LHCb Eduardo Rodrigues University of Glasgow SUPA Lectures, Glasgow, January 2011 Part IV CP violation and B Physics Part IV CP Violation and B Physics Chris Parkes

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

Chris Parkes3 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 B s Mixing  LHC (2009  )  LHCb (also ATLAS and CMS to some extent)  Discovered B s  μ  CP Violation in B s system  D mixing at 5σ

Chris Parkes4 Of the 6 orthogonality relations the CKM matrix satisfies the “bd” term is central in many B-meson decays: CP violation studies with B mesons? btd,s W W b t W W “The” unitarity triangle (“bd”) bu transitions bc transitions B 0 mixing Of the 6 orthogonality relations the CKM matrix satisfies the “bd” term is central in many B-meson decays: bu transitions bc transitions B 0 mixing

B factories, old and future experiments

Chris Parkes6 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-hadronsheavylong-lived ! B-hadrons are heavy and long-lived !

Chris Parkes7 Idea of an asymmetric "B factory" Oddone & Dorfan in PEP-II Tunnel, 2003 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

Chris Parkes8 B factories PEP-II (BaBar) and KEKB (Belle) Asymmetric beams  boosted B’s Time difference between B decays   z

Chris Parkes9  High rate – statistics limited channel Why study CP violation at a hadron collider?  Clean environment – no additional tracks  Initial state – B 0 B 0 or B + B -  B mesons ~ 20%  tot – simpler triggering  Rich programme but messy environment e + e - (BaBar) pp (D0)  Production of all types B s and b-hadrons _

Chris Parkes10  ~ 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) CDF and TeVatron, Fermilab

Chris Parkes11 CERN and LHCb 9 km diameter Geneva Jura CERN

Chris Parkes12 LHCb environment LHC environment  pp collisions at E CM = 8 / 14 TeV  t bunch = 25/50 ns  40/20 MHz bunch crossing rate  = cm -2 s LHCb interaction region Forward peaked, correlated production ~ 1 cm B p-p collision Measure distance production (primary vertex p-p) till decay (B decay vertex) to get time LHCb VErtex LOcator (VELO) Silicon detector discs along beam direction p p

Chris Parkes13 The LHCb the LHC – characteristics Forward spectrometer Acceptance: 1.9 <  < 4.9 Nr of B’s / year: Detector: excellent tracking excellent PID Reconstruction: - muons: easy - hadronic tracks: fine - electrons: OK -  0 ’s: possible but difficult - neutrinos: no 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 B flight path of the order 5-10mm RICH performance: Cherenkov radiation. Measures velocity, combine with momentum to get mass Particle identification in p range GeV , K ID efficiency > 90%, misID<~10% Mission statement - Search for new physics probing the flavour structure of the SM - Study CP violation and rare decays with beauty & charm hadrons Mission statement - Search for new physics probing the flavour structure of the SM - Study CP violation and rare decays with beauty & charm hadrons

Mixing in neutral B mesons

Chris Parkes15 Neutral B-mesons “identity card”: 2 types of neutral B mesons Neutral B system in nature Oscillations parameter Small lifetime differences Large mass differences (~100 times larger in B d case compared to K system) B 0 = db B s = sb B 0 = db B s = sb B=+1B=-1

Reminder of Natural Units,  =c=1 Energy GeV Momentum GeV/c (abbreviated to GeV) Mass GeV/c 2 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) -2 1barn= m 2 – Natural unit of xsec =1GeV -2 =0.389mb Charge - ‘Heavyside-Lorenz units’ ε 0 =1 Use dimensionless ‘fine structure constant’ Can quote mass in seconds -1

Chris Parkes17 b d u, c, t WW WW _ d b _ b d WW WW _ d b _ _ _ _ B0B0 B0B0  (and similarly for B s ) Neutral B-mesons mixing  Feynman (box) diagrams for neutral B-meson mixing:  Dominated by top quark contribution :

Chris Parkes18  Dominated by top quark contribution : b d u, c, t WW WW _ d b _ b d WW WW _ d b _ _ _ _ B0B0 B0B0  For B 0 s (and similarly for B s ) Neutral B-mesons mixing  Feynman (box) diagrams for neutral B-meson mixing: Sensitivity to a CKM triangle side and angle  Sensitivity to side and equivalent angle  s

Chris Parkes19  Dominated by top quark contribution : b d u, c, t WW WW _ d b _ b d WW WW _ d b _ _ _ _ B0B0 B0B0  (and similarly for B s ) Neutral B-mesons mixing  Feynman (box) diagrams for neutral B-meson mixing:

Chris Parkes20 ARGUS, 1987 Observed a fully reconstructed, mixed, event, with no possible background. Measured the like-sign lepton fraction, and found that ~17% of B 0 mesons mix before they decay  t B ~1.5 ps,  m~0.5/ps Phys. Lett. B 192, 245 (1987) Discovery of B 0 mixing First hint of a really large top mass !

Chris Parkes21 Belle: K. Abe et al., PRD 71, (2005)Babar: B. Aubert et al., PRD 73, (2006) Belle: B 0 lifetime BaBar:  m d Some state-of-the-art B 0 mixing measurements B 0 oscillates once every 8 decay times ! (2  m  

Chris Parkes22 Measuring B s mixing – tagging & decay time opposite-side K jet charge Decay mode tags b flavor at decay 2 nd B tags production flavorProper decay time from displacement (L) and momentum (p)  Need to determine: – Flavour at production  tagging – Flavour at decay, from final state – B decay length

Chris Parkes23 Bs Mixing Measurement CDF discovery 2006, LHCb measurement 2011 Oscillations occur at 3 trillion Hz ! Observed amplitude is not 1 as smeared -Mistag (B or B) of events -Resolution on time Line is fitted oscillations Points are data Low background Most precise measurement of |V td /V ts | Δm s = ± (stat) ± (syst) ps −1

Chris Parkes24 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: B 0 and B s Very different oscillation rates Very fast B s oscillations (3 trillion Hz!) Mixing through box diagrams with top quark Flavour tagging at production Flavour tagging at decay

Benchmark B decays: α, β, ϒ

Chris Parkes26  The CKM matrix in terms of the Wolfenstein parameters B 0 and B s mixing phases sensitivity CKM angle measurements with B decays “The” unitarity triangle (“bd”)   The standard techniques for the angles  : B 0 mixing (phase β) (+ single b  c decay) : B 0 mixing (phase β) + single b  u decay (phase γ)  : b  u (phase γ) (interference with b  c)

Chris Parkes27 Measurement of sin(2  ) – B 0  J/  K s decay Measurement type :  time-dependent CP asymmetries of B decay to CP-eigenstate final state The “golden mode” B 0  J/ K s :  Theoretically clean way of measuring the  angle  Clean experimental signature (J/  + μ - ; K s   +  - )  Large (for a B meson) branching ratio ~ The B-factories were built for the measurement of  ! c.f. CPLEAR K 0 to π + π - + e -iφ Amplitude 2 Amplitude 1 Amplitude 2  Process via interference with/without mixing

Chris Parkes28 Angles – measured from interference Both give same rate - Interference necessary but not sufficient Two routes A 1,A 2 to same final state - hence interference sensitive to phase

Chris Parkes29 Angles – measured from interference Additional phase κ that doesn’t flip under CP, allows ϕ to be measured

Oscillation & Decay 30 t=0t B0B0 B0B0 B0B0 B0B0 B0B0 B0B0 Amplitude Rate

Measuring a CKM angle 31 But in B systemand put Gives: This extra i is the phase difference (here  =90 0 ) we need 1. Origin of extra phase  2. Origin of weak phase ϕ If and henceLets assume we can write Making these substitutions The two phase differences give terms The rate difference is time dependent ( hence assumed i.e. no direct CP Violation)

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

Chris Parkes33 Aside on getting CKM phase or phase * Feynman rules: V ud if incoming d-quark or outgoing anti-d quark V ud * if incoming u-quark or outgoing anti-u quark Quantities to find:

Chris Parkes34 Which CKM angle is measured ?

Chris Parkes35 Showing that φ=2β from CKM elements

Chris Parkes36

Chris Parkes37 β accurately measured β=21.5±0.8 0 (HFAG summer 2012)

Chris Parkes38 Measurement of sin(2  ) – B 0   decay ? Tree diagrams only: Routes to final state with and without mixing. Interference of these gives angle. mixingdecay

Chris Parkes39 Measurement of sin(2  ) – B 0   decay ? 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

Chris Parkes40 Measurement of sin(2  ) – B 0   (and other hh) decays No identification Purity = 9.5% With pion identification Purity = 85%, Eff. =90% LHCb: particle identification is crucial ! From all channels α moderately well measured α=85.4±4.0 0 (CKM fitter Aug. 2013)

Chris Parkes41 B  D 0 K : - theoretically very clean way of measuring  - sensitivity to  from interference between the 2 diagrams - only requirement: D 0 and D 0 decay to common final state - final state contains D - final state contains D-bar Measurement of  – popular (family of) methods Currently least well measured angle but LHCb changing this Note – charged B here, so no mixing Weak phase But also relative strong phase (δ) between the amplitudes of the two diagrams - nuisance parameter

Chris Parkes42 In both cases only complex phase is in V ub element, so this measures γ Measuring gamma 1. Why is this γ ? 2. How to get round strong phase Interference of amplitudes sensitive to

Chris Parkes43 In both cases only complex phase is in V ub element, so this measures γ Measuring gamma 1. Why is this γ ? 2. How to get round strong phase Interference of amplitudes sensitive to or Hence using all four processes can get γ Combining all channels γ poorly measured yet γ=68.0±8.3 0 (CKM fitter Aug. 2013)

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

Chris Parkes45 Like sign dimuon asymmetry D0 Collab. B0/B0sB0/B0s B 0 /B 0 s t=0t B0/B0sB0/B0s B0/B0sB0/B0s B 0 /B 0 s B0/B0sB0/B0s dd b BoBo c μ-μ- ν W-W- D+D+ example decay: Produce BB pair (or B s ) If one oscillates before decaying get two like sign leptons (++ or --) If no CP Violation in mixing get N ++ =N --

Chris Parkes46 New Physics ? Situation unclear –improved measurements needed (excellent PhD project…) Like sign dimuon asymmetry: current results D0 – B and B s decays inclusively Tevatron: proton anti-proton – equal matter anti-matter LHC proton proton – production asymmetry, makes analysis more tricky but statistics higher LHCb – B s only: first result compatible SM and D0 ! Asymmetry B 0 s Asymmetry B 0 World average 2.9σ away from SM !

Direct CP Violation in B 0 /B s including discovery of CP Violation in B s system

Chris Parkes48 Time-integrated measurement: Direct CP Violation Direct CP Violation: two-body B 0 & B s decays

Chris Parkes49 Time-integrated measurement: Direct CP Violation Direct CP Violation: two-body B 0 & B s decays

Chris Parkes50 Time-integrated measurement: Direct CP Violation Direct CP Violation: two-body B 0 & B s decays Use f

Chris Parkes51 However several different two-body B decays Separate with Particle ID and mass for B 0 /B s Direct CP Violation: two-body B 0 & B s decays (also Λ b, 3-body backgrounds) B  hh, (h=K,π)

10.5σ Asymmetry Chris Parkes 52 PRL110, B B BsBs BsBs 6.5σ Asymmetry FIRST CP Direct CP Violation: two-body B 0 & B s decays

Dalitz Plots – three body decays B  hhh

Chris Parkes54 Dalitz Plot – Visualize three body decays Dalitz Plot: Scatter plot in m ab 2, m ac 2 If no intermediate structure then uniformly populated (inside kinematic bounds) If intermediate resonances, r, then plot will have internal structure Shorter-lived resonances – larger widths Richard Dalitz Energy Conservation sets boundaries of plot Q = T A +T B +T C, Q energy released in decay of P, T i K.E. of product i m 2 bc

Chris Parkes55 CP Violation in B +  hhh Make Dalitz plot for B +,B - Any difference is CP violation Dalitz Plot A CP in Dalitz plot bins Local regions of large CP violation (empty bands in plot are regions that have been cut-out as used as cross-checks) ρ 0 (770), f 0 (980) K*(890), K*(1430) χ c0 Resonances seen in plot

Rare B decays

Chris Parkes57 Rare Decay Loops

Chris Parkes58 Rare B decays – All active research topics at LHCb DECAYTYPEB.R. (approx.) B 0  K* 0  B s   B 0   Radiative penguin 4.0 x x x B 0  K* 0     Electroweak penguin1.2 x B s   B 0   K S Gluonic penguin 1.3 x x B s      Rare box diagram3.5 x Radiative penguin

Chris Parkes59 The B (s)   +  - decay (1/2) Really really rare! But well predicted in SM SM box SM Penguin Sensitive to New Physics in SUSY models Unique Experimental signature Easy to identify / trigger – good for ATLAS/CMS as well

60 25 year long search Phys.Rev.Lett. 108 (2012) SM theory Powerful constraint on SUSY

Chris Parkes61 Key Points – B section CKM Angles Measured from interference of two routes to same final state sin(2  ) – B 0  J/  K s sin(2  ) – B 0      decay, and the problem of ‘’penguin pollution’’ angle ϒ - B -  D 0 K -, and strong phases Semileptonic B asymmetry, D0 experiment discrepancy with SM Discovery of (Direct) CP Violation in B s system, LHCb B s  K - π + Dalitz Plots and use as tools for CP violation, LHCb B +  hhh Rare B Decays Discovery of LHCb