The LHCb Ring Imaging Cherenkov Detectors

1
The LHCbRing Imaging Cherenkov Detectors

• Introduction
• The RICH Project
• Requirements Design
• Construction of Subsystems
• Physics
• Conclusions

7. Int. Conference on Advanced Technology and
Particle Physics, Como, 17.10.2001
Stephan Eisenhardt University of Edinburgh
2
Participating Institutes
Centre Européenne pour la Recherche Nucléaire
Sezione di Milano
Sezione di Genova
University of Edinburgh
University of Glasgow
Imperial College
Rutherford Appleton Laboratory
University of Bristol
University of Oxford
3
LHCb Experiment

• Uses pp-collisions at the LHC
• Forward single-arm spectrometer
• Acceptance
• bending plane
• 10-300 mrad
• non-bending plane
• 10-250 mrad
• ? 1.88...4.89
• Open geometry
• easy access

4
LHCb Pit Experiment
VELO Inner Tracker Outer Tracker RICH 1 RICH
2 Calorimeters Myon System
5
Particle Identification
6
Particle Identification Layout
7
RICH Detectors
RICH Ring Imaging Cherenkov Detectors

• Acceptance
• 300 mrad RICH 1
• 120 mrad RICH 2
• Mirrors
• spherical for light collection
• tilted to have photodetectors
• outside the acceptance
• plane needed for RICH 2
• TDR 9/2000

8
Photodetector Requirements
Aerogel large rings
C4F10 small rings
RICH1
CF4
RICH2
9
RICH Photodetectors
baseline Hybrid Photo Diodes (HPD) ? talk by
Maria Girone (1600) backup Multianode
Photomultipliers (MaPMT)
10
MaPMT Results

• commercial product
• customised for LHCb
• highest possible segmentation
• 8x8 segmented anode dynode chain
• effective pixel size (3.2 mm)2
• with quartz lens to recover active area
• 38 ? 85
• Gain 3?105 at 800 V
• QE 25 at ? 380 nm

• Beam test
• 3x3 cluster of MaPMT
• RICH 1 Prototype
• read-out at 40 MHz
• APVm chip
• meets LHCb requirements

• HV -1000V 6000 events
• photon yield observed in data
• 6.51 ? 0.34 p.e.
• expect from simulation
• 6.21 p.e.

11
RICH 1 Construction
Interaction point
aerogel
half frame
gas volume
14 X0
spherical mirrors
photodetectors
Kapton seals
12
RICH 1 beampipe

• Very delicate structure
• low mass VELO window
• long lever arm beam pipe
• Special transport frame
• Wire support from RICH frame

13
RICH 1 beampipe seals

• Gas envelope uses beam pipe
• Sealed with Kapton foils
• gas tight fit around beam pipe
• three slit layers
• glued to beam pipe
• corrugated for pressure tolerance

Kapton seal prototype
14
RICH 1 Mirror Mounts

• Baseline glas 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
330 mrad acceptance
technical challenge!
15
Aerogel Radiator
16
RICH 2 Construction
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
17
RICH 2 frame

• Natural frequencies
• Fundamental frequency of
• 6Hz achievable

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

increasing deflection
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RICH 2 windows
max. deflection

• Sealed at beam pipe envelope and frame
• requirements
• low mass (X0)
• low deflection under pressure
• 1mm fibre skins 48mm PMI foam core
• optimal wrt. window deflection
• under pressure
• at 400Pa under-/overpressure 30mm
• Stress on beam pipe sheet
• _at_ 400Pa 1 ton
• optimisation of flanges
• material budget
• stress minimisation

50mm
19
RICH 2 Photodetector Windows

• Problem 1500x750x5 mm Quartz windows
• non-standard size ? not affordable
• Solution segmentation into 2 or 4 plates with
  gas tight joints
• 2 plates preferred and feasible
• Window transmission
• better than requirements

RICH-2 quartz window frame
production pane ? 1525mm
transmission vs. ?(150-230nm)
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Photodetector Monitoring

• At commissioning needed for
• fast debugging
• disentangle error sources (HV, Vbias, ODE, ...)
• from graphical pattern
• magnetic field distortions
• safety checks (light tightness)
• Monitoring programme
• photodetector functionality
• photodetector ageing
• HV, Vbias, low voltage
• mirror reflectivities
• alignment
• Subgroup founded to develop monitors
• work has started

21
RICH Performance

• results for HPDs MaPMTs
• same within errors
• simulation
• based on measured test beam HPD data
• global pattern recognition
• background photons included
• of detected photons / track
• Aerogel 7
• C4F10 33
• CF4 18
• angular resolution mrad
• Aerogel 2.00
• C4F10 1.45
• CF4 0.58

22
RICH at its best

• LHCb has unique feature
• overconstrain angles a, b, g, and dg
• Reminder observables of the Unitarity Triangles
• derived from the CKM matrix in the Wolfenstein
  approx.
• new strategies for measuring CKM angles
• e.g.
• combine Bs ? KK and Bd ? ?? ? angle ?
• ?? 40 ?? known, U-spin
• RICH at its best

23
PID Bd ? ?? ?

• sensitive to angle ?
• ?? 20 - 50 in 1 year
• ? dependent
• if P/T from elsewhere
• backgrounds have

24
PID Bs ? Ds K?
?

• rate asymmetries measure angle g -2dg
• expect large
• expect only 2400 events
• in 1 year of data taking
• ? s(g -2dg ) 60 - 140

25
Conclusions

• The RICH is essential for the LHCb physics
  programme
• Physics performance studies have been extended
• LHCb RICH is progressing since TDR
• design for subsystems are detailed and advanced
• transition from RD to construction
• In time to take data when LHC becomes
• operational in 2006

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Beetle Chip for MaPMT

• Beetle 1.0 works!
• BeetleXX 1.x
• design studies for improvements
• e.g.
• peaking time reduced to lt20ns
• I2C SEU hardened

• BeetleMA 1.0
• with test structure
• for MaPMT
• response matches design
• with MaPMT signals
• S/N 5.9

MaPMT spectrum with BeetleMA 1.0
BeetleMA 1.0
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RICH Electronics

• Pixel chip of HPD
• encapsulated, binary,
• 40 MHz, 321 MUX
• Level 0
• on detector
• Gbit optical links
• clocks, triggers - TTC
• Optical data links 100m
• Level 1
• in counting room
• buffers data L1 latency,
• transports to DAQ
• zero suppression
• TTC, DCS interface

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UK L0-L1 Demo. System

• Stand alone system
• as proof of principle for test bench use
• Nearly final setup (no TTCrx, ECS, DCS)
• Available 01/2002

L0 photodetector test bench
L1 stand alone or VME crate
DAQ PC DAQ control
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Photodet. Testing Facilities

• 500 HPD or 4000 MaPMT to serial tested for
• functionality within specs
• individual characteristics
• working parameters
• for 340k channels
• 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 UK L0-L1 demonstration 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 Construction
RICH 1
RICH 2
12.4 X0
14 X0
Mirrors
top view
side view
Photodetectors
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RICH 1 Installation

• Detailed planning of the installation procedure
  in the Delphi pit
• Complicated simulated in CAD models

• Magnetic shield plate
• blocking access to tunnel
• Additional civil engineering
• needed to make installation
• possible at all
• Tight space to move/work
• sometimes only mm left
• Observe interference
• RICH-1, beampipe,
• machine, VELO
• Most critical
• insertion of beam pipe and stress free mounting
  on RICH-1 frame

Magnetic shield plate
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RICH 2 Gas System

• by LHC Gas group
• control monitor p T

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

RICH-2
additional monitor systems