CP violation measurements in b hadrons at LHCb. María Vieites Díaz Universidade de Santiago de Compostela. On behalf of the LHCb collaboration

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1 CP violation measurements in b hadrons at LHCb María Vieites Díaz Universidade de Santiago de Compostela On behalf of the LHCb collaboration Meeting of the APS Division of Particles and Fields August 4 th, 217

2 Charge-Parity Violation: why the interest? The Standard Model (SM) of particle physics despite being very successful in its predictions fails to explain matter anti-matter differences in our universe. New sources of these asymmetries (CPV) are therefore expected in any satisfactory SM extension! Flavour transitions in the quark sector are parametrised by the CKM matrix CKMfitter group These parameters are over constrained in the SM great scenario to search for incompatibilities and small deviations due to New Physics (NP) effects Why b hadrons? related unitary triangles are less squeezed hence expect larger sensitivity to any CP violation effect. M. Vieites Díaz (USC) DPF 217 2

3 CPV phenomenology How: measure interfering amplitudes with different CKM phases Mixing X L,H = q X ± p X q/p = 1 Neutral meson mixing: P(X X ) P(X X ) Ex.: a s,d sl = R(B lx ) R(B lx ) R(B lx )+R(B lx ) Decay A(X f ) A(X f ) Amplitudes for CP conjugates differ Possible also for charged hadrons Only option for baryons (baryon number conservation) Ex.: B K + π vs B K π + Interference Mixing and Decay Interference of direct decay and decay after mixing Partial decay widths are sensitive to φ q = φ mix 2φ dec Decay-time dependent CP asymmetry: Γ(B(t) f ) Γ(B(t) f ) a CP = cosh( Γt 2 )+A Γ f Ex.: B J/ΨKs = C f cos( Mt) S f sin( Mt) Γ(B(t) f )+Γ(B(t) f ) sinh( Γt 2 ) M. Vieites Díaz (USC) DPF 217 3

4 Introduction LHCb β(s) γ Baryons Summary The LHCb detector LHCb Detector Performance M. Vieites Dı az (USC) DPF 217 4

5 Experimental challenges To measure CPV an experiment needs: Excellent vertexing: to separate primary from secondary vertexes to resolve fast oscillations Very good PID performance: to distinguish between topologically identical events to tag the initial flavour content Very large sample sizes to be sensitive to tiny variations Control over known CP asymmetries/effects To help with these, the LHCb: runs at lower instantaneous luminosity than ATLAS or CMS levels the luminosity, making trigger conditions constant throughout the runs takes data with different magnet polarities M. Vieites Díaz (USC) DPF 217 5

6 A word on PID and tagging Particle Identification LHCb RICH Performance π/k separation: ε K 9%, π K misid 5% π/µ separation: ε µ 97%, π µ misid 1 3% Calibrated via data driven methods Good control and understanding of the PID performance is critical to our analyses. Flavour tagging Efficiency: ε tag = Mistag: ω = N tag N tag +N untag N wrong N right +N wrong Tagging power: ε eff = ε tag (1 2ω) 2 Statistical uncertainty: 1 σ stat εeff N M. Vieites Díaz (USC) DPF 217 6

7 Status of β (s) measurements Accessible from the interference between mixing and decay Standard Model predictions Bs system: φ ccs s 2arg ( Vts V tb ) V cs V ( cb B system: φd ccs 2arg V cd V cb V td V tb = rad ) = rad PRD (215) 737 Golden modes provide exact match to the CKM angle: B s J/ψK + K (φ s = 2β s) and B J/ψK s (φ d = 2β) Latest published results: Decay Result Reference Bs J/ψπ+ π +.7±.68±.8 PLB B (214) Bs D+ s D s +.2±.17±.2 PRL (214) Bs J/ψK + K -.58±.49±.6 PRL (215) B D + D φ = PRL (216) Bs ψ(2s)φ ±.2 PLB B762, (216) B s J/ψK+ K (m K + K > m φ(12) ) ±.17±.34 arxiv: (217) Ongoing new analyses and updates: B s J/ψ( e+ e )φ with Run I B s (K + π )(K π + ) with Run I B (s) h+ h with Run I (update) B s J/ψK + K,B s J/ψπ+ π Run II M. Vieites Díaz (USC) DPF 217 7

8 Measurement of φ ccs s Flavour-tagged, time-dependent amplitude analysis with m K + K above the φ(12) threshold with full LHCb Run I data sample. = 2β s in B s J/ψK + K arxiv: (217) Analysis strategy Selection using multivariate analysis, background subtraction via sweights in m(j/ψk + K ) and multi-dimensional fit to the decay time, m K + K and the helicity angles. Reconstruction and selection efficiency vs decay time are measured on data (control channel: B J/ψK ( K + π )) Dominant systematics arise from resonance modelling and background subtraction First time that φ s is measured in final states dominated by a tensor M. Vieites Díaz (USC) DPF 217 8

9 Measurement of φ ccs s = 2β s in B s J/ψK + K arxiv: (217) Fit results Fit projections Bs J/ψK + K m K + K >1.5GeV φ s 119 ± 17 ± 34 mrad λ.994 ±.18 ±.6 Γ s.65 ±.6 ±.4 ps 1 Γ s.66 ±.18 ±.1 ps 1 + Bs J/ψφ φ s 25 ± 45 ± 8 mrad λ.978 ±.13 ±.3 Γ s.6588 ±.22 ±.15 ps 1 Γ s.813 ±.73 ±.36 ps 1 PRL 114 (215) 4181 Combining these also with the previous LHCb measurements using the B s J/ψπ+ π yields φ s = 1 ± 37 mrad PLB 736 (214) M. Vieites Díaz (USC) DPF 217 9

10 ) ) ) ) - - Introduction LHCb β (s) γ Baryons Summary TD CPV in B (s) h+ h LHCb-CONF Motivation Two battle fronts: Extremely rare B K + K and B s π+ π Sizeable sample for their high stats partners! Branching ratios are measured for the rare modes TD CPV analysis can be done with the high stats. samples Assuming U-spin symmetry, flavour tagged TD CPV analysis can constrain γ and φ s 2 Candidates / ( 5 MeV/c 2 Candidates / ( 5 MeV/c Pull [GeV/c [GeV/c K ] 2 2 ] K m K m 5 Pull LHCb B B K K K B s B s K K K B B K + πk - + π Λ b Λ b pk pk B s B s K KXK X Comb. Comb. bkg. bkg. 2 Candidates / ( 5 MeV/c 2 Candidates / ( 5 MeV/c Pull m π m [GeV/c [GeV/c ] ] + π π + π 5-5 LHCb B π + - s B π + π - s B B π + π - + π - B B K + πk - + π - B B π + π - X + π - X Comb. Comb. bkg. bkg. Figure2: 2: Distributions of of (left) (left) mm K + K + K and and (right) mm + + for for events selected applyingth criteriaofof SelectionA Aoror B, B, respectively. The The continuous (blue) curves represent the the results o the the best best fits fits to tothe the data data points. The The most most relevant contributions to tothe the invariant mass mass spectr are are reportedand and indicated. The The vertical scales are are chosento to magnifythe the relevant signal region The The bin-by-bin residual di erences betweenthe the fits fits and andthe the data, data, in inunits of of standardeviation (pull), are are also also shown. Table 1: 1: Systematic uncertainties on onthe the yields of of the the B B!! K K + K + K and andb s B! s! + + decays. Pull 5-5 Systematic uncertainty N(B N(B! K K + K K ) ) N(B N(B s s! + + ) ) Final state state radiation Most precise single measurement in B π + π Signal mass mass shape Comb. back. mass mass shape Part. reco. reco. back. mass mass shape Unique measurement performed of B s K + K Crossfeed back. mass mass shape negligible negligible PID PIDe e ciencies Better precision expected with the Sumin in quadrature inclusion of the SS taggers! M. Vieites Díaz (USC) The of the B K + 13 The significance of the B! K K 13 K signal to to di er fromthe thenull null hypothesis is is the DPF determined 217 by by performinga a likelihoodscan scanin inthe the signal yield, i.e. i.e. repeating1 the thefitfit fo

11 Status of γ measurements Least well measured angle of the CKM unitarity triangle ( ) No top quark coupling in its definition: γ = arg (theoretically clean) V ud V ub V cd V cb Single measurements aren t precise enough to challenge the SM big effort in producing a combination of results from many (GLW+ADS) channels Direct determination: γ = ( ) vs Indirect: γ = ( ) CKMfitter group M. Vieites Díaz (USC) DPF

12 Latest addition: B ± D ( D π or D γ)k ± Theoretically similar to the very well studied B ± D h ± PLB 76 (216) Experimental challenge of π /γ reconstruction at LHCb overcame these particles are ignored in the analysis Selection is then identical to that from B ± D h ± LHCb-PAPER Final fit is performed simultaneously over 12 (B B (K π) 3 D daughters) disjoint samples and accesses 19 CPV observables These are built from different (double) ratios of partial decay widths (GLW) and phase differences for both the fully reconstructed and the D modes The Run I results from the fully reconstructed B ± D h ± decays are updated with the same fit. The shape of the m(d h ± ) distribution allows to distinguish the π and the γ modes. M. Vieites Díaz (USC) DPF

13 Results from B ± D ( D π or D γ)k ± D Kπ LHCb-PAPER M. Vieites Díaz (USC) DPF

14 Latest LHCb γ combination LHCb-CONF Obtained from the combination of several time-integrated analyses and the time-dependent B s D s K ± Follows the same strategy as the previous LHCb combination: γ = ( ) New modes added since last publication: B ± D K ± ADS/GLW (new) B ± D K ± GLW (new) Bs Ds K ± TD (1 fb 1 3fb 1 ) B ± D K ± GLW (3 fb 1 5fb 1 ) JHEP 12 (216) 87 γ = ( ) (preliminary) most precise measurement to date! M. Vieites Díaz (USC) DPF

15 ) T ) T ) +3-3 ) +3-3 Introduction LHCb β (s) γ Baryons Summary Baryons enter the game too! CPV in Λ b pπ π + π Motivation Direct CP violation (CPV) had never been observed in baryon decays Large CPV effects are expected in charmless Λ b decays (A CP 2%) Y. K. Hsiao et al. Both tree and penguin diagrams contribute with similar amplitudes a CP at 3.3σ was seen! Observables construction Triple products in the Λ b rest frame: C ˆT = p p ( p h p h + ) sin Φ C ˆT = p p ( p h + p h ) sin Φ ˆT-odd asymmetries: A ˆT = A ˆT = N Λ b (C ˆT >) N Λ b (C ˆT <) N Λ b (C ˆT >)+N Λ b (C ˆT <) N Λ b ( C ˆT >) N Λ b ( C ˆT <) N Λ b ( C ˆT >)+N Λ b ( C ˆT <) Nature Physics 13 (217) 391 M. Vieites Díaz (USC) DPF ] -2 Asymmetries [1 4 LHCb (a) ap T-odd χ 2 /ndf=21.6/1 acp T-odd χ 2 /ndf=3.5/1 (b) Φ [rad] Figure 2: Distributions of the asymmetries (a) at b -odd P,(b)a p T b -odd CP in ten di eren values of the 2 /ndf for the Pπ + and CP conservation Φ hypotheses, represented are also quoted for at b -odd P and at b -odd CP,respectively. The measured asymmetries in this bin are πa - T b =(19.47 ± 6.96 ±.86)%, A T 7.4 ±.85)%, and a b fast -odd = (19.79 ± 4.95 ±.6)% corresponding to CP-violating observable: for localised CP violation 4. according to a likelihood ratio test base uncertainty only. aˆt odd CP = 1 2 (AˆT AˆT ) Candidates / ( 22.5 MeV/c 2 Pull 1 (a) Λ b (C >) π - slow P-violating observable: Candidates / ( 22.5 MeV/c 2 Pull LHCb 1 (b) Λ b (C <) LHCb 1 (c) Λ b (-C T >) Scheme B bin4 Scheme B bin4 Full fit 8 Full fit 8 Λb pπ - π + πaˆt odd - Λ b pπ - π + π - comb. comb. Part-rec. bkg P = (AˆT + Part-rec. bkg AˆT ) 6 B K + π - π - π + B K + π - π - π + Λb pk - π + π - Λb pk - π + π Candidates / ( 22.5 MeV/c 2 Pull LHCb Scheme B bin4 Full fit Λb pπ - π + π - comb. Part-rec. bkg B K + π - π - π + Λb pk - π + π - Candidates / ( 22.5 MeV/c 2 Pull (d) Λ

16 Summary and conclusions Results found so far are compatible with SM expectations but CPV knowledge remains having several grey areas Many of them are within the LHCb physics-case! With the statistics achieved by LHCb during the Run I & II, many new analyses have become feasible and high precision measurements are being performed. Some expectations on the precisions to achieve by the end of Run II would be: 4 for γ.8 in β < 2 mrad for φ s Stay tuned for many interesting new results! M. Vieites Díaz (USC) DPF

17 Thank you for your attention!...questions M. Vieites Díaz (USC) DPF

18 Backup slides M. Vieites Díaz (USC) DPF

19 Systematics in the TD CPV analysis of B (s) h+ h LHCb-CONF M. Vieites Díaz (USC) DPF

20 Results from B ± D ( D π or D γ)k ± D KK LHCb-PAPER M. Vieites Díaz (USC) DPF 217 2

21 Results from B ± D ( D π or D γ)k ± D ππ LHCb-PAPER M. Vieites Díaz (USC) DPF

22 T measurements of A bt, A bt,anda b -odd asymmetries. Results of asymmetry measurements in Introduction LHCb CP β (s) γ Baryons Summary Binning schemes for the Λ b pπππ measurements Table 2: For b! p + decay mode, definition of regions of phase space in scheme A and scheme B, used for the measurement of the asymmetries. Mass is in GeV/c 2 Nature unit. Physics 13 (217) Scheme A m p + m p slow m +, m slow + fast Region ( GeV/c 2 ) (GeV/c 2 ) (GeV/c 2, GeV/c 2 ) 1 (1., 1.23) (, ) 2 2 (1., 1.23) (, ) 2 3 (1.23, 1.35) (, ) 2 4 (1.23, 1.35) (, ) 2 5 (1.35, 5.4) (.9, 2.) (m + <.78 m slow + <.78) (, ) fast 2 6 (1.35, 5.4) (.9, 2.) (m + <.78 m slow + <.78) fast (, ) 2 7 (1.35, 5.4) (.9, 2.)!(m + <.78 m slow + <.78) fast (, ) 2 8 (1.35, 5.4) (.9, 2.)!(m + <.78 m slow + <.78) fast (, ) 2 9 (1.35, 5.4) (2., 4.) (m + <.78 m slow + <.78) fast (, ) 2 1 (1.35, 5.4) (2., 4.) (m + <.78 m slow + <.78) fast (, ) 2 11 (1.35, 5.4) (2., 4.)!(m + <.78 m slow + <.78) fast (, ) 2 12 (1.35, 5.4) (2., 4.)!(m + <.78 m slow + <.78) fast (, ) 2 Scheme B Region i (i =1, 2,...,1) ( i 1, 1 1 phase space regions of b! p + decays are reported in Table 3 for binning scheme A and scheme B. The measured asymmetries for b! p + decays in phase space 185 M. Vieites Díaz (USC) DPF