# Presentation: 823648

## Particle Identification with the LHCb Experiment

-  Chris Jones
- University of Cambridge
- On behalf of the LHCb Experiment
- IV INTERNATIONAL SYMPOSIUM ON LHC PHYSICS AND DETECTORS

## Introduction

- LHCb Goals and Detector Overview
- Hadron Identification
- System Requirements
- Design Status
- Reconstruction and Performance
- Lepton Identification
- Methods and Performance
- Summary

## Experimental Goals

- Large Samples of b decays
- At LHC startup, Nbb = 1012  / year
- b production predominately at small polar angles
- LHCb optimized as single forward arm spectrometer

- Precision Measurements of CP Violation in b decays

- Hadron and Lepton ID
- Many pure hadronic final states
- Particle identification (/K) essential
- Leptonic final states
- Efficient electron/muon ID
- Flavour tagging

- Example decays

## LHCb Experiment

**LHCb Experiment**

- Acceptance :
- 15-300mrad (bending)
- 15-250mrad  (non-bending)
- Particle ID
- RICH detectors
- Calorimeters
- Muon Detectors
- For complete overview see other LHCb speakers

- Dedicated B physics Experiment at the LHC
- pp collisions at 14TeV

- RICH1
- Z ~ 1.0-2.2 m

- RICH2
- Z ~ 9.5-11.9 m

- Calorimeters
- Z ~ 12.5-15.0 m

- Muon System
- Z ~ 15.0-20.0 m

## Physics with Hadron Identification

- Require /K separation for 1-150 GeV/c

- Two independent detectors
- “RICH1” : Aerogel and C4F10
- “RICH2” : CF4

## RICH System

- RICH2

- RICH1

- Note Scale Difference

- y-z view

- x-z view

- Different radiator media
- Spherical Mirrors
- Focus Cherenkov radiation
- Tilted to keep photon detectors outside acceptance
- Secondary flat mirrors
- Photon detectors further out of acceptance
- Maximise radiator length within z footprint
- Helps with magnetic shielding
- Acceptance
- Rich1 25-300mrad
- Rich2 15-120mrad

## RICH1 Design

**RICH1 Design**

- Extensively redesigned for LHCb re-optimisation
- X0 reduced from 14% to 8.3%
- 5.7% due to radiators
- I reduced from 4.5% to 3.1%
- Entrance window removed. Sealed to VELO instead
- Low mass mirrors
- Glass coated Be, carbon-fibre composites
- Increased Magnetic Field for trigger
- Increased Shielding
- Maintain field at photon detectors to <10 Gauss
- Secondary flat mirrors
- Vertical orientation to increase B field on axis

- VELO Exit Window

- mirrors

- Photon Detectors

- Magnetic Shielding

## Rich2 Engineering

- Tracking station removal
-  20% length increase
- EDR approved 03/2002
- Extensive structural analysis
- Magnetic fields
- Gravitation deflections
- Seismic event stability

- Super-Structure

- Mirrors

- Entrance Window

- Magnetic Shielding

- Photon Detectors

- Exit Window

## Photon Detector Requirements

- Coverage of 2.6 m2 with highest possible acceptance
- Granularity of 2.5 x 2.5 mm2
- Single photon sensitivity for  = 200-600nm
- LHC speed readout at 40 MHz

**Baseline** : **H**ybrid **P**hoton **D**etectors (coll. CERN, DEP)
**Backup**   : **M**ulti-**A**node **P**hoto**M**ultipiler  (Hamamatsu)

- 83mm

- 18mm

## Cherenkov Radiators

**Cherenkov Radiators**

- Overall the 3 radiators provide excellent /K separation over the full momentum range

## Cherenkov Rings

- C4F10 (small)     Aerogel  (large)

- CF4

## More Realistic Simulation...

- Full GEANT3 based simulation used in performance studies
- Fully realistic background simulation
- Very busy environment  RICH pattern recognition is a complex task

## RICH Pattern Recognition

- Pattern recognition approaches
- Track based : Global
- Precise treatment of overall event
- Offline reconstruction
- Track based : Local
- Fast single track approach
- Other approaches also under study
- E.g Ring Finders, Maximum Entropy.

- Observed

- Predicted

- Cherenkov Angle resolution (mrad)
- Aerogel   1.82
- C4F10      1.26
- CF4         0.59
- No. Detected Photons
- Aerogel   7
- C4F10      30
- CF4         23

## Hadron ID : Physics Performance

- Signal Purity improved from 13% to 84% with RICH
- Signal Efficiency 79%

**RICH essential for hadronic decays**
- Example :** ****B****s**** ******** ****K****+****K****-**
- Sensitive to CKM angle ****

## Muon Identification

- Muons selected by searching for muon stations hits compatible with reconstructed track extrapolations
- Compare track slopes and distance of muon station hits from track extrapolation

- For P>3GeV/c
- eff = 96.7  0.2 %
- misid = 2.50  0.04 %

## Electron Identification

- Discriminating variables
- Electromagnetic Calorimeter cluster energy / reconstructed track momentum (E/P)
- Energy deposition in pre-shower detector (EPS)

## Combined ID with RICH

- RICH Electron ID

- RICH Detectors can also discriminate leptons
- RICH alone has too high background rates
- Combining lepton ID with RICH information can also improve lepton identification performance

- Momentum / GeV/c

- Electron Efficiency

- Pion Mis-ID

## Lepton ID : Physics Performance

- Tuned Performance :-
- El. Eff. = 78%
-  mis-ID rate 1.0%

- Tuned Performance :-
-  Eff. = 86%
-  mis-ID rate 1.0%

- Performance example
- J/ reconstruction in Bs J/l+l-

-  Electron background predominately secondary electrons and ghosts
-  Rejected efficiently with PT cut

## Conclusions

- LHCb has been re-optimised for reduced material budget
- Major re-design of RICH1 - Work progressing well
- RICH2 project is now entering construction stage
- Calorimeter and Muon projects well advanced

**LHCb on schedule for first data at the LHC startup in 2007**

**Particle ID using is essential for the LHCb physics program**

## Additional Material

## Pixel Hybrid Photon Detector

- Encapsulated 1024 pixel sensor
- PhotoCathode
- Total diameter of 83mm
- Active diameter of 72mm
- 82% active area
- HV -20kV, giving 5000 photo-electron signal
- S20 photocathode with QE > 20%

- Cross-focussing and 5 times demagnification
- Anode
- Silicon pixel detector, bump bonded to readout chip
- Number requirements
- RICH1 : 168 HPDs
- RICH2 : 262 HPDs

## MaPMTs

- 8x8 array of 64 dynode chains
- 2.1 mm pixel size, 0.2mm gap
- 3.105 gain at 800V
- Bialkali photo cathode
- QE = 22% ( = 380  nm)
- UV glass window
- Active area fraction 38%
- Increased to 85% with Quartz lens

## Transition to Geant4

- Transition to Object-Oriented GEANT4 simulation well under way

## Bremsstrahlung Correction

- Correction require to account for Bremsstrahlung before and after the Magnet
- Simplified in re-optimsed LHCb detector due to removal of material inside the magnet

- Momentum p = E2
- Eo = E1 + E2

- Magnet

- Calorimeter