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LHCb detector CP violation in Standard Model Few examples of measurements of B s mesons:

LHCb experiment sensitivity to CKM phases and New Physics from mixing and CP violation measurements in B decays. Marek Szczekowski Soltan Institute for Nuclear Studies, Warsaw. LHCb detector CP violation in Standard Model Few examples of measurements of B s mesons:

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LHCb detector CP violation in Standard Model Few examples of measurements of B s mesons:

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  1. LHCb experiment sensitivity to CKM phasesand New Physics from mixing and CP violationmeasurements in B decays Marek Szczekowski Soltan Institute for Nuclear Studies, Warsaw • LHCb detector • CP violation in Standard Model • Few examples of measurements of Bs mesons: - Δms from Bs0 - Bs0 mixing in Bs0 Dsπ - CP asymmetries in Bs0 Ds K - CP asymmetry in Bs0 J/ψφ • Conclusions DIS 2004, Strbske Pleso,April 2004

  2. muon identification LHCb detector pp collisions at  s = 14 TeV σbb  500 µb σinelastic  80 mb L = 2 1032 cm-2s-1 nB /107s in 4π~1012 B+ / Bd / Bs / Λb 40 / 40 / 10 / 10 % Tracking e/γ/π0 identification π/K/p separation hadron identification DIS 2004, Strbskie Pleso,April 2004

  3. Example of B event <nch>b 34 π±or K± σz ~ 140 μm K+ Bs0 σz ~ 440 μm σz ~ 50 μm Ds± L K- b-hadron π± primary vertex lepton K- • 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 (<L>~ 1 cm in LHCb) momentum p from decay products (range ~ 1–100 GeV) • Taggingstate of B0: was it originally produced as B0 or B0 ?e.g. charge of lepton or kaon from decay of the other b hadron can be used DIS 2004, Strbskie Pleso,April 2004

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

  5. BsDsK Time and mass resolutions στ= 40 fs σM(Ds) = 5.5 MeV/c2 σM(Bs) = 13.8 MeV/c2 for Δms=30 ps-1 oscillations have a period of 210 fs  sufficient resolution very good mass resolution useful in background rejection DIS 2004, Strbskie Pleso,April 2004

  6. RICH 2 RICH 1 π/K/p separation e (KK) = 88% e (π K) = 3% Example: separation of Bs DsK and Bs Dsπ DIS 2004, Strbskie Pleso,April 2004 Two RICH systems are essential

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

  8. 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 ? DIS 2004, Strbskie Pleso,April 2004

  9. 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 trianglein 2007 when LHCb will start to take data: β - large Bd-Bd mixing phase (Vtd) χ - small Bs-Bs mixing phase (Vts) γ - bu decay phase (Vub) measurementof the angle g will be crucial Bs mesons provide access to the second unitarity triangle DIS 2004, Strbskie Pleso,April 2004

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

  11. Δms and ΔΓs from Bs-Bs mixing Acos(Δmst)  free parameter A=1 for true Δms • Present limits: (95% CL) • Channel with largest sensitivity for LHCb: Bs  Ds-p+ • Decays Bs0 Ds.-π+ and Bs0 Ds.+π- are flavour specific:  no CP asymmetry can be used to extract • ~ 80,000 reconstructed events/yearwith S/B ~ 3 expected • High branching ratio and fully reconstructed decay for Ds.- K- K+π- Decay length resolution ~ 200 mmproper time resolution ~ 40 fs DIS 2004, Strbskie Pleso,April 2004

  12. LHCb Δms limits from Bs-Bs mixing To observe mixing we must know what was originally produced: Bs0 or Bs0 tagging of production state: efficiency = 54.6 ± 1.2 % mistag rate = 30.0 ± 1.6 % Reconstructed proper-time for Bs0 decays tagged as not mixedshows clear oscillations Rate (Bs0 Ds-π+) Error on the amplitude A of oscillationsvsDms:5s measurement in one yearfor Dmsup to 68 ps-1sensitivity limit much larger than SM prediction (14.4 –26 ps-1) Error on amplitude A Dms DIS 2004, Strbskie Pleso,April 2004

  13. Dsπ vs. DsK • With the same topology Bs Dsp is a background for Ds K with ~ 12 –15  higher branching ratio • the background can be eliminated by cut on difference in log-likelihood between K and phypotheses in RICH After cuts contamination only ~ 10% Since Dsphas no CP asymmetry, it can be usedto control systematic errors:eg to measure any possible productionasymmetry of Bs and Bs DIS 2004, Strbskie Pleso,April 2004

  14. CP asymmetries in Bs Ds K+ Four distinct decay modes, flavour-nonspecific channels  common to B0 and B0 decays: T1 Vus s Vcs s T2 Ds+ K+ u c Vcb* Vub* b c b u • CP violation asymmetry arises from interference between two tree diagrams via Bs mixing: Bs Ds+K-with Bs Bs Ds+K- and Bs Ds-K+ with Bs Bs Ds-K+ • |T1|  |T2 | large asymmetries • CP asymmetries measure g - 2c (gis the phase of Vub)if c will be determined in Bs J/yf decays a clean method to measureγ since only tree diagrams contribute • Insensitive to new physics, new particles appear in loops • Branching ratio for Ds- K-K+p-gives ~ 5400 events/year Bs0 Bs0 K- Ds- s s s s Vus* s Vcs* s K- Ds- u c Vcb Vub b c b u Bs0 Bs0 K+ T1 Ds+ T2 s s s s T1 Bs0 f = Ds.-K+ T2 Δms T2 Bs0 f = Ds.+K- T1 DIS 2004, Strbskie Pleso,April 2004

  15. Asymmetries in Bs  DsK Asymmetries for 5 years of LHCb data taking s(g) ~ 14 in one year • Large Dmsrapid oscillations have to be resolved • Unknown strong phase difference DT1/T2 between tree diagrams • forDs-K+ asymmetry the phase is arg(λ) =DT1/T2 + (g - 2c) • for Ds+K- asymmetry the phase is arg(λ) = DT1/T2 - (g - 2c) • With fits to two time-dependent asymmetries it is possible to extract both DT1/T2and(g - 2c) Δms=25 ps-1 DIS 2004, Strbskie Pleso,April 2004

  16. CP asymmetry in Bs J/ Vcb* b c J/ψ c Bs0 Vcs s  s s • Dominated by single amplitude no CP violation in decay • Bs counterpart of the golden mode B0 J/y KS • CP asymmetry arises from interference of Bs J/y fand Bs Bs J/y fin S.M. asymmetry very small sin 2c= 22~0.04sensitive probe for contributions from New Physics: observation of sizeable asymmetry implies existence of NP • 120,000 events/year with J/y m+m- or e+e-, f  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 termsL(t) = R-L-(t) (1+cos2qtr)/2 + (1-R-) L+(t) (1-cos2qtr) qtris thetransversity angle • Fit for sin 2c, R- and DGs/Gs(DGs/Gs 0.1 expected) s(sin 2c) ~ 0.06, s(DGs/Gs) ~ 0.02 in one year Bs0 A fCP= J/ψ  Δms A Bs0 DIS 2004, Strbskie Pleso,April 2004

  17. LHCb Physics Reach in 1 year (2fb–1) DIS 2004, Strbskie Pleso,April 2004

  18. 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 DIS 2004, Strbskie Pleso,April 2004

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