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

2 Nov 2006J. Kroll (Penn)3 Two-State Quantum Mechanical System Common decay modes ! 2-state QM system Eigenstates of 2-state system (neglecting CP violation) “Light” (CP-even) “Heavy” (CP-odd) mass & width Antiparticle exists at time t! Start (t=0) with particle

2 Nov 2006J. Kroll (Penn) 4 Importance of Neutral B Meson Oscillations Cabibbo-Kobayashi-Maskawa Matrix weak mass fundamental parameters that must be measured Oscillation frequencies (  m d,  m s ) determine poorly known V td, V ts |V td /V ts | measures one side of Unitary Triangle New particles in loops alter expectations  test Standard EWK Model

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

2 Nov 2006J. Kroll (Penn)6 Some History 1986: 1 st evidence of B mixing from UA1 C. Albajar et al., PLB, 186, 247 (1987) 1987: Definitive observation of B 0 mixing by ARGUS - indicates UA1 must be B s, heavy top (>50 GeV) confirmed by CLEO 1990’s: LEP, SLC, Tevatron - time-integrated meas. establishes B s mixes - measure time-dependent B 0 oscillations - lower limits on B s oscillation frequency 2000: B factories improve precision of B 0 oscillation frequency 2006: Tevatron discovers B s oscillations - two-sided 90% CL limit by DØ - 1 st measurement of oscillation frequency by CDF - definitive observation of oscillation signal by CDF H. Albrecht et al., PLB, 192, 245 (1987) V. M. Abazov et al., PRL, 97, (2006) A. Abulencia et al., PRL, 97, (2006) & hep-ex/ , acc. by PRL This talk

2 Nov 2006J. 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 For a fixed value of  m s, data should yield Amplitude “A” is 1, at the true value of  m s Amplitude “A” is 0, otherwise “mixed”: particle decays as antiparticle Units: [  m] = ~ ps -1, ~ =1 then  m in ps -1. Multiply by £ to convert to eV

2 Nov 2006J. Kroll (Penn)8 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)9 April 2006: Result from the CDF Collaboration Probability that random fluctuations mimic this signal is 0.2% (3  ) Assuming signal hypothesis: measure  m s A. Abulencia et al., Phys. Rev. Lett., 97, (2006) Since then goal has been to observe signal with > 5  significance

2 Nov 2006J. Kroll (Penn)10 Ingredients in Measuring Oscillations opposite-side K – jet charge Decay mode tags b flavor at decay 2 nd B tags production flavor Dilution D = 1 – 2w w = mistag probability Proper decay time from displacement (L) and momentum (p)

2 Nov 2006J. Kroll (Penn)11 Key Experimental Issues Uncertainty on Amplitude Signal size Signal to Background Proper time Resolution Production flavor Tag performance efficient tracking, displaced track trigger excellent mass resolution Particle identification: TOF, dE/dx lepton id, Kaon id with TOF Silicon mounted on beampipe (Layer 00) Fully reconstructed signal crucial CDF’s strengths

2 Nov 2006J. 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

2 Nov 2006J. Kroll (Penn)13 Example: Fully Reconstructed Signal Cleanest decay sequence Also use 6 body modes: Add partially reconstructed decays: Hadronic signal increased from 3600 to 8700

2 Nov 2006J. Kroll (Penn)14 Semileptonic Signals Semileptonic signal increased from to 61500

2 Nov 2006J. Kroll (Penn)15 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)16 Semileptonics: Correction for Missing Momentum Reconstructed quantity Correction Factor (MC)Decay Time

2 Nov 2006J. Kroll (Penn)17 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) 18 Results: Amplitude Scan A/  A = 6.1 Sensitivity 31.3 ps -1 Hadronic & semileptonic decays combined

2 Nov 2006J. Kroll (Penn) 19 Measured Value of  m s - log(Likelihood) Hypothesis of A=1 compared to A=0

2 Nov 2006J. Kroll (Penn) 20 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) 21 Asymmetry (Oscillations) in Time Domain

2 Nov 2006J. Kroll (Penn) 22 Summary of CDF Results on B 0 s Mixing Observation of B s Oscillations and precise measurement of  m s Precision: 0.7% Probability random fluctuation mimics signal: 8 £ Most precise measurement of |V td /V ts | A. Abulencia et al., hep-ex/ , accepted by Phys. Rev. Lett. ( 2.83 THz, eV) 20 year quest has come to a conclusion

2 Nov 2006J. Kroll (Penn)23 Backup Slides

2 Nov 2006J. Kroll (Penn)24 Weakly Decaying Neutral Mesons Flavor states (produced mainly by strong interaction at Tevatron)

2 Nov 2006J. 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 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)26 Example of Candidate candidate Same-side Kaon tag Opposite-side Muon tag Zoom in on collision pt.

2 Nov 2006J. Kroll (Penn)27 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)28  ime integrated oscillation probability must measure proper time dependent oscillation to measure  m s

2 Nov 2006J. Kroll (Penn)29 Antiparticle exists a time t! Form asymmetry A(t) = cos(  m s t)  m s is oscillation frequency

2 Nov 2006J. Kroll (Penn)30 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)31 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)32 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) 33 Determination of |V td /V ts | Previous best result: D. Mohapatra et al. (Belle Collaboration) PRL (2006) CDF