Unveiling the Mysteries of Flavour Physics at LHCb Lyon, 30 Octobre 2013

1. Shaking Penguins & Boxes at LHCb Lyon, le 30 Octobre 2013 Yasmine Amhis LAL, OrsayFrance If you have questions : amhis@lal.in2p3.fr

2. Sometimes this is how a flavour physics talk in a conference sounds like…

4. Le Questionnaire de Proust What is the Process ? A tree, a penguin ? What is the observable ? What does it probe ? SM, NP, QCD ? What is the statistics? Is it a rare decay ? What is the topology ? Are you ever going to see it? What about the systematics? Do we really care about it ?

5. Let’s start shaking things Apologies, I won’t have time to discuss the other experiments….

6. LHC a Flavour Factory • Large cross sections @ 7 TeV : • σinelpp ~ 60 mb [JINST 7 (2012) P01010 • σinel(pp  charm)~ 6 mb [LHCb-CONF-2010-013] • σinel(pp  beauty )~ 0.3 mb [PLB 694 (2010) 209] In high energy collisions, bb/cc pairs are produced predominantly in the forward or backward directions Initial motivation for the design

7. The LHCb detector

8. Tracking • Proper time measurement : • Identify b-hadrons (cτ ~ 450 μm) , also in the trigger • Perform time dependent analyses. VELO 21 modules r-φ sensors • Invariant mass measurement : • Identify the signal (Bd and Bs are only 90 MeV apart) • Separate signal from background active zone : 8mm from the LHC beam : retractable Δp/p ~ 0.4 %

9. Particle ID 9

10. Particle ID 10

11. Working with pile up

12. LHCb detectors efficiency

13. Trigger System in 2012 1/200 eventscontain B hadrons → we have to select onlythese! Hardware: High PT signals in calo and muon systems Software: partial reconstruction Software: global reconstruction (very close to offline)

14. LHCb 600 people

15. Indirect Searches – Model Independent Searches Four examples of how to look for New Physics How can New Physics affect a frequency? How can New Physics affect a phase ? How can New Physics enhance a suppressed decay ? How can New Physics affect angular observables ?

16. Boxe diagram Neutral Bs meson

17. Boxe diagram Neutral Bs meson

18. Boxe diagrams Neutral Bs meson Time Evolution : Diagonalizing this Hamiltonian leads to two mass eigenstates with masses MH(L) and decay width ΓH(L)

19. The B0(s) neutral system Time Evolution Δms = MH – ML, ΔΓs = ΓH – ΓL, Γs = (ΓL+ΓH)/2

20. Color Suppressed Tree & Penguin(s)When the Bs decays…

21. Phases phases • Measure relative phase difference • ϕs=ϕM − 2ϕD between two “legs/paths/routes”. • In SM + Ignoring penguins • ϕD~ 0 • ϕsSM~ϕM • is predominantly determined by arg(Vts) • is predicted to be small ~ -0.04 • [Charles et al. Phys. Rev. D84 (2011) 033005] • New Physics (NP) can add large phases: ϕs = ϕsSM+ϕsNP

22. Theoretically : • b→ccs tree dominance leads to precise prediction of ϕs in SM. • SP → VV, admixture of CP-odd and CP-even states, measure also ΔΓs. • Experimentally : • Relatively large branching ratio. • Easy to trigger on muons from J/ψ → μ+μ-. • The Observables • 3 “P-wave” amplitudes of KK system ( A0, Aperp, Apara) • 1 “S-wave” amplitude (As) • 10 terms with all the interferences (see the next slide) • ϕs, ΔΓs, , Γs…

23. How we work together ?

24. How we work together ? Angles Mass Time Flavour Tagging

25. A few more words Time dependent Angular terms

26. A few more words Time dependent Angular terms

27. La Sainte Trinité du jour ϕs ΔΓs Γs

29. Event selection Simple cut based selection kinematics + particle identification Attempts to use MVA, but no significant improvement was observed

30. Selection Results About 28 000 signal events with very high purity !

31. Trigger Acceptance(*) “Unbiased” “Very biased” (*) C’estquandmêmeune machine hadronique !

32. Mode acceptances on the decay time Corrections needed: Track Reconstruction Online and Offline Vertexing φand PV • Total systematic error on the lifetime is 8.7 fs . • Main effect due to the track reconstruction in the Velo. • Partly due to the limited size of the control sample.

33. Decay time resolution sWeights extracted from J/ψ mass sWeights extracted from J/ψ mass fit • We measure from data using prompt J/ψ which decay at • t = 0 ps triggered with the unbiased triggers. • Model is a triple Gaussian. • Width is found to be about 45 fs.

34. Angles and their acceptances Forward geometry of LHCb + selections cuts : distorted angular acceptance Determined using MC

35. Flavour Tagging Time dependent CP asymmetry needs to identify the initial flavour of reconstructed Bs0 mesons (initial state a b or b quark). Compare this to e+e- colliders: eD2 ~ 30%

36. Dmsfrom Bs → Dsp+ • Very high statistics • Low background level • Can resolve Bs mixing frequency due to high boost Use flavour tagging to determine flavour at production, pion charge for flavour at decay

40. Dmsfrom Bs → Dsp+

41. How can New Physics affect a Phase? CKM Elements QCD corrections Input from Lattice Short Distance Contributions

42. Revenonsànos moutons

43. Sticking all the pieces together Results I

44. Sticking all the pieces together Results II ΔΓs > 0 and Φscompatible with SM – oh well !

45. Putting it all together

46. The Event ! Example of a blind analysis

47. A very rare FCNC b μ ? μ s

48. A very rare FCNC b μ ? μ s

49. How do wemeasure a BR ? Number of observed decay Efficiency Integrated luminosity bb cross section Fraction of b quarks that hadronize into a Bs Have large systematic errors

50. How do wemeasure a BR ? The trick is to normalizewith respect to anotherdecaywith a verywellknown BR: Most of systematicuncertainties cancel in the ratio of efficiency This cancellationisvery efficient if you have a normalizationchannelsimilar to your signal and selected in the sameway!