1. PRODUCTION and CERTIFICATION of Multi Wires Proportional Chambers for the LHCb Muon System at CERN K.Mair for the LHCb Muon Group CERN* Poster anlässlich der 55. Jahrestagung der Österreichischen Physikalischen Gesellschaft, September 2005 * J.-S. Graulich (Université de Genève), A. Kachtchouk (Petersburg Nuclear Physics Institute), K.Mair (CERN), B. Schmidt (CERN), T. Schneider (CERN) 5 Muon Stations Calorimeters Tracker RICH-2 Vertex Locator Magnet RICH-1 Muon Detectors Iron Filters The Large Hadron Collider beauty experiment for precise measurements of CP violation and rare decays: The aim of the LHCb experiment is to fully investigate CP violation in the B d and B s systems, and to possibly reveal new physics beyond the Standard model. Multi Wire Proportional Chambers (MWPC) in the LHCb Muon System MWPC Production at CERN 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 500 kHz/cm 2 total of 1368 MWPC in the Muon System for fast muon triggering and offline muon identification Design Parameters: Wire: Gold-plated Tungsten, 30 μm Ø Wire spacing: 2 mm Wire length: 250 to 310 mm Wire mechanical tension: 65 gr Gas gap: 5 mm Gas mixture: Ar/CO 2 /CF 4 (40:55:5) Operation Voltage: HV = 2.650 kV Field on wires: 262 kV/cm Field on cathodes 6.2 kV/cm Gas gain: G ≈ 50 000 Gain uniformity: ≤ 30% Rate/channel: < 1 MHz Cross section of a 4-gap MWPC Anode Wires Cathode Pads Segmentation: Catode Pads on PCB with gold-coated copper foil Gold plated tungsten anode wires grouped in strips 4-gap MWPC-Sandwich: 2 double-side wired panels in between 3 non-wired cathode panels Chamber Certification 3. Gas Gain Uniformity Test 2. Chamber Conditioning 1. Gas Leak Test Wire Conditioning: apply negative HV up to -2300V tip-like dirt on wires → e - -emission electromagnetic wire cleaning test: apply positive HV up to +2900V check currents with radioactive source Cathode Conditioning: apply positive HV, turn gamma-ray on observe Malter currents due to deposits on cathode (~15% of all gaps) “heal” with gamma–ray exposure (GIF) and CF 4 (~ 100 hours exposure time) no dark current → conditioning finished Specifications: < 2 mbar leak / hour at 5 mbar overpressure Measurement principle: Test against a gas-tight-proved reference chamber measure overpressure for 4 hours measure internal parameters: T, P Procedure: panel fixed between 2 bolts along HV and read-out bar to guide wire 1 bolt ring-like, 1 bolt double spiral bolt pitch 2mm panel in wiring automate first wire aligned by hand, then automatic spooling wires glued and soldered to panel 2. Panel Wiring 3. Panel Finalization wires cutting components soldering final inspection (microscope) HV training 4. Chamber Assembly Automatic Wiring Machine sandwich: 3 non-wired, 2 wired panels gap size defined by 2.5 mm bars + 2.5 mm spacers between layers gas tight by O-rings T Ch = T Ref = const. dV/V ~ d(  P Ch -  P Ref )/P Ch absolute error on P atm cancels out Wiring Tolerances: nominal wire distance: 2 mm 95% of all distances within  50 μm all within  100 μm nominal wire tension: 65 gr all values above 50 gr 1. Panel Production Cathode Panel: Printed Circuit Board (PCB) coated by 35 μm copper 5 μm nickel, 0.2 μm gold Cathode Panel  TEST: half gap size HV bar read out bar side bar panel Non-wired Panels: Gas inlets Connectors for pad read out Kapton foil Wired Panels: 2 wire fixation bars (HV, read-out), 2 side-bars bar thickness defines half-gap size: 2.5 mm Precise bars gluing  TEST: wire pitch: measured by 2 cameras with telecentric lenses wire tension: measurement of wire oscillation, excited by high voltage pulses Specification: Nominal Gas Gain: G 0 = 50 000 uniformity within one gas gap: 95% of gap area must provide a gas gain within  30% G 0 uniformity between different gas gaps: average gap gas gain variation within  25% G 0 Principle: 241 Am source emits 60 keV gamma rays excitation of copper in panel → 8 keV gamma rays (absorption length less than 1 mm) photoelectric effect in Ar (gas) → electrons of few keV collected signal on anode → ADC counts distribution with peak position proportional to gas gain MWPC Sandwich Test setup Principle camera shot of 3 wires wire distance measurement wire pitch and tension measuring device Specification: half-gap size: 2.5 mm tolerance:  50 μm [mbar] Relative Gas Gain distribution over one gas gap relative gas gain [G 0 ] pad number in y pad nr in x wire sample