Eyes for the RICH not a celeb. watchdog

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Eyes for the RICH(not a celeb. watchdog)

• Introduction to LHCb
• RICH detectors
• Hybrid Photon Detectors

Stephan Eisenhardt University of Edinburgh
Edinburgh, 23.03.2006
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Large Hadron Collider

• 14 TeV pp collider, 25ns bunch-crossing
• using the LEP tunnel
• LHC is the most intensive source of B-mesons
• Bd0, Bu, Bs0, Bc and also b-baryons
• ?bb 500 ?b ?inelastic 80 mb
• luminosity
• ltLgtLHC 1034 cm-2 s-1
• ltLgtLHCb 2x1032 cm-2 s-1
• LHCb 1012 bb / 107 s
• single pp events
• (occupancy,
• radiation damage)

IP8 LHCb
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Experimental Goals
Precision Measurements of CP Violation in b decays

• Large Samples of b decays
• from 14 TeV pp collisions Nbb 1012 / year
• from the start of LHC
• b production predominately at small polar angles
• LHCb optimized as single forward arm spectrometer

• Hadron and Lepton ID
• many pure hadronic final states
• particle identification (?/K) essential
• leptonic final states
• efficient electron/muon ID
• flavour tagging

Example decays
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LHCb Experiment

• Single-arm spectrometer for precision
  measurements of CP violation in B-meson system
• Search for signals of New Physics beyond
  Standard Model

• Trigger
• efficient for leptonic and hadronic (multi-body)
  final states (e.g. Bd ? pp)

• Particle ID
• RICH / Calorimeters / Muon Detectors
• Charged particle identification over momentum
  range 2-100 GeV/c

• Ring Imaging CHerenkov counter (RICH)
• using 2 RICH detectors

• acceptance
• 10 (250) 300 mrad (non) bending plane

• vertexing
• Proper time resolution
• 43 fs Bs ? Dsp (K)
• 30 fs Bs ? J/y f

• no tracking stations in magnet region
• magnetic field at RICH 1
• vertical RICH1

RICH1 2-60 GeV/c
RICH2 17-100 GeV/c
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Feb 2006 Setup Muon System
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Feb 2006 Setup Preshower
PS lead wall suspended from top
top
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LHCb Trigger

• luminosity chosen to
• get one pp interaction per bunch crossing
• to control
• radiation damage, occupancy, pile-up
• ? ltLgtLHCb 2 x1032 cm-2 s-1
• lower than for other LHC experiments
• available from 1st year of LHC
• tuneable

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LHCb Trigger Layout

• Level 0
• 40MHz input
• 1MHz output 1/40 reduction
• 4ms latency
• TOFcables lt1000ns
• processing lt1200ns
• decision unit lt500ns
• readout supervisor lt800ns
• contingency 500ns
• Level 1
• 1MHz input
• 40kHz output 1/25 reduction
• variable latency up to 58ms
• HLT
• L2L3
• 40kHz input
• 200Hz output to disc/tape 1/200 reduction

L1 efficiency of L0 selected and offline accepted
events
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LHCb L0 L1 Trigger

• derandomiser (L0 L1)
• synchronise date from sub-systems
• zero-suppression _at_ L1
• data package sorting and packaging _at_ L1

L2L3
L1
L0
L1
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LHCb RICH System
RICH2
RICH1
side view

• RICH Ring Imaging CHerenkov detector
• 3 radiator media
• aerogel, C4F10, CF4
• spherical mirrors
• focusing? ring image
• tilt ? outside acceptance
• secondary flat mirrors
• ? magnetic shielding
• acceptance
• RICH1 25-300mrad
• RICH2 15-120mrad

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Cherenkov Detector Layout

• require ?/K separation for 1ltplt150 GeV/c
• two independent detectors

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RICH performance
detected photons per saturated track

• RICH 1 RICH2
• Aerogel C4F10 CF4
• npe 5.3 23.4 16.4

contributions to Cherenkov angle resolution
mrad Aerogel C4F10 CF4 chromatic 2.07 0.80 0.47
emission pt. 0.34 0.80 0.33 pixel 0.57 0.57 0.16
PSF (HPD) 0.26 0.26 0.09 total 2.19 1.29 0.60
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RICH hadron ID performance
log-likelihood ?-K separation
Ds (p-K)

• select K if maximum-likelihood hypothesis is K or
  p, otherwise p
• chose cut on likelihood

3s
momentum GeV/c

• for true p in B events
• 3s limit 380 GeV

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RICH 1 Construction
VELO
RICH1
7.5 X0 (RICH TDR 14 X0)
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RICH 1 VELO
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RICH 1 Windows

• direct sealed to VELO
• stainless-steel bellow
• 37 N/mm axial stiffness
• 5000 N/mm radial stiffness
• VELO and RICH in electrical contact

• Exit window
• Rohacell core
• Carbon Fibre skins
• 0.6X0

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RICH 1 Spherical Mirrors

• Carbon Fiber Reinforced Plastic (CFRP) composite
  material
• 70 carbon fiber reinforcement material
• 30 resin matrix material
• meeting NASA standards for chemical resistance,
  outgassing, radiation
• Reflective coating
• aluminium directly on surface
• gt90 reflectivity
• protective layer SiO2 or MgF2
• Results
• size one mirror / quadrant
• surface roughness few nm
• radius of curvature s lt1
• spot size (95 of light) D0 lt 2.5mm
• 1.5X0 for 6kg/m2 mirror

glass mandrel
early RICH1 CMA prototype
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Aerogel

• structure n(SiO2)2n(H2O)
• foamed silicon ? light 22 litres 3 kg
• baked out in tiles of up to 20x20x6cm3
• transmission T
• exponential l4 dependence
• limited by
• Rayleigh scattering
• red emission dominant
• clarity C (with n1.030?0.001 _at_ 400nm)
• Matsushita (hydrophobic) C 0.009 mm4 cm-1
• Novosibirsk (hydroscopic) C 0.005 mm4 cm-1
• larger tiles
• higher yield of unscattered photons
• but more difficult to handle

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RICH1 - Aerogel Radiator

• Two retractable halves
• Carbon Fibre case
• 4.4 X0 (3.3 of aerogel)
• 1.2 ?I (0.8 of aerogel)
• tile sizes 20x20x5cm3 and smaller
• total 22 litres 3kg
• Natural ageing
• sealed hydroscopic tile
• C increased by 10 over two years

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RICH 2 Construction
12.4 X0
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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

increasing deflection
increasing deflection
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RICH 2 Windows

• 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

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RICH 2 On Tour

• a week in the life of RICH 2
• Monday 13.11.2006 Saturday 18.11.2005
• or
• how to transport a 70 tons
• fragile main sail over 10 km
• with
• lt 1deg. tilt (5cm/2.5m)
• lt 0.2g acceleration
• and
• wind, rain frost

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Preparation Monday, Tuesday

• Loading of the Omega Base in bldg 180.
• Installation of Shock Logger, Accelerometers,
  Levelmeter.
• Installation of the Lifting Beam.
• Dismounting Mounts under.

? Didier Piedigrossi
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Transport Tuesday Evening
? Didier Piedigrossi
? Maximilien Brice

• Dismounting the Lifting Beam.
• Wrapping.

Departure 630 !
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Transport Tuesday Evening
? Didier Piedigrossi
Driver took the South Direction ..But not to
Frascati!
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Transport Tuesday Evening
? Didier Piedigrossi
? Didier Piedigrossi
All was going well..
Steep Was Well Compensated.
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Transport

• Wind, Rain and Cold Were Coming.
• In Emergency
• Nacelle.
• Awnings.
• Nitrogen.

? Caterina Bertone
..Then a Front Boggy Failed! And RICH2 Was
Abandoned.
? Didier Piedigrossi
(Corrosion in a Welding of the Reinforced Arm.)
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Transport Thursday Evening
? Didier Piedigrossi
New Start.. Cold but Nice Weather!
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Transport Friday 5 am!
Lock too hard over.. ..Direction Arm of the
Boggy Failed.. and then Hydraulic Pipe Damaged!
? Didier Piedigrossi
Few meters before the Entrance.. (and after a
pneumatic leak in the last roundabout!)
? Didier Piedigrossi
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Transport - Friday
Will it pass..
? Didier Piedigrossi
..with a Clearance of few Centimeters.
? Didier Piedigrossi
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Transport - Friday

• Put Temporary RICH2 on Blocks.
• Lower down the Omega Base.
• (Trailer Free at 3 pm.)

? Didier Piedigrossi

• Unwrapping.
• Installation of the Lifting Beam.

? Didier Piedigrossi
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Transport - Friday
? Patrice Loiez
Taking off 434 pm.
Wheels for Vertical Drive
? Patrice Loiez
Landing 525 pm.
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Transport Friday, Saturday

• (No more monitoring of the shocks!)
• Installation on the Lastra Platform.
• Removing of the Lifting Beam.
• Transfer from Shaft to Cavern.

• Unwrapping.
• Removing of the Brackets.
• Support Beams of Central Tube.
• Installation of the Lifting Beam.

? Peter Loveridge
? Patrice Loiez
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Transport Saturday
? Peter Loveridge
? Peter Loveridge

• Installation of the Mounts under the
  Superstructure.

Stayed in air for a while
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finally, at rest.

• Saturday 7pm.
• Installation on its finalposition.
• Removed the lifting beam for magnetic mapping.
• Survey the RICH2position.? RICH2 is tilted 3
  mm backward.? At the bottom located at 0.3
  mm.? 1.2 mm too low.

? Peter Loveridge
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RICH 2 Mirror Alignment

• Mirrors adjusted to lt0.1mrad precision
• In-situ monitoring before, during and after
  transport
• a photograph of test pattern every hour
• comparison to picture zero by subtraction
• senitivity 0.05mrad

image of test pattern
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finally, at rest. (2)
before
after
differential enhanced contrast
? still well aligned!
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RICH Event Display

• single event in the full GEANT3 based simulation
  used in performance studies

photodetector area 2.6 m2 single photon
sensitivity 200 - 600 nm quantum efficiency
gt20 good granularity 2.5 x 2.5 mm2
active area fraction 65 of electronic
channels 500k LHCb DAQ rate 40MHz rad.
tolerant 3kRad/year
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New Technology
extension of our senses
new technology
understand tools on fundamental level
new knowledge in fundamental processes
correct interpretation of results
LHCb RICH Hybrid Photo Diodes
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Hybrid Photon Detector

• Photon detector
• Quartz window, S20 photocathode
• Typical ? QE dE gt 0.7eV
• Cross-focussing optics (tetrode structure)
• De-magnification by 5
• Active diameter 75mm
• ? 484 tubes for overall RICH system
• 20 kV operating voltage (5000 e eq. Si)
• Anode
• 256?32 pixel Si-sensor array
• small pixels ? low noise
• bump-bonded to binary readout chip
• assembly encapsulated in vacuum tube
• LHCb readout mode 8-fold binary OR
• ? effective 32?32 pixel array
• pixel size 500mm?500mm sufficient

Anode
Vacuum photon detector
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HPD Production Anode
20 ?m
Detector chip (Canberra - B)
Assembly probing
High T bump-bonding (VTT - FIN)
Readout chip (IBM - F)
Wafer probing
Packaging (HCM - F)
Anode testing
Visual inspection and plating control
Ceramic carrier (Kyocera - JP)
Brazing (DEP - NL) and gold-plating (CERN)
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HPD Production Tube
HPD tube production (DEP - NL)
Vacuum bake-out_at_ 300C
Photo-cathode deposition and vacuum sealing
HPD cabling and potting
Tube body assembly
Final HPD testing
Anode incoming inspection and testing
Anode testing
QE measurement and anode testing
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HPD Production Status
Expected
today
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HPD Tests

• Photon Detector Test Facilities (PDTF)
  (Edinburgh Glasgow)
• test rate 1 HPD / day / site
• 2 test stations per site
• Quantum Efficiency (Edinburgh) and Backpulse
  (Glasgow) measurement setups for 10 of HPDs
  under commission
• stable software for data acquisition
• ongoing improvements on data analysis software
• highest priority database for test results

PDTF station
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HPD Test Profile
results up to 25.02.2006
136
109
PDTF delivered 136 tested 109 pass 104 fail
5 _at_ CERN delivered 15 accepted
14 rejected 1 pre-production 9
76
today
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Mechanical Tests

• 107 HPD passed, 2 HPD failed
• 2 leaned by 0.4mm
• (Tower of Pisa)
• ? tubes rejected
• sent back to DEP for repotting

point of first possible contact
mechanical test jig
HPD ? 83.0mm (0.0mm, -0.1mm) Teflon tape
0.1mm Jig ? 83.4mm
gap 0.1mm
any contact failure
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Quantum Efficiency

• Excellent blue sensitivity _at_ 270nm
• Reasonable low red sensitivity _at_ 800nm
• anti-correlated to blue sensitivity
• cause of thermal e--emission (dark count)
• Setup for independent verification at PDTF is
  under commission

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SW Tools I

• HVrampUp

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SW Tools II

• LongLED
• Alice mode

cylindrical reflection reflection on Al coating
? will be shadowed!

• LongLED_LHCb
• LHCb mode
• taken just after

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Leakage Current

• typical value is 1mA (within specs)
• class of 8 HPD with LCgt5mA
• 7 still perform fine
• 1 did not properly deplete (LC25.1mA)
• ? tube rejected

• strong correlation with of bake-outs
• 3 HPD with 3 bake-outs all LCgt10mA
• ? limit to max. 2 bake-out

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Bias Voltage Scan

• with correct timing

LED jump
Edi2 Gla1 distributions match
noisy pixel
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Bias V Scan - Timing Study

• BiasVscan
• timing varied
• Dt 4ns
• correct setting
• turn-on _at_ 35V
• new default -8ns
• ? compatible with
• CERN data
• ? margin ?4ns

too early vdrift in anode too large - Q
arrives before strobe
too late vdrift, min increases - larger BiasV
needed for Q to arrive before strobe ends
too early
too late
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Dark Count

• contractual specs DC lt 5kHz/cm2
• safety margin factor 1000
• before we exceed 1 occupancy
• 16 out of 124 HPDs exceed 5kHz/cm2
• two types
• high red sensitivity
• increased IFB probability
• perfectly fine to be used in RICH
• 1 HPD showed problem (H546002)
• DC gt 400 kHz/cm2
• intermittent strong ion feedback
• 3 times baked out
• ? tube rejected

contract spec

• max
• 5kHz/cm2

rejected H546002 DC gt 400 kHz/cm2
including 15 CERN HPD
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Ion Feedback

• due to e- ionising residual gas atoms
• ? ion produces bunch of photoelectrons at PC
• ? cluster of hits with 200-300ns delay
• we find very low IFB ? very good tube vacuum

HPD response to LED pulses with varied delay
contract spec

• max
• 1

ltIFBgt 0.03
Very low IFB ltlt1
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Tube Classification

• guideline for usability in RICH
• class A clear pass in all aspects
• class B may fail specs, but recommended for
  usage
• HPDs with slightly increased dark count
• class E flagged with an issue, still usable in
  RICH
• HPDs with increased LC or 15 dead pixels
• class F clear fail ? reject
• 5 failed HPDs
• 2x mechanics Tower of Pisa
• hope to recover
• 1x anode failure
• 1x intermittent IFB
• 1x pixel chip failure
• (not discussed here)

pass 104 of 109 gt95
fail 5 of 109 lt 5
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Two-body Decays RICH at its best
No RICH

• LHCb has unique feature
• over-constrain angles
• a, b, g, and dg
• new strategies for measuring CKM angles
• e.g. combine Bs ? KK and Bd ? ?? ? angle ?
• ?? 5º - 10º ?? known, U-spin
• signal improvement with RICH
• purity 13 ? 84
• efficiency ? 79
• RICH at its best!!

With RICH
Bs ? KK
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PID Bd ? ?? ?

• sensitive to angle ?
• ?? 5º - 10º in 1 year
• ? dependent
• if P/T from elsewhere to 0.1
• P/T might be as high as 0.2
• backgrounds have
• signal improvement with RICH
• purity ? 84
• efficiency ? 90

No RICH
With RICH
Tree (T)
Penguin (P)
Bd ? pp
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PID Bs ? Ds K?
?
No RICH

• rate asymmetries measure angle g -2dg
• both diagrams of O(?3) ? expect large
• expect only 2400 events
• in 1 year of data taking
• ? s(g -2dg ) 3º16º
• depends on (g-2dg), strong phase and xs
• signal improvement with RICH
• purity 7 ? 66
• efficiency ? 88

With RICH
Bs ? DsK
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The End

• almost
• of 10 years of RD and now commissioning
• O(500) people (physicists engineers) spending
  their life on realising this experiment
• The End?? no!! The Beginning!
• of LHCb coming to life
• of 10 years of exciting physics
• and possibly some surprises around the corner

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