF 6 ): q  V gap -V T V gap =V 0 -IR I =  q(V gap ) (  = particle flux) If  low  I small  V gap  V 0

42. VCI 2004Gaia Lanfranchi-LNF/INFN42 Principle of RPC operation qiqi ---- ------- +++++++ ++++ q=Gq i V0V0 gas Electrodes d,S,  particle G~10 6 -10 7 ; G  1 for V 0 < V T Due to space-charge effects (especially with SF 6 ): q  V gap -V T V gap =V 0 -IR I =  q(V gap ) (  = particle flux) If  low  I small  V gap  V 0

43. VCI 2004Gaia Lanfranchi-LNF/INFN43 High flux conditions If    we must have q  0, i.e. V gap  V T and I max =(V 0 – V T )/R Linear dependence on HV Exponential temperature dependence of I via R: More generally: Saturation with flux

44. VCI 2004Gaia Lanfranchi-LNF/INFN44 Principle of RPC operation qiqi ---- ------- +++++++ ++++ q=Gq i V0V0 gas Electrodes d,S,  particle G~10 6 -10 7 ; G  1 for V 0 < V T Due to space-charge effects (especially with SF 6 ): q  V gap -V T V gap =V 0 -IR I =  q(V gap ) (  = particle flux) If  low  I small  V gap  V 0

45. VCI 2004Gaia Lanfranchi-LNF/INFN45 High flux conditions If    we must have q  0, i.e. V gap  V T and I max =(V 0 – V T )/R Linear dependence on HV Exponential temperature dependence of I via R: More generally: Saturation with flux

46. VCI 2004Gaia Lanfranchi-LNF/INFN46 Current saturation X obtained fitting I at different  At GIF   1/Abs 0.7 where Abs is the filter setting (Abs=1,2,5,.......) (1)

47. VCI 2004Gaia Lanfranchi-LNF/INFN47 Principle of RPC operation Electrodes d,S,  G~10 6 -10 7 ; G  1 for V 0 < V T Due to space-charge effects (especially with SF 6 ): q  V gap -V T V gap =V 0 -IR I =  q(V gap ) (  = particle flux) qiqi ---- ------- +++++++ ++++ q=Gq i V0V0 gas particle If  low  I small  V gap  V 0

48. VCI 2004Gaia Lanfranchi-LNF/INFN48 High flux conditions If    we must have q  0, i.e. V gap  V T and I max =(V 0 – V T )/R Linear dependence on HV Exponential temperature dependence of I via R: More generally: Saturation with flux I =  q(V gap ),  = particle flux, q = G q i qiqi --- - --- --- - +++ +++ +++ ++ q= Gq i V0V0 gas particle

49. VCI 2004Gaia Lanfranchi-LNF/INFN49 Current saturation X obtained fitting I at different  At GIF   1/Abs 0.7 where Abs is the filter setting (Abs=1,2,5,.......) (1)

50. VCI 2004Gaia Lanfranchi-LNF/INFN50 Measurement of R  R can be measured in a non-destructive way from the slope of I-V 0 curve  Its changes can be easily monitored  Precise knowledge of X is unimportant if X is large (an estimate is sufficient) We can obtain R by fitting I vs. V 0 curve