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

CP Violation 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl Aim: Understand sources of CP Violation Theory: Standard Model: CP implemented by complex phase in CKM matrix Natural: no reason for CKM matrix to be real Beyond Standard Model: many extensions predict new interactions which produce CP Natural: Standard Model is not complete 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 Combination ??? “Measure all angles of CKM matrix”

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

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

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

Vertex Detector 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl 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.

Main Tracking Station 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl Outer Tracker: Strawtube-like drift chambers (Honeycombs) Cell radius: 5mm (Module type I and II) and 8 mm (type III) Resolution: < 200  m Inner Tracker: Size 40 x 60 cm 2 High granularity MSGC or MCSC Modular Design to keep all cell occupancies < 10% Multilayer with y u v y orientations (5  stereo) Perfomance:  p/p = 0.3 %, constant between 5 GeV/c and 200 GeV/c Mass resolution:  m B = 15.2 MeV/c 2 in B d  +  -  m D = 4.2 MeV/c 2 in D S  K + K -  - from B S decays

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

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

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

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

CKM Triangles 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

LHCb Physics Menu 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl  : B d  J/  K S  : B d  +  - B d  D *  B d   +  : B S  D S K  : B d  DK *  : B s  J/   Non CP physics: rare B and  decays D meson oscillations B C decays …….

Angle  : B d  J/  K S 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl Ideal to measure complex phase in CKM Matrix: solid Standard Model prediction large predicted asymmetry reasonable branching ratio easy signature B d  J/  K S  + -  +  - B d  J/  K S  + -  +  - “Golden” Decay Channel 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 x S are measured (with B d  J/  K S and B S  D S  ), the CKM matrix is fully determined: Further measurements check Standard Model predictions

Angle  : B d  +  - Two contributions to CP: T from oscillations, as in B d  K s P from penguin, as in B d  K +  - Experiment (CLEO): limit for BR(B d  +  - ) decreases: less statistics (LHC) more background from B d  K +  - and B s  K +  - (RICH) penguin contribution more important  Theoretical uncertainty is large 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl Measure CP in B d  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)

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

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

B s Decays 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl 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 B s Oscillations Excellent K identification with RICH to suppress D S  in D S K (branching ratio factor 15 higher)

Angle  and  B S  D S  : 120k reconstructed and tagged decays, oscillation measurements at > 5  possible up to x s = 75 B S  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 B S  D S K: 2.4k reconstructed and tagged decays Background: particle identification and mass resolution 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl

Angle  Complementary measurent: measure 6 branching ratios 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl Check ! Selftagging: K * flavor tags B 0 flavor, no extra tagging required CP reach in one year depends on value of strong phase shift  T2/T1 :

Summary 3 July 1998 Hyperons98, Genoa Werner Ruckstuhl Channel Events  (sin 2  ) = 0.01 B d  J/  K S 56.0k  (sin 2  ) = 0.06 B d  +  - 6.9k K/   (  +  ) = B s  D s K 37.1k K/ ,  t  (  ) = B d  DK * 300 K/   (  ) = 0.02 B s  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 CP reach in one year: