Measurement of CP Violation Parameter β and Search for New Physics from BaBar Experiment

Transcription

1 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Measurement of CP Violation Parameter β an Search for New Physics from BaBar Experiment Chunhui Chen Department of Physics University of Marylan Experimental HEP Seminar University of Pennsylvania January 18 th, 2008

2 Open Questions in Particle Physics Stanar Moel has explaine almost all the experimental observables in high energy physics so far, but The question of flavor: Why are there three families of matter? Why are the neutrino masses so small? Why asymmetry between matter & anti-matter (CP violation)? The question of mass: Does the Higgs boson in SM exist? Mass hierarchy problems? The question of the ark universe: What is the ark matter in the universe? What is the nature of ark energy? An more Are there uniscovere principles of nature: New symmetries, new physical laws, new particles? New Physics? Chunhui Chen, University of Marylan University of Pennsylvania, January 18,

3 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, New Physics : : It s s all aroun us! Stanar Moel (25 free parameters): extraorinarily successful explanation of only ~5% of Universe

4 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, History of the CP Violation CP: left-hane particles right-hane anti-particles C: charge conjugate; P: parity CP conserve 1964 CP-even: K S π + π CP-o: K L π + π π 0 J. Cronin V. Fitch CP violate in neutral kaons K L π + π (~10-3 ) Unexpecte, not fitting existing moels, change unerstaning of weak interaction! Is CP violation a funamental feature of Nature or just an accient in kaons? 1987 Proposal to buil asymmetric B factories to stuy CP violation in B ecays (first coll. meeting 1993 first collisions in 1999) 2001: CP violate in B 0 J/ψK S (sin2β 0) 2004:CP violate B 0 K - π + Br(B 0 K - π + ) Br(B0 K+π - ) 2004 Precise stuy of CP violation in B ecays (large effects, theoretically clean, Important test of Stanar Moel).

5 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Why Stuy CP Asymmetry CP violation (CPV) allowe in Stanar Moel (SM): Common origin with the quark mass an their mixing Spontaneous electroweak symmetry breaking (EWSB) introuce by Higgs coupling Probing the EW scale as well, complementary to other stuies at energy frontier, e.g.: high P T Physics at Tevatron & LHC Excellent probe for new Physics (NP) beyon SM Does the SM explain the observe CP violation effects? 0ne of the conitions to generate matter ominate Universe: Sakharov conitions (1967): Violation of charge conjugation C & parity P asymmetries CP Violation in SM is not large enough Baryon number violation, e.g., proton ecay Deviation from thermal equilibrium

6 CP Violation: CKM Matrix & EWSB In the SM, electroweak symmetry breaking (EWSB) arises from the Higgs mechanism, which gives mass to the W an Z bosons via interaction with the Higgs boson: m W = 1 g = m Z θ 2 υ cos W v = vacuum expectation value ~ 250 GeV Yukawa interaction of quarks with the Higgs fiel: Quark mixing: flavor (weak) eigenstate mass eigenstate relate by CKM matrix jl Vij W u il V ij : the CKM matrix that coupling the left-hane i th generation of up-quark (u,c,t) with the left-hane j th generation of own-quark (,s,b) Chunhui Chen, University of Marylan University of Pennsylvania, January 18,

7 CKM Matrix Phenomenology weak eigenstates = V CKM mass eigens, ' V ' = s V ' b V u c t V V V us cs ts V V V ub cb tb s b 3x3 complex unitary matrix: V + V=1 4 free parameters 3 angles 1 phase, change sign uner CP Observe experimental hierarchy Wolfenstein parameterization: L. Wolfenstein, PRL, 51, p (1983) Expane matrix in small parameter: λ = V us = sinθ Cabibbo 0.22 V CKM ( i ) λ /2 λ Aλ ρ η 2 2 λ 1 λ /2 Aλ 3 2 λ ( ρ η) λ A 1 i A 1 Complex Phase: changes sign uner CP (Origin of CP violation in SM) Range are 95% CL, PDG: PL. B 592, 1 (2004) Chunhui Chen, University of Marylan University of Pennsylvania, January 18,

8 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Unitarity Triangle & Search NP in B Decays * * * Unitarity: VV u ub + VV c cb + VV t tb = 0 UT as a summary of SM B Physics Vu Vus Vub V = V cs cb c V V Vt Vts Vtb CP violation in: B ππ, ρρ,ρπ. ( ρ, η ) + phases α Raiative penguin ecays B 0 an B0 s mixing CP violation in: B DK, Dπ, etc. Γ(b ulν) γ β CP violation in: B 0 J/ ψk s, etc. ( 0,0) ( 1,0 ) Moel Inepenent test SM & search for NP: Overconstarint of unitarity triangle Reunant measurement of same CKM phases: sin2β

9 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, ( ρ, η ) α γ β ( 0,0) ( 1,0 ) Most precisely measure CKM angle Important measurements for the test of SM an search for NP Overconstraint unitarity triangle Possible eviation of measure sin2β in ifferent moes ue to NP

10 B Physics v.s.. Conventional Search of NP Conventional search: irect observation Eg: observation of Higgs or new particles at LHC Approach in B physics: m B =5.28GeV, New Physics scale Λ NP TeV FCNC forbien at tree level in SM Deviation from SM ue to virtual loops effect sensitive to NP Λ NP >>E experiment Lesson learne in B 0 mixing: Observation of B 0 mixing in ARGUS experiment in 1987 b 0 B Quantum loop process: rate epens on mass of virtual top quarks an W bosons circulating in loop an quark couplings Implication: m top >50 GeV/c 2, heavier than expecte t W 0 t W First evience of heavy top, long before it is irectly observe at 170 GeV/c 2 in Tevatron Chunhui Chen, University of Marylan University of Pennsylvania, January 18, b B

11 How to Measure CKM angles (β)( Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Use mixing inuce CPV: CPV through interference between mixing an ecay amplitue B 0 an B 0 ecay ifferently: Non-exponential ecay Time-epenent ecay rate asymmetry: A CP = Γ( B Γ( B 0 0 f f CP CP ) Γ( B ) + Γ( B S sin( m t) C cos( m t) 0 0 f f CP CP ) ) Asymmetry S= η CP sin2β Inirect CPV Direct CPV C: irect CP violation C 0 S: mixe inucte CP violation relate to CKM angles Special case: one weak phase in ecay amplitue C=0 S=constant sin2β (eg: B 0 J/ψK 0 ) Clean way to extract CKM phases

12 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Inepenent Measurement of β Determination angle β by measuring sin2β: Can use three ifferent categories of B 0 ecays b W c c s b W c c b W uct,, g s s s B 0 J/ψK 0,ψ(2S)K S,η c K S, χ c1 K S,J/ψK *0 ( Κ 0 Κ S π 0 ) B 0 D* + D*, D + D,D* + D, B 0 φk 0,K + K K S, η K S, B 0 J/ ψπ 0 K S K S K S, ωk S, ρk S

13 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Measure sin2β in b ccs Moes B 0 J/ψK 0 (K 0 K S or K L ),ψ(2s)k S,η c K S, χ c1 K S,J/ψK *0 ( Κ 0 Κ S π 0 ) 0 B b W c c s J /ψ 0 K 0 B b W uct,, g s c c 0 K J /ψ Decay ominate by Single Weak Phase: C=0 an S= η CP sin2β η CP =+1(-1) for CP even: J/ψK L (o: J/ψK S ) state Correction ue to penguin iagram is small S 10-3 & C 10-3 (hep-ph/ : Factorization + Perturbative QCD) Theoretically clean way to measure sin2β Same principle for B 0 ψ(2s)k S,η c K S, χ c1 K S,J/ψK* 0 ( Κ 0 Κ S π 0 )

14 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Experimental Methos Prouce an reconstruct B mesons Measure ecay time of reconstructe B meson Mean ecay proper time of B ps (10-12 secon) Nee precise position measurement (vertexing) Determine initial flavor of reconstructe B meson: B Flavor Tagging

15 The PEP-II B Factory (SLAC) e - (9.0GeV) x e + (3.1 GeV) E CM = 10.58GeV; βγ = 0.56 Electron (9 GeV) Positron (3.1 GeV) + ee ϒ(4 S) BB L = 1 state Chunhui Chen, University of Marylan University of Pennsylvania, January 18,

16 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, PEPII Performance: Integrate Luminosity PEP-II Peak lum: cm - 2 sec -1 Deliver for BaBar >496fb -1 >470 Million BB pairs!!

17 BaBar Detector Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Detail see: Nucl.Instrum.Meth.A479:1-116,2002 Detector of Internally Reflecte Cherenkov light (PID) 144 quartz bars PMTs 1.5T solenoi ElectroMagnetic Calorimeter 6580 CsI(Tl) crystals e + (3.1GeV) Drift Chamber 40 layers e - (9GeV) Instrumente Flux Return Iron / Resistive Plate Chambers or Limite Streamer Tubes (muon / neutral harons) Trigger L1 ~2KHz, L3 120Hz Trigger eff. ~98% Silicon Vertex Tracker 5 layers, ouble sie strips High luminosity offer great challenges to our etector Collaboration foune in 1993 Detector commissione in institutes, 11 countries, ~600 physicists

18 BaBar Detector Chunhui Chen, University of Marylan University of Pennsylvania, January 18,

19 Reconstruction of B Decays Chunhui Chen, University of Marylan University of Pennsylvania, January 18, For exclusive B reconstruction, two nearly uncorrelate kinematic variables are use: Energy Difference E = E E * * B beam Energy-substitute mass mes * * ( Ebeam ) ( B ) 2 2 = p Signal at E ~ 0 σ( E) MeV Signal at m ES ~m B σ(m ES ) ~ 2.6 MeV Combinatorial backgroun

20 Signal Yiel an Purity Chunhui Chen, University of Marylan University of Pennsylvania, January 18, BBbar pairs B 0 J/ψK S Signal: N~7000 Purity > 92% Backgroun

21 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, ϒ(4 S) B B βγ = 0.56 Determine t t an B Flavour ϒ(4S) resonance e - e + B 0 _ B 0 Tag sie µ + J/ψ µ - K S Reco sie t = z / βγc z ~ 260µm Fully reconstruct a B meson (B rec ) that ecays to CP/Flavor eigenstate Reconstruct inclusively vertex of other B meson (B tag ) with remaining charge tracks Compute ecay proper time ifference ( t) between B rec an B tag Use their vertex ( z) ifference: t z/ βγ c σ( z) ~ 60µm for B reco an σ( z) ~ 170µm for B tag ϒ(4S) prouce coherent B pair B 0 meson ecays to flavor eigenstates ~ 100% Determine the flavor of B tag infer the initial flavor of B rec Eg: b c e or b c s K Effective tagging efficiency at BaBar: 30.4 ±0.3% (same technique use for all time-epenent CP analyses)

22 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, CP Analysis: Time Distribution Perfect flavor tagging & time resolution Realistic mistag probability & finite time resolution S = 0.70 C = 0.00 _B _ 0 tag: + B 0 tag: -1 B_ 0 tag: + B 0 tag: -1 f CP=± t t 1 τ CP= ± m 1 4τ τ ( f t ) = ( t) = e [ 1e ± (1[ 1 ± 2( w ) C ( cos C cos m t m+ S t sin + S sin ) m] ) ] R 4τ R: etector t resolution, w: wrong tag fraction BFlav an CP sample have the same w an R Combine unbinne maximum likelihoo fit to t spectra of Bflav an CP samples Float both sin2β an C: 66 free parameters All parameters extracte from ata

23 CP violation fit result from B 0 (cc)k ( * )0 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, sin2β=0.714 ±0.032±0.018 C=0.049±0.022±0.017 (Worl Average) sin2β=0.68 ±0.025 C=0.012±0.020 Antimatter Matter PRL 99, (2007)

24 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, From sin2β to β: cos2β Measurement 2 solutions of β β an π/2-β ambiguity Solve by several cos2β measurement: Time-epenent CP violation: B 0 J/ψK* 0 (K S π 0 ) B 0 D ( * )0 h 0 (D 0 K S ππ ) B 0 D* + D* K S cos2β > 0 as expecte in SM PRD71:032005,2005 PRL99:231802,2007 PRD74:091101,2006

25 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, UT from CP Violation & Inirect Measurement Overconstraine: growing set of inepenent measurements are consistent with CKM picture Now: looking for New Physics as correction to CKM

26 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Measure sin2β in b cc (B 0 D ( * )+ D ( * )- ) moe Another implication of overconstraine: reunant approaches to same CKM parameter B 0 D* + D*, D + D,D* + D,D* - D + 0 B 0 B b b W W uct,, g c c c c If no penguin contribution C=0 an S=-sin2β Penguin contribution: not negligible Expecte to be small (Phys.Rev.D61:014010,2000) ~5% for B 0 D ( * )+ D ( * )- (HQET + factorization) Possible NP contribution in loop (Phys.Lett.B395:241,1997) sin2β significant ifferent from J/ψK S moe Large non zero irect CP violation B 0 D* + D* - P VV ecay, Mixe CP-even (L=0,2) an CP-o (L=1) state S=-(1-2R T )sin2β, Nee angular analysis to extract R T (CP o fraction)

27 B 0 D* + D* - Signal Yiel Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Data: 348fb -1 Nsig=617 ±33 Signal eff. 2 times of Belle s: Better Reconstruction of soft π + from D* + D 0 π + Decay at Babar ue to SVT Five ouble sie Silicon layer Small mass ~4% interaction length Large ~90% geometrical coverage in ϒ(4S) C.M. Stanalone tracking ability (Design stuie in the R&D, not a coincience) Efficiency ~ 85% at 100 MeV/c BaBar SVT fit eff vs P* slow pi

28 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Time-integrate integrate Transversity Analysis (B 0 D* + D* - ) θ 1 : angle between π - momentum in D* - rest frame an D* - flight irection in B rest frame θ tr : angle between normal z to D *- ecay plane an π + flight irection in D* + rest frame φ tr : corresponing azimuthal angle Phy.Rev.D43:2193,1991 R T =0.25 Integrate over θ 1 an φ tr : R T =0.05

29 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Acceptance Effect Different transversity component has ifferent acceptance I 0,I,I II acceptance moments: (eff. Integral over phase space) CP even an o terms may have ifferent acceptance efficiencies Equal to same constant acceptance is uniform Moel acceptance moments from the MC an fixe the parameter in the fit Acceptance moments oes not eviate much from uniform α parameter: Fixe to zero by efault R T sensitive to α only if I 0,I ll are significant ifferent

30 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Acceptance & Angular Resolution Effect R T,fit R T,true No Acceptance in PDF With Acceptance in PDF Acceptance effect by soft pion reco. Eff. Depens on minimum p T of track that can be reconstructe A small effect ue to BaBar SVT performance: High eff. for low momentum charge tracks Reco eff. measure from ata (D* + helicity angle) Small corresponing sysmatic uncertainties True R T No Resolution in PDF Angular resolution not negligible: Unlike other angular analysis Large uncertainties of soft pion tracking parameters Significant bias for small R T Moel resolution using MC simulation Semi-numerical convolution R T,fit R T,true With Resolution in PDF True R T

31 Measurement Result of CP-o Fraction Chunhui Chen, University of Marylan University of Pennsylvania, January 18, PRD-RC 76, (2007) (348fb -1 ) R T =0.143 ± ± Signal + backgroun Systematic Uncertainty Angular resolution Acceptance Moments α Parameter scan Floating bg parameter Backgroun Peaking backgroun Total Goo agreement with previous BaBar & Belle results: R T =0.125 ± ± (BaBar: Phys.Rev.Lett.95:151804,2005, 209fb -1 ) R T =0.19 ± 0.08 ± 0.01 (Belle: Phys.Lett.B618:34-42,2005,140fb -1 ) Goo agreement with the theoretical calculation (Factorization) R T ~ 0.06 Phys.Rev.D61:014010,2000, Phy.Rev.D42:3732,1990 R T ~ 0.1 Eur.Phys.J.C46: ,2006

32 Time-epenent CP + Angular Analysis Chunhui Chen, University of Marylan University of Pennsylvania, January 18, If CP analysis by fit t only: S=-(1-2R T )sin2β Loss of statistical power Nee to assume the same C an S for CP-even an O components Solution: time-epenent CP an angular analysis (2D PDF) Correction for acceptance not necessary if float R T No bias for CP parameters 2-Dimentional signal PDF z=cosθ tr CP parameters for CP-even states CP parameters for CP-o state

33 CP violation Fit fit Configuration result from B 0 D* + D* - Unbinne maximum likelihoo fit to m ES, t, an cosθ tr istributions (79 parameters) Tagging an t resolution parameters fixe from BFlav Most parameters are etermine from ata, except Angular resolution Valiate fitting proceure using signal & generic MC No biase for CP parameters C + =-0.05 ± 0.14 ± 0.02 C =-0.23 ± 0.67 ± 0.10 S + =-0.72 ± 0.19 ± 0.05 S =-1.83 ±1.04 ± 0.23 B 0 D* + D* - Assume same C an S for CP-even & o terms C=-0.02 ± 0.11 ± 0.02 S=-0.66 ± 0.19 ± 0.04 Result consistent with SM expectation No evience of irect CP violation Mix inuce CP violation: 3.7σ PRD-RC 76, (2007) (348fb -1 ) Chunhui Chen, University of Marylan University of Pennsylvania, January 18,

34 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Fit Configuration CP Violation in B 0 D + D -, D* + D - & D* - D + B 0 D + D - Phys. Rev. Lett. 99, (2007) (348fb -1 ) Result consistent with SM expectation C=0.11±0.22±0.07, S=-0.54±0.34±0.06 No evience of irect CP violation seen by Belle C=-0.91±0.23±0.09 (Belle) S=-1.13±0.37±0.09 (Belle) Inconsistent with Belle s result: > 3σ Nee more ata B 0 D + D - B 0 B 0 B 0 D* + D - & D* - D + Significance of CP violation: > 4σ Result consistent with SM expectation No evience of irect CP violation PRL98:221802,2007

35 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Measure sin2β in b sss (Penguin) Moes B φk W 3 theoretically-clean moes φks, η Ks, 3Ks B 0 b u, c, t 0 B g Internal Penguin New physics in loops? 0 B b ~ br g ~ + (δ 23 ~ s R RR ) g s s s φ 0 K S s Ks 0 K S E.g.: SUSY contribution with new phases s s s s s φ η

36 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Summary of BaBar/Belle b s Results Naïve average of all b s moes (BaBar+Belle) sin2β eff =0.67±0.04 Consistent with sin2β in Golen moes Poor fit: χ 2 =32/16 of (C.L. 0.01) Nee extremely cautious when interoperating the average Assumption of Gaussian errors not justifie for all measurements Average without f 0 K 0 moe: sin2βeff=0.56±0.05 χ 2 =16/15 of (C.L. 0.25) 2σ from the one in charmonium moes More statistics crucial for moe-by by-moe stuies

37 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Summary of CKM Phase β Measurement [ 21.5 ± 1. ] β = 0 β etermine at 1 egree precision Base on sin2β in charmonium moes an cos2β >0 No sign of NP from sin2β eff measure in B 0 D ( * )+ D ( * ) Possible hints of NP effect from sin2β eff in penguin moe: hits of 1-2σ eviation from SM (nee more statistics)

38 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Constraining NP from Flavor (B) Physics New Physics New source of CP violation E.g. SUSY: 59(41) new CP-conserving (violating) parameters (phases) New Physics scale is expecte to be ~ 1 TeV Moel-Inepenent constraint from B Physics Assume 3 generation of CKM, no NP in tree level A new amplitue to B mixing r 2 e i2θ A SM + A SM A NP SM allowe region New Physics Flavor Problem: Why no NP effect in B ecays? If new physics lives at the TeV scale, a generic flavor structure is isfavore Minimal Flavor Violation New Physics Stanar Moel <~ 40% Λ NP >> TeV!

39 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Current Status of B Physics Significant unerstaning of CP violation in last 10 years Firmly establishe CKM mechanism as the primary source of CP violation we have observe so far in the quark sector. Test SM with precise measurements from B factories. No obvious sign of eviation from SM. Too small to explain the matter & anti-matter asymmetry in Universe Any new physics foun at the LHC has to obey constraints provie by BaBar an Belle More open questions arouse: New Physics flavor puzzle: (why no NP evience in B if Λ NP 1TeV?) CP violation in the lepton sectors?

40 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Looking into the Future The ultimate frontier machine will be the LHC. We may finally have a first clean glimpse of the physics beyon the Stanar Moel Many interesting physics programs: The ( one of ) highest priority (ies): Search for & observe SM Higgs Search for & iscover NP beyon SM: Pay attention to flavor physics sector: Help isentangle ifferent NP scenarios using precision measurements from flavor physics Unerstan LHC etector Essential to achieve groun breaking iscoveries at LHC Ongoing etector R&D for the future HEP experiments LHC upgrae, ILC an new neutrino experiments etc. Key to unerstan the NP seen in LHC an future of particle physics

41 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Conclusion an Prospect the beginning of the 21 st century will be as important for physics as the beginning, the first 50 years, of the 20 th century, an the LHC is going to be the first machine to make the first iscovery - T.D. Lee A bright future for particle physics! We are lucky to be here to make it happen!

42 Aitional Slies for Reference Chunhui Chen, University of Marylan University of Pennsylvania, January 18,

43 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Important Discrete Symmetries Parity, P: Reflect a system through the origin, thereby converting right-hane into left-hane coorinate systems Thought to be conserve by all the interactions just as C & T symmetries before 1956 (C.S.Wu experiment emonstrate P violation in weak interaction) Charge Conjugate, C: Change particles into anti-particles an vice versa Time Reversal, T: Reverse the arrow of time, reversing all timeepenent quantities, e.g. momentum Goo symmetries of strong an electromagnetic forces r r p p L L + e e + γ γ t t

44 The Unitarity Triangle Chunhui Chen, University of Marylan University of Pennsylvania, January 18, V is unitarity Im V i3 V * k3 V i2 V * k2 Re geometric representation: triangle in complex plane V i1 V * k1 There are 6 triangles Kaon UT flat Beauty UT n.b. these triangles are rescale by one of the sies

45 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Prouction of B Mesons σ (e + e - Harons)(nb) ϒ(1S) ϒ(2S) ϒ(3S) ϒ States = (bb) resonances Mass (GeV/c 2 ) Cross Section at ϒ(4S): ϒ(4S) PEP-II BABAR Off On bb ~1.1nb cc ~1.3 nb, ss ~ 0.3nb uu ~ 1.4 nb ττ ~ 0.9 nb Collect 11 BB Luminosity= cm -2 sec -1 B factory is also a Charm/Tau factory E CM MΥ(4S) (MeV) + ee ϒ(4 S) BB L = 1 state

46 Signal Yiel an Purity Chunhui Chen, University of Marylan University of Pennsylvania, January 18, PRL 99, (2007) 348 fb -1 ata Signal Moel: single Gaussian Backgroun: η f =-1 an BFlav Argus function [1-(m ES -m 0 ) 2 ] 1/2 exp[κ(1-(m ES -m 0 ) 2 ] enpoint m 0 fixe to GeV Backgroun: η f =+1 Using MC an sieban Peaking backgroun Small contributions Estimate using large MC BFlav sample: 0 (*) B D h + h + = π + ρ + a + 1 (,, ) Use for tag & resolution etermination See later slies

47 0 B 0 B Ientify B Flavor (B tagging) 0 0 ϒ(4S) prouce coherent B pair: ϒ(4 S) B B B 0 meson ecays to flavor eigenstates ~ 100% Determine the flavor of B tag infer the initial flavor of B rec Effective tagging efficiency at BaBar: 30.4 ±0.3% Leptons Tag: b Kaons Tag: b W - e - ν W - c b c c W + s u K - Chunhui Chen, University of Marylan University of Pennsylvania, January 18, B b W + W + 0 B c W - e + ν s u K+

48 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Flavour Tagging Performance Multivariate algorithms (neural network) to ientify B tag flavor 6 tagging categories efine: w=w(b 0 )-w(b 0 ) Figure of merit Q= ε(1-w 2 ) From m ES fit of BFlav sample Efficiency Average Mistag Fraction Mistag Fraction Difference From t fit of BFlav sample Effective Tagging Efficiency

49 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Resolve β & π/2-β ambiguity in B 0 D* + D* K S Time-epenent ecay rate asymmetry in half D* ± K S Dalitz plane Phys.Rev.D61:054009,2000. J 0,J c,j s1 an J s2 : Amplitue integral over half Dalitz plane s ± =m 2 (D* ± K S ) η y = +1( 1) for s + >s (s + <s ) J c /J 0 : ecay asymmetry in half Dalitz plane between B 0 & B 0 2J s1 /J 0 : ilution ue to mixing of CP-even an o states 2J s2 /J 0 : preicte to be positive in theory Moel-epenent interpretation: epening on the existence of broa D + s1 resonance contribution Measure J c /J 0 0 inicate unknown broa D s1 resonance B 0 D* D S1 (2536) + Phys.Rev.D74:091101, ±17 event 209fb -1 ata Phase space istribution

50 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Resolve β & π/2-β ambiguity in B 0 D* + D* K S Phys.Rev.D74:091101,2006 (209fb -1 ata) η y = 1 (s + <s ) Significantly 0 evience of broa resonance D + s1 with large Contribution to the ecay η y =+1 (s + >s ) cos2β>0 at 94% CL if J s2 /J 0 >0 Moel epenent interoperation Consistent with SM expectation Consistent with other measurements

51 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, B 0 D ( * )+ D ( * )- Signal Reconstruction Many sub ecay moes use for B 0 D ( * )+ D ( * )- reconstruction (22 moes) D* - moes: D 0 π -, D - π 0 D + moes: K - π + π +, K S π +,K - K + π + D 0 moes: K - π +, K - π + π 0, K - π + π + π -, K S π + π - At least one of D* + D 0 π + Reuce backgroun using E an mass Likelihoo L mass L MASS = G(m D0 ) x G(m D0 ) x G(m D*+ ) x G(m D*- ) Mass constraint for D 0 an D + afterwars Optimize E an L mass cuts using MC for each sub ecay moes After applying cuts, select best caniate base on L mass per event ~ caniate per event, >95% correct selection Other variables: CLEO fisher, Dalitz weight, D ecay length significance Not necessary for B 0 D* + D* - moe Useful for B0 D* + D -, D* - D +, an D + D - moes

52 Chunhui Chen, University of Marylan University of Pennsylvania, January 18, Fit Configuration CP violationfit result Configuration from B 0 D* + D - & D* - D + B 0 D* + D - B 0 D* - D + D* + D - & D* - D + : not CP eigenstates A(D* + D - )/A(D* - D + )=Re iδ S ± =2Rsin(2 β±δ)/(1+r 2 ) (S + +S - )/2=2Rcos δsin2β/1+r 2 Analyze D* + D - an D* - D + separately: Phys. Rev. Lett. 99, (2007) (348fb -1 ) B 0 D* + D - B 0 D* - D + C + =+0.18 ± 0.15 ± 0.04 C =+0.23 ± 0.15 ± 0.04 S + =-0.79 ± 0.21 ± 0.06 S =-0.44 ± 0.22 ± 0.06 If no CP violation: C + =-C - an S + =-S - Significance of CP violation: > 4σ