The ATLAS B-Physics programme

1. The ATLAS B-Physics programme James R Catmore ATLAS group, University of Lancaster United Kingdom The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch) Institute of Physics HEPP Conference 2005, Dublin, Republic of Ireland

2. Overview of ATLAS Weight: 7000 tonnes Length: 46m Muon chambers Barrel toroid Radius: 11m EM calorimeter Forward calorimeter End-cap toroid Hadronic calorimeter Inner detector The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

3. The LHC Environment • pp collisions: 14 TeV centre of mass energy • Luminosity: • 2007: 100 days @ 0.5 x 1033 cm-2s-1Tuning • 2008-2009: 200 days @ 2 x 1033 cm-2s-1 “Low” • 2010+: 1034 cm-2s-1 “High” • Drops by factor ~2 during 10 hour run • 1 proton bunch crossing every 25ns • 4.6/23 pp collisions/crossing @ low/high luminosity • ~1% of pp collisions produce a bb pair • At luminosity 2 x 1033 cm-2s-1 • bb events produced with rate of 106 Hz • 10Hz output to permanent storage for B-physics so highly selective and adaptable B-physics trigger required The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

4. The ATLAS Trigger System Region of interest data LVL1 LVL2 Event filter Calorimeters Muon Systems Tracking Read-out buffers Event Builder Distributed storage & analysis(“Grid”) Pipeline memory 1 GHz interaction rate 75 kHz 1 kHz 100 Hz The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

5. B-physics trigger strategies As luminosity drops during the run, more triggers are turned on The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

6. The current ATLAS B-physics studies The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

7. Bs meson physics • B mesons mix: • Mixing parameters: • ΔMsBs→Dsπ, Bs→Dsa1 • ΔΓs , φsBs→ J/ψ(μμ) φ, Bs→ J/ψ(μμ) η ,s ,s The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

8. μ+μ- B0S J/ψφ B0S K+K-  A┴A║A0 2 1 J/ K+ φ - B0S Physics with BS→J/ψφ • Aim: measurement of ΔГs and φs • S → V V decay so three final state helicity configurations: • To extract φs we must separate out the helicity amplitudes → angular analysis: 3 angles in inner detector …so final state is made up of linear combinations of helicity amplitudes which are CP-eigenstates with different parities p p The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

9. Physics with BS→J/ψφ Accurately modelled by EvtGen The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

10. Physics with BS→J/ψφ • Experimental technique: • Identify BS→J/ψφ decays, collect angular distribution • Fit distribution against theoretical expression to extract the parameters, using a Maximum Likelihood Estimator • Magnitudes and forms of εtag, εrec ,, ρ, b estimated with simulation • Correlations between parameters are of critical importance The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

11. Physics with BS→J/ψφ The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

12. Physics with BS→J/ψφ xs - φs region ATLAS (3yr @ 1033cm-2s-1) Statistics: 300 000 LHCb (5yr @ 5 x 1032cm-2s-1) performance as given in 2000 Statistics: 240 000 Allowed by Standard Model (updated 2003) New physics: Left-right symmetric model (NP-LR) Fleischer, Ball, 2000 The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

13. Rare Decays • FCNC processes b→d, b→s • forbidden at tree level: occur at lowest order as loops • sensitive to deviations from S.M. e.g. B→μμ Standard Model: Br(Bd→μμ) ≈ 1.5 x 10-10 Br(Bs→μμ) ≈ 3.5 x 10-9 ATLAS measurement Combing the two samples: 4.3σsignificance forBr(Bs→μμ) 95% C.L. upper limit for Br(Bd→μμ) = 3x10-10 The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

14. Conclusions • ATLAS is well placed to perform a diverse range of precise measurements on B-physics events • A flexible trigger strategy will allow efficient use of beam-time • Precise measurements to test sensitivity of CPV or other NP indicators in charm and charmless decays will be carried out • In rare muonic decays already after 1yr @ 1034cm-2s-1 sensitivity down to BR ~ 3 x 10-10 • Rare semi-muonic and rare radiative decays: statistics allow the testing of the sensitivity of angular distributions to NP • QCD tests: b-quark, b-b production, origin of Lb polarization, doubly HF production mechanisms (Bc) The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

15. Additional Slides The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

16. Is it a B or a B? (Tagging) Jet charge tag For Bd→ J/ψ(μ6μ3)K0S Tagging efficiency εtag = 0.64 Wrong-tag fraction Wtag = 0.42 b/b? b/b? Signal B/B-meson εtag(electron) = 0.012 εtag(muon) = 0.025 Wtag(electron) = 0.27 Wtag(muon) = 0.24 b/b? b/b? Lepton tag from semi-leptonic decay Signal B/B-meson The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

17. where W+ = Pdf (Bd→ J/ψK0S) W- = Pdf (Bd→ J/ψK0S) Measuring sin(2β) with Bd→ J/ψ K0S • Decay into a CP eigenstate (CP=-1) • So far the study assumed no direct CP violation, the plan is to include it The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

18. Measuring sin(2β) with Bd→ J/ψ K0S • To achieve high sensitivity: • Triggers selecting J/ψ→μμ, J/ψ→ee • Combined tagging techniques: lepton tag and jet-charge tag 3 years @ 1033 cm-2 s-1: The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

19. arg(P/T) CP violation with Bd→π+π- • Decay into a CP = +1 state: • Penguin diagrams contribute without suppression so large hadronic uncertainties • Difficult to isolate the decay from other similar decays (Bd→K+π-, Bs→K+K-, Bs→K- π+, Λb→pπ-, Λb→pK-) • Low branching ratio • Maximum likelihood: The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

20. CP violation with Bd→π+π- The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

21. Theory Experiment • Measurement highly dependent on the trigger scheme • ΔMs determination not sensitive to value of ΔΓs with these channels 1 year @ 1033 cm-2 s-1: Bs meson physics: ΔMs measurement • Bs→Ds(φ(KK))π, Bs→Ds (φ(KK))a1(ρ0π+): B(t=0) = Bs • p-(t), p+(t) = probability of decay in the state B(t) = Bs , B(t) = Bs The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

22. Physics with BS→J/ψφ The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)

23. SM MSSM C7g >0 MSSM C7g <0 More Rare Decays Semi-muonic decays: Bd→μμK0*, Bd→μμφ m+ (a) Branching ratios: enhancement from beyond the S.M. (b) Forward-backward asymmetry m- b s ? m+ Bd Three points: mean values of AFB in three q2/MB2 experimental regions with error bars q K*0 m- The ATLAS B-physics programme James R Catmore (James.Catmore@cern.ch)