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CP violation in B decays: prospects for LHCb

Explore sources of CP Violation in B decays, measuring complementary channels with precise predictions and detector requirements for efficient trigger and reconstruction.

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CP violation in B decays: prospects for LHCb

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  1. CP violation in B decays: prospects for LHCb Werner Ruckstuhl, NIKHEF, 3 July 1998

  2. CP Violation • Aim: Understand sources of CP Violation • Theory: • Standard Model: CP implemented by complex phase in CKM matrixNatural: no reason for CKM matrix to be real • Beyond Standard Model: many extensions predict new interactions which produce CPNatural: Standard Model is not complete Combination ??? • Measurement: • Precise measurement of many complementary channels with reliable Standard Model prediction: • No (small) QCD corrections due to final state interaction • CP in oscillations and decays (and interferences) • Different combinations of CKM elements • Channels with large and small (no) CP within Standard Model “Measure all angles of CKM matrix” 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  3. Detector Requirements Efficient trigger and reconstruction of many different channels, both hadronic and leptonic final states • Robust and flexible trigger • high pT leptons and hadrons • secondary verteces • Good proper time resoution • CP asymmetries in fast oscillating Bs • reduce background • Good mass resolution • reduce background • Particle Identification • tagging (muons, electrons and kaons) • reduce background (/K separation in RICH) 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  4. Detector Acceptance Single arm forward spectrometer: Easy access to all detector components for maintenance and fexible for upgrades 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  5. LHCb Detector Tracking System: Vertex Detector: Silicon Microstrip Main: MSGC or MCSC (inner) + Honeycombs (outer) Muon: Cathode PadsandMultigap Resistive Pads RICH system (3 radiators):  - K separation at >3 for momenta between 1 GeV/c (K tag) and 150 GeV/c (Bd + -) Calorimeters:Preshower + ECAL (Shashlik) + HCAL(Scintillating-tile) Average Luminosity: 2 x 10-32 cm-2s-1 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  6. Vertex Detector • Precise Vertex Determination: • Precise Detector: Silicon Microstrip Counters • First point of measurement close to decay point • No material between measurement and decay vertex Install silicon counters in LHC vacuum, as close as possible to the beams (10 mm), limited by radiation damage. For injection of beam move silicon out by 3 cm. In LHCb Vertex information is used in Level 1 Trigger: r- geometry, which also makes occupancy per strip more homogenous. 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  7. Main Tracking Station Modular Design to keep all cell occupancies < 10% Multilayer with y u v y orientations (5 stereo) Inner Tracker: Size 40 x 60 cm2 High granularity MSGC or MCSC Outer Tracker: Strawtube-like drift chambers (Honeycombs) Cell radius: 5mm (Module type I and II) and 8 mm (type III) Resolution: < 200 m Perfomance: p/p = 0.3 %, constant between 5 GeV/c and 200 GeV/c Mass resolution: mB = 15.2 MeV/c2 in Bd +- mD = 4.2 MeV/c2 in DS K+K-- from BS decays 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  8. RICH Detectors Cover full kinematic range: three radiators 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  9. RICH Detectors pmin ~ 1 GeV/c K tag pmax~ 150 GeV/c two-body B decays -K separation (in ) vs. Momentum (full pattern recognition) 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  10. RICH Beam Test • Beam Test RICH 1 prototype (1/4 scale) • Resolution and Nb. Photon as expected 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  11. RICH Simulation • Full GEANT simulation of tracks • Details Simulation of Cherenkov photons • Full pattern recognition of rings 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  12. CKM Triangles 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  13. LHCb Physics Menu : Bd  J/ KS : Bd + - Bd D*Bd  +: BS  DSK : Bd DK* : Bs  J/  • Non CP physics: • rare B and  decays • D meson oscillations • BC decays • ……. 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  14. Angle : Bd  J/ KS Bd  J/ KS  +- + - “Golden” Decay Channel • Ideal to measure complex phase in CKM Matrix: • solid Standard Model prediction • large predicted asymmetry • reasonable branching ratio • easy signature Aim of LHCb: Very precise measurement on the long term:Systematics, checks with control channels CP reach in one year (55.6k tagged events): When sin(2) and xS are measured (with Bd  J/ KS and B S  DS) , the CKM matrix is fully determined: Further measurements check Standard Model predictions 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  15. Angle : Bd + - • Two contributions to CP:T from oscillations, as in BdKsP from penguin, as in Bd K+- • Experiment (CLEO): limit for BR(Bd +-) decreases: • less statistics (LHC) • more background from Bd K+- and Bs K+- (RICH) • penguin contribution more important Theoretical uncertainty is large • Measure CP in Bd K+-: • Information about penguin contribution • measure asymmetry in experimental background CP reach in one year: 6.9 k tagged events with ~ 6% background (sin 2)  0.06 (depends on penguin) 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  16. Angle  Branching ratios: Bd + -Bd K+ - Bs K+K - Bs K+ - Other channels for  measurement under study (theoretically clean): Bd : involves 0 detection Bd D*: Same method as BS  DSK, but small || expected 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  17. Angle  and  •  from BS  DSK: • Theory: Only tree diagrams involved: clean prediction • Best candidate for precise measurement of a second CKM angle Experiment: not easy to measure •  fromBS  J/  : • same decay diagram as “Golden” Decay Bd  J/KS • very small CP violation in SM •  sensitive to new physics • Bonus: Polarization in VV decay, used to separate • CP eigenstates: good measurement of S • BS  DS: • similar to BS  DSK, determination of mS and S 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  18. Bs Decays • Detector Requirements: • Excellent tracking to reconstruct the four particle final states with high efficiency and low combinatorial background (good mass and vertex resolution • Good time resolution to resolve fast Bs Oscillations • Excellent K identification with RICH to suppress DS in DSK (branching ratio factor 15 higher) 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  19. Angle  and  BS  DS: 120k reconstructed and tagged decays, oscillation measurements at > 5 possible up to xs = 75 BS  J/  : 44k reconstructed and tagged decays,  measurements at percent level possible down to / << 0.1, depends on ratio of decay amplitudes into CP=+1 and CP=-1 state BS  DSK: 2.4k reconstructed and tagged decays Background: particle identification and mass resolution 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  20. Angle  Complementary measurent: measure 6 branching ratios Check ! Selftagging: K* flavor tags B0 flavor, no extra tagging required CP reach in one year depends on value of strong phase shift T2/T1: 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

  21. Summary CP reach in one year: Channel Events (sin 2) = 0.01 Bd  J/ KS 56.0k (sin 2) = 0.06 Bd +- 6.9k K/ ( +) = 0.11-0.23 Bs  DsK 37.1k K/, t ( ) = 0.07-0.31 Bd DK* 300 K/ ( ) = 0.02 Bs  J/  44.0k t • LHCb experiment: • optimized to profit from the high B production at LHC for a rich and broad B physics program • flexibility and high efficiency in trigger and reconstruction • good resolutions and particle identification • control of systematics 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

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