HERA-B%20RICH

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

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Detector
Readout Cards 16 ch, using two ASD08 (amplifier,
shaper, discriminator) chip each
Base Board Socket, voltage divider, output
circuitry for 4 multianode PMTs
Photon Detectors
M16 PMT Hamamatsu 16-anode multiplier
Plastic Molding
Lens System 21 image reduction
Spherical Mirrors
Planar Mirrors
Super Module Crate made from plastic molded iron
sheets magnetic shield and mounting structure
C4F10 radiator
1488 M16s 752 M4s
Photon Detectors
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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 (?)

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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

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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

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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)
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Detected Photon Yields

• Basic Cherenkov relation independent
  of radiator composition
• Design value (corresponds to 47L(cm)ltqcgt2
  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
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Uncorrected Data

• Yield in pure N2
• Scan rings with mixed C4F10

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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
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Compare with ECAL
RICH/ECAL vertical residuals (radians)

• Upper/Lower half-planes have systematic offset
  0.5 mrad
• Within a half-plane, sV, H 0.7 mrad

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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

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Asymmetry Data
Conclusions
Nominal

• 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

Upper Shifted 4 mm
1 mrad shift
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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

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Results with Shifted Photon Detectors

• Mean offsetslt 0.2 mrad
• Overall RMS 0.7 mrad

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Position Dependence of Residuals
1 mrad/box
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Comments on aligning using ECAL

• Advantages
• Only system available on regular basis
• Matches RICH acceptance
• Disadvantages
• Not a tracking systemmust 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

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Match RICH rings with OTR tracks

• TDC information not used
• Horizontal offset 0.5 mrad
• RMS horizontalmatch lt 1 mrad
• Vertical RMS broadened by OTR stereo

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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

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Critical RICH Parameters

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

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Spring 99 Data

• Critical RICH parameters already at or near
  design specs Design Measured
• 13,000 10,000-13,000
• D 1 mrad 0.7 1.0 mrad syst.
  err. 0.5 mrad
• Particle ID in ECAL/RICH mode differs from design
  mainly because of poor dp/p

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Consequences for Particle ID
Todays ECAL/RICH tracking
With Design Tracking
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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!!!