Results on B decays from BaBar

Transcription

1 Results on B decays from BaBar Vasilii Shelkov Lawrence Berkeley National Laboratory BaBar Collaboration 1

2 The BaBar Collaboration 2 9 Countries, 72 Institutions, 554 Physicists

3 3

4 Instrumented Flux Return DIRC stand-off box 1752 PMTs in water Electro Magnetic Calorimeter Quartz bars Drift Chamber e + (3.1 GeV) - 4e (9. GeV) Silicon Vertex Detector

5 Unique features of Babar - asymmetric beams which create mean 26 µm primary vertex displacement & 5(1)µm SVT B CP (B TAG ) vertex resolution to measure it - novel 3D particle ID device DIRC more than 3. sigma p/k separation up to 3.4 Gev/c, with 1.6 ns timing to fight backgrounds - fine segmentation of hadronic detector IFR provides us with the opportunity to look for neutral K L clusters - DAQ ability to take data continuously at KHz rate and 2-4 Kbytes event size with <1% avr. deadtime, with 4.2 ns between bunch crossings (LEP 22ns, Tevatron - 396ns, LHC 25 ns) 5 - rolling calibrations & very prompt(1-3 days delay) offline reconstruction providing multi-layered access to data( nano, micro, mini )

6 BaBar daily datataking efficiencies 6

7 BaBar daily recorded luminosity Design daily luminosity 7

8 PEP-II/BaBar 1999/2 integrated luminosity 8

9 PEP-II and BaBar in numbers Integrated: L ON = 21.1 fb -1, L OFF = 2.5 fb -1, L 24Hr = fb -1 Peak: PEPII: Plans: L PEAK = 3.1 x 1 33 I LER = 155(26) ma, I HER = 8(11) ma N bunches = 692, IP beam sizes = 147x5 microns new run starts on January 15 th (cosmics), and February 7 th, 21 (colliding beams) 9

10 Resolution for π and Ks π γ γ σ 1 = 2.8 MeV σ 2 = 11. MeV Κ S π + π 1

11 Cherenkov angles for π and K from D * D π +, D K - π + π K 11

12 12 B Physics: CP -?, SM CP -??, New Physics -??? Two-Photon Physics: glueballs(gg), 4-quark(qqqq), hybrid(qqg), molecules (KK) mesons γγ ππ, γγ KK - tests of the perturbative QCD Tau Physics: ν τ mass limit(τ ΚΚπν); m S quark mass; CP violation in the vector/axial interference in τ Κπν, ΚΚπν, secondaryclass currents τ η π/κ ν; CP, lepton structure τ electric dipole moment Charm Physics: Physics reach of BaBar DD mixing; CP in D K + K - ; rare/forbidden, leptonic, semileptonic, hadronic decays measurements of f Ds, tests of HQET

13 Unitarity Triangle. b u l ν B Κπ B πρ, a π V ud V ub * ( ρ, η) α V td V tb * B B mixing B ργ CP violation 13 B πππ B ππ, Κπ B D cpk γ V cd V * cb b c l ν β B J/ψΚ S, J/ψΚ L B ψ(2s)κ S B φκ S

14 B physics search for CP G B mesons are heavy (m B >>Λ QCD ) to be substituted by b quark field G Like neutral K mesons, B s have mass eigen-states which are not flavor eigen-states B B mixing G In the Standard Model, the flavor-changing neutral currents (FCNC) are forbidden, and no direct couplings b s, b d are expected: b d t t d b penguins w - g,γ,ζ b t s,d 14 G The CPT theorem forbids partial rate asymmetries which are CP violating to occur on the tree level, BUT in the SM the interference of tree, box, and penguin diagrams can cause the time dependant/integrated rates differences due to a single weak phase in CKM: δ CKM = γ =arg(vub * )

15 Physics topics Charmless B decays G B -> π + π, K + π, K + K - G quasi two body and three body B decays G B ->K * γ B decays to exclusive charm states G G G G G B ->D *+ ρ, B ->D *+ π B ->J/ψΚ S, B ->J/ψΚ, B ->Y(2S)K S,. B lifetime measurements B mass measurements B ->J/ψΚ L Measurements of BB mixing and sin2β G mixing with dilepton B events G mixing with semileptonic and hadronic B events G measurement of sin2β 15

16 Charmless 2-body B decays to charged pions and kaons G Physics motivation Direct CP violation in Kπ channel: CKM angle γ Time dependant CP measurement for π + π : CKM angle a G Analysis method Background dominated by continuum Fisher discriminant Particle ID using kaon selector and likelihood methods DIRC performance at high momentum is critical... θ c (rad) a) π K K-π separation (σ) b) BABAR BABAR p (GeV/c) p (GeV/c)

17 Cut-based analysis using kaon selector ππ Κπ KK G G G Cut on event shape variables to reduce background Use Cherenkov angle to select ππ, Kπ, KK candidates Fit mass distribution to determine signal yields ππ Κπ Energy-substituted mass E KK N(ππ ππ) = N(Kπ) = Events /.25 GeV/c 2 Events /.25 GeV/c (a) m ES (GeV/c ) (b) m ES (GeV/c ) 2 2 Events /.2 GeV Events /.2 GeV (d) E (GeV) (e) E (GeV) N(KK) = 1+-4 Events /.25 GeV/c (c) Events /.2 GeV (f) m ES (GeV/c ) E (GeV)

18 Branching fraction results G Global likelihood fit using m ES, E, Fisher discriminant, and Cherenkov angle PRELIMINARY B(Kπ) (1-6 ) Mode π + π K + π N S Stat.Sign. B(1-6 ) CLEO BELLE K + K ( < 15) 2.1 <6.6 <1.9 < h + h BABAR (statistical only) ± ± Theory predicts: ± ± Br(π + π ) = (9.+/ 2.)x σ 2σ 3σ 4σ 5σ B(ππ) (1-6 )

19 1 tons! 19 DIRC with open doors

20 Studies of Charmless Quasi-Two-Body and Three-Body B Decays We consider channels mediated by b u tree or b s penguins Many have potential for CP violation studies Quasi-two-body modes B + ω h +, ω π π + π - B ω K γγ B + η K +, η' ηπ + π B η'k Cut-based blind analysis, validated with control samples: B(B + D π + (Κπ)π + )(x1-4 ) 2.21 ±.11 [2.3 ±.2] PDG B(B + D π + (Κππ )π + )(x1-4 ) 6.79 ±.32 [7.37 ±.84] PDG B + D π + signal 2 Three-body modes (B 3h) B + Κ π + B + ρ π + B + ρ Κ + B + π + π + π B + Κ + π + π B ρ ± π (where h = π/k) ±

21 Selected Results m ES and E for B ρ ± π ± m ES vs. E for B + η K + Dalitz plot for K + π + π after full analysis cuts 21

22 22 PRELIMINARY Summary of Results We have produced several competitive measurements of branching ratios and upper limits, and anticipate further results in the near future: ωh + ωk η ηππ K + η ηππ K s BR/1-6, 9% CL <24 <14 62±18±8 <112 # σ CLEO value 14.3 ± 3.6 < 21 8 ± 1 89 ± 18 BR/1-6, 9%CL # σ CLEO value BR/1-6, 9%CL # σ CLEO value K * π + ρ K + K + π + π <28 <29 33±11± < 16 < 17 < 28 ρ π + π + π + π ρ ± π 24±8±3 <22 49± ± 3.4 < ± 8.4 All analyses are statistics-limited. Main sources of systematics are: tracking efficiency: 2.5%/track; π efficiency: 5%/π ; Monte Carlo statistics: 2-7% ± -5

23 Measurement of the B ->K*γ Branching Ratio Beam energy known more precisely than particle energies PRELIMINARY Data PRELIMINARY E* = E K* +E - E γ beam M = ( ES E2 beam -p2 B )1/2 B(B ->K* γ)=( (stat) (sys) )x1-5 BABAR B(B ->K* γ)=( (stat) (sys) )x1-5 CLEO 23 Standard Model Expectation B(B ->K* γ) = ( ) x 1-5

24 Search for B ->(K, K*)l + l - : results 24 PRELIMINARY E (GeV) E (GeV) B + -> K + e + e - M ES (GeV/c 2 ) B -> K*e + e - M ES (GeV/c 2 ) E (GeV) E (GeV) B + -> K + µ + µ - M ES (GeV/c 2 ) B -> K*µ + µ M ES (GeV/c 2 ) Mode e + e - K + µ + µ K + e + e - K* µ + µ K* # obs. evts 2 1 Total 3 # bkg. evts % C.L. limit < 12.8 x 1-6 < 8.3 x 1-6 < 24.7 x 1-6 < 25.2 x 1-6 For the purpose of setting the limit, we assume that all events in the signal region could be due to signal processes Background is not subtracted The number of background events is extracted from sideband in data Total expected number of signal events is about 1 (estimated from GEANT MC based on Ali et al. predictions).

25 Measurement of the Branching Ratios for * and + B D π B D ρ * + G may exhibit small CP asymmetries interesting in the future G example of flavor tagging G Fully reconstruct and estimate yields in the modes: B G Count total B events recorded G Measure B reconstruction efficiencies with MC * + * + G Extract B( B D π ), B( B D ρ ) Branching Ratios and Estimate Errors: B D * + π + D π K * Nreconstruc cted D π ) = * + + N.5 2 [ B( D D π ) B( D K π + )] ε ( B BB π + B D * + ρ π π + D π K π + 25

26 E (GeV).3.2 B D π * + Combinations/15 MeV B A B AR PRELIMINARY m ES (GeV/c 2 ) B = (2.9 ±.3 (stat) ±.3 (syst) )x1-3 (2.76 ±.21)x1-3 PDG Combinations/2.5 MeV E (GeV) B A B AR m ES (GeV/c 2 )

27 B D ρ * + E (GeV) Combinations/15 MeV B A B AR 5 PRELIMINARY m ES (GeV/c 2 ) Combinations/2.5 MeV E (GeV) B A B AR 27 B = (11.2 ± 1.1 (stat) ± 2.5 (syst) )x1-3 (6.8 ± 3.4)x1-3 PDG m ES (GeV/c 2 )

28 Exclusive B Decays to Charmonium B J/ψK * (K + p - ) B Y(2S)K B J/ψK s (π + π s (π + π ) ) B + χ B + J/ψK + c1 K + 28 PRELIMINARY B J/ψK Decay from K s π + π - from K s π π Energy Substituted Mass / GeV Branching Fraction (1 4) 1.2 ± 1. ± ± 2. ± 1.2 B J/ψK* 13.8 ± 1.1 ± 1.8 B Ψ(2S)K B + J/ψK ± 1.9 ± 1.8 B + J/ψK* ±.5 ± 1.1 B + Ψ(2S)K ± 1.4 ± ±.7 ± 1.1 B + χ c1 K ± 1.6 ±.9

29 Exclusive B Decays to Charmonium PDG (2) B A B A R

30 An Event of the CP Sample A candidate in the Golden Mode B CP with: J J / ψ KS, K + / ψ µ µ S π + π A negative kaon is found in the decay products of the other B meson, which is therefore tagged as a B z is measured precisely, thanks to the Silicon Vertex Detector 3

31 A Completely-Reconstructed Event π µ + Κ B A candidate in the mode CP with: ψ (2S) K S, K + ψ (2S) µ µ S π + π π + π π + π + µ The other B meson is fullyreconstructed in the mode: B D D * + * + π f D π s D K π + 31

32 Amplitude Analysis of B->J/ψK * BABAR CLEO PRELIMINARY A 2 A 2 φ.13 ±.6 ±.2.6 ±.6 ± ±.39 ±.2 Fraction of CP odd. Longitudinal Polarization BABAR φ.1 ±.27 ±.1 32 Will be used for future sin(2β) measurement.

33 B and B + Mass Measurement G Using J/ψK * (K + π ), J/ψK s (π + π ) and J/ψK + candidates. B and B + masses measured from reconstructed mass Mass difference measured from energy-substituted mass 33 PRELIMINARY ± ± ± ± ± ± ± ± ± M(B ) = MeV ( PDG) M(B + ) = MeV ( PDG) M(B ) -M(B + ) = MeV ( PDG)

34 Will be used for a future sin(2b) measurement. B J/ΨK L PRELIMINARY " K L identified as neutral clusters. " Direction measured. " Energy inferred from constraining J/y + K L to the B mass. Measured Yield: 82 ± 14 (stat) ± 9 (syst) events Expected Yield : 93 events 34

35 B lifetimes from fully reconstructed hadronic B decays Inclusive vertex reconstruction 1 cβγ Measure t = ( z z ) opp rec opp Event topologies similar to those in CP measurements Use the same techniques to reconstruct t Fully reconstructed hadronic B decay, e.g. B D - π + K + π - π - 35

36 Sample of fully reconstructed B mesons in 2-body decay modes 221 ± 58 B /B purity: 86 % 7.4 fb -1 on peak 2261 ± 53 B + /B - purity: 89 % 36 B D * - π + B D * - ρ + B D * - a 1 + B D - π + B D - ρ + B D - a 1 + B J/ψK * ( K + π - ) Extract background t distribution from candidates in the mass sideband. B - D π - B - D* π - B - J/ψ K - B - Y(2S) K -

37 B Lifetime Measurements B /B B + /B - PRELIMINARY t (ps) τ B = 1.56 ±.52 (stat) ±.29 (syst) ps [PDG= ±.32] t (ps) τ B + = 1.62 ±.49 (stat) ±.35 (syst) ps [PDG= ±.28] 37 τ B +/ τ B = 1.65 ±.44 (stat) ±.21 (syst) [PDG= 1.62 ±.29]

38 B B mixing and sin2β G B B oscillations have been studied for almost 15 years with time integrated approach at Y(4S)(Argus, Cleo) and time dependant technique at Z pole( LEP) G in the SM it s described by the second order box diagram and can be used to extract V td, but large theoretical uncertainty of f B remains the biggest systematic error G the observable used to measure B B oscillations is the numbers of B B (unmixed) and B B,B B (mixed) pairs plotted as a function of their vertexes separation z = t cβγ H ± 1 Γ t ( t; Γ, md, D) = Γe d a 4 [ 1± D cos m t] R( t; ) 38 where + is for unmixed, - is for mixed events D=(1-2w), w mistag probability, m d the mixing parameter, R( t;a) vertex resolution function and a vector of parameters of the resolution function

39 B B mixing and sin2β G The log-likelihood function is then constructed from the sum of H ± over all mixed and unmixed events, and over different tag types, i, each with its own characteristics dilution factor D i tagging ln L = ln H + ( t; Γ, md, Di, ai ) + ln H ( t; Γ, md, Di, a i unmixed mixed i ) 39 G due to the presence of background 3 more components are added: B B B ±,1 ±,2 ±,3 = ( 1± D ) δ ( t) R -zero lifetime Γ2 = 2 Γ3 = 2 1 (1 ± (1 ± D D 2 3 ) e ( Γ 2 t ) cos( m 3 R t)) e ( Γ 3 t ) R - non-zero lifetime, no mixing -non-zero lifetime, with mixing

40 B B mixing and sin2β G parameters of the fits: oscillation frequency m d, tagging separation Q = ε D and 3 parameters of the z resolution function are extracted from the fit G these parameters and their errors are used for sin2β fit and all sorts of effects associated with this approximation were studied At BaBar there were 3 different techniques used to measure B B oscillations: with hadronic decays B->D * h with semileptonic decays B->D * l ν used to understand CP time dependant fits and assess systematics 4 with inclusive dilepton events superior statistics! G most of the ground work is done the sin2β measurement is next.

41 41 βγ=.56 ϒ(4S) Dileptons: an inclusive approach for B mixing B + ± ± N( )( t) N( A( t) = + ± ± N( )( t) + N( 2 additional parameters in the fit to take into account the fraction of mistagged events (cascade leptons). l - < z> = 25 µm B l + )( t) )( t) B Flavor => sign of the direct lepton Inclusive approach => large BR (~4%) Mixture of B and B ± => Fraction R fitted Fit of m and the fraction R

42 Dilepton Mixing: Results With 7.7 fb -1 on-resonance and 1.1 fb -1 off-resonance data m d = (.57 ±.15(stat) ±.22 (syst)) D ps -1 Preliminary m d =.472 ±.17 PDG Dilepton sub-sample enriched in B with partial reconstruction of B D*l ν Very Preliminary 42

43 Mixing: Comparison with Other Measurements PRELIMINARY Time-dependent analyses from LEP experiments and SLD, and from CDF Time-integrated measurement from CLEO not shown Different systematics: timedependent analysis with pure B sample and clean tagging Note: measurements from other experiments are combinations of multiple measurements 43

44 1 e j tj [1 ± D sin 2fi sin m d t ] 4 Measurement of sin2β The area of the unitarity triangle, the Jarlskog Invariant, is proportional to the amount of CP violation in the Standard Model B tag B CP e - e + If we can measure the flavor of a decay (B tag ) occurring at a time t, then at that time, the flavor of the other B ( B ) is known. D z f - f + f + f - f ± ( t ; ; m d ; D sin 2fi) = 44

45 Dilutions and resolution function efficiency mistag rate effective ε 45 In the likelihood fits, we use event-by-event time resolution errors. We introduce two scale factors S 1 and S 2 and the corresponding fractions of events (f 1 and f 2 ). The parameters of the resolution function are fitted to data:

46 The Result 12 J/ψΚ s (π + π & π π ) candidates with tagged flavor PRELIMINARY Asymmetry BABAR Preliminary -5 5 t (ps) 46 sin2β=.12±.37 (stat) ±.9 (syst)

47 sin2β: Comparison with Other Results.12 ±.37 ±.9 PRELIMINARY 47 From global fits sin2β=

48 BaBar/PEP-II schedule 7 3 Integrated Lumi [fb-1] N(J/ψ ψ Κ S ) ~ 9 tagged 2 N(J/ψ ψ Κ L ) ~ 6 tagged 1 N(π+π ) ~ 7 tagged N(Κ+π ) 7 tagged Peak Lumi [1**33] Yearly Lumi Cumulative Lumi Peak Lumi Yearly Lumi Cumulative Lumi Peak Lumi Year 48 ~25M BB ~65M BB

49 Conclusion - BaBar and PEP-II completed its first Physics Run recording 21.6 fb -1 of on-peak data and achieving 3.1x1 33 peak luminosity - Overall performance of PEP-II/BaBar was better than the design, understanding of the detector and data quality are constantly improving getting very close to the design levels for all the sub-detectors - Results presented here are based on the 8fb -1 data set, but analysis of the full 1999/2 dataset is well under way and new BaBar results will be coming out very soon! - With full 99/ data set we expect to get down to.2 statistical error in the measurements of Sin2β - New run will start within weeks and we hope to accumulate another 3-35 fb -1 of data by Summer 21 49