ITEP Beam Chambers P.Gorbunov (U. of Toronto and ITEP, Moscow)

1. ITEP Beam ChambersP.Gorbunov (U. of Toronto and ITEP, Moscow) • Features: • X-Y MWPCs with cathode DL r/o • working area: 120×120 mm2 • gas: Ar-CO2 (80:20); HV: 2.25 kV • detection efficiency ≈ 100% • accuracy: 120 – 200 μ • readout channels: 6 (analog) • availability: 4 (currently in H6) • built in 2002 • Successfully used in Fcal TB2003 and OPERA’2002 (nuclear emulsion) CBT EC2 Planning meeting CERN

2. Technical features • Two identical chambers (X- and Y-) in common housing • Anode planes: 25 wires, 20 μ, 6 mm spacing • Cathode planes: 31 wires, 100 μ, 4 mm spacing, ┴to anodes • Anode-to-anode: 26 mm • Calibration pulser signals can be injected to cathode wires 7,16 or 25 (3000 pulser events at start of each run) • Lumped delay line with 10 ns cells • More on the design and comparison with MC simulation: • cern.ch/atlas-fcaltb/Memos/Hardware/BPB/BPC_Note1-2003.pdf • cern.ch/atlas-fcaltb/Memos/Hardware/BPC/ITEP_BPC_design_Rus.doc (in Russian) • Real rate limit: ~30 kHz • No multitrack measurement (rejection only) CBT EC2 Planning meeting CERN

3. Readout electronics 10 ns±1% 4 mm • Analog constant-fraction shaping (to reduce time-walk) : front-end • TDC LeCroy 2228A (11 bit, 250 ps) • ADC LeCroy 2249A • Extternal NIM discriminators LeCroy 623 • Custom calibration pulser L calibration pulses R w7 w16 w25 D TDC ADC X ≈ GX ( tL– GRLtR - t0 ) CBT EC2 Planning meeting CERN

4. Y “old” ITEP BPCs CH#1 CH#2 CH#3 CH#4 X Y X Y X Y X Y X Y X Y cryostat beam Z B9 1.6 m Z 27 m X 2.2 m 27000mm 100mm ITEP BPCs in H6 beam line • two “stations” of 2 BPCs: near & far • an auxiliary mid-station with 4 “old” BPCs (300 μ resolution) • advantages of arranging BPCs in pairs: • better space resolution (<100 μ, important for the near station!) • δ-electron rejection (see below) • easier cabling CBT EC2 Planning meeting CERN

5. Space resolution σX(mm) • has been studied in dedicated test beam measurements, confirmed in H6: σ = 110-200 μ, depending on the hit position. • σ is ~constant across the measurement direction (across anodes) and deteriorates towards the edge cathode wires • MC shows that the tails of dX >1 mm are due to δ-electrons • The cut |dX|<1 mm has ε=97% (|dX|<0.5 mm: ε=95%) and largely eliminates δ-electrons 0.2 0.1 x dX (meas-pred), mm CBT EC2 Planning meeting CERN

6. BPC calibration • Internal calibration (GX, to) –with an external pulser, at start of run • GRLand G adjustment, mutial alignment of all chambers: with beam tracks • For most of the BPCs, the calibration drift during FCal TB runs was negligible. Exeptions: ch. 1 and one case of a faulty TDC to (Y5) to (Y1) GX (Y1) Bad TDC CBT EC2 Planning meeting CERN

7. Multi-track rejection >1 track • Can rely on external counters… trust but verify! • tR+ tLfor single tracks has a lower limit = Σ line delay • Anode signal amplitude Summary • ITEP BPCs: new beam chambers, designed for high-accuracy measurements • No visible ageing effects • robust, easy to maintain and read-out CBT EC2 Planning meeting CERN

8. BPC resolution: H6 data dX=X(1)-X(2), 30x40 mm2 dY=X(5)-X(6), 60x60 mm2 Y X X Y σ12≈150 μ σ56≈190 μ CBT EC2 Planning meeting CERN

9. Y D C B A X Impact point prediction Fcal1 Fcal-1 response, ADC counts X, cm Y, cm CBT EC2 Planning meeting CERN