Performance and Aging of the BaBar Drift Chamber

Transcription

1 A B Performance and Aging of the BaBar Drift Chamber Michael H. Kelsey Stanford Linear Accelerator Center BAB R & L. de r unhoff 2008 Super B Factory Workshop, SLAC February 2008

2 Outline Drift Chamber Design and Operation Aging and Wire Damage Tracking, de/dx, and Physics Data Acquisition Upgrade Summary Michael H. Kelsey SuperB

3 BaBar Drift Chamber IP Dimensions in mm 24 cm inner radius 81 cm outer radius 2.8 m length IP 37 cm behind center Be & Al inner cylinder Carbon fiber/nomex outer 2.5 (1.2) cm Al end plates All electronics on rear Michael H. Kelsey SuperB

4 BaBar Drift Chamber Small hex cells (1 2 cm) HEX2 - Wire 168 Isocrones every 50 ns HEX2 - Wire 185 Isocrones every 50 ns 10 superlayers of 4 layers each Axial and stereo ( 4 ) cells/superlayer Sense wires 20 µm W-Rh (Au) Field wires 120 µm Al (Au) Guard wires 80 µm Al (Au) Michael H. Kelsey SuperB

5 Construction High-bay Class 1000 clean room at TRIUMF Chamber volume enclosed in Class 100 clean tent Measured at particles/m 3 No contact with wire in chamber or inner surfaces Automated wire stringing Operators attached wire from spool to steel rod Pulled by robot (magnet grip) to opposite endplate Feedthroughs, crimping outside clean tent Michael H. Kelsey SuperB

6 Operating Parameters Gas mixture 80% helium, 20% isobutane, ppm water, 80 ppm O 2 Designed to operate at 1960V Initially operated without water vapor Discharges observed in small region of chamber Reduced to 1900V (October 1999 July 2000) 1930V January 2001 December V since January 2007 Michael H. Kelsey SuperB

7 Initial Damage May 1999: 80:20, O 2 < 10 ppm, H 2 O < 100 ppm 28 July 1999: Large spikes in HV current Current (µa) HV problem in SL6, OUT y(cm) Hit Map High Charge 2000/05/ Current (µa) Day in July Minutes from 7/28/99 7 AM x(cm) October 1999: Turned off affected region, added water = No discharges observed in chamber since Michael H. Kelsey SuperB

8 Gain vs. Time Expect continuous decrease G = G 0 exp( AQ) due to aging (charge accumulation) DCH Gain Since Startup (May Present) Corrected Gain A B C D E F Accumulated Charge (mc/cm) Steps due to operating changes (voltage), transitions between runs (gas mix), etc. Michael H. Kelsey SuperB

9 Gain vs. Time G(Q) = {G 0 + G i Q>Qi } exp( AQ) Corrected Gain DCH Gain May Feb 2008 Aging rate: ± %/(mc/cm) over mc/cm Accumulated Charge (mc/cm) Michael H. Kelsey SuperB

10 Long-term Effects Sudden damage always a concern, not observed Transient discharges, voltage trips Buildup of deposits on wires Self-sustaining discharge (Malter effect) Long-term studies of aging remediation Lu Changguo (Princeton) Pisa Frontier Detectors Meeting (2003) Adam Boyarski (SLAC) DESY Aging Workshop (2001) IEEE NSS/MIC (2003) Other groups (Colorado, Montreal, Novosibirsk,...) Accumulated several lifetime dose Michael H. Kelsey SuperB

11 Suppressing Damage Running chamber without water vapor allows polymer (dielectric) buildup, increases likelihood of discharges Presumed mechanism for damage seen in July 1999 Princeton test chamber run dry up to 130 mc/cm, saw discharges, high singles rate, 10% drop in gain Adding ppm H 2 O eliminated discharges Gain stabilized at 0.9 of initial value, up to 300 mc/cm Poor performance returned when water removed Michael H. Kelsey SuperB

12 Reconstruction Performance Hit resolution σ(resid) 125 µm Target: 140 µm in middle region of cell Momentum σ(p T )/p T = 0.45% % p T (GeV/c) Target: 0.21% % p T Tracking > 95% matching with SVT de/dx resolution 7.5%, ± ( )% bias Early test results: 7.0% Michael H. Kelsey SuperB

13 Physics Performance Reconstruction of K 0 S π + π at large radii 2 MeV/c BeamPipe SVT RMS hwhm Support DCH Fits in DCH comparable to DCH+SVT Decay Radius ) 2 Events/(0.5 MeV/c o N. Entries = 4932 Sig. Events = mean = MeV RMS = MeV χ 2 /Ndof = /192 hwhm = MeV frac1 = sigma1 = MeV frac2 = sigma2 = MeV frac3 = sigma3 = MeV frac4 = 0 sigma4 = 0.5 MeV Decay Radius (X Vtx 2 +Y Vtx ) o 2 M(π + π - ) GeV/c )-M(K s Jumps due to material scattering uncertainty and fewer hits per track fit Michael H. Kelsey SuperB

14 High Rate Data Acquisition Modular, parallel electronics 4-buffer pipeline per channel FEA 3 FEA 2 FEA ch 144 ch 96 ch 24 ch 16x FEE to DIOM 16 elements per quadrant via 1 GHz fiber to processor Original 1995 design Readout time set by single element s occupancy { } N (32mi + 4) T DAQ = ns N non-empty chips, m i = 1 8 wires (32 bytes) each = 45 hits requires 200 µs (5 khz) Michael H. Kelsey SuperB

15 High Rate Data Acquisition Replace multiplexer with modern FPGA Implement feature extraction in firmware Charge (waveform) integration Leading edge (hit time) finding Pedestal subtraction Calibration constants in FPGA memory Data volume reduced 32 6 bytes/channel Identical data format used for reconstruction Essentially no deadtime up to 10 khz trigger rate Michael H. Kelsey SuperB

16 Front-end Upgrade New boards installed during Run 5 (Oct 2005) Improved diagnostics, programmability vs. original Firmware downloadable through FPGA to EPROM via normal DAQ path Pass-through firmware (emulates original frontend) software selectable through DAQ command Michael H. Kelsey SuperB

17 Summary BaBar Drift Chamber operated for nine years Tracking performance up to design de/dx performance good Excellent operational efficiency No substatial problems after startup Excellent aging rate 0.3% / (mc/cm) Clean-room construction, comprehensive QA/QC procedures Real-time monitoring of environment and data quality Electronics upgraded to support luminosity Michael H. Kelsey SuperB

18 Supplemental Information Michael H. Kelsey SuperB

19 Michael H. Kelsey SuperB

20 The PEP-II B Factory Asymmetric e + e collider: E(e + ) = 3.1 GeV, E(e ) = 9 GeV GeV CMS: Υ(4S) B + B, B 0 B 0 B decay length increased from 30 µm (CMS) to 250 µm (lab), allowing precision time-dependent measurements As of 2008/02/12 00:00 PEP-II delivers L > cm 2 s 1 (3 design) 433 fb 1 at Υ(4S), 9% off-peak ] Integrated Luminosity [fb BaBar Run 1-7 PEP II Delivered Luminosity: /fb BaBar Recorded Luminosity: /fb BaBar Recorded Y(4s): /fb BaBar Recorded Y(3s): 21.52/fb Off Peak Luminosity: 47.11/fb Delivered Luminosity Recorded Luminosity Recorded Luminosity Y(4s) Recorded Luminosity Y(3s) Off Peak 18 fb 1 at Υ(3S) = 30 fb 1 plan 200 BaBar operates at > 95% efficiency Michael H. Kelsey SuperB

21 BaBar Detector Michael H. Kelsey SuperB

22 BaBar Drift Chamber Main tracking detector in BaBar Surrounds beam pipe, final focus magnets, and silicon vertex tracker Michael H. Kelsey SuperB

23 Construction QA/QC Continuous QA/QC monitoring Tension measured during stringing Before and after crimping Daily evaluation of wires and feedthroughs Replacement done during subsequent shift Stringing completed in 3 months (Aug Nov 1997) Just 19 of 28,768 wires outside specification Tension, crimps, continuity Assembly fixture repositioned vertically Wires removed and restrung in situ Michael H. Kelsey SuperB

24 Commissioning Tested at voltage with operating gas Mixed in radioisotope ( 133 Xe) Pulses, singles rates measured for all 7,104 cells Shipped fully operational, ready for comissioning Commissioned at SLAC with production DAQ system before installation in IR-2 Michael H. Kelsey SuperB

25 Accumulated Charge Measure aging vs. accumulated charge per unit wire length cm 7104 cells = 19.6 km sense wire µa w/beams (0.25 na/cm) Recorded every second Accumulated Charge (mc/cm) DCH Dose May Feb Total charge 33.7 mc/cm in nine years Michael H. Kelsey SuperB

26 Quantifying Gain Normalize to absorb environmental effects Pressure and temperature density Detailed gas mixture (He:i-C 4 H 10, H 2 O, O 2 ) Precise operating voltage Compute de/dx for tracks from Bhabha-scattering events [e + e e + e (γ)] Relativistic plateau of Bethe-Bloch curve, fixed average value Normalization done hourly Michael H. Kelsey SuperB

27 Gain vs. Time Fit Details G(Q) = {G 0 + G i Q>Qi } exp( AQ) χ 2 /dof = / 418 A(%) = ± G 0 = ± G 1 = ± (Q 1 = 0.3) G 2 = ± (Q 2 = 1.2) G 3 = ± (Q 3 = 2.8) G 4 = ± (Q 4 = 4.4) G 5 = ± (Q 5 = 8.7) G 6 = ± (Q 6 = 19.0) G 7 = ± (Q 7 = 20.8) G 8 = ± (Q 8 = 22.4) G 9 = ± (Q 9 = 26.5) G 10 = ± (Q 10 = 32.5) Michael H. Kelsey SuperB

28 Other Chambers Aging [mc/cm] [%/(mc/cm)] Experiment Gas Mix Charge G/G Aging CDF Ar:Eth:Alc 130 <1 20 (Run 2) 50:50:1 ZEUS Ar:Eth:CO 2 83:5: < 0.1 H1 Ar:Eth:H 2 O 50:50:0.1 < 10 > 1 HERA-B Ar:CF 4 :CO none (test) 65:30:5 BaBar He:i-C 4 H 10 :H 2 O :20:0.4 From 2001 DESY Workshop presentations Michael H. Kelsey SuperB

29 Suppressing Damage Lu Changguo, Princeton Michael H. Kelsey SuperB

30 Suppressing Damage Lu Changguo, Princeton Michael H. Kelsey SuperB

31 Remediating Damage Excess current can trigger self-sustaining discharges Maximum safe current significantly reduced over time 500 Anode Current (na) Time (Min) Adam Boyarski, SLAC Training with oxygen (500 ppm) gradually raises current limit to original construction. Maintained after O 2 removed. Further study underway to confirm long-term performance Michael H. Kelsey SuperB

32 Remediating Damage Additives (alcohol, water, oxygen) can suppress discharges, allow running at higher currents Before With Additive After Additive (%) Imax Time (hr) Imax Imax Cured? Methylal >8 No No 2-Propanol >12 No 0.5 >10 No 0.25 > No H 2 O >27 No 0.18 >9 0.5 No O >32 >40 Yes >29 >16 Yes >35 >14 Yes CO >40 >27 Yes O 2 +H 2 O Partly ( ) Adam Boyarski, SLAC Temporary ppm O 2 running appears to cure discharge problem. Current limit restored to initial level. Michael H. Kelsey SuperB

33 Track Fitting Residuals of hits vs. distance from wire Resolution (cm) Mean 125 µm Signed distance from wire (cm) σ(resid) 125 µm Design target: 140 µm in middle region of cell d(t): pair of 7th order Chebyshev functions, each side of cell, corrected for angle and position in cell. Michael H. Kelsey SuperB

34 Track Fitting Momentum resolution from cosmic rays 2.0 σ(p t )/p t (%) A Transverse Momentum (GeV/c) σ(p T )/p T = 0.45% % p T (GeV/c) Design target: 0.21% % p T Michael H. Kelsey SuperB

35 Tracking Efficiency 1.0 Efficiency V 1900 V a) Transverse Momentum (GeV/c) Pseudo-efficiency Count DCH+SVT tracks vs. total SVT tracks Measure acceptance in 1.0 momentum or p T Efficiency V 1900 V polar angle azimuth (not shown) A Polar Angle (radians) b) DCH and SVT not independent Michael H. Kelsey SuperB

36 de/dx, Particle ID BABAR K π 10 3 e p<0.6 GeV/c d 0.6<p<0.8 p K π BA BAR µ Track momentum (GeV/c) K π π p>1 GeV/c 80% truncated mean (arbitrary units) <p<1 Drift Chamber K/π Separation de/dx vs momentum K π K (arb. units) DCH de/dx - de/dx(k) Good π/k separation up to 700 MeV/c Confirms results in DIRC region, adds PID coverage outside DIRC acceptance Michael H. Kelsey SuperB

37 Physics Performance (II) B D ( ) D ( ), D + π + D 0, D 0 K π + (Monte Carlo generated events) Momentum σ(p)/p D 0 K π + σ(mass) 6.5 ± 0.2 MeV/c 2 D π + D 0 σ(mass) 0.80 ± 0.03 MeV/c 2 Michael H. Kelsey SuperB

38 High Rate Data Acquisition Readout time scales with HV current, luminosity (uniform occupancy) Readout time (µs) I DCH (µa) Deadtime (%) Deadtime Projection Existing DAQ With upgrade Luminosity (x 10 cm -2 s -1 ) M. Cristinziani, 2004 C. Jessop, 2004 Readout trigger rate = non-linear deadtime Michael H. Kelsey SuperB