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Andreas Höcker Laboratoire de l’Accélérateur Linéaire, Orsay

The Measurement of sin2 β (eff) in Loop-Dominated B Decays with B A B AR. Andreas Höcker Laboratoire de l’Accélérateur Linéaire, Orsay. For the B A B AR Collaboration. ICHEP 2004 August 16 - 22, 2004, Beijing, China. hoecker@lal.in2p3.fr.

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Andreas Höcker Laboratoire de l’Accélérateur Linéaire, Orsay

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  1. The Measurement of sin2β(eff) in Loop-Dominated B Decays with BABAR Andreas Höcker Laboratoire de l’Accélérateur Linéaire, Orsay For the BABAR Collaboration ICHEP 2004 August 16 - 22, 2004, Beijing, China hoecker@lal.in2p3.fr Preliminary analyses documented in BABAR-CONF-04/33, 04/25, 04/40, 04/19, 04/30 A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  2. The Quest for New Physics in B Decays Since the successful and precise measurement of sin2β in decays (in perfect agreement with the SM), considerable effort at B Factories towards the search for specific signs of New Physics (NP)….WHY ? • The gauge hierarchy Problem (Higgs sector, scale ~ 1 TeV) • Baryogenesis (CKM CPV too small) • The strong CP Problem (why is  ~ 0 ?) • Grand Unification of the gauge couplings • ... many more see, e.g., the instructive talk by Y. Grossman at LP’03: hep-ph/0310229 Conflict between limits from flavor physics  1 TeV (e.g., K0, D0, B0 mixing), and NP scale (1 TeV)  NP cannot have a generic flavor structure Requires flavor suppression and/or generic suppression and/or alignment Note that: if NP contributes significantly to CPV in loop decays, we naturally expect it to be different among the modes  averaging only useful in case of SM A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  3. Confronting Loop Decays with Tree Dominance decays are tree and penguin diagrams, with equal dominant weak phases decays are pure “internal” and “flavor-singlet” penguin diagrams High virtual mass scales involved: believed to be sensitive to New Physics Both decays dominated by single weak phase Tree: Penguin: New Physics? 3 ? A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  4. Penguin Olympia Naive (dimensional) uncertainties on sin2 One may identify golden, silver and bronze-plated s-penguin modes: Gold Color-suppressed tree Silver Color-suppressed tree Bronze Note that within QCD Factorization these uncertainties turn out to be much smaller ! A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  5. All Results are PRELIMINARY ! Definition of Time-dependent CP asymmetry observables: CP observables with: ~ –CPsin(2) and ~ 0 for b  ccs, sss A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  6. Highlights on Common Analysis Techniques Strong DIRC Particle ID to separate pions from kaons Event shape monomials (L0,L2), and B kinematics optimally combined in Multivariate Analyzer [MVA] (Neural Network (NN) or Fisher Discriminant) New NN-based B-flavor tagging with “Q” up to 30.6 % Unbinned maximum-likelihood fit using beam-energy-substituted B mass (mES), B-energy difference (E), the resonance mass and decay angle, the MVA, and t Likelihood components are signal (correctly and misreconstructed), continuum background, charmed and charmless B-related backgrounds; as many likelihood-model parameters as possible are determined simultaneously from the fit to reduce systematic errors Tagging-performance parameters and t resolution parameters determined simultaneously from fit to fully reconstructed B decays to charm A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  7. Analysis of B0  K0 227106B pairs full background continuum bkg ML fit finds 114 ± 12 signal events 98 ± 18 signal events • Systematic errors dominated by • opposite-CP background • PDF modeling • Tag-side CP violation combined fit : sin2 [cc] @ 0.9 A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  8. Analysis of B0/+  K0/+ 227106B pairs B0KS (statistical errors only) Complementary penguin mode: Significant direct CP violation would be hint for New Physics B0KL Fit finds 400 ± 23 signal events A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  9. Analysis of B0  K+K–KS (I) 227106B pairs Excluding  : dominant contribution (85%) of inclusive BR  much more statistics than KS • Unknown a prioriCP content: CP-even fraction must be determined experimentally • Angular moments analysis (main result): Study  [K+K–] helicity angle distribution and: Average moments computed from sum of background-corrected signal weights, returned by ML fit (“sPlot” technique [Pivk-Le Diberder, physics/0402083]) • Isospin analysis (cross check) [Belle, PRD 69, 012001 (2004)] (statistical error only) A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  10. Analysis of B0  K+K–KS (II) Results from CP fit Fit finds 452 ± 28 signal events (excluding KS events) • Systematic errors dominated by • Fit bias • Tag-side CP Violation ML fit: use C=0: sin2 [cc] @ 0.7 CP content A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  11. Analysis of B0  ’KS 227106B pairs Large statistics mode: , we exploit: Reconstruct in multiple final states: ’  +–, 0 and   , +–0 and KS+–,00 3.0 Fit finds 819 ± 38 events No CPV found in control sample ML fit : sin2 [cc] @ 3.0 Systematic errors dominated by: Fit bias (MC statistics) A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  12. Analysis of B0  f0KS 209106B pairs New, silver-plated s-penguin mode with [BABAR, hep-ex/0406040] Requires thorough estimate of CP dilution due to interference in B0  +–KS Dalitz plot Fit finds 152 ± 19 events CPV @ 2.3 ML fit : • Systematic errors dominated by • Fit bias & interference with other modes sin2 [cc] @ 0.6 A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  13. Analysis of B0  0KS (I) 227106B pairs • Challenging vertexing (t) due to lifetime of KS : • require at least 4 SVT hits (~60% of events) for t measurement • determine t from global fit to entire decay tree (use Ebeam, IP (+2B)-constraint) • keep remaining “no-t”events for direct CPV measurement mass-constrained Replace E and mES by: and  reduced correlation, improved resolution (mmiss) Fit finds 300 ± 23 events A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  14. Analysis of B0  0KS (II) ~ SM sPlot 1 2 3 physical limit • Systematic errors dominated by • Background tagging asymmetry • SVT alignment, vertexing ML fit : sin2 [cc] @ 1.3 No bias in control sample decays without using J/-decay tracks for vertexing A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  15. sin2 (and related direct-CP) Results from BABAR s-penguin average at 2.7 from sin2[cc] (BABAR only) no indication for direct CP violation A. Höcker – sin2 in Loop-Dominated Decays with BABAR

  16. Conclusion BABAR has new sin2(eff) results for all s-penguin analyses, most using 227106B pairs Introduced and observed new silver-plated s-penguin mode Sophisticated vertexing allows time-dependent measurement of CPV in The significant decrease in the statistical errors begins to provide precision measurements of CP violation in loop processes The “Stamodometer” indicates for the different modes: ... and overall: s-penguins A. Höcker – sin2 in Loop-Dominated Decays with BABAR

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