Observation of B 0 s – B 0 s Oscillations The CDF Collaboration 1 st St. Ocean City, NJ, Feb. 7, 2003, H 2 O 35 0 F Joseph Kroll University of Pennsylvania DPF Waikiki, HI 2 Nov 2006

J. Kroll (Penn)2 Results presented today are contained in two papers: A.Abulencia et al. (CDF Collaboration) Phys. Rev. Lett (2006) A.Abulencia et al. (CDF Collaboration) hep-ex/ , accepted by PRL Parallel session presentations: V. Tiwari (CMU), J. Miles (MIT)

2 Nov 2006J. Kroll (Penn)3 Two-State Quantum Mechanical System Produce flavor states: Common decay modes ! 2-state QM system M. Gell-Mann & A. Pais, Phys. Rev., 97, 1387 (1955) States with mass & lifetime (neglecting CP violation) “Light” (CP-even) “Heavy” (CP-odd)

2 Nov 2006J. Kroll (Penn)4 Antiparticle exists a time t! Form asymmetry A(t) = cos(  m s t)  m s is oscillation frequency

2 Nov 2006J. Kroll (Penn)5 Measure Amplitude versus Oscillation Frequency Time DomainFrequency Domain Units: [  m] = ~ ps -1. We use ~ =1 and quote  m in ps -1 To convert to eV multiply by £ 2

2 Nov 2006J. Kroll (Penn)6 Start 2006: Published Results on  m s Results from LEP, SLD, CDF I  m s > 14.4 ps -1 95% CL see Amplitude method: H-G. Moser, A. Roussarie, NIM A384 p. 491 (1997)

2 Nov 2006J. Kroll (Penn)7 April 2006: Result from the CDF Collaboration Probability “Signal” is random fluctuation is 0.2% Under signal hypothesis: measure  m s V. M. Abulencia et al., Phys. Rev. Lett. Vol. 97, (2006)

2 Nov 2006J. Kroll (Penn)8 Since then CDF has focused on turning evidence (3  ) into an observation (>5  ) Use the same 1 fb -1 data set with improved analysis Tevatron has delivered 2 fb -1 CDF has collected 1.6 fb -1 this analysis

2 Nov 2006J. Kroll (Penn)9 Why is this Interesting? Flavor oscillations occur through 2 nd order weak interactions e.g. All factors known well except “bag factor” £ “decay constant” From measurement of  m s derive |V * tb V ts | 2 C. Gay, Annu. Rev. Nucl. Part. Sci. 50, 577 (2000) Calculated on lattice, uncertainty ~ 10%

2 Nov 2006J. Kroll (Penn)10 B Meson Flavor Oscillations (cont) Measure  m s !  m s /  m d Theoretical uncertainties reduced Ratio measures |V td /V ts | This is why  m s is high priority in Run II Well measured:  m d = § ps -1 (1%) (PDG 2006) from Lattice QCD calculations – see Okamoto, hep-lat/

2 Nov 2006J. Kroll (Penn)11 Slide giving example of new physics

2 Nov 2006J. Kroll (Penn)12 Experimental Steps for Measuring B s Mixing 1. Extract B 0 s signal – decay mode must identify b-flavor at decay (TTT) Examples: 2. Measure decay time (t) in B rest frame (L = distance travelled) (L00) 3. Determine b-flavor at production “flavor tagging” (TOF) “unmixed” means production and decay flavor are the same “mixed” means flavor at production opposite flavor at decay Flavor tag quantified by dilution D = 1 – 2w, w = mistag probability

2 Nov 2006J. Kroll (Penn)13 Schematic of Oscillation Event opposite-side K – jet charge

2 Nov 2006J. Kroll (Penn)14 Key Experimental Issues flavor tagging power, background displacement resolution momentum resolution mis-tag rate 40%  L) ~ 50  m  p)/p = 5%

2 Nov 2006J. Kroll (Penn)15 What’s Special About CDF & Tevatron Tevatron delivered required luminosity Unique trigger (SVT) made kaon identification possible high efficiency, high purity flavor tag Inner layer of silicon (L00) large sample of completely reconstructed B s Crucial for lifetime resolution & background reduction provided decay distance resolution Detector for particle identification (TOF)

2 Nov 2006J. Kroll (Penn)16 Semileptonic B 0 s Decay Modes Fully reconstructed ( ,  0 ) better decay time resolution Lower statistics Signal 8,700 Not fully reconstructed poorer decay time resolution Higher statistics Signal 61,500 Hadronic } { }{ Majority of signal collected with displaced track trigger

2 Nov 2006J. Kroll (Penn)17 Example: Fully Reconstructed Signal Cleanest decay sequence Four charged particles in final state: K + K -  +  - Also use 6 body modes:

2 Nov 2006J. Kroll (Penn)18 Semileptonic Signals

2 Nov 2006J. Kroll (Penn)19 Proper Time & Lifetime Measurement production vertex 25  m £ 25  m Decay position Decay time in B rest frame  B 0 s ) = 1.??? § 0.0?? ps (statistical error only) PDG 2006: § ps

2 Nov 2006J. Kroll (Penn)20 Decay Time Resolution: Hadronic Decays = 86 £ s ¼ period for  m s = 18 ps -1 Oscillation period for  m s = 18 ps -1 Maximize sensitivity: use candidate specific decay time resolution Superior decay time resolution gives CDF sensitivity at much larger values of  m s than previous experiments

2 Nov 2006J. Kroll (Penn)21 Semileptonics: Correction for Missing Momentum Reconstructed quantity Correction Factor (MC)Decay Time

2 Nov 2006J. Kroll (Penn)22 Same Side Flavor Tags Need particle id TOF Critical (dE/dx too) Charge of K tags flavor of B s at production Our most powerful flavor tag:  D 2 = 4-5% Opposite-side tags:  D 2 = 1.8%

2 Nov 2006J. Kroll (Penn) 23 Results: Amplitude Scan A/  A = 6.1 Sensitivity 31.3 ps -1 Hadronic & semileptonic decays combined

2 Nov 2006J. Kroll (Penn) 24 Measured Value of  m s - log(Likelihood) Hypothesis of A=1 compared to A=0

2 Nov 2006J. Kroll (Penn) 25 Significance: Probability of Fluctuation Probability of random fluctuation determined from data Probability = 8 £ 10  8  (5.4  ) Have exceeded standard threshold to claim observation 28 of 350 million random trials have L <

2 Nov 2006J. Kroll (Penn) 26 Asymmetry (Oscillations) in Time Domain

2 Nov 2006J. Kroll (Penn) 27 Determination of |V td /V ts | Previous best result: D. Mohapatra et al. (Belle Collaboration) PRL (2006) CDF

2 Nov 2006J. Kroll (Penn) 28 Summary of CDF Results on B 0 s Mixing Observation of B s Oscillations and precise measurement of  m s Precision: 0.7% Probability of random fluctuation: 8 £ Most precise measurement of |V td /V ts | A. Abulencia et al., hep-ex/ , accepted by Phys. Rev. Lett. ( 2.83 THz, eV)

2 Nov 2006J. Kroll (Penn)29 Backup & Alternate Slides

2 Nov 2006J. Kroll (Penn)30 Weakly Decaying Neutral Mesons Flavor states (produced mainly by strong interaction at Tevatron)

2 Nov 2006J. Kroll (Penn)31 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 2 nd 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

2 Nov 2006J. Kroll (Penn)32 Example of Candidate candidate Same-side Kaon tag Opposite-side Muon tag Zoom in on collision pt.

2 Nov 2006J. Kroll (Penn)33 Measuring Resolution in Data Use large prompt D meson sample CDF II, D. Acosta et al., PRL 91, (2003) Real prompt D + from interaction point pair with random track from interaction point Compare reconstructed decay point to interaction point

2 Nov 2006J. Kroll (Penn)34  ime integrated oscillation probability must measure proper time dependent oscillation to measure  m s