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Shaking Penguins & Boxes at LHCb

Shaking Penguins & Boxes at LHCb. Lyon, le 30 Octobre 2013 Yasmine Amhis LAL, Orsay France If you have questions : amhis@lal.in2p3.fr. Sometimes this is how a flavour physics talk in a conference sounds like…. Le Questionnaire de Proust . What is the Process ?

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Shaking Penguins & Boxes at LHCb

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  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…

  3. 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 ?

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

  5. 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

  6. The LHCb detector

  7. 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 %

  8. Particle ID 9

  9. Particle ID 10

  10. Working with pile up

  11. LHCb detectors efficiency

  12. 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)

  13. LHCb 600 people

  14. 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 ?

  15. Boxe diagram Neutral Bs meson

  16. Boxe diagram Neutral Bs meson

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

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

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

  20. 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

  21. 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…

  22. How we work together ?

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

  24. A few more words Time dependent Angular terms

  25. A few more words Time dependent Angular terms

  26. La Sainte Trinité du jour ϕs ΔΓs Γs

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

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

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

  30. 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.

  31. 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.

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

  33. 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%

  34. 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

  35. Dmsfrom Bs → Dsp+

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

  37. Revenonsànos moutons

  38. Sticking all the pieces together Results I

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

  40. Putting it all together

  41. The Event ! Example of a blind analysis

  42. A very rare FCNC b μ ? μ s

  43. A very rare FCNC b μ ? μ s

  44. 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

  45. 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!

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