UK Participation in the LHCb Experiment

1
UK Participation in the LHCb Experiment

• Motivation
• Experiment
• RICH
• Vertex Detector
• UK Role
• Conclusions

PPC meeting Coseners 2. 11. 2000
Franz Muheim University of Edinburgh
2
UK Institutes
LOI
TP
University of Edinburgh 1999
University of Glasgow LOI
Imperial College LOI
Rutherford Appleton Laboratory 1999
University of Bristol 2000
University of Oxford LOI
3
Introduction

• CPV only observed in neutral kaon system
• theoretical uncertainties
• Standard Model
• 3 generation CKM matrix allows for CPV
• predicts large CPV asymmetries for B mesons
• No real understanding
• Baryogenesis additional source of CPV needed
• why is strong CPV small?
• New physics around the corner?

UnitarityTriangles
4
in B Meson System

• Standard Model makes accurate predictions
• precision tests of CKM elements and CPV
  phases, of the 3 sides and 3 angles need to
  measure 5 directly
• CPV predicted in many decays
• consistency checks
• need larges samples of Bd, Bu, Bs, Bc
  mesons
• Ideal to search for new physics
• Can extract parameters of SM and new physics

5
Large Hadron Collider

• By 2005 BABAR, BELLE, CLEO-III, CDF, D0, HERA-B
• 1st test of CKM matrix , 3 sides vs sin 2b
• LHCb is a 2nd generation experiment
• precision measurements of CP overconstrain CKM
  elements
• large statistics, Bs mesons
• LHC is the most intensive source of B mesons
  (Bd, Bu, Bs, Bc)
• ?bb 500 ?b ?inelastic 80 mb
• Luminosity ltLgtLHCb 2 x1032 cm-2 s-1 ltLgtLHC
  1034 cm-2 s-1
• 1012 bb / 107 s

LHC
6
LHCb Experiment

• LHCb Detector
• forward single arm spectrometer
• Challenges
• Trigger leptonic and hadronic final states
  (eg Bd -gt pp)
• Particle Identification ?-K separation 1
  GeV lt p lt 150 GeV
• Vertexing proper time resolution 43 fs Bs -gt
  Dsp(K) 30 fs Bs -gt J/y f

bb angular production
7
LHCb Experiment

• Acceptance 10 - 300 (250) mrad
  (non)-bending plane
• Open geometry easy access

Vertex
RICH1
RICH2
8
Particle Identification
Momentum vs polar angle
Momentum

• Requires RICH system with 3 radiators
• RICH system divided into 2 detectors

• Excellent charged particle Identification
  required from 1 - 150 GeV/c

9
RICH System Overview
Ring Imaging Cherenkov Detectors
RICH1
RICH2

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

Photo detectors
10
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
• Photodetector choice 12/99
• Pixel HPD is baseline, MaPMT is backup

CF4
HPD or MAPMT
11
Hybrid Photo Diodes
Pixel HPD (baseline)

• Quartz window, thin S20 photo cathode ?QE dE
  0.77 eV
• 32 x 32 Si pixel array 500 ?m
• Cross-focusing optics
• demagnification 5
• 50 ?m point-spread function
• 20 kV operating voltage
• Encapsulated binary electronics
• Tube, encapsulation industry
• Pixel sensor

-20 kV
61 pixel HPD

• Existing prototype external read-out

? 80 mm
12
HPD RD Results

• Simultaneous detection of Cherenkov rings from
  aerogel and C4F10 radiators

RICH 1 1/4-scale prototype
13
HPD RD Results II
Testbeam

• Testbeam Setup
• RICH 1 prototype
• 3 HPDs
• Figure of merit
• N0 ? 202 cm-1

LED
Spectrum
14
HPD Electronics
Pixel chip
Occupancy 3 RICH 1 lt 1 RICH 2

• ALICE / LHCb
• pixel size 50 ?m x 425 ?m
• 8 pixels 1 LHCb unit
• 40 MHz read-out clock
• tests are currently ongoing
• Bump bonding chip-sensor

50 mm
15
MAPMT (backup)
Multianode Photo Multiplier Tube

• 8x8 dynode chains, pixel 2x2 mm2
• Gain 3.105 at 800 V
• UV glass window Bialkali photo cathode,
  QE 22 at ? 380 nm

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

16
MAPMT RD Results
3x3 Cluster Test

• Beam test
• RICH 1 Prototype
• CF4 _at_ 700 mbar
• 40 MHz Read-out APVm chip

• Observe in data 6.51 ? 0.34 p.e.
• Expect from simulation 6.21 p.e.

17
RICH Performance

• 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

?-K separation
18
Bd -gt ?? ?

• sensitive to CKM angle ?
• Adir and Amix depend also on P/T and strong
  phase ?
• ?? 20 - 50 in 1 year
• ? dependent
• if P/T from elsewhere
• Backgrounds have

Tree T
Penguin P
19
Bs -gt Ds?K?

• Both diagrams of O(?3)
• expect large
• Rate asymmetries measure angle g-2dg
• Expect 2400 events in 1 year of data taking
• s(g-2dg) 60 .. 140

20
RICH Construction
Photo detectors
RICH 1
Beam-pipe
14 X0
Kapton beam-pipe seal
Mirrors
21
RICH Construction II
RICH 2
12.4 X0
Finite Element Analysis Static deflections Natural
frequencies
Mirrors
Side view
Top view
Photo detectors
22
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

23
Technical Design Report
Division of responsibilities

• Submitted 7.9.2000
• other institutes
• CERN
• Genova, Milano

24
RICH Project Schedule
25
Vertex Detector
VErtex LOcator Design

• Si strip detectors p-n, n-n, single sided,
  double metal read-out 220 ?m thick, 1800 wedges
• Optimized for Level 1 trigger (L1)
• Alternate r and phi strip detectors varying strip
  pitch 20 - 40 ?m in r
• Detector halves retracted by ? 30 mm
  in y during injection
• 8 mm from beam during physics
• Radiation damage
• may replace detectors after a few years

Si detectors
Si Strip Layout radial phi
26
VELO Design
Optimisation
Toblerone RF shield

• Use Liverpool MAP farm (300 Linux PCs)
• 3.5 Million events
• optimize of stations, positions, outer inner
  radii
• 25 stations, mounted in toblerone RF shields
• 220 k channels
• 9.5 hits/ track
• Proper time resolution
• st 43 fs Bs -gt Dsp
• sensitive up to xs 75 (1 year)

27
VELO RD Tests
Testbeam
Setup 200 mm p-n Micron

• irradiated prototypes
• cluster finding efficiency
• resolution
• signal shape

• Analogue read-out
• Front-end chip design
• sub micron - BEETLE
• DMILL - SCTA128_VELO

28
VELO Summary

• Geometry
• smallest pitch where most important for impact
  parameter resolution, at inner radius pixels
  of 20 x 6300 ?m2
• optimum for L1 trigger
• constant occupancy lt 5 x 10-3
• Thin detectors
• read out at outer rim
• minimize multiple scattering
• S/N 15 sufficient for L1 trigger
• Number of readout channels
• 220 k reflects in cost
• Technical Design Report expected by April 2001
• UK responsibilities
• Silicon detectors, hybrids, and assembly

29
UK Costs
30
Conclusions

• LHCb is progressing rapidly since Technical
  Proposal
• Major technology choices made, e.g. pixel
  HPD baseline for RICH photo detectors
• Technical Design Reports
• Magnet approved,
• RICH ECAL submitted
• other subsystems on track
• UK groups have large responsibilities for
• RICH
• Vertex detector
• Software / Computing
• Construction starts soon

31
New Methods

• New strategies for measuring CKM angles - direct
• combine Bd -gt ??K - charged and neutral B to
  extract g
• ?? 20 - 70 ambiguous solutions
• combine Bs -gtKK and Bd -gt ??
• ?? 40 ?? known, U-spin
• LHCb RICH at its best
• combine Bd,s -gtDd,s D-d,s
• O(100k) events per year
• ?? a few 0
• Overconstrain CP angles a, b, g, and dg

32
Rare Decays

• Bs -gt mm-
• Standard Model branching ratio 3.7 x
  10-9 ideal to search for new physics - FCNC
• Expected signal (bkgd) 11 (3.3) 1 year
• Bd -gt Kmm-
• Standard Model branching ratio 1.5 x
  10-6 dimuon mass spectrum, forward-backward
  asymmetry
• combine with Bd -gt r mm- Vts/Vtd
• Expected signal (bkgd) 22400 (1400) 1 year
• Bd -gt Kg
• Standard Model branching ratio 5 x
  10-5 search for new physics in CPV
  asymmetry O(1) in SM
• Expected signal 26000 1 year

33
LHCb CP Sensitivities
Parameter Channels Evts/year ?(1
year) LHCb feature 2(??) Bd??? 4900 ?P/T
0 2?-5? PID, hadron trigger Bd?r? 1300 3?-6?
PID, hadron trigger 2?? Bd ? D? 340000 gt
11? PID, hadron trigger ? Bd?J/?Ks 37000 0.6?
?-2?? Bs ?DsK 2400 6?-14? PID, hadron
trigger, ?t ? Bd ? DK 400 10? PID, hadron
trigger ?? Bs ? J/yf 44000 0.6? ?t Bs
oscillations xs Bs ? Ds? 120000 up to 75 hadron
trigger, ?t Rare Decays BR Bs ?
?? lt2?10-9 ?t Bd ? K mm 22400 PID