Charmless B Decays at B A B AR

1. Charmless B Decays at BABAR Carlo Dallapiccola University of Massachusetts, Amherst For the BaBar Collaboration C. Dallapiccola, Charmless B Decays from BaBar

2. Overview • Charmless B Decays • bu (CKM-suppressed Tree |Vub/Vcb|2  0.006) • bs,d (Penguins, induced FCNC) Higgs, SUSY particles can contribute to loops additional phases  CP violation • Decay Modes • 2Body  pp, Kp, KK • Quasi-2Body  • 3Body  C. Dallapiccola, Charmless B Decays from BaBar

3. Motivation: CP Violation • Significant amplitudes for Penguins for most modes • PT interference  possible direct CP violation • “Pure” Penguin  K(*), K0 Negligible direct CP violation in SM  probe new physics! • =weak(strong) P-T phase diff. • Pbs   • Pbs   C. Dallapiccola, Charmless B Decays from BaBar

4. Motivation: CP Violation • Indirect CP violation via interference with • bu Treedominated: B0p+p-/rp  sin2 • Penguins not negligible: • Pure Penguin: B0K0’K0  sin2b • Compare with sin2b from charmoniun modes • New physics in Penguin loops • Measure as many of the charmless BR as possible • Factorization tests  constraints on g from BKp  extract a from Bpp (isospin) • Importance of final state interactions C. Dallapiccola, Charmless B Decays from BaBar

5. background B pp signal CMS track momentum Experimental Issues • BRs O(10-5)  high luminosity B-Factory • Run1: Oct. 99 – Oct. 2000 20.7 fb-1(4S)  22.7 million BB 2.6 fb-1 Off-peak  udsc continuum • Large bkgd from : • (4S) boosted by bg=0.56 • 1.6 < ph < 4.4 GeV/c for Bhh’ • dE/dx from tracking devices provides little K- separation DIRC performance critical C. Dallapiccola, Charmless B Decays from BaBar

6. Background Suppression • Topological variables (CMS) • Fox-Wolfram moments: R2 • Cosine of B thrust axis wrt rest of event: cosT • Cosine of B decay axis wrt beam axis: cosB • Energy flow of tracks/clusters around B thrust axis • Combine many of these (correlated) quantities into a Fisher Discriminant/Neural Network C. Dallapiccola, Charmless B Decays from BaBar

7. cosT Signal Bkgd Signal Bkgd cosB Signal Bkgd Fisher Background Suppression ~103 background rejection factor Neural Net C. Dallapiccola, Charmless B Decays from BaBar

8. Quartz bar Active Detector Surface Cerenkov light Particle DCH DIRC K-p Separation: DIRC • The DIRC is able to identify particles via a measurement of the cone angle of their emitted Cherenkov light in quartz • Want good /K separation for wide momentum range (up to 4 GeV) C. Dallapiccola, Charmless B Decays from BaBar

9. Cherenkov angle >8s ~2.5s Track momentum (GeV/c) Proton rejection cut K-p Separation: DIRC • DIRC c resolution and K- separation measured in data  D*+ D0+  (K-+)+ decays C. Dallapiccola, Charmless B Decays from BaBar

10. Exclusive B Reconstruction •  B mesons ~ rest (325 MeV/c) • Bhh’ decays s(mES)  2.5 MeV/c2 (DE)  25 MeV Fully reco B MC Kinematic separation of KK, Kp, pp decays in DE C. Dallapiccola, Charmless B Decays from BaBar

11. B3Body: +-p0 • Cut-based: cosT,Fisher (F), cosqH, mES, E • Cuts optimized for each Dalitz region • signal in C. Dallapiccola, Charmless B Decays from BaBar

12. B3Body:  • Asymmetry also measured: 5 signif C. Dallapiccola, Charmless B Decays from BaBar

13. B3Body: K*0+ • Similar to rp analysis  cut-based • K*0K+p- BR(B+K*0p+)=(15.5  3.4  1.5)  10-6 Significance = 5.3 C. Dallapiccola, Charmless B Decays from BaBar

14. B(Quasi-)2Body • Use unbinned maximum likelihood (ML) fits • Retain high efficiency with multi-dimensional signal-background discrimination • Cut-based analyses as cross checks P = product of PDFs for uncorrelated observables = {mES, DE, F, qc, mres, qH,…} C. Dallapiccola, Charmless B Decays from BaBar

15. BQuasi-2Body: (/)K(*) • Tree is CKM suppressed  b s Penguin Signals in K* and ’K C. Dallapiccola, Charmless B Decays from BaBar

16. BQuasi-2Body: (/)K(*) • Signal also in B++  b u Tree dominates C. Dallapiccola, Charmless B Decays from BaBar

17. Inclusive B’Xs • High rate for B’Xs first observed by CLEO For 2.0 < p’ < 2.7 GeV/c QCD anomaly interpretation (g-g-’ coupling) • Reconstruct Xs in 8 modes: C. Dallapiccola, Charmless B Decays from BaBar

18. BQuasi-2Body: K(*) • ~Pure Penguin K0  CP eigenstate (sin2) C. Dallapiccola, Charmless B Decays from BaBar

19. BQuasi-2Body: a0p • ML fit with NN, m(gg), mES, DE Cut-and-count cross check 3.7s statistical significance C. Dallapiccola, Charmless B Decays from BaBar

20. B2Body: pp/Kp/KK • ML fits to signals in following topologies (simultaneous fits to contributions with charged K and p): All Charged Modes C. Dallapiccola, Charmless B Decays from BaBar

21. B2Body: pp/Kp/KK • Bh+h- data analyzed with 50% more data from Run2 • No updated BRs, but B0K+p- direct CP updated • 30.4 fb-1 C. Dallapiccola, Charmless B Decays from BaBar

22. B2Body: pp/Kp/KK h+p0 K0p+ K0p0 C. Dallapiccola, Charmless B Decays from BaBar

23. B(Quasi-)2Body: CP Asymmetries Excluded 90% CL 30.4 fb-1 20.7 fb-1 • No evidence of direct CP C. Dallapiccola, Charmless B Decays from BaBar

24. Summary • Search for 28 charmless hadronic B decay modes • Signals observed in 17 of them • Approaching BR sensitivities of O(10-6) • No evidence yet for direct CP violation • Sensitivity of ~10% for some modes • Important modes: • Constraining  • Constraining/Measuring a • Measuring b  K0 • Still taking data • Results here based on ~23 million pairs ~115 million pairs by end of Run2 (Summer 2002) C. Dallapiccola, Charmless B Decays from BaBar