James Weatherall for the BaBar Collaboration. The Legacy of LEP and SLC Siena, October 9 th 2001

Transcription

1 James Weatherall for the BaBar Collaboration The Legacy of LEP and SLC Siena, October 9 th 21

2 7KH%D%DU&ROODERUDWLRQ &RXQWULHV,QVWLWXWLRQV 3K\VLFLVWV Canada [4/16] U of British Columbia McGill U U de Montréal U of Victoria China [1/6] Inst. of High Energy Physics, Beijing France [5/5] LAPP, Annecy LAL Orsay LPNHE des Universités Paris 6/7 Ecole Polytechnique CEA, DAPNIA, CE-Saclay Germany [3/21] U Rostock Ruhr U Bochum Technische U Dresden Italy [12/89] INFN, Bari INFN, Ferrara Lab. Nazionali di Frascati dell INFN INFN, Genova INFN, Milano INFN, Napoli INFN, Padova INFN, Pavia INF, Pisa INFNN, Roma and U "La Sapienza" INFN, Torino INFN, Trieste Norway [1/3] U of Bergen Russia [1/13] Budker Institute, Novosibirsk United Kingdom [1/8] U of Birmingham U of Bristol Brunel University U of Edinburgh U of Liverpool Imperial College Queen Mary & Westfield College Royal Holloway, University of London U of Manchester Rutherford Appleton Laboratory USA [35/276] California Institute of Technology UC, Irvine UC, Los Angeles UC, San Diego UC, Santa Barbara UC, Santa Cruz U of Cincinnati U of Colorado Colorado State Florida A&M U of Iowa Iowa State U LBNL LLNL U of Louisville U of Maryland U of Massachusetts, Amherst MIT U of Mississippi Mount Holyoke College Northern Kentucky U U of Notre Dame ORNL/Y-12 U of Oregon U of Pennsylvania Prairie View A&M Princeton SLAC U of South Carolina Stanford U U of Tennessee U of Texas at Dallas Vanderbilt U of Wisconsin Yale

3 CP violation with BABAR Machine,detector,physics principles Measurement of sin2β (includes mixing) Results on asymmetries in B decays Towards sin2α Summary π + π Siena, October 9 th 21 3

4 The Unitarity Triangle β measured through time dependent decay rate asymmetries in b -> ccs decays such as B -> J/ψ Ks a f ( t) = ( ± 1) sin ( 2 ) sin ( PW) V V V ud cd ud V V V * ub * cb * ub η (,) B B ± * * + VcdVcb + VtdVtb γ DK ± d B ππ,ρπ D * π (ρ,η) α B β J/ Ψ V V K S td cd = V V 1 * tb * cb Siena, October 9 th 21 4

5 ψ Interference between decays (to CP eigenstate) with and without mixing produces asymmetry in t e Υ( 4S) + e B rec B tag µ J /ψ + + µ K S π π Exclusive B Meson Reconstruction z t z / <βγ> c l K B-Flavor Tagging Siena, October 9 th 21 5

6 *H9H RQ*H9H e + e - Y(4S) B B FRKHUHQW QHXWUDO%SDLUSURGXFWLRQDQG GHFD\SZDYH ERRVW RI<6LQODEIUDPHβγ

7 DIRC (PID) 1.5T solenoid CsI(Tl) EMC e + (3.1GeV) Drift Chamber e - (9GeV) Instrumented Flux Return Silicon Vertex Tracker SVT: 97% efficiency, 15µm z resol. (inner layers, perpendicular tracks) Tracking : σ(p T )/p T =.13% P T +.45% DIRC : K-π separation >3.4σ for P<3.5GeV/c EMC: σ E /E = 2.3% E -1/4 1.9%

8 ϒ(4S) B 2 B 1 All particles detected Total E, p in Y(4S) frame: E* B, p* B E = E * B - s / 2 m ES = (s/4 p * B 2 ) E : σ~15 MeV m ES : σ~3mev Siena, October 9 th 21 8

9 Before tagging Events: 441 Purity: 97% J/ψ K S K K S -> π π S ->π + π - Events: 95 Purity: 87% Events: 85 Purity: 96% Events: 56 Purity: 74% ψ6 K S J/ψ K* Sample GDWD [ %% SDLUV IE RQSHDN χ F K S Purity 74% After tagging 8% J/ψ K L [charmonium] K S 48 96% -1 Jpsi K L % +1 Jpsi K* (K S π ) Full CP sample tagged events 5 83 CP mixed Events: 41 Purity: 95% 257 6%

10 Ranked Categories: Lepton charge of fastest electron or muon Kaon Net charge of identified kaons NT1/NT2 Neural Net (slow pions, Jet Charge ). Different cuts on NN output e -,µ - b c s K - Lepton, Kaon tagging NN tagging

11 Sample of B decays to self-tagging modes, B FLAV, used for measurement of tagging performance: Q i = ε i D i2, D i = 1-2w i D i = Dilution, w i = wrong tag fraction ε i = fraction of events that were tagged Tagging category ε (%) w(%) Q (%) Lepton 1.9 ± ± ±.5 Kaon 35.8 ± ± ±.9 NT1 7.8 ± ± ±.4 NT ± ± ±.3 ALL 68.4 ± ± 1.2 Siena, October 9 th 21 11

12 FLAV States with definite flavour for measurement of lifetimes, mixing and z resolution and tagging performance for sin2β measurement Cabibbo favoured open charm decay: e.g.b D (*)- π + /ρ + /a 1 + Charmonium decays: e.g. B + J/ψ K + Charged B Mesons N B + / B 85 purity 85% Neutral B Mesons N B / B 94 purity 83% Siena, October 9 th 21 12

13 FLAV 2.7 fb -1 on-resonance Asymmetry A mixing ( t) (1-2w) cos ( m d t) m d =.519 ±.2(stat) ±.16 (syst) h ps -1 Siena, October 9 th 21 13

14 perfect flavor tagging & time resolution realistic mis-tagging probability & finite time resolution tag B B = tag B B = tag B B = tag B B = f t / Bd e CP, ± ( t ) = m 2 B L[LQJ &3 7LPHHYROXWLRQ d "f "f CP, + CP, ( 1.( 1 2 ).sin 2 sin( P t ) ) " f B tag tag = B " B = B same mis-tagging probability ω and time-resolution function R( t) B d R

15 Fit data with global, unbinned maximum likelihood including: Mistag fractions, t resolutions (B FLAV sample) sin2β(tagged sample of CP eigenstate events) Total of 44 parameters embody mistag rates, resolution function and backgrounds β effect sin(2β) Mistags (avg, delta B -antib ) Signal t resolution (run1, run2) Background time dependence Background t resolution Background mistags TOTAL Free params

16 β VLQβ =.59 ±.14 stat ±.5 syst

17 P(.59) if CP conserved: < P(.59) if CP conserved (η CP = 1): < Prob(L<L MEAS ) = 27% Result submitted to PRL, July 5 (hep-ex/1719)

18 Resolution function for t=.3 Residual uncertainties in SVT alignment Mistag fraction differences B CP versus B FLAV samples =.3 Background in selected CP events =.2 Level, composition and CP asymmetry Total Sys Total Stat K S K L K * Full Siena, October 9 th 21 18

19 Consistent with the SM but more data needed to be sure )ROORZLQJ+ FNHU HWDO KHSH[ PDQ\RWKHUUHFHQW JOREDO&.PDWUL[ DQDO\VHV Siena, October 9 th 21 19

20 α π + π Decay distributions f + (f - ) when tag = B (B ) ( t/ τ) e f± ( t) = [1 ± S f sin( md t) m Cf cos( md t)] 4τ tree diagram X penguin diagram E G X E X S f C f 2Im( λ) = 2 1+ λ 2 1 λ = 2 1+ λ For single weak phase λ q p A A f f = η f e 2i( β+γ) C ππ =, S ππ = sin2α G = η f e 2iα X For additional weak phase λ 1 must fit for direct CP Im (λ) sin2α need to relate asymmetry to α C ππ, S ππ = sin2α eff

21 π + π ( 3-1 Simultaneous ML fit to BRs and CP coeffs: 8 event types (sig+bg: π + π, K + π, K - π +, K + K - ) Discriminating variables (m ES, E, F,θ c1,θ c1, t) Mistags and resolution function from sin2β analysis Resolution function for background from sidebands Preliminary Results (65 ππ and 217 Kπ events) S(π + π ) = (stat) ±.11(syst) -.56 C(π + π ) = (stat) ±.14(syst) -.47 A CP (K ± π ) = -.7 ±.8(stat) ±.2(syst)

22 We have observed CP violation in the B system at the 4σ level sin(2β)=.59±.14±.5 First measurement with B π + π also presented measurement possible but more data needed This is only the start of a long road More data for greater precision and comparison of channels Start to really test the Standard Model Anticipate data set of 1 fb -1 by next summer sin2β known to better than.1 B π + π asymmetry measured to.3 Siena, October 9 th 21 22

23 Siena, October 9 th 21 23

24 29fb -1 on resonance => BB pairs ( ) Improvements since last winter Enhanced tracking, Ks reconstruction 3% more CP events per unit luminosity Improved vertex reconstruction and knowledge of tracking system alignment Sensitivity increased by 1% J/ψK L selection optimized for added sensitivity to sin2β Added new modes (J/ψ K * (Ksπ ), χ c1 Ks) β Siena, October 9 th 21 24

25 Resolution dominated by B tag vertex reconstruction Biases scale with per-event error Fixed to 8ps with no offset, accounts for <1% of events Scaled by per-event error Siena, October 9 th 21 25

26 ππ π π + π t for π + π enriched sample K + π Siena, October 9 th 21 26

27 ππ π Fisher for signal and BG Where the α i are tuned for signal/bg separation Θ c for π/k samples