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Direct CP asymmetries and charmless branching fractions with B A B AR

ICHEP 2002. Direct CP asymmetries and charmless branching fractions with B A B AR. Adrian Bevan. For the B A B AR Collaboration. g. Overview. Motivation : Direct CP Violation (CPV) New Physics sensitivity e.g. X S g, fK Penguins

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Direct CP asymmetries and charmless branching fractions with B A B AR

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  1. ICHEP 2002 Direct CP asymmetries and charmless branching fractionswith BABAR Adrian Bevan For the BABAR Collaboration

  2. g Overview • Motivation: Direct CP Violation (CPV) New Physics sensitivity e.g. XSg, fK Penguins • Event SelectionMethods • Results: Charmless decays, K*g, D0CPK- • Summary and outlook University of Liverpool

  3. direct CPV Direct CP Violation • need interference between diagrams with different strong (i) and weak phases (i) : • Direct CPV only seen in ; ' ~ few 10-6 • theory predicts large asymmetries in B+/0(few to 80%) • Diagrams from New Physics (e.g. SUSY) can modify SM asymmetries/branching fractions University of Liverpool

  4. direct CPV • Experimentally - look for CP asymmetries: • Neutral B – time dependent asymmetry • Charged B – time integrated asymmetry (no mixing); also used for some B0 results (e.g. K0p0) C≠0 direct CPV; e.g. for , pp … University of Liverpool

  5. Searching for direct CPV • Large ACP requires amplitudes of similar order • b→u: suppressed tree: charmless decays • large predicted ACP • b→s,d: penguins: radiative decays • small predicted ACP • Understand penguins • Access to a and g • Sensitive to New Physics effects via loops • minimal SUGRA: B→Xs, K+, K0+ … • R-parity Violating SUSY: KS … • SUSY searches – K* University of Liverpool

  6. Experimental Issues • small branching fractions • large continuum background (u,d,s,c) • other B background • charge bias • detector: trigger, tracking; reconstruction • event selection, particle ID, analysis • Proof of principle • ACP in J/yp, J/yK PRD 65 091101 (2002) • AJ/y = 0.01  0.22  0.01 • AJ/yK = 0.003  0.030  0.004 small systematic error: few per mille University of Liverpool

  7. signal MESs ~ 3 MeV B background Event Selection Techniques Use beam energy to constrain mass & energy DE s ~ 15-80 MeV; larger with neutrals University of Liverpool

  8. u,d,s,c u,d,s,c background Signal Arbitrary Units B event Fisher Discriminant Event Selection Techniques B events are spherical u,d,s,c is jet-like • Fisher Discriminants • Thrust • Sphericity • Fox-Wolfram moments • flavour-tagging (e, , K, slow  from other B) • Maximum Likelihood fits or cut based analysis • off-resonance & E sidebands are used to parameterise light quark background University of Liverpool

  9. RESULTS University of Liverpool

  10. B→K+p0 B→K+p- Two body decays can measure  eg. B→+-, +0, 00  eg. B→K+-, K0+ using Fleischer Mannel bound ACP can be sizeable see Jim Olsen’s talk Plots have an optimised cut on likelihood ratio University of Liverpool

  11. 5% DACP New results ~88106 B pairs Preliminary ~60106 B pairs hep-ex/0206053 All upper limits are @ 90% C.L. University of Liverpool

  12. light q background data B background bin efficiency B→hhh, h=, K Motivation • measure  using a full Dalitz plot • look for direct CPV in charge asymmetry Method • cut based analysis across the Dalitz plot for branching ratio: sum over Dalitz plot • B backgrounds: J/K, D/DK, X-feed; D→, K, KK • subtract open charm from J/, (2s) and D0 • measure Br(B-→D0p-)as a cross check University of Liverpool

  13. B→KKK B→KKK Preliminary B→Kpp D0 B→Kpp BB y(2s) J/y University of Liverpool

  14. 56.2106 B pairs Branching fractions measured across the Dalitz plot (90% C.L.) (90% C.L.) • Main systematic uncertainties • PID 3 ~ 6% • tracking 2.4% Preliminary University of Liverpool

  15. B+→K+ Events / (0.0025 GeV/c2) (→pp, rp) MES (GeV/c2) B→K(*), K,  sensitive to  sensitive to ,g • B→K(*), suppressed tree; ACP 4~30% (theory) • B→K, , penguin; ACP ~6% (theory) preliminary PRD 65 (2002) 051101 University of Liverpool

  16. Signal yield = events DE (GeV) MES (GeV/c2) Preliminary ~60106 B pairs B0→wK0 First Observation! 6.6 s significance (statistical) • penguin • sensitive to a, g • expect small ACP • ML fit • dominant systematic • uncertainty: • background shape • neutral eff • tracking Signal region University of Liverpool

  17. fK+ N(B→K+) / 2 MeV B→K(*),  Motivation: • ACP~2% in SM • New Physics (ACPup to 30%) • sin2 if no new physics see Doug Wright’s talk PRD 65 (2002) 051101 PRL 87 151801 (2001) University of Liverpool preliminary

  18. see Erich Varnes’ talk B-→D0(CP)K- • ACP may be large • access to g • Doreconstructed: • in Kp, Kppo, Kppp • in K+K- (CP=+1 eigenstate) Preliminary University of Liverpool

  19. ~22.7106 B pairs B →K* Phys Rev Lett 88 101805 (2002) • Acp≤1% in SM. • SUSY can enhance to ~20% Reconstruct ACP(B→K*)= -0.044  0.076  0.012 [-0.170, 0.082] (90% C.L.) University of Liverpool

  20. continuum B-background total fit B0→+- ~88106 B pairs Other results: see talk on a • via isospin analysis and direct CPV from time evolution of B→ +- Cpp= -0.30  0.25  0.03 Spp = 0.02  0.34  0.03 Factorization predicts 0.4 Br(B0→p+p-)=(4.6 0.6  0.2)10-6 Br(B+→p+p0) =(5.5 1.00.6)10-6 Br(B0→p0p0) < 3.6 10-6 Preliminary University of Liverpool

  21. Summary and outlook • First CP results from B0→ • Branching fractions and ACPmeasured in many decays • ACP precision achieved 5~20% • No direct CPV signal yet … • watch for future updates University of Liverpool

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