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New b s measurement at CDF

New b s measurement at CDF. F. Bedeschi, INFN-Pisa BEACH 2010 Perugia, 22 June 2010. Introduction Context SM description The measurement Fit strategy Signals Flavor tagging Results. The Context. Great SM success in B d /B u sector Thanks B-factories!

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New b s measurement at CDF

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  1. New bs measurement at CDF F. Bedeschi, INFN-Pisa BEACH 2010 Perugia, 22 June 2010 • Introduction • Context • SM description • The measurement • Fit strategy • Signals • Flavor tagging • Results F. Bedeschi, INFN-Pisa

  2. The Context • Great SM success in Bd/Bu sector • Thanks B-factories! • ...but no evidence for new physics there • Bs sector can still provide surprises • Natural physics for Tevatron experiments • In 2006 Dms measurement from Bs mixing • Right on the SM expectations! • Next step is measurement of CP violating phases eg. bs • …some excitement there so far A/A = 6.05 F. Bedeschi, INFN-Pisa

  3. d f S M i i i 2 1 t t t ¾ e v a o n r o m e x p e c a o n s . Status July 2009 • Previous CDF+D0 combined results intriguing F. Bedeschi, INFN-Pisa

  4. N N ¡ ¹ ¹ B B B B a = l s N N + ¹ ¹ B B B B Related measurements • Semileptonic asymmetry • Related to DG, Dm and bs • SM expectation ~ 10-5 • Old results from CDF and D0: • Intriguing new D0 result F. Bedeschi, INFN-Pisa

  5. bs in SM • bs is the phase of –Vts • ≠ 0 in O(l4) CKM expansion • VCKM = • Quite well constrained assuming SM and very small CKM fitter. Sept. 2009 0.01812±0.0008 All real F. Bedeschi, INFN-Pisa

  6. p m 1 2 ¼ j j q m 1 2 Basic Theory • 2 state effective theory: • Describes mixing and CP violation • M,  hermitian • CPT invariance: M11 =M22 ,11 =22 • After diagonalization: • Eigenvalues: • Eigenstates: F. Bedeschi, INFN-Pisa

  7. Á S M i M M ¢ N P e = 1 2 1 2 s Ds- W- b c c B Ds+ s s Origin of off-diagonal terms • m12 from box diagram • Top quark dominant • M12  V2ts  e-2is • New physics possible in loops! • 12 from common final states • For Bs dominated by Ds+Ds- • / ~ 0.10 • G12 mostly real: s ~ -2s • Tree level dominated • Hard to see new physics here •  = 2Re{12/ m12}| m12 | = 2 |12| cos  F. Bedeschi, INFN-Pisa

  8. ¯ ¯ ¡ ¢ ¡ 1 2 ¯ ¯ Á Á A i t s n a n = = S L ¯ ¯ M ¢ M ¯ ¯ 1 2 Measured quantities • Mixing frequency (theory limited): • DM = 2 |M12| • Width difference (statistics limited): • DG = 2|G12| cos f • Semileptonic asymmetry (stat.+syst. limited) • Bs – Bs bar interference in decay to common final state such as J/yf (statistics limited) • -Im(p/q) ~ sin(2bs) ~ -sin f This measurement F. Bedeschi, INFN-Pisa

  9. 2 2 2 j j j j j j A A A 1 + + = = = ? 0 ¹ A f A · ¹ ¸ · ¸ A ! A f p q f f A = ¡ = i 2 ¡ ¡ ¡ t t i ¹ ¹ 2 ¡ ¡ t t j ( ) ( = ) ( = ) m j ( ) ( = ) ( = ) f B A ¢ ¢ m i i f 2 2 B A ¢ ¢ t t i i t f 2 2 ¡ t t t < > ¡ < > e e c o s m s n m e e c o s m s n m = f = f ¹ A A q p f f Analysis strategy Simplified time evolution (DG=0) and f = CP-eigenstate • Study time evolution of BsJ/yf decay • No SM weak phases in = ±1 • Sign depends on CP of final state • ... but J/yf is vector-vector  mixture of CP-even and CP-odd • Need to perform full angular analysis to separate the components • L=0 and L=2 are CP-even, L=1 is CP-odd • prefer to use “transversity basis”: A0, A//: CP-even, A┴ : CP-odd • Phys. Lett. B 369, 144 (1996), 184 - hep-ph/9511363 • Need to introduce more hadronic decay amplitudes and their phases: • A0, A//, A┴ ( ), d//, d┴ (phases relative to A0) F. Bedeschi, INFN-Pisa

  10. Full Bs decay rate formula time dependence terms angular dependence terms terms with bsdependence terms with Dms dependence present if initial state of B meson (B vs anti-B) is determined (flavor tagged) ‘strong’ phases: - Identification of B flavor at production (flavor tagging) → better sensitivity to bs F. Bedeschi, INFN-Pisa

  11. Improvements over past • Luminosity: 2.9  5.2 fb-1 • Signal optimization with NN • ~ 6500 BsJ/yf, S/N ~ 1 • Improved flavor tagging completely recalibrated (see later) • Inclusion of f0 scalar component (BsJ/yf0) (see later) Optimized for best bs resolution F. Bedeschi, INFN-Pisa

  12. Flavor tagging • Opposite side (OST) • Jet / lepton charge • Combined with NN • Calibrate with 52,000 J/yK+ • e = 94.2±0.4%, D = 11.5±0.2% • eD2 = 1.2% • Same side Kaon (SSKT) • Sign of soft kaon near Bs • Dilution from simulation • Calibrate with ~ 13,000 BsDs(3)pi • From mixing amplitude scan • eD2 = 3.2±1.4% Dms= 17.79 Old CDF result F. Bedeschi, INFN-Pisa

  13. CDF Run II Preliminary 5.2 fb-1 Results: Bs lifetime & DG • Point measurement assuming SM • Set bs = 0 • Most precise measurement of Bs lifetime and DG PDG 2009 averages: ts= 1.472+0.024-0.026 ps DGs = 0.062+0.034-0.037 ps-1 ct (cm) CP-even (Bslight) and CP-odd (Bsheavy) components have different lifetimes → DG ≠ 0 F. Bedeschi, INFN-Pisa

  14. Results: polarization amplitudes • bs = 0 fit • Most precise measurement Signal fit projection CDF preliminary Background fit projection F. Bedeschi, INFN-Pisa

  15. CP Violation Phase bs with 5.2 fb-1 at CDF • Final confidence regions in bs-DGs space: • Full fit results • Low statistics & dilutions • Some parameters very non-Gaussian, including bs • Contours corrected for • Non-gaussian effects • Systematics • Note fit symmetry • bs projection • [0.02, 0.52] U [1.08, 1.55] at 68% C.L. Agreement with SM expectation is at ~0.8s level Agreement with SM prediction at ~1 s level F. Bedeschi, INFN-Pisa

  16. Effect of s-wave resonance (Suggested in arXiv:0908.3627v1 [hep-ph] 25 Aug 2009) • Effect of BsJ/y f0 • Fit prefers ~ 2% • Consistent with m(KK) fit • < 6.7% @ 95% CL Not adjusted for non-Gaussian errors F. Bedeschi, INFN-Pisa

  17. Conclusions & prospects • Best measurement of Bs lifetime, DG and polarization amplitudes • Tighter constraints on bs • Improved agreement with SM (~1s) • Future improvements • Statistics doubled (10 fb-1) by end of 2011 Tevatron run • More data ~ 25-30% from track based triggers • Additional decay modes: • y(2S)f • J/y f0, f0pp (CP-eigenstate) F. Bedeschi, INFN-Pisa

  18. Getting hot LHCb CDF+DØ Probability of 5 observation s --- 10/fb (2011) --- 8/fb (2010) Tevatron 2011: discover or exclude NP in wide range of phases. LHCb competitive (if everything turns out as expected) F. Bedeschi, INFN-Pisa

  19. Backup slides Backup slides F. Bedeschi, INFN-Pisa

  20. Opposite Side Tagging Calibration and Performance • OST combines in a NN opposite side lepton and jet charge information • Initially calibrated using a sample of inclusive semileptonic B decays • predicts tagging probability on event-by-event basis • Re-calibrated using ≈ 52,000 B+/- → J/Ψ K+/-decays • OST efficiency = 94.2 +/- 0.4%, OST dilution = 11.5 +/- 0.2 % - Total tagging power = 1.2% F. Bedeschi, INFN-Pisa

  21. Same Side Tagging Calibration • Event-by-event predicted dilution based on simulation • Calibrated with 5.2 fb-1 of data • Simultaneously measuring the Bs mixing frequency Dms and the dilution scale factor A - D – event by event predicted dilution • ξ – tagging decision = +1, -1, 0 for Bs, Bs and un-tagged events • Fully reconstructed Bs decays selected by displaced track trigger F. Bedeschi, INFN-Pisa

  22. Detector Angular Efficiency • CP even and CP odd final states have different angular distributions → use angles r = (,,) to statistically separate CP even and CP odd components • Detector acceptance distorts the angular distributions → determine 3D angular efficiency function from simulation and account for this effect in the fit CDF Simulation of Detector Angular Sculpting cos(θ) cos(ψ) Φ(rad) F. Bedeschi, INFN-Pisa

  23. S-Wave • As noted in arxiv:0812.2832v3, the final state in Bs→ J/Ψ KK decays can be in an s-wave state with a ~6% contribution in a +/-10 MeV window around the Φpeak • Systematic effects from neglecting such contribution were first investigated by Clarke et al in arxiv:0908.3627v1 where it is shown that: - 10% un-accounted s-wave contamination in the Φ region leads to - 10% bias in the measured 2bs , towards the SM prediction - 15% increase in statistical errors • S-wave contribution can be either non-resonant or from the f0(980) resonance • To account for potential s-wave contribution, enhance the likelihood function to account for the s-wave amplitude AS and interference between s-wave and p-wave • Time dependence of the s-wave amplitude AS is CP-odd, same as A┴ • Mass and phase of s-wave component are assumed flat (good approximation in a narrow +/- 10 MeV around the Φ mass) F. Bedeschi, INFN-Pisa

  24. S-Wave Cross Check Using KK Mass Spectrum - Cross check the result from angular fit by fitting the KK invariant mass spectrum - From a fit to the Bs mass distribution with wide KK mass range selection (0.980,1.080 GeV), determine contributions of combinatorial background, mis-reconstructed B0, and Bs events - Good fit of the KK mass spectrum with 2% f0 contributions Barely visible S-wave component F. Bedeschi, INFN-Pisa

  25. Non-Gaussian Regime - Pseudo-experiments show that we are still not in perfect Gaussian regime → quote confidence regions instead of point estimates - In ideal case (high statistics, Gaussian likelihood), to get the 2D 68% (95%) C.L. regions, take a slice through profiled likelihood at 2.3 (6.0) units up from minimum • In this analysis integrated likelihood ratio distribution (black histogram) deviates from the ideal c2 distribution (green continuous curve) • Using pseudo-experiments establish a “map” between Confidence Level and 2Dlog(L) • All nuisance parameters are randomly varied within +/- 5s from their best fit values and maps of CL vs 2Dlog(L) re-derived • To establish final confidence regions use most conservative case non-Gaussian correction for wide variations of nuisance parameters F. Bedeschi, INFN-Pisa

  26. Systematic Uncertainties F. Bedeschi, INFN-Pisa

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