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Radiative and Rare B-Decays at BaBar

Beauty 2003. Radiative and Rare B-Decays at BaBar. Carsten Hast , SLAC for the BaBar Collaboration Pittsburgh, October 17. All results are preliminary unless journal ref. is given limit values are 90% CL unless otherwise specified. Overview.

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Radiative and Rare B-Decays at BaBar

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  1. Beauty 2003 Radiative and Rare B-Decays at BaBar Carsten Hast, SLAC for the BaBar Collaboration Pittsburgh, October 17 All results are preliminary unless journal ref. is given limit values are 90% CL unless otherwise specified

  2. Overview Since this talk is nicely framed between a theoretical introduction and a Belle summary and outlook I will focus on newer results and analysis techniques from BaBar • FCNC • b  Knn • Purely Leptonic Decays • b  tn • b  mn • b  Kll and b  K*ll • B  Xsll • Radiative Decays • B0 K2*0(1430) g andB+  K2*+(1430) g Carsten Hast, SLAC

  3. EMC 6580 CsI(Tl) crystals 1.5 T solenoid DIRC (PID) 144 quartz bars 11000 PMs e+ (3.1 GeV) e- (9 GeV) Drift Chamber 40 stereo layers Instrumented Flux Return iron / RPCs (muon / neutral hadrons) Silicon Vertex Tracker 5 layers, double sided strips The BaBar Detector SVT+DCH: (pT)/pT = 0.13 %  pT+0.45 %, good dE/dx DIRC: K- separation 4.2  @ 3.0 GeV/c  2.5  @ 4.0 GeV/c EMC: Very good electron identification and p0 reconstruction IFR: Decent muon identification Carsten Hast, SLAC

  4. PEP- II Lumi Performance and Recorded BaBar Lumi Best Peformance PEPII peak Luminosity:6.582x1033 cm-2 sec-1 Integrated Luminosity Shift: 135.2 pb-1 in 24 hours:391.2 pb-1 124.1106 BB 89.7106 BB 82 fb-1 on-peak data for analysis Carsten Hast, SLAC

  5. signal background Standard Variables in U(4S) Frame e+e-U(4S)  BB B produced almost at rest in U(4S) frame For B decay with no missing particles use beam energy to constrain mass and energy of the reconstructed B 0 for signal mB for signal background E and mESprovide uncorrelated measurement of energy and mass Carsten Hast, SLAC

  6. B+K+nn Search • A rare flavour changing neutral current (FCNC) bsdecay • SM prediction: Br (BK)  410–6 • Summed over all neutrino species • The best upper limits (@90% CL): • CLEO: Br (BK)  2.410–4 • BABAR: Br (BK)  9.410–5 Semi-Leptonic B-tags: BDlX (X  , 0 or nothing) 50.7 fb-1 • New search (80 fb-1) with hadronic B-tags PRL 86 2950 (2001) hep-ex/0207069 • BD0(*) ()(K)(K0s)(0) • (D* D0 and D0 K , K0, K3, Ks) • B constraining kinematic variables:DE and mES Carsten Hast, SLAC

  7. BK MC Data B+B MC B0B0 MC cc MC u,d,s MC B+K+nn Search II • Identify tag B in signal DE and mES area • All remaining tracks and neutrals • belong to the recoiling • signal-side B • One well identified Kaon • no p0 • Missing momentum not • in the beam pipe • “extra” Energy < 300 MeV Carsten Hast, SLAC

  8. B+K+nn Upper Limit • Selected events: 3 • Expected background events: 2.70.8 Br ( B K ) < 1.05  10  4 @ 90% CL hep-ex/0304020 • Combining this result with the previous, (Br (BK)  9.410–5) • statistically independent BABAR result, yields a new limit: Br ( B K ) < 7.0  10  5 @ 90% CL Going to PRL Carsten Hast, SLAC

  9. Btn Search 2 analyses of the 1999-2002 data sample: ~81 fb1 Reconstruct one B meson as SemiLeptonic B-tag B  Dl X Hadronic B-tag B  DXhad The remaining neutrals and tracks are signal candidates •  (e, ) (e, )  • (e, ) (e, )  • (, 0, )  very clean but low efficiency (~ 0.25 – 0.30 %) The two samples of tag B mesons are statistically independent Carsten Hast, SLAC

  10. event veto Only one charged track having low impact parameter Track is not identified as a kaon Track is an identified lepton Residual neutral energy is used to model PDFs to extractsignal and background contributions Three preselections 1 track, 0 0 1 track, 1 0 3 tracks, 0 0 Track is not identified as a kaon Track is identified as lepton or pion Additional cuts on Missing momentum Residual neutral energy Track momentum Invariant masses Background mainly from Vcb events Signal efficiency: 11.3% t Signal Selection SemiLeptonic B-Tag Hadronic B-Tag Signal Background Events/0.07 GeV Eleft (GeV) Eleft (GeV) • Signal efficiency: 22.5% Carsten Hast, SLAC

  11. Expected Bkg from MC 40.9  3.8 Expected Bkg in onpeak data (sideband extrapolation) 39.9  2.8 Observed events onpeak data 47.7  7.0 Events/0.07 GeV Eleft (GeV) Btn Results SemiLeptonic B-Tag Hadronic B-Tag Selection Total Bkg Data candidates e e       0    6.7 2.0 0.6 5.0 1.7 0.4 11.2 2.5 0.5 10.4 2.6 1.2 4.3 1.4 0.3 10 8 6 7 4 All 37.6 4.7 1.5 35 Br ( B    ) < 7.7  10  4 hep-ex/0304030 Combined limit Br ( B  ) < 4.110 4 @ 90% CL Br ( B    ) < 4.9  10  4 hep-ex/0303034 SM prediction: < 9.2105 hep-ex/0305034 Carsten Hast, SLAC

  12. CM frame Bmn Search Signal Monte Carlo Data sample 1999–2002: ~81fb–1 Two Body decay  p(m) ~ mB/2 • One well identified muon • All the rest is from the companion B • do particle identification • No additional leptons allowed • After the companion B was found, p(m) is re-reconstructed in the signal B rest frame B rest frame Carsten Hast, SLAC

  13. Bmn Search All other tracks and neutrals make the Companion-B Signal Monte Carlo Carsten Hast, SLAC

  14. Upper Limit for Bmn Data • Signal Selection efficiency: 2.09% • Selected events: 11 • Expected background: 5.0 • Bg fluctuation prob. to the signal: 4% +1.8 1.4 B MC Data Sideband Signal box B ( B  ) < 6.6  10  6 @ 90% CL BABAR-CONF-03-007 Carsten Hast, SLAC

  15. b K(*) l l penguin diagram b s ll box diagram b s ll Updated result on 113 fb-1 accepted by PRL Reconstruct K+, Ksp+p-, K*0 K+ p-, K*+ Ksp+ Lepton identification for e+e- with p(e) > 0.5 GeV/c, m+m- with p(m) > 1.0 GeV/c Carsten Hast, SLAC

  16. J/y veto y’ veto DE [GeV] DE [GeV] Mll [Gev/c2] Mll [Gev/c2] b K(*) l l Peaking Background Events with the same final state: B  J/y K(*), y’ K(*) Signal is scattered in this above area 500 fb-1 B  J/y K(*), y’ K(*)Monte Carlo little to no contribution outside these veto bands Carsten Hast, SLAC

  17. b K(*) l l Peaking Background II Background from lepton miss-identification B  h+h- K(*) h+h- K(*) events in data convolved with rates for h to fake e, m 0.33 events 0.01 events # Events # Events mES [Gev/c2] mES [Gev/c2] Included as part of the fit to data Carsten Hast, SLAC

  18. b Kl l Results 2-D unbinned maximum LH fit to mES and DE on all 4 decays K+ee/mm and Ks0ee/mm 8.4s excess over background Br(bK ll) = (6.5 +1.4-1.3 +/- 0.4 ) 10-7 accepted by PRL Carsten Hast, SLAC

  19. b K*l l Results 3-D unbinned maximum LH fit to mES, DE and mKp 3.3 s excess over background Constrain: K*ee = 1.33 X K*mm Gtot(B0) = 1.08 X Gtot(B+) Br(bK* ll) = (8.8 +3.3-2.9 +/- 1.0 ) 10-7 accepted by PRL Carsten Hast, SLAC

  20. b K(*) l l Results Comparison of mll in data with simulation, normalized to the measured Br Fits well Carsten Hast, SLAC

  21. Semi-Inclusive B Xsl l Sum of exclusive modes approach: reconstruct Xs with 1 K± or K0s p+p-, # (p + p0)  2, # p0  1 10 modes, ~50% of BR(B  Xs l+l-) (75% if assumed KS=KL) Similar analysis as b K(*) ll but with higher combinatoric background B Xsm+m- B Xse+e- mES [Gev/c2] mES [Gev/c2] Carsten Hast, SLAC

  22. Semi-Inclusive B Xsl lResults + Data Monte Carlo Br(B  Xs e+e-) = (6.6 ± 1.9 ± 1.91.6) 10-6 Br(B  Xsm+m-) = (5.7 ± 2.8 ± 1.71.4) 10-6 Br(B  Xs l+l-) = (6.3 ± 1.6 ± 1.81.5) 10-6 Carsten Hast, SLAC

  23. B0 K2*0(1430) g andB+ K2*+(1430) g BaBar Preliminary BaBar Preliminary Br (B+ K2*+(1430) g ) Br (B0 K2*0(1430) g ) BaBar (12.2 +/- 2.5 +/- 1.1)10-6 (14.4 +/- 4.0 +/- 1.3)10-6 Belle ( 13 +/- 5 +/- 1) 10-6 Cleo (16.6 +/- 5.9 +/- 1.3) 10-6 Carsten Hast, SLAC

  24. Summary (1) • FCNC • b  Knn 3 bg events expected 3 seen • Purely Leptonic Decays • b  tn difficult • b  mn looks quite interesting • Radiative Decays • B0 K2*0(1430) g andB+  K2*+(1430) gBaBar is in the game Carsten Hast, SLAC

  25. B sl lSummary Br(bs ll) in good agreement within experiments and prediction Next step: measure angular and kinematic distributions …and have fun with the next talk covering all the other interesting rare results measured by Belle Carsten Hast, SLAC

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