B Physics at the LHC Neville Harnew University of Oxford

OUTLINE Introduction The LHC experiments Physics prospects Major changes to LHCb News on detector optimization ATLAS, CMS Physics prospects Particle ID and angle a Measurement of angle g Importance of high statistics, angle b Rare decays Summary and conclusions

Physics motivation Unitarity Triangles Standard Model Bd0  p+ p- Bd0  r p Bd0  DK*0 BS0  DSK Bd0  D* p, 3p BS0  DS p Bd0  J/y KS0 BS0  J/y f Standard Model predicts large CP violating asymmetries for B mesons CP violation predicted in many (often v.rare) decays need large samples of Bd, Bu, Bs mesons, B baryons Need consistency checks

CP violation in 2007 s(sin2b) < 0.02 (world average) ~ s(sin2a) ~ 0.1 s( g ) ~ v.large |Vtd/Vts| from DmS by CDF & D0 limited by theory |Vub/Vcb| from bu by BaBar & Belle ~ a b g |Vtd/Vts| |Vub/Vcb|

bb angular distribution Advantages of the LHC bb angular distribution LHCb makes advantage of: bb production sharply peaked forward-backward Low luminosity is sufficient (2.0 x 1032 cm-2s-1) Vertex detector close to interaction region.

LHCb Experiment (“classic”) Acceptance 10 – (250) 300 mrad (non) – bending plane Particle ID p-K separation 1<p<150 GeV/c Vertexing Proper time resolution 43 fs Bs -> Dsp (K) 30 fs Bs -> J/y f

LHCb Light No tracking stations in magnet region “Vertical” RICH-1 No magnetic shielding plate RESULT : an improved detector

Major re-design of LHCb LHCb material budget Increased significantly since Technical Proposal. Detector is being reoptimized. Beampipe Al  Be-Al alloy VELO reduced number of stations 25  21 & thinner Si RICH-1 composite mirror and mirror support outside acceptance. Tracking stations from 9  4 Trigger optimization Include Level-0 information B-field to provide PT information. B-field to provide PT information s(1/p)~0.2/p  0.01 /GeV New RICH-1 design required by presence of B-field. 2-mirror geometry Magnetic shielding box Retain Aerogel & C4F10 B  p+p- rate improved by factor 2 ~0.7 X0 and ~0.2 l0 now reduced by factor ~2

ATLAS/CMS Experiments Acceptance |h| < 2.5 Particle ID ATLAS v.limited p-K separation, ~0.8s from TRD Vertexing Special pixel B layer R~5cm “Low” luminosity running Lumi 1033 cm-2s-1 Only 30fb-1 (3 years) Specialist B triggers BUT : Possible staging of DAQ -need to wait and see ATLAS

Power of LHCb particle ID B0  h+h- Mass resolution ~17 MeV Purity = 84% ; Efficiency = 90% B  p+p-

ATLAS particle ID ATLAS use event-by-event max likelihood using: Proper time Reconstructed mass K/p separation variable (~0.8 s) Takes into account asymmetry only in: B0  p+p- BS  K+K- Not easy ! B0  h+h- Mass resolution ~ 70 MeV

ATLAS : Measurement of a After 30 fb-1 (3 years) s(a) LHCb (1 year) 2a

Measurement of g at LHCb Importance of redundancy Importance of particle ID Importance of BS modes Re-optimization of LHCb currently in progress. All performance figures are pre - detector optimization.

Measurement of angle g (1)  Measurement of angle g (1) Expect 2400 events in 1 year of data taking s(g-2dg) = 30 160 Depends on (g-2dg) strong phase diff and xs . ( ) Bs -> Ds K + - 4 Rate asymmetries measure angle g-2dg Theoretically clean

 Measurement of g (2) From Bd  +- , Bs  K+K- ACP = AdircosDmt + AmixsinDmt ~5k events per year in each channel Invoke U-spin symmetry & relate pp and KK coefficients to extract g (Fleischer CERN-TH/2000-101) s(g) ~ 5 – 10o [theory]

Assumes perfect knowledge (blue) and 10% uncertainty (red) in |h|  Measurement of g (3) Bd  D*-+ , D*+- Measures 2b+g ( ) 4 Time-dependent decay rates Relies on efficient hadron trigger CP asymmetry very small (need large statistics) s (2b + g) in degrees 1 year 5 years - Inclusive D* reconstruction ~ 500 k events/year with S/B~5 - Add D*a1 channels ~ 360 k events/year - Get b from B->J/y Ks (2b + g) in degrees Assumes perfect knowledge (blue) and 10% uncertainty (red) in |h|

LHCb sensitivity per year : s(g) ~ 10O Measurement of g (4) Bd D0 K*0 signal From Bd0 D0 K*0 Determination of g from the measurement of 6 time-integrated decay rates : Bd D0 K*0 , Bd D0 K*0 , Bd D0CP=+1 K*0 K+p - K- p + K+K-, p+p- Visible BR’s ~ 10-8  10-7 Measurement only possible with forward detector with particle ID LHCb sensitivity per year : s(g) ~ 10O

Bd0  J/y Ks sworld(sin 2b) ~ 0.02 or better by 2006 What will LHC bring to this topic ? STATISTICS ! Each LHC experiment gives s(sin 2b) ~ 0.02 in 1 year True precision measurement of this parameter Eg. Fit for direct CP-violating contribution

Rare decays Bs0  mm Standard Model BR ~ 4x10-9 Here the General Purpose Detectors have an advantage : high pT di-muon triggering at high (1x1034) luminosity. CMS : 100 fb-1 (107s at 1034 cm-2s-1) ~26 signal events 6.4 events background Muon trigger : 2 m’s with pT > 4 GeV | h| < 2.4 Search also for Bd0  mm Standard Model BR ~ 1x10-10

LHCb efficiencies & yields Performance figures are for 1 year’s running. Trigger efficiencies for reconstructable events Event yields are for tagged events Performance figures are currently being re-evaluated. 45% Preliminary 64% 35%

Performance figures (1 year)

After 1 year of LHC (2008)

or maybe … … maybe g will provide a surprise

Summary A precision study of CP violation will be performed at the LHC. Physics beyond the SM will be probed. Redundancy of measurements in many channels. LHCb provides good particle ID, vertexing. An efficient & flexible trigger is essential. ATLAS/CMS measure lepton channels very well, but are not competitive in hadronic modes. Detector construction of all 3 expts progressing well. LHC will be ready for data-taking in 2007. ATLAS, CMS and LHCb will all be there on day 1.