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The Observation of B 0 s – B 0 s Oscillations

The Observation of B 0 s – B 0 s Oscillations. The CDF Collaboration. DPF Waikiki, HI 2 Nov 2006. Joseph Kroll University of Pennsylvania. 1 st St. Ocean City, NJ, Feb. 7, 2003, H 2 O 35 0 F. Tevatron has delivered 2 fb -1. CDF has collected 1.6 fb -1. this analysis 1.0 fb -1.

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The Observation of B 0 s – B 0 s Oscillations

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  1. The Observation of B0s – B0s Oscillations The CDF Collaboration DPF Waikiki, HI 2 Nov 2006 Joseph Kroll University of Pennsylvania 1st St. Ocean City, NJ, Feb. 7, 2003, H2O 350 F

  2. Tevatron has delivered 2 fb-1 CDF has collected 1.6 fb-1 this analysis 1.0 fb-1 Today’s Results Made Possible by Excellent Tevatron Performance Today’s results Reported in 2 papers by A. Abulencia et al. (CDF collaboration): PRL, 97, 021802 (2006) hep-ex/0609040, accepted by PRL see also Parallel session presentations: V. Tiwari (CMU) , J. Miles (MIT) J. Kroll (Penn)

  3. Common decay modes ! 2-state QM system Eigenstates of 2-state system (neglecting CP violation) “Light” (CP-even) “Heavy” (CP-odd) Start (t=0) with particle Antiparticle exists at time t! Two-State Quantum Mechanical System mass & width J. Kroll (Penn)

  4. Importance of Neutral B Meson Oscillations fundamental parameters that must be measured Cabibbo-Kobayashi-Maskawa Matrix mass weak Oscillation frequencies (md, ms) determine poorly known Vtd, Vts |Vtd/Vts| measures one side of Unitary Triangle New particles in loops alter expectations  test Standard EWK Model J. Kroll (Penn)

  5. All factors well known except from Lattice QCD calculations - see Okamoto, hep-lat/0510113 Limits precision on Vtd, Vts to ~ 10% Theoretical uncertainties reduced in ratio: ~ 4% PDG 2006 J. Kroll (Penn)

  6. Some History 1986: 1st evidence of B mixing from UA1 C. Albajar et al., PLB, 186, 247 (1987) 1987: Definitive observation of B0 mixing by ARGUS - indicates UA1 must be Bs, heavy top (>50 GeV) - 1989 confirmed by CLEO H. Albrecht et al., PLB, 192, 245 (1987) 1990’s: LEP, SLC, Tevatron - time-integrated meas. establishes Bs mixes - measure time-dependent B0 oscillations - lower limits on Bs oscillation frequency 2000: B factories improve precision of B0 oscillation frequency 2006: Tevatron discovers Bs oscillations - two-sided 90% CL limit by DØ - 1st measurement of oscillation frequency by CDF - definitive observation of oscillation signal by CDF V. M. Abazov et al., PRL, 97, 021802 (2006) A. Abulencia et al., PRL, 97, 021802 (2006) & hep-ex/0609040, acc. by PRL This talk J. Kroll (Penn)

  7. How Do We Measure Oscillation Frequency? Measure asymmetry A as a function of proper decay time t “unmixed”:particle decays as particle “mixed”:particle decays as antiparticle For a fixed value of ms, data should yield Amplitude “A” is 1, at the true value of ms Amplitude “A” is 0, otherwise Units: [m] = ~ ps-1, ~=1 then m in ps-1. Multiply by 6.582£ 10-4 to convert to eV J. Kroll (Penn)

  8. Start 2006: Published Results on ms ms > 14.4 ps-1 95% CL Results from LEP, SLD, CDF I Amplitude method: H-G. Moser, A. Roussarie, NIM A384 p. 491 (1997) see http://www.slac.stanford.edu/xorg/hfag/osc/PDG_2006/index.html J. Kroll (Penn)

  9. April 2006: Result from the CDF Collaboration A. Abulencia et al., Phys. Rev. Lett., 97, 062003 (2006) Probability that random fluctuations mimic this signal is 0.2% (3) Assuming signal hypothesis: measure ms Since then goal has been to observe signal with > 5 significance J. Kroll (Penn)

  10. Ingredients in Measuring Oscillations Decay mode tags b flavor at decay opposite-side K– jet charge 2nd B tags production flavor Proper decay time from displacement (L) and momentum (p) Dilution D = 1 – 2w w = mistag probability J. Kroll (Penn)

  11. CDF’s strengths Key Experimental Issues Uncertainty on Amplitude Signal size efficient tracking, displaced track trigger excellent mass resolution Particle identification: TOF, dE/dx Signal to Background Production flavor Tag performance lepton id, Kaon id with TOF Silicon mounted on beampipe (Layer 00) Proper time Resolution Fully reconstructed signal crucial J. Kroll (Penn)

  12. Improvements that led to Observation • Same data set (1 fb-1) • Proper decay time resolution unchanged • Signal selection • Neural network selection for hadronic modes • add partially reconstructed hadronic decays • use particle id (TOF, dE/dx) (separate kaons from pions) • looser kinematic criteria possible due to lower background • additional trigger selection criteria allowed • Production Flavor tag • opposite-side tags combined using neural network • also added opposite-side kaon tag • neural network combines kinematics and PID in same-side K tag J. Kroll (Penn)

  13. Example: Fully Reconstructed Signal Cleanest decay sequence Add partially reconstructed decays: Also use 6 body modes: Hadronic signal increased from 3600 to 8700 J. Kroll (Penn)

  14. Semileptonic Signals Semileptonic signal increased from 37000 to 61500 J. Kroll (Penn)

  15. <t> = 86 £ 10-15 s ¼ period for ms = 18 ps-1 Oscillation period for ms = 18 ps-1 Decay Time Resolution: Hadronic Decays Maximize sensitivity: use candidate specific decay time resolution Superior decay time resolution gives CDF sensitivity at much larger values of ms than previous experiments J. Kroll (Penn)

  16. Correction Factor (MC) Decay Time Reconstructed quantity Semileptonics: Correction for Missing Momentum J. Kroll (Penn)

  17. Same Side Flavor Tags Charge of K tags flavor of Bs at production Need particle id TOF Critical (dE/dx too) Our most powerful flavor tag: D2 = 4-5% (Opposite-side tags: D2 = 1.8%) J. Kroll (Penn)

  18. Results: Amplitude Scan Sensitivity 31.3 ps-1 A/A = 6.1 Hadronic & semileptonic decays combined J. Kroll (Penn)

  19. Measured Value of ms Hypothesis of A=1 compared to A=0 - log(Likelihood) J. Kroll (Penn)

  20. Significance: Probability of Fluctuation Probability of random fluctuation determined from data 28 of 350 million random trials have L < -17.26 Probability = 8 £ 10-8(5.4) Have exceeded standard threshold to claim observation -17.26 J. Kroll (Penn)

  21. Asymmetry (Oscillations) in Time Domain J. Kroll (Penn)

  22. Summary of CDF Results on B0s Mixing A. Abulencia et al., hep-ex/0609040, accepted by Phys. Rev. Lett. Observation of Bs Oscillations and precise measurement of ms Precision: 0.7% Probability random fluctuation mimics signal: 8£10-8 ( 2.83 THz, 0.012 eV) Most precise measurement of |Vtd/Vts| 20 year quest has come to a conclusion J. Kroll (Penn)

  23. Backup Slides J. Kroll (Penn)

  24. Weakly Decaying Neutral Mesons Flavor states (produced mainly by strong interaction at Tevatron) J. Kroll (Penn)

  25. Key Features of CDF for B Physics • “Deadtime-less” trigger system • 3 level system with great flexibility • First two levels have pipelines to reduce deadtime • Silicon Vertex Tracker: trigger on displaced tracks at 2nd level • Charged particle reconstruction – Drift Chamber and Silicon • excellent momentum resolution: R = 1.4m, B = 1.4T • lots of redundancy for pattern recognition in busy environment • excellent impact parameter resolution (L00 at 1.5cm, 25m £ 25m beam) • Particle identification • specific ionization in central drift chamber (dE/dx) • Time of Flight measurement at R = 1.4 m • electron & muon identification J. Kroll (Penn)

  26. candidate Example of Candidate Zoom in on collision pt. Same-side Kaon tag Opposite-side Muon tag J. Kroll (Penn)

  27. Measuring Resolution in Data Use large prompt D meson sample CDF II, D. Acosta et al., PRL 91, 241804 (2003) Real prompt D+ from interaction point pair with random track from interaction point Compare reconstructed decay point to interaction point J. Kroll (Penn)

  28. Time integrated oscillation probability J. Kroll (Penn) must measure proper time dependent oscillation to measure ms

  29. Antiparticle exists a time t! Form asymmetry A(t) = cos(mst) ms is oscillation frequency J. Kroll (Penn)

  30. Measure Amplitude versus Oscillation Frequency Time Domain Frequency Domain 2G Units: [m] = ~ ps-1. We use ~=1 and quote m in ps-1 To convert to eV multiply by 6.582£ 10-4 J. Kroll (Penn)

  31. Key Experimental Issues flavor tagging power, background displacement resolution momentum resolution (L) ~ 50 m mis-tag rate 40% (p)/p = 5% J. Kroll (Penn)

  32. Decay position production vertex 25m £ 25 m Decay time in B rest frame Proper Time & Lifetime Measurement (B0s) = 1.??? § 0.0?? ps (statistical error only) PDG 2006: 1.466 § 0.059 ps J. Kroll (Penn)

  33. Determination of |Vtd/Vts| D. Mohapatra et al. (Belle Collaboration) PRL 96 221601 (2006) Previous best result: CDF J. Kroll (Penn)

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