1. DIS 2004, Strbske Pleso,April 20041 LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays LHCb detector CP violation in Standard Model Few examples of measurements of B s mesons: - Δm s from B s 0 - B s 0 mixing in B s 0  D s π - CP asymmetries in B s 0  D s K - CP asymmetry in B s 0  J/ψ φ Conclusions Marek Szczekowski Soltan Institute for Nuclear Studies, Warsaw

2. DIS 2004, Strbskie Pleso,April 20042 LHCb detector pp collisions at  s = 14 TeV σ bb  500 µb σ inelastic  80 mb L = 2 10 32 cm -2 s -1 n B /10 7 s in 4π ~10 12 B + / B d / B s / Λ b 40 / 40 / 10 / 10 % Tracking π/K/p separation e/γ/π 0 identification hadron identification muon identification

3. DIS 2004, Strbskie Pleso,April 20043 Example of B event Selection of a specific B decay event from large background  effective trigger Reconstruction of final state  measurement of momenta and identification of particles Measurement of proper time of B decay: t  mL / pc  decay length L ( ~ 1 cm in LHCb)  momentum p from decay products (range ~ 1–100 GeV) Tagging state of B 0 : was it originally produced as B 0 or B 0 ?  e.g. charge of lepton or kaon from decay of the other b hadron can be used Bs0Bs0 π ± or K ± Ds±Ds± K+K+ K-K- π± π± b-hadron leptonK-K- primary vertex σ z ~ 50 μm σ z ~ 140 μm σ z ~ 440 μm L b  34

4. DIS 2004, Strbskie Pleso,April 20044 Tracking in LHCb VELO: silicon strips 21 stations sensors R and φ TT stations: silicon strips Outer Tracker: straw drift chambers Inner Tracker: silicon strips δp/p = 0.35 –0.55 % tracks from B decays

5. DIS 2004, Strbskie Pleso,April 20045 Time and mass resolutions Bs DsKBs DsK σ τ = 40 fs σ M(Ds) = 5.5 MeV/c 2 σ M(Bs) = 13.8 MeV/c 2 for Δm s =30 ps -1 oscillations have a period of 210 fs  sufficient resolution very good mass resolution useful in background rejection

6. DIS 2004, Strbskie Pleso,April 20046 π/K/p separation separation of B s  D s K and B s  D s π RICH 1 RICH 2  (K  K) = 88%  (π  K) = 3% Example: Two RICH systems are essential

7. DIS 2004, Strbskie Pleso,April 20047 Trigger pile-up Efficiency: 30 – 60 % Level-0: p T of , e, h,  Level-1: Impact parameter Rough p T ~ 20% HLT: Final state reconstruction 40 MHz 1 MHz 40 kHz 200 Hz output σ bb ~ 500 μb, < 1% of inelastic cross-section with high background multi-level trigger is needed to select interesting events: - L0: high p T electrons, muons or hadrons - L1: vertex structure and p T of tracks - High Level Trigger: full reconstruction

8. DIS 2004, Strbskie Pleso,April 20048 Flavour physics puzzle The fundamental question: what distinguishes different generations of quarks and leptons ? - three families of particles have the same quantum numbers, but very different properties (hierarchical masses, small mixing angles) - in Q.M. we expect similar energy levels and large mixing for a set of states with the same quantum numbers. THESE FACTS SUGGEST THAT THERE IS AN ORDERED STRUCTURE BEHIND THE FLAVOUR. - hidden flavour quantum numbers that distinguish different generations - new quantum number  new symmetry: A FLAVOUR SYMMETRY - allows the top quark Yukawa coupling - forbids all other Yukawa couplings  massless quarks - no mixing between states with different quantum numbers - experiments show that new symmetry has to be only approximate, small breaking allows small quark masses and some mixing. WHAT IS THIS SYMMETRY ?

9. DIS 2004, Strbskie Pleso,April 20049 CP violation and unitarity triangles Nine unitarity relations of the Cabibbo-Kobayashi-Maskawa (CKM) matrix Two are the most relevant in the analysis of CP violation in B-meson sector: The unitary triangle in 2007 when LHCb will start to take data:  measurement of the angle  will be crucial β - large B d -B d mixing phase (V td ) χ - small B s -B s mixing phase (V ts ) γ - b  u decay phase (V ub ) B s mesons provide access to the second unitarity triangle

10. DIS 2004, Strbskie Pleso,April 200410 Formalism for CP violation Two mass eigenstates B l and B h : Time dependent rates for initial flavour eigenstates B s and B s decaying to final states f and f : where Asymmetry: In S.M.:

11. DIS 2004, Strbskie Pleso,April 200411 Present limits: (95% CL) Channel with largest sensitivity for LHCb: B s  D s   + Decays B s 0  D s. - π + and B s 0  D s. + π - are flavour specific:  no CP asymmetry can be used to extract ~ 80,000 reconstructed events/year with S/B ~ 3 expected High branching ratio and fully reconstructed decay for D s. -  K - K + π - Decay length resolution ~ 200  m  proper time resolution ~ 40 fs Δm s and ΔΓ s from B s -B s mixing Acos(Δm s t)  free parameter A=1 for true Δm s

12. DIS 2004, Strbskie Pleso,April 200412 Error on the amplitude A of oscillations vs  m s : 5  measurement in one year for  m s up to 68 ps -1 sensitivity limit much larger than SM prediction (14.4 –26 ps -1 ) To observe mixing we must know what was originally produced: B s 0 or B s 0 tagging of production state: efficiency = 54.6 ± 1.2 % mistag rate = 30.0 ± 1.6 % Reconstructed proper-time for B s 0 decays tagged as not mixed shows clear oscillations LHCb Δm s limits from B s -B s mixing Rate (B s 0  D s - π + ) Error on amplitude A msms  m s [ps -1 ] 15 20 25 30  m s ) 0.0090.0110.0130.016

13. DIS 2004, Strbskie Pleso,April 200413 With the same topology B s  D s  is a background for D s K with ~ 12 –15  higher branching ratio the background can be eliminated by cut on difference in log-likelihood between K and  hypotheses in RICH After cuts contamination only ~ 10% Since D s  has no CP asymmetry, it can be used to control systematic errors: eg to measure any possible production asymmetry of B s and B s D s π vs. D s K

14. DIS 2004, Strbskie Pleso,April 200414 CP asymmetries in B s  D s  K + CP violation asymmetry arises from interference between two tree diagrams via B s mixing: B s  D s + K  with B s  B s  D s + K  and B s  D s  K + with B s  B s  D s  K + |T 1 |  |T 2 |  large asymmetries CP asymmetries measure  (  is the phase of V ub ) if  will be determined in B s  J/   decays  a clean method to measure γ since only tree diagrams contribute Insensitive to new physics, new particles appear in loops Branching ratio for D s   K  K    gives ~ 5400 events/year T1T1 T2T2 Four distinct decay modes, flavour-nonspecific channels  common to B 0 and B 0 decays: Bs0Bs0 Bs0Bs0 Bs0Bs0 Bs0Bs0 K+K+ K+K+ K-K- K-K- Ds-Ds- Ds+Ds+ Ds+Ds+ Ds-Ds- b bb b ss sss ss s s ss s u u u u c c c c V cb V ub V ub * V cb * V cs * V us * V cs V us Bs0Bs0 Bs0Bs0 ΔmsΔms f = D s. - K + f = D s. + K - T1T1 T2T2 T1T1 T2T2 T1T1 T2T2

15. DIS 2004, Strbskie Pleso,April 200415 Large  m s  rapid oscillations have to be resolved Unknown strong phase difference   between tree diagrams for  D s  K  asymmetry the phase is arg(λ) =    (  for D s + K  asymmetry the phase is arg(λ) =    (  With fits to two time-dependent asymmetries it is possible to extract both    and  (  Asymmetries for 5 years of LHCb data taking   (  ) ~ 14  in one year Asymmetries in B s  D s K Δm s =25 ps -1

16. DIS 2004, Strbskie Pleso,April 200416 CP asymmetry in B s  J/  Dominated by single amplitude  no CP violation in decay B s counterpart of the golden mode B 0  J/  K S CP asymmetry arises from interference of B s  J/  and B s  B s  J/   in S.M. asymmetry very small  sin 2    ~ 0.04  sensitive probe for contributions from New Physics: observation of sizeable asymmetry implies existence of NP 120,000 events/year with J/      or e  e ,  K  K  For VV decays final state is admixture of CP-even and CP-odd contributions  separation requires angular analysis of decay products Likelihood is sum of CP-odd and CP-even terms L(t) = R  L  (t) (1+cos 2  tr )/2 + (1  R  ) L  (t) (1  cos 2  tr )  tr is the transversity angle Fit for sin 2 , R  and  s /  s (  s /  s  0.1 expected)  (sin 2  ) ~ 0.06,  (  s /  s ) ~ 0.02 in one year Bs0Bs0 J/ψ  c c s s s b V cb * V cs Bs0Bs0 Bs0Bs0 ΔmsΔms f CP = J/ψ  A A

17. DIS 2004, Strbskie Pleso,April 200417 LHCb Physics Reach in 1 year (2fb –1 ) LHCb Physics Reach in 1 year (2fb –1 ) ChannelYieldPrecision  B d  J /  K s 240 000  0.6 o  B s  D s K B d  , B s  KK B d  D 0 K * B d  D CP 0 K * 5400 26000, 37000 500 3400 600  14 o  6 o  8 o  B s  J /  120 000  2 o |V td /V ts  B s  D s  80 000  m s up to 68 ps  rare decays B d  K   35 000  (A CP dir )  0.01

18. DIS 2004, Strbskie Pleso,April 200418 Conclusions To discover new physics or help interpret new physics discovered in other experiments a comprehensive study of heavy flavour physics is needed: - measure α, β, γ, χ in many decays with high precision - look at rare decays and mixing LHCb will be able to explore flavour physics with the required sensitivity and flexibility needed to discover, confirm or clarify new phenomena. The LHCb experiment will be ready for first LHC collisions in 2007