LHCb

1. CP Violation Part IV CP Violation and B Physics Eduardo Rodrigues University of Glasgow SUPA Lectures, Glasgow, January2011 LHCb Part IV CP violation and B Physics Chris Parkes

2. Outline • PHENOMENOLOGY AND EXPERIMENTS • CP violation and Kaon physics • CP violation and B physics • B factories, old and future experiments • Mixing in neutral B mesons • Benchmark B decays • Rare B decays • CP Violation and D physics • Concluding remarks • Present status and future ahead

3. Overview of B (and D) physics CPV experiments • B factories (2000  2010): • electron-positron at γ(4S) resonance • BaBar(SLAC, USA), Belle (KEK, Japan) • Discovered CP Violation in B system, angle β • Tested CKM mechanism • D mixing established • BelleII for high luminosity Super KEK-B starts 2015 • TeVatron run II (2001  2011): • Proton- anti-proton • CDF, D0 • Discovered Bs Mixing • LHC (2009  ) • LHCb(also ATLAS and CMS to some extent) • Discovered Bsμμ • CP Violation in Bssystem • D mixing at 5σ

4. W d,s b t W CP violation studies with B mesons? • Of the 6 orthogonality relations the CKM matrix satisfies • the “bd” term is central in many B-meson decays: • Of the 6 orthogonality relations the CKM matrix satisfies • the “bd” term is central in many B-meson decays: bu transitions bu transitions bc transitions bc transitions B0 mixing B0 mixing “The” unitarity triangle (“bd”) b t d,s W W

5. B factories, old and future experiments

6. Ingredients of B physics experiment Oscillations time dependent measure time from distance (d=γct) travelled in experiment hence B needs to be produced boosted Symmetric e+e- won’t work ! p-p ok, partons different energies B decays (lifetime=1.5ps) – observe decay products Bs oscillations very fast excellent Vertex Detector Final state decay products (mostly) : pion, kaon; electron, muon, Need excellent particle ID B-hadrons are heavy and long-lived !

7. Idea of an asymmetric "B factory" • ϒ(4s) since heavy enough to decay into BB • Produce the (4S) with a strong boost in lab frame – different energies e-, e+ • BB in coherent state – oscillate together (EPR Paradox) • Find if B or B at decay time from final state • Deduce the t from the distance between the two B vertices along the boost axis Oddone & Dorfan in PEP-II Tunnel, 2003

8. B factories PEP-II (BaBar) and KEKB (Belle) • Asymmetric beams boosted B’s • Time difference between B decays  z

9. Why study CP violation at a hadron collider? _ e+ e- (BaBar) pp (D0) • High rate • statistics limited channel • Clean environment • no additional tracks • Initial state • B0B0 or B+B- • B mesons ~ 20% stot • simpler triggering • Production of all types • Bs and b-hadrons • Rich programme but messy environment

10. CDF and D0 @ TeVatron, Fermilab • ~ 6.23 Km long • √s = 1.96 TeV • Started operation in 1987 Run I : collected about 100 pb-1 until 1996 Run II: between 2001 and 2011 (after long shutdown until 2000)

11. LHC @ CERN and LHCb Jura Geneva 9 km diameter LHC CERN

12. LHCbenvironment Forward peaked, correlated production • LHC environment • pp collisions at ECM = 8 / 14 TeV • tbunch = 25/50 ns 40/20 MHz bunch crossing rate • <L> = 4.1032cm-2 s-1 @ LHCb interaction region p p ~ 1 cm p-p collision Measure distance production (primary vertex p-p) till decay (B decay vertex) to get time B LHCbVErtexLOcator (VELO) Silicon detector discs along beam direction

13. The LHCbexperiment @ the LHC – characteristics Forward spectrometer Acceptance: 1.9 < h < 4.9 Nr of B’s / year: 1012 Detector: excellent tracking excellent PID Reconstruction: - muons: easy - hadronic tracks: fine - electrons: OK - p0’s: possible but difficult - neutrinos: no Mission statement - Search for new physics probing the flavour structure of the SM - Study CP violation and rare decays with beauty & charm hadrons B flight path of the order 5-10mm p p Tracking: Silicon & Straw tubes Magnetic field Calorimeters: Electromagnetic & Hadronic calorimeters - Critical (with muons) for triggering Vertexing: High precision silicon detectors (10μm position resolution) very close to collision point RICH performance: Cherenkov radiation. Measures velocity, combine with momentum to get mass Particle identification in p range 1-100 GeV p, K ID efficiency > 90%, misID<~10%

14. Mixing in neutral B mesons

15. Neutral B system in nature Neutral B-mesons “identity card”: 2 types of neutral B mesons B0 = db Bs = sb B0 = db Bs = sb B=-1 B=+1 Small lifetime differences Large mass differences (~100 times larger in Bdcase compared to K system) Oscillations parameter

16. Energy GeV Momentum GeV/c (abbreviated to GeV) Mass GeV/c2 Length (GeV/c)-1c=0.197GeVfm=1 [1fm=1E-15m] Natural unit of length 1GeV-1=0.197fm Time (GeV/ )-1=6.6E-25GeVs Natural unit of time 1GeV-1=6.6E-25s Cross-section (GeV/c)-21barn=10-28m2 Natural unit of xsec =1GeV-2=0.389mb Charge - ‘Heavyside-Lorenz units’ ε0=1 Use dimensionless ‘fine structure constant’ Reminder of Natural Units, =c=1 Can quote mass in seconds-1

17. Neutral B-mesons mixing • Feynman (box) diagrams for neutral B-meson mixing: b d W- u, c, t u, c, t _ _ W+ - b d B0 B0 d b u, c, t _ W+ W- _ _ _ _ u, c, t b d (and similarly for Bs) • Dominated by top quark contribution :

18. Neutral B-mesons mixing • Feynman (box) diagrams for neutral B-meson mixing: b d W- u, c, t u, c, t _ _ W+ - b d B0 B0 d b u, c, t _ W+ W- _ _ _ _ u, c, t b d (and similarly for Bs) • Dominated by top quark contribution : Sensitivity to a CKM triangle side and angle b For B0 For B0 Sensitivity to side and equivalent angle bs s

19. Neutral B-mesons mixing • Feynman (box) diagrams for neutral B-meson mixing: b d W- u, c, t u, c, t _ _ W+ - b d B0 B0 d b u, c, t _ W+ W- _ _ _ _ u, c, t b d (and similarly for Bs) • Dominated by top quark contribution :

20. Discovery of B0 mixing ARGUS, 1987 Observed a fully reconstructed, mixed, event, with no possible background. Measured the like-sign lepton fraction, and found that ~17% of B0 mesons mix before they decay  tB~1.5 ps, Dm~0.5/ps First hint of a really large top mass ! Phys. Lett. B 192, 245 (1987)

21. Some state-of-the-art B0 mixing measurements BaBar: md Belle: B0 lifetime Belle: K. Abe et al., PRD 71, 072003 (2005) Babar: B. Aubertet al., PRD 73, 012004 (2006) B0 oscillates once every 8 decay times ! (2p/Dm t)

22. Measuring Bsmixing – tagging & decay time Decay mode tags b flavor at decay opposite-side K jet charge 2nd B tags production flavor Proper decay time from displacement (L) and momentum (p) • Need to determine: • Flavour at production  tagging • Flavour at decay, from final state • B decay length

23. Bs Mixing Measurement CDF discovery 2006, LHCb measurement 2011 Most precise measurement of |Vtd/Vts| • Oscillations occur at 3 trillion Hz ! • Observed amplitude is not 1 as smeared • Mistag (B or B) of events • Resolution on time Low background Line is fitted oscillations Points are data Δms= 17.768 ± 0.023 (stat) ± 0.006 (syst) ps−1

24. Key Points – B experiments & mixing • Dedicated Experiments • Asymmetric e+e- collider B Factories (Babar, Belle, Belle II) • pp collider (LHCb) • B needs to be boosted • Excellent Vertexing and Particle ID • Neutral systems: B0 and Bs • Very different oscillation rates • Very fast Bs oscillations (3 trillion Hz!) • Mixing through box diagrams with top quark • Flavour tagging at production • Flavour tagging at decay

25. Benchmark B decays: α, β,ϒ

26. CKM angle measurements with B decays • The CKM matrix in terms of the Wolfenstein parameters • B0 and Bs mixing phases sensitivity • The standard techniques for the angles • b : B0mixing (phase β) (+ single b  c decay) • : B0 mixing (phase β) + single b  u decay (phase γ) • g : b u (phase γ) (interference with b c) “The” unitarity triangle (“bd”) a g b

27. The B-factories were built for the measurement of b ! Measurement of sin(2b) – B0 J/YKsdecay Measurement type : • time-dependent CP asymmetries of B decay to CP-eigenstate final state The “golden mode” B0 J/Y Ks : • Theoretically clean way of measuring the bangle • Clean experimental signature (J/Yμ+μ-; Ksπ+π-) • Large (for a B meson) branching ratio ~ 10-4 c.f. CPLEAR K0 to π+π- • Process via interference with/without mixing Amplitude 2 Amplitude 1 Amplitude 2 + e-iφ

28. Angles – measured from interference Two routes A1,A2 to same final state - hence interference sensitive to phase Both give same rate - Interference necessary but not sufficient

29. Angles – measured from interference Additional phase κ that doesn’t flip under CP, allows ϕ to be measured

30. Oscillation & Decay t=0 t B0 Amplitude B0 B0 Rate B0 Amplitude B0 B0 Rate

31. Measuring a CKM angle 1. Origin of extra phase k But in B system and put This extra i is the phase difference (here k=900) we need Gives: 2. Origin of weak phase ϕ If and hence Lets assume we can write Making these substitutions ( hence assumed i.e. no direct CP Violation) The two phase differences give terms The rate difference is time dependent

32. Measuring a CKM angle simplifying Time dependent oscillations with amplitude of asymmetry given by phase ϕ As x~1, only part of an oscillation seen

33. Aside on getting CKM phase or phase * Feynman rules: Vud if incoming d-quark or outgoing anti-d quark Vud* if incoming u-quark or outgoing anti-u quark Quantities to find:

34. Which CKM angle ismeasured ?

35. Showing that φ=2β from CKM elements

37. β accurately measured β=21.5±0.80 (HFAG summer 2012)

38. Measurement of sin(2a) – B0ppdecay ? Routes to final state with and without mixing. Interference of these gives angle. mixing decay Tree diagrams only:

39. Penguin Pollution Measurement of sin(2a) – B0ppdecay ? But there is another route to this same final state with non-negligible amplitude Hence not a clean measurement of α Solutions: use channels with small penguin contributiuons, or correct for penguin effect

40. Measurement of sin(2a) – B0pp(and otherhh) decays LHCb: particle identification is crucial ! From all channels α moderately well measured α=85.4±4.00(CKM fitter Aug. 2013) No identification Purity = 9.5% With pion identification Purity = 85%, Eff. =90%

41. Measurement of g – popular (family of) methods Currently least well measured angle but LHCb changing this B  D0 K : - theoretically very clean way of measuring g - sensitivity to g from interference between the 2 diagrams - only requirement: D0 and D0 decay to common final state - final state contains D - final state contains D-bar Note – charged B here, so no mixing But also relative strong phase (δ) between the amplitudes of the two diagrams - nuisance parameter Weak phase

42. Measuring gamma 1. Why is this γ ? In both cases only complex phase is in Vub element, so this measures γ 2. How to get round strong phase Interference of amplitudes sensitive to

43. Measuring gamma 1. Why is this γ ? In both cases only complex phase is in Vub element, so this measures γ Combining all channels γpoorly measured yet γ=68.0±8.30(CKM fitter Aug. 2013) 2. How to get round strong phase Interference of amplitudes sensitive to or Hence using all four processes can get γ

44. Hot Topic - Semi-leptonic B Asymmetry CP Violation in mixing

45. Like sign dimuon asymmetry D0 Collab. t=0 t B0/B0s • Produce BB pair (or Bs) • If one oscillates before decaying • get two like sign leptons (++ or --) • If no CP Violation in mixing get • N++ =N-- B0/B0s B0/B0s B0/B0s example decay: ν B0/B0s μ- W- b c Bo D+ B0/B0s d d

46. Like sign dimuon asymmetry: current results Tevatron: proton anti-proton – equal matter anti-matter LHC proton proton – production asymmetry, makes analysis more tricky but statistics higher D0 – B and Bsdecays inclusively LHCb– Bs only: first result compatible SM and D0 ! AsymmetryB0s World average 2.9σ away from SM ! Asymmetry B0 New Physics ? Situation unclear –improved measurements needed (excellent PhD project…)

47. Direct CP Violation in B0/Bs includingdiscovery of CP Violation in Bs system

48. Direct CP Violation: two-body B0 & Bs decays Time-integrated measurement: Direct CP Violation

49. Direct CP Violation: two-body B0 & Bs decays Time-integrated measurement: Direct CP Violation

50. Direct CP Violation: two-body B0 & Bs decays Time-integrated measurement: Direct CP Violation Use f