The Observation of B 0 s – B 0 s Oscillations: a 20 Year Perspective 23 Nov 2006, Music Pier, Ocean City, NJ, photo: Tom Welsh Joseph Kroll University of Pennsylvania CKM 2006 Nagoya Dec 2006

15 Dec 2006J. Kroll (Penn) CKM I only show published resultsReferences highlighted in green If two uncertainties are shown: 1 st is statistical, 2 nd is systematic Outline Reminder of the importance of measuring  m d,s Measurements of time integrated mixing probability  Measurements of  m d Measurements of  m s

15 Dec 2006J. Kroll (Penn) CKM Our Story Begins 20 Years Ago UA1 1986: Evidence for B 0 & B 0 s mixing From the Abstract: “Combined with the null result from searches for B 0 $ B 0 oscillations at e + e - colliders, our results are consistent with with transitions in the B 0 s system as favoured theoretically” C. Albajar et al., Phys. Lett. B 186, 247 (1987) B 0 s not yet directly observed B mixing probability: H.-G. Moser, “Dimuon Production at the CERN p-pbar Collider, RWTH Aachen, PITHA (1987)

15 Dec 2006J. Kroll (Penn) CKM 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

15 Dec 2006J. Kroll (Penn) CKM “If there is any place where we have a chance to test the main principles of quantum mechanics in the purest way – does the superposition of amplitudes work or doesn’t it – this is it.” comment concerning K 0 ’s R. P. Feynman in Lectures on Physics Vol. III

15 Dec 2006J. Kroll (Penn) CKM 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 td /V ts | measure one side of Unitary Triangle New particles in loops alter expectations  test Standard EWK Model

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

15 Dec 2006J. Kroll (Penn) CKM Some History Important prehistory: 1983: long B hadron lifetime 2006 APS Panofsky Prize 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 (maximally) - 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) & PRL, 97, (2006) M. Artuso et al., PRL, 62, 2233 (1989) too many references to list individually Belle: K. Abe et al., PRD 71, (2005)Babar: B. Aubert et al., PRD 73, (2006)

15 Dec 2006J. Kroll (Penn) CKM : B Hadron Lifetime Measurement 2006 Panofsky Prize: Bill Ford, John Jaros, Nigel Lockyer MAC: E. Fernandez et al., PRL (1983) MarkII: N. Lockyer et al., PRL (1983) Signed impact parameter (no Silicon) c sample b sample background e,  thrust axis 500  m 100  m SLC & SLD:  xy = 3.5  m  Z = 17  m PEPII

15 Dec 2006J. Kroll (Penn) CKM Methods to Measure  m Time Integrated (assuming  = 0) Measure probability B decays as B: Mixing first established with time integrated quantities Time Dependent (required for  m À  ) Measure probability B decays as B as a function of proper decay time t  m = oscillation frequency (LEP, LHC, SLC, Tevatron)

15 Dec 2006J. Kroll (Penn) CKM First Signature for B Mixing: Like-Charge Leptons Based on semileptonic B decay: Account for: Coherentincoherent

15 Dec 2006J. Kroll (Penn) CKM UA1: 1 st Evidence for B Mixing C. Albajar et al., Phys. Lett. B 186, 247 (1987) Measured: Expected: for no mixing, but b ! c ! l etc. Determined: no mixing disfavored at 2.9  Combination of B 0 & B 0 s mixing

15 Dec 2006J. Kroll (Penn) CKM ARGUS: Observation of B 0 Oscillations H. Albrecht et al., PLB, 192, 245 (1987) 1 fully reconstructed event with two B 0 ’s (two  + ) Measured  d using r from - dileptons (4.0  ) - lepton+B 0 ’s (3.0  ) important uncertainty: B 0 to B + ratio

15 Dec 2006J. Kroll (Penn) CKM Early 90’s: B 0 s Mixing Established Z-pole, hadron colliders R. Akers et al., ZfP, C60, 199 (1993) Example: OPAL Extracted: Data favor maximal  s B s mixing “discovered” +  d from CLEO Fraction of B s mesons produced B s mixing probability

15 Dec 2006J. Kroll (Penn) CKM : First Direct Evidence of B s Signal Well known background poorly known background (small) P. Abreu et al. (Delphi) Phys. Lett. B 289, 199 (1992) also: D. Buskulic et al. (Aleph) Phys. Lett. B 294, 145 (1992) P. D. Acton et al. (Opal) Phys. Lett. B 295, 357 (1992) Sample: 270 K hadronic Z

15 Dec 2006J. Kroll (Penn) CKM Time Dependent Measurement of  m d Requires 3 pieces of information per event –Flavor of B at production –Flavor of B at decay –Proper decay time of B Flavor of B at production – several techniques “opposite-side” use other B hadron in event: leptons, jet-charge, kaons “ same-side” use associated particles produced in fragmentation Flavor of B at decay –requires signal (B 0 ) fraction –inclusive (reconstruct secondary vertex, use “jet-charge”) –partial (lepton, charm) –semi-exclusive or exclusive (lepton+charm, hadronic) Proper decay time –resolution depends on method used to reconstruct B decay

15 Dec 2006J. Kroll (Penn) CKM ALEPH: 1 st Time Dependent Measurement R. Akers et al., ZfP, C60, 199 (1993) w. lepton tag from “other” B Experimental Effects perfect proper time effects prod. flavor mistag, backgnd Measured Asymmetry D 0 Decay Length (cm) D

15 Dec 2006J. Kroll (Penn) CKM State of the Art:  m d Belle: K. Abe et al., PRD 71, (2005) Babar: B. Aubert et al., PRD 73, (2006) Belle: B 0 lifetime BaBar:  m d

15 Dec 2006J. Kroll (Penn) CKM  m d is “easy”: B 0 oscillates once every 8 decay times  m s is a different story…

15 Dec 2006J. Kroll (Penn) CKM How Do We Look for “Fast” Oscillation? 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 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 Amplitude method: H-G. Moser, A. Roussarie, NIM A384 p. 491 (1997)

15 Dec 2006J. Kroll (Penn) CKM Start 2006: Published Results on  m s Results from LEP, SLD, CDF I  m s > 14.4 ps -1 95% CL source: Frequency  m s (ps -1 ) 15  m s = 15 ps -1 Amplitude 1 0 >3.4 cycles per lifetime Average 0.48 § 0.43

15 Dec 2006J. Kroll (Penn) CKM Ingredients in Measuring B s 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  = efficiency  D 2 = effective tagging power Proper decay time from displacement (L) and momentum (p)

15 Dec 2006J. Kroll (Penn) CKM Aleph: Golden Event D. Buskulic et al., PLB (1993) Bonus: Same-side K + Opp.-side e - Produced as This paper reported the 1 st precise measurement of m(B s )

15 Dec 2006J. Kroll (Penn) CKM Key Experimental Issues Uncertainty on Amplitude Signal size Signal to Background Proper time Resolution Production flavor Tag performance Full reconstruction critical a large  m s For limit on  m s must know S/B, D,  t

15 Dec 2006J. Kroll (Penn) CKM Example of e + e - Analysis: SLD Electron beam polarization Provided unique flavor tag Inclusive vertexing method exploiting unique CCD detector K. Abe et al., PRD 67, (2003) Limits

15 Dec 2006J. Kroll (Penn) CKM Highlights of Tevatron Analyses Details see F. Bedeschi (CDF) & G. Weber (DØ) in WG3

15 Dec 2006J. Kroll (Penn) CKM The Challenge CDF: Run Event 1859

15 Dec 2006J. Kroll (Penn) CKM DØ Semi-muonic Signals & Lifetime Oscillation analysis Lifetime Measurement Signal: 26,700most precise single measurement Signal: 5,176 V. M. Abazov et al., PRL (2006)

15 Dec 2006J. Kroll (Penn) CKM CDF: Semileptonic Signals Total signal: 61500

15 Dec 2006J. Kroll (Penn) CKM Semileptonics: Correction for Missing Momentum Reconstructed quantity Correction Factor (MC)Decay Time Reconstructed momentum fraction proper decay time (ps) T = 2  /  m s resolution (fs)

15 Dec 2006J. Kroll (Penn) CKM CDF Fully Reconstructed Signal Cleanest decay sequence Also use 6 body modes: Also partially reconstructed decays: Total hadronic signal 8700

15 Dec 2006J. Kroll (Penn) CKM 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

15 Dec 2006J. Kroll (Penn) CKM Same Side Flavor Tags Particle id very important CDF TOF critical (dE/dx too) Charge of K tags flavor of B s at production So far only used by CDF Most powerful flavor tag:  D 2 = 4-5% Opposite-side tags: CDF:  D 2 = 1.8% DØ:  D 2 = 2.5% A. Ali, F. Barreiro ZfP C (1986); M. Gronau, A. Nippe, J.L. Rosner, PRD (1993); M. Gronau, J.L. Rosner PRD (1994)

15 Dec 2006J. Kroll (Penn) CKM March 2006: Result DØ Collaboration V. M. Abazov et al., Phys. Rev. Lett. Vol. 97, (2006)

15 Dec 2006J. Kroll (Penn) CKM DØ Result (Continued) 17 <  m s < 21 ps 90% CL 1 st reported direct experimental upper bound V. M. Abazov et al., PRL (2006) Probability “Signal” is random fluctuation is 5%

15 Dec 2006J. Kroll (Penn) CKM 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., PRL (2006) Next goal was to observe signal with > 5  significance likelihood ratio

15 Dec 2006J. Kroll (Penn) CKM Resulting Improved Analysis A/  A = 6.1 Sensitivity 31.3 ps -1 Hadronic & semileptonic decays combined A. Abulencia et al., PRL (2006) published on-line on 12 Dec 2006

15 Dec 2006J. Kroll (Penn) CKM Measured Value of  m s - log(Likelihood) Hypothesis of A=1 compared to A=0

15 Dec 2006J. Kroll (Penn) CKM 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 <

15 Dec 2006J. Kroll (Penn) CKM Asymmetry (Oscillations) in Time Domain Period 0.35 ps Aside: for B 0 Period = 12.6 ps

15 Dec 2006J. Kroll (Penn) CKM 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 | ( 2.83 THz, eV) A. Abulencia et al., PRL (2006)

15 Dec 2006J. Kroll (Penn) CKM Why CDF? Tevatron delivered required luminosity “Deadtime-less” 3-level trigger 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 (25  m £ 25  m beam) Silicon layer on beampipe (Layer00) at 1.5cm Particle identification –specific ionization in central drift chamber (dE/dx) –Time of Flight measurement at R = 1.4 m –electron & muon identification

15 Dec 2006J. Kroll (Penn) CKM Conclusions 20 year quest has come to a conclusion –B s oscillations observed –  m s precisely measured –fundamental parameters measured –rapid oscillations made it very challenging to observe Long B lifetime and significant B mixing prerequisite to observe CP violation at the B factories Next step is to look for CP violation in B s decays –expect sin2  s to be very small (few % asymmetry) –large value  unambiguous signal of new physics More exciting times ahead for flavor physics

15 Dec 2006J. Kroll (Penn) CKM Backup Slides

15 Dec 2006J. Kroll (Penn) CKM Time of Flight Detector (TOF) 216 Scintillator bars, 2.8 m long, 4 £ 4 cm 2 R=140 cm read out both ends with fine mesh PMT (operates in 1.4 T B field – gain down ~ 400) anticipated resolution  TOF =100 ps (limited by photostatistics) Kaon ID for B physics Measured quantities: s = distance travelled t = time of flight p = momentum Derived quantities: v = s/t m = p/  v

15 Dec 2006J. Kroll (Penn) CKM Two Types of Flavor Tags Opposite side Same sideBased on fragmentation tracks or B ** + Applicable to both B 0 and B 0 s − other b not always in the acceptance − Results for B + and B 0 not applicable to B 0 s + better acceptance for frag. tracks than opp. side b Reminder: for limit on  m s must know D Produce bb pairs: find 2 nd b, determine flavor, infer flavor of 1 st b

15 Dec 2006J. Kroll (Penn) CKM Types of Opposite Side Flavor Tags Lepton tags Jet charge tag Kaon tag mistags from jet from b (b) has negative (positive) charge on average low  high D high  low D Largest  D B factories Not used in present analysis TOF

15 Dec 2006J. Kroll (Penn) CKM Calibrate with Large Statistics Samples of B + & B 0 Example: semileptonic signals Results:  D 2 = 1.54 § 0.05 [  m d = § (stat) § (syst)] Hadronic signals: B + (D 0  + ) = 26,000 B 0 (D -  + ) = 22,000

15 Dec 2006J. Kroll (Penn) CKM Compare Performance Data and Simulation Check prediction for kaon tag on B +, B 0 Good agreement between data & MC Systematic based on comparisons K K  

15 Dec 2006J. Kroll (Penn) CKM Same Side Flavor Tags Based on correlation between charge of fragmentation particle and flavor of b in B meson TOF Critical (dE/dx too)

15 Dec 2006J. Kroll (Penn) CKM Kaons Produced in Vicinity of B’s Larger fraction of Kaons near B 0 s compared to B 0, B +, as expected

15 Dec 2006J. Kroll (Penn) CKM Example of Candidate candidate Same-side Kaon tag Opposite-side Muon tag Zoom in on collision pt.

15 Dec 2006J. Kroll (Penn) CKM 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

15 Dec 2006J. Kroll (Penn) CKM Proper Time & Lifetime Measurement production vertex 25  m £ 25  m Decay position Decay time in B rest frame

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

15 Dec 2006J. Kroll (Penn) CKM Improvement from Neural Net Selection

15 Dec 2006J. Kroll (Penn) CKM Scans for Individual Signatures