Mixing and CP violation in beauty and charm at LHCb Jinlin Fu INFN e Università di Milano On behalf of the LHCb collaboration Moriond QCD 217 La Thuile, March 25 April 1, 217
Introduction Violation of CP symmetry (CPV) is a necessary condition for the Baryon Asymmetry of the Universe [1] CPV is present only in the weak interactions via CKM mechanism in the SM, but is too small to explain the absence of antimatter in the universe Possibly there are other sources of CPV beyond SM. B and D hadrons are a fantastic laboratory to search for CPV effects extensively. [1] A. D. Sakharov, Violation of CP invariance, C asymmetry, and baryon asymmetry of the universe, JETP Lett. 5, 24-27 (1967), Sov. Phys. Usp. 34, 392-393 (1991) J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 2
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 3 Overview Combined measurement of CKM angle γ JHEP 12(216) 87 Search for CPV in b! p h+ h, h = K, decays Nature Physics(217) DOI:1.138/nphys421 Search for CPV in b! pk µ+ µ decays arxiv:173.256, submitted to JHEP Charm mixing and CPV in D! K ± decays arxiv:1611.6143, submitted to PRD A measurement in D! K + K and D! + decays arxiv:172.649, submitted to PRL
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 4 Combined measurement of CKM angle γ JHEP 12(216) 87 arg( V udv ub V cd V cb ) Direct measurement: measured in the interference between b c and b u transitions. theoretically clean measurement: δγ/γ O(1-7 ) J. Brod, J. Zupan, JHEP 141(214)51 but single measurement not very sensitive, due to small BR ~1-7 need to combine many decay modes Indirect measurement: extracted from global fits to CKM triangle Discrepancies between direct and indirect measurements could indicate new physics.
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 5 Combined measurement of CKM angle γ JHEP 12(216) 87 arg( V udv ub V cd V cb ) Combine observables from a wide range of decays with run 1 dataset ( L int =3fb 1 ), use a frequentist approach Most precise measurement =(72.2 +6.8 7.3 )o Consistent with B factory with better precision BaBar Belle = (69 +17 16 ) = (68 +15 14 ) PRD 87, 5215 (213) arxiv:131.233 (213)
Search for CPV in, b! p h+ h Transitions governed by b udu tree and b duu penguin amplitudes of similar magnitude. Large relative weak phase in SM from CKM elements, arg( VtbVtd * /VubVud * ) = α Potential non negligible CPV effects in SM h = K, Nature Physics(217) DOI:1.138/nphys421 I.I. Bigi, arxiv:168.6528 W. Bensalem et al.,plb538(22) 39-32 M. Gronau, J. Rosner, PLB749(215) 14-17 W. Bensalem et al.,prd66(22) 944 J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 6
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 7 Triple product asymmetries Use 4-body topology to build triple products Nature Physics(217) DOI:1.138/nphys421 / sin, for b b rest frame / sin, for b P-odd ( ˆT -odd ) asymmetries: A ˆT (C ˆT )= N(C ˆT >) N(C ˆT <) N(C ˆT >)+N(C ˆT <), for b A ˆT (C ˆT )= N( C ˆT >) N( C ˆT <) N( C ˆT >)+N( C ˆT <), for b P-violating variable CP-violating variable a ˆT -odd P = 1 2 (A ˆT + Ā ˆT ) production/reconstruction asymmetries don t affect results
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 8 Signal yields Nature Physics(217) DOI:1.138/nphys421 First observation of b! p + and b! p K+ K decays Events/(9 MeV/c 2 ) 15 1 5 L int =3fb 1 N sig (p + ) =6646±15 N sig (p K + K ) =13±56 LHCb (a) Full fit Λ pπ π + π b Part-rec. bkg. Comb. bkg. B K + π π π + Λ pk π + π b Events/(9 MeV/c 2 ) 4 2 LHCb (b) Full fit pπ K + K Λ b Part-rec. bkg. Comb. bkg. B K K + K + π B s K K + π π + pk + K K Λ b pk π + π Λ b 5.2 5.4 5.6 5.8 6 m(pπ π + π ) [GeV/c 2 ] 5.2 5.4 5.6 5.8 6 m(pπ K + K ) [GeV/c 2 ]
First evidence for CPV in baryons For b! p + decays: Global measurements consistent with CP symmetry Local measurements: combined 2 binning results, CP symmetry 3.3σ deviation. Nature Physics(217) DOI:1.138/nphys421 Asymmetries [%] 2 2 2 2 LHCb ap T-odd acp T-odd Scheme A χ 2 /ndf=27.9/12 χ 2 /ndf=21.1/12 5 1 ++,N*,ρ (77), Φ Phase space bin Asymmetries [%] 2 2 2 2 LHCb ap T-odd acp T-odd Scheme B χ 2 /ndf=2.7/1 χ 2 /ndf=3.5/1 1 2 3 Φ [rad] For b! p K+ K decays: Global and local measurements consistent with CP symmetry J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 9
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 1 Search for CPV in b! pk µ+ µ arxiv:173.256, submitted to JHEP b sµ+µ- FCNC process, limited amount CPV predicted in SM makes it particularly sensitive to New Physics R. Gauld, F. Goertz and U. Haisch, arxiv:131.182, JHEP1(24) 69 M. A. Paracha, I. Ahmed, and M. J. Aslam, arxiv:148.4318, PTEP 215(215) 33B4 A. K. Alok et al., arxiv:113.5344, JHEP11(211) 122
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 11 CP odd observables arxiv:173.256, submitted to JHEP Triple product asymmetries to built a ˆT odd CP C ˆT = ~p µ + (~p p ~p K ) / sin C ˆT = ~p µ (~p p ~p K +) / sin measurements A CP A raw = N( b!pk µ+ µ ) N( b!pk+ µ µ + ) N( b!pk µ+ µ )+N( b!pk+ µ µ + ) A CP ( b! pk µ+ µ )+A prod ( b ) A reco(k + )+A reco (p) A CP = A CP ( b! pk µ+ µ ) A CP ( b A raw ( b! pk µ+ µ ) A raw ( b! pk J/ )! pk J/ )
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 12 Asymmetry measurements First observation of b! pk µ+ µ arxiv:173.256, submitted to JHEP L int =3fb 1 Nsig = 6 ± 44 A CP a ˆT odd CP = ( 3.5 ± 5.stat ±.2syst ) x 1-2 = ( 1.2 ± 5.stat ±.7syst ) x 1-2 consistent with CP symmetry
Charm mixing and CPV ± D! K in arxiv:1611.6143, submitted to PRD Mass eigenstates flavour eigenstates D D mixing D mixing well established with very slow rate: x, y < 1-2 p 2 + q 2 = 1 y=( 1 2 )/( 1 + y = y cos K x sin D1,2 i = q D i ± p D i x = 2(m1 x = x cos m2 )/( 1 + 2 ) K + y sin K 2) K CPV in charm expected < 1-3 in SM, and not yet observed. CPV and mixing parameters extracted by measuring time-dependent ratio R(t) = WS/RS q ± R(t) = ± RD ± ± t RD y ( ) + DCS interference + RD 6= RD x+ 6= x y + 6= y J. FU (UNIMI & INFN) + (x± )2 +(y ± )2 t 2 ( ) 4 Moriond QCD 217 mixing direct CPV CPV in mixing and interference 217.3.27 13
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 14 Charm mixing and CPV in ) Events / (.5 MeV/c 2 7 6 5 4 3 2 1 /σ 4 2 2 4 L int =3fb 1 LHCb (a) m(d Data Fit Background 2 25 21 215 22 225 π s ) [MeV/c 2 ] ) Events / (.5 MeV/c 2 D! K ± /σ 7 6 5 4 3 2 1 LHCb (b) arxiv:1611.6143, submitted to PRD Data 2 4 25 21 215 22 225 2 2 m(d π s ) [MeV/c ] 2 4 m(d Fit Background 1.7x1 6 RS 6.7x1 3 WS 2 25 21 215 22 225 π s ) [MeV/c The double-tagged (DT) selection ( B D* + ( D π + )µ X, D Kπ ) leads to very pure samples DT allows better measurements at lower decay time than prompt selection ( D* + D π +, D Kπ ) from previous measurement. arxiv:139.6534, PRL111(213) 25181 2 ]
Charm mixing and CPV in D! K ± arxiv:1611.6143, submitted to PRD R(t) ± = R ± D + q R ± D y± ( t )+ (x± ) 2 +(y ± ) 2 4 ( t )2 6 LHCb ] -3 [1 + R 5.5 5 4.5 4 3.5 3 6 5.5 D D Prompt Doubly Tagged World s best measurements on charm mixing parameters, consistent with CP symmetry. Results with DT samples consistent with the prompt Simultaneous fit to DT and prompt samples improve precision by 1~2% J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 15 ] -3 [1 - R ] -3 [1 - - R + R 5 4.5 4 3.5 3.8.6.4.2.2.4.6.8 D D No CPV No Direct CPV All CPV allowed 5 1 t/τ
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 16 measurement in and A D! K + K D! + arxiv:172.649, submitted to PRL Given small mixing parameters (x, y < 1-2 ), the time-dependent asymmetry approximated as: PRD85(212) 129 A CP (t) (D (t)!f) (D (t)!f) (D (t)!f)+ (D (t)!f) ' af dir A t D A, the asymmetry between the D and D effective decay widths A ˆD!f ˆD!f ˆD!f +ˆD!f Neglecting sub-leading amplitudes, = and independent of the final state. a f dir A PRD75(27) 368 EPJC5(27) 579
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 17 A Extract by linear fit of the asymmetry as function of the proper decay time A (K + K ) measurement in A ( + ) A = (.3±.32±.1)x1-3 = (.46±.58±.12)x1-3 consistent with CP symmetry A(t) [%] Assuming only indirect CPV contributes to A, two values can be averaged PRD75(27) 368 to one single value: A = (.13±.28±.1)x1-3 consistent with results using µ-tagged sample at LHCb. Combine two results: most precise measurement D! K + K A(t) [%] JHEP154(215)43 2 1 LHCb D! K + K Data Fit 1 2 4 6 8 2 1 1 and A CP (t) =a f dir A t D L int =3fb 1 LHCb D! + Data Fit 2 2 4 6 8 A = (.29±.28)x1-3 D! + arxiv:172.649, submitted to PRL 2 t/ D 2 t/ D
J. FU (UNIMI & INFN) Moriond QCD 217 217.3.27 18 Summary Most precise measurement =(72.2 +6.8 7.3 )o First evidence for CPV in baryons found in with a statistical significance of 3.3σ b! p + decays No CPV found in b! p K+ K and b! pk µ+ µ decays World s best measurements on Charm mixing parameters in D! K ± decays, no CPV found. Most precise measurement of A in D! K + K and D! + decays, no CPV found.