Particle Identification in the LHCb Experiment

1
Particle Identification in the LHCb
Experiment
Paul Soler University of Glasgow and Rutherford
Appleton Laboratory (on behalf of LHCb RICH group)
III LHC Symposium on Physics and Detectors Chia,
Sardinia, Italy. 29 October 2001.
2
Participating Institutes
Sezione di Milano
CERN
Sezione di Genova
University of Bristol
University of Edinburgh
University of Glasgow
University of Oxford
Imperial College
Rutherford Appleton Laboratory
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LHCb Experiment

• LHCb Detector forward single arm spectrometer
• Acceptance
• 10-300 mrad bending
• 10-250 mrad non-bending

RICH1
RICH2
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Particle Identification
Momentum vs polar angle
Momentum

• RICH system divided into 2 detectors and 3
  radiators aerogel, C4F10, CF4

• Excellent Particle Identification (p-K
  separation) required from 1 - 150 GeV/c

5
RICH System Overview
RICH1
RICH2
Photo detectors

• Acceptance
• 300 mrad RICH 1
• 120 mrad RICH 2
• Radiators thickness L, refractive index n, angle
  ?c, ?/K threshold
• Aerogel C4F10 CF4
• L 5 85 167 cm
• n 1.03 1.0014 1.0005
• qc 242 53 32 mrad
• p 0.6 2.6 4.4 GeV
• K 2.0 9.3 15.6 GeV

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Photo Detectors
Aerogel large rings
C4F10 small rings

• Photo detector area 2.6 m2
• Single photon sensitivity 200 - 600 nm, quantum
  efficiency gt 20
• Good granularity 2.5 x 2.5 mm2
• Large active area fraction ? 73
• LHC speed read-out electronics 40 MHz
• LHCb environment magnetic fields, charged
  particles

CF4
Hybrid Photodiodes (HPD) baseline
Multi-Anode PMT (backup)
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Hybrid Photo Diodes (HPD)

• Quartz window, thin S20 photo cathode ?QE dE
  0.77 eV
• 32 x 32 Si pixel array 500 ?m
• (Canberra)
• 450 tubes for RICH system
• Cross-focusing optics
• demagnification 5
• 50 ?m point-spread function
• 20 kV operating voltage
• Encapsulated binary electronics
• Tube, encapsulation industry (DEP)

Pixel HPD (baseline)
-20 kV
61 pixel HPD

• Existing prototype external read-out

? 80 mm
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HPD RD Results
Testbeam

• Testbeam Setup
• RICH 1 prototype
• 3 HPDs
• Figure of merit
• N0 ? 202 cm-1 (35 PE/ring)

Cherenkov Photons
Single photoelectron spectra visible
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HPD Electronics
Pixel chip
Occupancy Max Mean RICH 1 8.2
1.2 RICH 2 2.6 0.4

• ALICE / LHCb development
• (0.25 ?m CMOS)
• ALICE pixel size 50 ?m x 425 ?m
• LHCb pixel size 62.5 ?m x 500 ?m
• 8 pixels 1 LHCb super-pixel
• 500 ?m x 500 ?m
• 40 MHz read-out clock
• Bump bonding chip-sensor

50 mm
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Pixel HPD Chip Status

• Chips received only operate up to 10 MHz (ALICE
  requirements)
• Bump-bonding sensor-pixel chip VTT Finland, good
  quality
• Lab tests within LHCb requirements
• Threshold scans 700 e- (lt2000 e-)
• Noise 90 e- (lt250 e-)
• Signal 5000 e-
• Wire bonding to ceramic carrier Edgetek (Paris),
  good quality
• LHCb chip redesign to achieve 40 MHz submission
  IBM November
• All current and voltage DACs redesigned and
  correctly layed-out
• Improved uniformity of pulser
• Clock skew being improved
• HPD Pixel chip resubmission after October review
  31 October, 2001

HPD pixel chip assembly with ceramic carrier
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Magnetic Field Tests

• Prototype with a phosphor screen anode read out
  by a CCD (resolution 150 mm) for magnetic field
  tests.
• Distortions tolerable up to 10 Gauss
• Flipping of B field shows no change in position
  residuals (within resolution).

Axial field
Transverse field
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MAPMT (backup)
Multianode Photo Multiplier Tube

• 8x8 dynode chains, pixel 2x2 mm2
• (effective size with lenses 3.2x3.2 mm2)
• Gain 3.105 at 800 V
• UV glass window, bialkali photo cathode
  QE 22 at ? 380 nm
• Test beam data 6.51 ? 0.34 p.e.
• Expect from simulation 6.21 p.e.

• MAPMT active area fraction 38 (includes
  pixel gap)
• Increase with quartz lens with one flat and one
  curved surface to 85

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RICH1 Engineering
Photo detectors
Beam-pipe
14 X0
Kapton beam-pipe seal
Mirrors
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Aerogel

• Hydroscopic Aerogel provides the best quality
• clarity 0.0045 ?m4/cm-1
• refractive index 1.034
• radiation hard
• Thickness present choice 5 cm

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RICH1 Mirrors

• Baseline glass mirrors with 3-leg spider
• (carbon fiber with screw adjusters)
• Minimize dead material within acceptance
• Alternatives
• glass 6mm 4.5 X0 , 1.5 ?l
• berillium 5mm 2 X0 , 1 ?l
• composite 1 X0 , 0.5 ?I

very good repeatability stability
beam pipe
330 mrad acceptance
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RICH2 Engineering
frame
exit window low mass
12.4 X0
plane mirrors
magnetic shield box backward lid (4 tons) to
shield against magnetic stray field of 150 Gauss
spherical mirrors on supporting planes
photodetectors with individual magnetic shields
beam pipe envelope supported by windows
entry window low mass
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RICH2 Engineering

• Natural frequencies
• Fundamental frequency 6Hz
• Negligible movement

• Finite Element Analysis
• Deflections under load
• (mag. shield 2x11000kg, tracker unit 200kg)
• max. deflections lt5mm achievable

increasing deflection
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RICH2 Gas Enclosure

• Gas enclosure windows sealed at beam pipe and
  frame
• 1mm fibre skins 48mm PMI foam core 30mm at
  400Pa
• Stress on beam pipe sheet _at_ 400Pa 1 ton

Tube Flange

• Photodetector window
• 1500x750x5 mm (two plates)
• Optical transmission
• gt90 above 200 nm

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RICH Electronics

• Pixel chip
• encapsulated, binary, 40 MHz, 321 MUX
• Level 0
• on detector
• Gbit optical links
• clocks, triggers - TTC
• Level 1
• in counting room
• buffers data L1 latency, transports to DAQ
• zero suppression
• TTC, DCS interface

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Electronics Test Bench

• Stand alone system for demonstration and test
  bench use
• Nearly final setup (no TTCrx, ECS, DCS) available
  01/2002

L0 photo detector test bench
L1 stand alone or VME crate
DAQ PC DAQ control
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Photodetector Test Facilities

• 500 HPD or 4000 MaPMT to be tested for
• functionality within specifications
• individual characteristics
• working parameters
• full automation needed
• selection of detectors according to test results
• position in detectors wrt. occupancy
• to be operational in mid 2002
• in the case of HPDs
• use the electronics test-bench system
• estimated time for all measurements scans
• for one tube 24hrs
• (including handling and resting in the dark)
• 2 test facilities needed for 1 1/2 years
• (Edinburgh Glasgow)

MaPMT test setup
ODE
MaPMT
xy-table
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RICH Gas and Monitoring

• by LHC Gas group
• control monitor p T

• Ultrasound gas monitor
• Measure variation of
• sound speed
• v (?RT/M)1/2
• monitor gas composition Fabry-Perot monitor
• Measure fringes (depend on distance d, ?, and n)
• monitor dispersion n(?)

RICH-2
additional monitor systems
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RICH Alignment

• Misalignment mirrors fit photons from data to
• Dq A cos(f) B sin(f)
• In RICH2 (two mirrors) can only perform relative
  alignment
• Minimise c2 for two mirror tilts
• Photons from ambiguous mirror combinations (20)
  degrade performance
• Seed alignment lt1 mrad for no degradation

1 mrad misalignment
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RICH Performance
3s ?-K separation 3-80 GeV/c (2s 1-150 GeV/c)

• Simulation
• based on measured test beam HPD data
• global pattern recognition
• background photons included
• of detected photons
• 7 Aerogel 33 C4F10 18 CF4
• Angular resolution mrad
• 2.00 Aerogel 1.45 C4F10 0.58 CF4

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Bd -gt ?? ?

• sensitive to CKM angle ?
• ?? 20 - 50 in 1 year
• depends on P/T and strong phase ?
• Backgrounds also have

Penguin P
Tree T
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Bs -gt Ds?K?

• Rate asymmetries measure angle g-2dg
• Expect 2400 events in 1 year of data taking
• s(g-2dg) 60 .. 140

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Conclusions

• Physics performance studies show that the RICH is
  essential for the LHCb physics programme.
• The RICH design of LHCb with two detectors and
  three radiators provides 3s p-K separation from
  3-80 GeV/c
• LHCb RICH is progressing since TDR
• Pixel HPD chip has incurred a delay but is not in
  critical path (project under review).
• Design for subsystems are detailed and advanced
• Transition from RD to construction
• In time to take data when LHC becomes
• operational in 2006