1 / 35

Measurement of sin2 b at B A B AR

Measurement of sin2 b at B A B AR. Update B 0  (cc) K 0 Update B 0  D *+ D *- New B 0  f K 0 S New B 0  J /  p 0. Douglas Wright Lawrence Livermore National Laboratory For the B A B AR Collaboration. 31st International Conference in High Energy Physics

kali
Download Presentation

Measurement of sin2 b at B A B AR

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measurement of sin2b at BABAR Update B0(cc)K 0 Update B0D*+D*- New B0f K0S New B0J/ p0 Douglas Wright Lawrence Livermore National Laboratory For the BABARCollaboration 31st International Conference in High Energy Physics Amsterdam, 24 July 2002

  2. Weak interaction of quarks in the Standard Model f2 f3 f1 CKM Matrix Unitarity Triangle CP violation will arise from complex component of Vub, Vtd Doug Wright, ICHEP Amsterdam

  3. B0-B0 mixing introduces time-dependant CP violation fCP u,c,t d b u,c,t b d top quark box introduces: VtbVtd* W W Dmd = mH - mL Sensitive to overall phase of lf even if no Direct CP Violation Direct CP violation if multiple amplitudes with different phases Doug Wright, ICHEP Amsterdam

  4. CP asymmetry in B0 (cc)K0 • Theoretically clean: Tree level dominates and CP only from B0-B0mixing • Relatively large branching fractions • Clear experimental signatures B0 K0 lf = hfe-i2b, hf=±1 Doug Wright, ICHEP Amsterdam

  5. Experimental technique at the (4S) resonance m- Flavor tag and vertex reconstruction K- Btag Brec B0 B0 Coherent BB pair Start the Clock e+e-  (4S)  BB Boost: bg= 0.55 (4S) m- m+ KS p+ p- Exclusive B meson and vertex reconstruction Doug Wright, ICHEP Amsterdam

  6. SLAC B Factory performance PEP-II top luminosity: 4.60 x 1033cm-2s-1 (exceeded design goal 3.0 x 1033) PEP-II delivered 99 fb-1 BaBar recorded 94 fb-1 In this analysis On peak 81 fb-1 88M BB pairs Off peak 10 fb-1 9 GeV e- on 3.1 GeV e+ Boost bg = 0.55 IP beam size 147 mm x 5 mm Doug Wright, ICHEP Amsterdam

  7. BABAR Detector SVT: 97% efficiency, 15 mm z hit resolution (inner layers, perp. tracks) SVT+DCH: (pT)/pT= 0.13 %  pT+0.45 % DIRC: K- separation 4.2  @ 3.0 GeV/c  2.5  @ 4.0 GeV/c EMC:E/E = 2.3 %E-1/4 1.9 % Doug Wright, ICHEP Amsterdam

  8. Vertex and Dt Reconstruction BREC direction BREC Vertex BREC daughters Interaction Point Beam spot TAG Vertex z BTAG direction TAG tracks, V0s • Reconstruct Brec vertex fromcharged Brec daughters • Determine BTag vertex from • All charged tracks not in Brec • Constrain with Brec vertex, beam spot, and (4S) momentum • Remove high c2 tracks (to reject charm decays) • High efficiency: 95% • Average Dz resolution ~ 180 mm (dominated by BTag) (<|Dz|> ~ 260 mm) • Dt resolution function measured from data Doug Wright, ICHEP Amsterdam

  9. Lepton tag: primary leptons from semileptonic decay Kaon1 tag: high quality kaons, correlated K- andp+s (from D*) Kaon2 tag: lower quality kaons, ps from D* Inclusive tag: unidentified leptons, low quality K, p, leptons No tag: event is not used for CP analysis B Flavor tagging method b c s K- Using tracks with or without particle identification, and kinematic variables, a multilevel neural network assigns each event to one of five mutually-exclusive categories: New and improved tagging method Doug Wright, ICHEP Amsterdam

  10. Tagging errors and finite Dt resolution dilute the CP asymmetry perfect tagging & time resolution typical mistagging & finite time resolution • Need to knowmistag fraction wandDt resolution function Rin order to measure CP asymmetry. • Can extract these from data with B0-B0 mixing events. Doug Wright, ICHEP Amsterdam

  11. Fully reconstruct self-tagged modes: Use self-tagged Bflav sample to measure w and R B0D(*)-p+/ r+/ a1+ Ntagged=23618 Purity=84% B0 J/yK*0(K+p-) Ntagged=1757 Purity=96% • Apply Btag to other side, fit for B0-B0 mixing Bflav sample is x10 size of CP sample Doug Wright, ICHEP Amsterdam

  12. Tagging performance from Bflav sample ~1-2w This new tagging method increases Q by 7% compared to the method used in our previous result: PRL87 (Aug 01). Doug Wright, ICHEP Amsterdam

  13. sin2b golden sample: (cc)KS (hf = -1) y(2S)Ks J/yKs(p+p-) J/yKs(p0p0) cc1Ks Recent addition: B0 hc Ks where hc K+K-p0 or K+Ks p- hcKs Energy-substituted mass Doug Wright, ICHEP Amsterdam

  14. sin2b samples: J/y KL and J/y K*0 J/y KL J/yK*0(Ksp0) hf = +1 Ntagged = 988 Purity = 55% • Data hf = +0.65±0.07 Ntagged = 147 Purity = 81% Signal J/y Bkg Fake J/y Bkg • Vector-Vector mode: mixture of CP+ and CP- • Use angular analysis to determine CP- fraction • Treat CP- component as dilution  effective hf • Use mBconstraint to determine pKL • J/y background shape estimated from Monte Carlo • Fake J/y background shape estimated from data sidebands Doug Wright, ICHEP Amsterdam

  15. Simultaneous unbinned maximum likelihood fit of CP and mixing samples sin2b likelihood fit Fit Parameters 34 total sin2b 1 BCP Mistag fractions w for B0 and B0 tags 8 Bflav Signal Dt resolution function R 8 Bflav Background properties 17 BCP+Bflav (mostly from mES sidebands in data) B lifetime fixed (PDG 2002) tB= 1.542 ps Mixing frequency fixed (PDG 2002) Dmd = 0.489 ps-1 Doug Wright, ICHEP Amsterdam

  16. Fit results hf =-1 hf =+1 sin2b = 0.755  0.074 sin2b = 0.723  0.158 sin2b = 0.741  0.067 (stat)  0.033 (sys) Doug Wright, ICHEP Amsterdam

  17. sin2b fit results by decay mode Consistency of CP Channels: P(c2) = 57% Doug Wright, ICHEP Amsterdam

  18. Dramatic effect in golden modes with lepton tag (cc)KSwith lepton tag Ntagged = 220 Purity = 98% Mistag fraction 3.3% sDt 20% better than other tag categories sin2b = 0.79  0.11 Doug Wright, ICHEP Amsterdam

  19. Cross-check on data control samples Observed no asymmetry as expected Doug Wright, ICHEP Amsterdam

  20. Sources of Systematic Error s(sin2b) Description of background events 0.017 CP content of background components Background shape uncertainties Composition and content of J/y KL background 0.015 Dt resolution and detector effects 0.017 Silicon detector alignment uncertainty Dt resolution model Mistag differences between BCP and Bflav samples 0.012 Fit bias correction 0.010 Fixed lifetime and oscillation frequency 0.005 TOTAL 0.033 Steadily reducing systematic error: July 2002 = 0.033 July 2001 = 0.05 Doug Wright, ICHEP Amsterdam

  21. Standard Model comparison One solution for b is in excellent agreement with measurements of unitarity triangle apex r = r (1-l2/2) h = h (1-l2/2) Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001 Doug Wright, ICHEP Amsterdam

  22. Search for non-Standard Model effects in (cc)KS • If another amplitude (new physics) contributes a different phase, then • In the Standard Model |lf | = 1 (which we assume in the nominal sin2b fit) Sf - hf sin2bCf0 • Fit |lf| and Sf using the clean (cc)Ksmodes (hf =-1, Ntagged = 1506, Purity = 92%): | lf| = 0.948  0.051 (stat)  0.017 (syst) Sf = 0.759  0.074 (stat)  0.032 (syst) Consistent with the Standard Model expectation of |lf|=1 and nominal fit sin2b = 0.755  0.074 for (cc)Ks modes alone. Doug Wright, ICHEP Amsterdam

  23. (b ccd) mode B0D*+D*- D* - • Cabbibo-suppressed mode with tree level weak phase same as b ccs • Penguin contribution uncertain, expected to be small < 0.1 Tree • Not a CP eigenstate, mixture of CP even (L=0,2) and CP odd (L=1) • Resolve using angular analysis (in transversity basis) Vcd D* + B0 D* - B0 D* + Ntagged= 102 Purity = 82% Reconstruct D*+D0p+ or D+p0 , but not both to p0 mode Doug Wright, ICHEP Amsterdam

  24. CP composition of B0D*+D*- • We measure CP odd fraction (corrected for acceptance) to be small: R = 0.07  0.06 (stat) 0.03 (syst) Doug Wright, ICHEP Amsterdam

  25. CP asymmetry fit B0D*+D*- • Improved fitting strategy since winter conferences: • Parameterize in terms of CP even (l+) and odd (l) components, include angular information from partial-wave analysis • Fix CP odd component to l=1, Im(l) = -0.741 |l+|= 0.98  0.25 (stat)  0.09 (syst) Im(l+)= 0.31  0.43 (stat)  0.10 (syst) If penguins are negligible, then Im(l+) = - sin2b Im(l+)measurement ~2.7s from BaBar sin2bin charmonium, assuming no penguins. Doug Wright, ICHEP Amsterdam

  26. (b ccd) mode B0D*+D- • D*D not CP eigenstate • Possible strong phase contribution (and still have penguins) • Different (but related) decay time distributions for B0D*+D- B0D*- D+ D+ D*+ D _ D*_ B0 CP conjugation strong phase D*_ D _ D+ D*+ B0 D*D 56 fb-1 Ntagged= 85 Purity = 52% S+- = - 0.43  1.41  0.20 C+- = 0.53  0.74  0.13 S-+ = 0.38  0.88  0.05 C-+ = 0.30  0.50  0.08 Update to full data set in progress Doug Wright, ICHEP Amsterdam

  27. (bccd) mode B0J/yp0 • Cabibbo and color-suppressed mode with comparable tree and penguin contributions Vcd Tree: ~VcbVcd* ~ O(l3) same weak phase as bccs Ntagged= 49 Purity = 59% hf= + 1 Penguin:~VcbVcd* + VubVud* ~ O(l3) adds additional weak phase Doug Wright, ICHEP Amsterdam

  28. CP asymmetry fit for B0J/yp0 hf= + 1 In absence of penguins Cyp=0, Syp = - sin2b Doug Wright, ICHEP Amsterdam

  29. sin2b from penguin mode B0fKS • Charmless decay dominated by (b sss) gluonic penguins • Weak phase same as b ccs, but sensitive to new physics in loops • Small branching fraction O(10-5) • Significant background from qq continuum • Using only fK+K- Ntagged = 66 Purity = 50% hf= - 1 Doug Wright, ICHEP Amsterdam

  30. CP asymmetry fit for B0fKS +0.52 - 0.50 • Fix |lfK| = 1, fit: SfK = -0.19 (stat)  0.09 (syst) • Cross check on B+fK + SfK = 0.26  0.27 • Analysis of B0h’KS in progress Dt (ps) If no new physics, SfK = sin2b Doug Wright, ICHEP Amsterdam

  31. Conclusion Million BB pairs • New measurement of sin2b from charmonium modes (88 x106BB) Submitted to PRL July 17, 2002 (hep-ex/0207042) Results have been improving by more than just luminosity gain sin2b = 0.741 ± 0.067 (stat) ± 0.033 (syst) July 00 • Begun to probe the same CP-violating phase and possibly new physics via penguin modes: B0f K0S B0J/ p0 and open charm modes: B0D*+D*- B0D*+D- Feb 01 (First BaBar results) July 01 Mar 02 July 02 The Standard Model remains unscathed, but the high statistics future of BaBar will provide further opportunities to challenge the theory. Doug Wright, ICHEP Amsterdam

  32. Doug Wright, ICHEP Amsterdam

  33. sin2b in subsamples Doug Wright, ICHEP Amsterdam

  34. Tagging performance Doug Wright, ICHEP Amsterdam

  35. Monte Carlo correction We evaluated the size of any potential bias on sin2b by fitting the full MC in two ways: • Fitting data-sized signal MC samples with mistag fractions and Dt resolution fixed to the MC truth values (see plot). Average bias = +0.012  0.005. • Same as above except mistag fractions and Dt resolution from Breco MC. Average bias = +0.014  0.005. One possible source of bias comes from neglecting the known correlation between the mistag fractions (or dilutions) and sigma Dt. • Estimates from toy and full MC inticate a bias at the level of +0.004. We correct the fitted sin2b by subtracting 0.014 and assign a systematic error of 0.010 to this correction. Doug Wright, ICHEP Amsterdam

More Related