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HERA-B RICH

This report discusses the status of the HERA-B RICH detector, including its components, performance, ongoing activities, expected performance, issues in alignment and resolution, and the alignment of RICH with ECAL.

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HERA-B RICH

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  1. HERA-B RICH Fall ’99: Status and Prospects University of Texas at Austin University of Barcelona University of Coimbra, Portugal DESY, Hamburg University of Houston Northwestern University J. Stefan Institute and University of Ljubljana, Slovenia

  2. Detector Readout Cards 16 ch, using two ASD08 (amplifier, shaper, discriminator) chip each Base Board Socket, voltage divider, output circuitry for 4 multianode PMT’s Photon Detectors M16 PMT Hamamatsu 16-anode multiplier Plastic Molding Lens System 2:1 image reduction Spherical Mirrors Planar Mirrors Super Module Crate made from plastic molded iron sheets; magnetic shield and mounting structure C4F10 radiator 1488 M16’s 752 M4’s Photon Detectors

  3. Photon Detectors • ASD Summary • 4-8 single hot channels (faulty boards) • 3 full boards, 2 half-boards faulty • 90 dead channels (broken lines in cables) • PMT Summary • 6 missing • 11 dead (mostly in unpopulated regions) • 13 faulty (?)

  4. The Bottom Line • 98% of channels installed and working • Photon yield and resolution agree with design report expectations • Hardware issues: • Two fallen mirrors replaced/remounted • Traced to poor adhesive batch • Safety wires improved • System appears stable • Radiator gas leaks fixed • Improvements to re-circulation-purification system implemented • Present C4F10 concentration ~ 50% • Complete filling later this Fall • Present efforts concentrating on “fine-tuning” performance

  5. Ongoing Activities • Studies to refine alignment • Correlations with tracking systems to “fine-tune” alignment of individual detector modules/mirrors • Refine ring-finding/particle-ID routines • Likelihood analyses • Speed-up (?) stand-alone ring-finding • Monitoring performance/database updates • Run-by-run ring-radius determination • Hot/dead channels • Hardware • Gas system: review/refill C4F10 by end of year • PMTs: exchange faulty channels

  6. Expected Performance • Cherenkov relations: • Widths of bands • Critical RICH parameters: which depend on: • relative photon yield path length/detection efficiency • D angle error/photon dispersion/optical quality/cell size (independent of qC and p!) (usually smaller than q2 term)

  7. Detected Photon Yields • Basic Cherenkov relation: independent of radiator composition • Design value:(corresponds to 47L(cm)<qc>2 in PDG notation) • Actual limiting angle does depend on radiator: • Biases in measurement of yield • Efficiency in ring-finding • Nearby conversion pairs • Shadowing by beam-shroud • Acceptance Relative biases will Change with radius

  8. Uncorrected Data • Yield in pure N2 • Scan rings with mixed C4F10

  9. Issues in Alignment and Resolution • RICH measures angles: xhit/R, yhit/R • Dispersion and granularity set scale • sgas = 0.4 mrad • scell = 1.6/12 mrad  •  Nphoton = 5 - 6 • Spherical aberrations important • Scale as (projection of ray from origin)3 • Distort ring shape and displace center • Analytic expressions for distortions and shifts exist at required accuracy D  0.6 mrad sV,H 0.15 mrad Overall goal: sV,H 0.3 mrad

  10. Compare with ECAL • Upper/Lower half-planes have systematic offset ~ 0.5 mrad • Within a half-plane, sV, H ~ 0.7 mrad RICH/ECAL vertical residuals (radians)

  11. Self-consistent Test of Alignment • Examine Upper/Lower detector yields vs position • Symmetry of detector placement w.r.t. mid-plane of mirrors • Signal/background • Define Up/Down photon asymmetry: • Expect:

  12. Asymmetry Data • Photon detectors are close to symmetric (within ~ 0.2 mrad) in their nominal geometric positions • Vertical spot size OK •  (2.8/11.4)40 mrad • Background photons ~25% • Implies occupancy ~1%, consistent with observed occupancies • Background is subtracted in usual stand-alone ring-finding algorithm Conclusions: Nominal Upper Shifted 4 mm 1 mrad shift

  13. How to Reconcile RICH – ECAL ? • Most sensitive geometrical parameter in RICH is placement of photon detectors within respective focal planes. • dq/dx = 0.16 mrad/mm (in focal plane) • ECAL and U/L asymmetry data suggest a symmetric displacement of each set of supermodules by 2 mm • At limit of estimated survey errors • Not unique • New set of geometrical constants generated with this shift

  14. Results with Shifted Photon Detectors • Mean offsets< 0.2 mrad • Overall RMS~ 0.7 mrad

  15. Position Dependence of Residuals 1 mrad/box

  16. Comments on aligning using ECAL • Advantages • Only system available on regular basis • Matches RICH acceptance • Disadvantages • Not a tracking system—must make assumptions about track directions • Efficiencies differ for different particle types • Response not uniform/constant • Biases apparent at boundaries of active regions • Biases due to photon/track overlap • Resolution at limit needed for RICH alignment

  17. Match RICH rings with OTR tracks • TDC information not used • Horizontal offset ~0.5 mrad • RMS horizontalmatch < 1 mrad • Vertical RMS broadened by OTR stereo

  18. Preliminary Conclusions on Alignment • Small adjustments to nominal detector positions are indicated by the data • System is at the design level of accuracy with only this correction • The ultimate accuracy of the RICH will be better than the design specification • Comparisons will be performed with other tracking systems to understand potential optical errors • Adjustments to individual detector supermodules and mirrors • Ultimate accuracy in track direction of ~0.3 mrad/ plane seems feasible • Initial matching with OTR promising

  19. Critical RICH Parameters • Measure N/q2 and D directly from fits to rings that match with ECAL • No corrections for partial rings

  20. Spring ’99 Data • Critical RICH parameters already at or near design specs:DesignMeasured • 13,00010,000-13,000 • D 1 mrad0.7 – 1.0 mradsyst. err. ~0.5 mrad • Particle ID in ECAL/RICH mode differs from design mainly because of poor dp/p

  21. Electrons: 15 17.5 GeV/c p — K: 46 58 GeV/c Consequences for Particle ID Today’s ECAL/RICH “tracking” With Design Tracking:

  22. Summary • RICH working at design performance level • Photon yields and resolution at or near specifications • Occupancies as expected (magnet on) • Stand-alone ring finding gives post-magnet tracks to ~0.5 mrad • Ongoing effort to “institutionalize” performance monitoring • Automatic database updating of critical parameters • Continuing alignment studies should reduce optical errors to below design specifications • We encourage the use of RICH information by everyone • Global alignment studies • Physics!!!

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