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Observation of B s Mixing with CDF II

Observation of B s Mixing with CDF II. Alessandro Cerri CERN (LBNL). Dec 11 th 2006. Synopsis. Introduction B s mixing in the last 12 months Flavor physics How the Tevatron contributes Detector Benchmarks B s Mixing Observation Is BSM physics dead? Conclusions.

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Observation of B s Mixing with CDF II

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  1. Observation of Bs Mixing with CDF II Alessandro Cerri CERN (LBNL) Dec 11th 2006

  2. Synopsis • Introduction • Bs mixing in the last 12 months • Flavor physics • How the Tevatron contributes • Detector • Benchmarks • Bs Mixing Observation • Is BSM physics dead? • Conclusions

  3. What happened in the last year… • Mar 2006: D0 came out with a result based on 1fb-1 (Moriond) • Jun 2006: CDF releases a preliminary result (but not the last word) on 1fb-1 • Signal search start showing evidence • Not enough statistical power for ‘observation’ (5) • If signal is theremeasure • Sep 2006: CDF went back and improved the analysis • Signal shows up at >5 • We therefore claim observation and measurement of This last analysis will be today’s subject!

  4. The Flavor Sector: CKM Matrix W d’ u Quarks couple to W through VCKM: rotation in flavor space! VCKM is Unitary

  5. Last year… TeVatron contribution is critical!

  6. The Tevatron as a b factory • (4s) B factories program extensive and very successful BUT limited to Bu,Bd • Tevatron experiments can produce all b species: Bu,Bd,Bs,Bc, B**, b,b See PRD 71, 032001 2005 • Compare to: • (4S)  1 nb (only B0, B+) • Z0 7 nb • Unfortunately • pp 100 mb b production in pp collisions is so large (~300 Hz @ 1032 cm-2 Hz) that we could not even cope with writing it to tape!

  7. Detector & Techniques

  8. CDF and the TeVatron TOF COT Si Detector: L00,SVX II, ISL • Renewed detector & Accelerator chain: • Higher Luminosity higher event rate • Detector changes/improvements: • DAQ redesign • Improved performance: • Detector Coverage • Tracking Quality • New Trigger strategies for heavy flavors: displaced vertex trigger Delivered: 1.6 fb-1 On tape : 1.4 fb-1 Good w/o Si: 1.2 fb-1 Good w Si: 1.0 fb-1

  9. SVT: a specialized B physics trigger The CDF Trigger ~2.7 MHz Crossing rate 396 ns clock Detector Raw Data • Level 1 • 2.7 MHz Synch. Pipeline • 5544 ns Latency • ~20 KHz accept rate Level 1 storage pipeline: 42 clock cycles Level 1 Trigger SVT L1 Accept Level 2 Trigger Level 2 buffer: 4 events • Level 2 • Asynch. 2 Stage Pipeline • ~20 s Latency • 250 Hz accept rate L2 Accept DAQ buffers L3 Farm Mass Storage (30-50 Hz) requirements • Good IP resolution • As fast as possible Customized Hardware

  10. …and a successful endeavor!  ~ 48 m Single Hit Road Detector Layers Superstrip • The recipe: specialized hardware • Clustering • Find clusters (hits) from detector ‘strips’ at full detector resolution • Template matching • Identify roads: pre-defined track templates • with coarser detector bins (superstrips) • Linearized track fitting • Fit tracks, with combinatorial limited to clusters within roads • SVT is capable of digesting >20000 evts/second, identifying tracks in the silicon • CDFII has been running it since day -1 SVT is the reason of the success and variety of B physics in CDF run II

  11. Benchmarks

  12. Knowledge of non-(4s)-produced b (PDG’04)

  13. Measure: Branching Ratios First-time measurement of many Bs and b Branching Fractions Hep-ex/0508014 Hep-ex/0502044 http://www-cdf.fnal.gov/physics/new/bottom/050310.blessed-dsd/ http://www-cdf.fnal.gov/physics/new/bottom/050310.blessed-dsd/ Hep-ex/0601003 http://www-cdf.fnal.gov/physics/new/bottom/050407.blessed-lbbr/lbrBR_cdfpublic.ps

  14. Lifetimes: fully reconstructed hadronic modes • Testbed for our ability to understand trigger biases • Large, clean samples with understood backgrounds • Excellent mass and vertex resolution • Prerequisite for mixing fits! Efficiency (AU) (B+) = 1.661±0.027±0.013 ps (B0) = 1.511±0.023±0.013 ps (Bs) = 1.598±0.097±0.017 ps 2 3 0 1 4 Proper decay length (mm) Systematics (m) KK http://www-cdf.fnal.gov/physics/new/bottom/050303.blessed-bhadlife/

  15. Hadronic Lifetime Results • World Average: B+ 1.653  0.014 ps-1 B0 1.534  0.013 ps-1 Bs 1.469  0.059 ps-1 Excellent agreement! ~3000 candidates

  16. lDs Lifetime Results lifetimes measured on first 355 pb-1 compare to World Average: Bs: (1.469±0.059) ps K  K Ds l l Bs

  17. Bs Mixing

  18. Why so much fuss around ms?    • Vtdis derived from mixing effects • QCD uncertainty is factored out in this case resorting to the relative Bs/Bd mixing rate (Vtd/Vts) • Beyond the SM physics could enter in loops!

  19. B production at the TeVatron • Production: ggbb • NO QM coherence, unlike B factories • Opposite flavor at productionone of the b quarks can be used to tell the flavor of the other at production • Fragmentation products have some memory of b flavor as well

  20. Bs Mixing 101 Nunmix-Nmix A= Nunmix+Nmix cos(m t) A  ms [ps-1] • ms>>md • Different oscillation regime  Amplitude Scan Perform a ‘fourier transform’ rather than fit for frequency B lifetime Bs vs Bd oscillation

  21. Amplitude Scan: introduction • Mixing amplitude fitted for each (fixed) value of m • On average every m value (except the true m) will be 0 • “sensitivity” defined for the average experiment [mean 0] • The actual experiment will have statistical fluctuations • Actual limit for the actual experiment defined by the systematic band centered at the measured asymmetry • Combining experiments as easy as averaging points! Just an example: Not based on real data! Is this an effective tool to search for a signal?

  22. Bs Mixing Ingredients Proper time resolution Flavor tagging Signal-to-noise Event yield

  23. Flavor Tagging Nright-Nwrong D= Nright+Nwrong Reconstructed decay Fragmentation product “Same Side” AmplitudeDAmplitude B meson • Flavor Taggers: • Opposite Side • Lepton (e,) • Average charge • Kaon (bcs) • Same Side: • Kaon (hadronization) Several methods, none is perfect !!!

  24. Bs Mixing: tagging performance Measured from Bd/Bs data ~5% of the Events are effectively used!

  25. Bs Mixing Ingredients: ct Proper time resolution

  26. Proper time resolution BsllDs K  K K K  BsDs Ds l l Ds Bs  Bs ~0.5% ~15% s æ ö m ç ÷ P s = s Ä s B ct Å t ç ÷ ct L K P P xy è ø t t Semileptonic modes: momentum uncertainty Fully reconstructed: Lxy uncertainty

  27. Mixing in the real world Proper time resolution Flavor tagging power

  28. Bs Mixing: CDF semileptonic Hep-ex/0609040 ms>16.5 @ 95% CL Sensitivity: 19.3 ps-1 Reach at large ms limited by incomplete reconstruction (ct)!

  29. Bs Mixing: CDF hadronic Hep-ex/0609040 Total: ~8700 events! ms>17.1 @ 95% CL Sensitivity: 30.7 ps-1 This looks a lot like a signal!

  30. Bs Mixing: combined CDF result Hep-ex/0609040 ms> 17.2 ps-1 @ 95% CL Sensitivity: 31.3 ps-1 Develop a sound statistical approach -prior to opening the box-to assess statistical significance! Minimum: -17.26 What is the probability for background to mimic this?

  31. Likelihood Ratio Hep-ex/0609040

  32. Likelihood Ratio Hep-ex/0609040 • Combined hadronic+semileptonic likelihoods gives 5 significance • Parabolic fit to minimum yields: • the measurement is very precise! (~2.5%) ms = 17.77 ± 0.10(stat) ± 0.07 (syst) ps-1 combined likelihoods from hadronic and semileptonic channels

  33. Systematic Uncertainties I Hadronic Semileptonic • Mostly related to absolute value of amplitude, relevant only when setting limits • cancel in A/A, folded in confidence calculation for observation • systematic uncertainties are very small compared to statistical

  34. Systematic Uncertainties II: ms • systematic uncertainties from fit model evaluated on toy Monte Carlo • have negligible impact • relevant systematic unc. from lifetime scale All relevant systematic uncertainties are common between hadronic and semileptonic samples

  35. ms and Vtd • inputs: • m(B0)/m(Bs) = 0.9830 (PDG 2006) •  = 1.21 +0.047 (M. Okamoto, hep-lat/0510113) •  md = 0.507 ± 0.005 (PDG 2006) -0.035 |Vtd| / |Vts| = 0.2060 0.0007(exp) +0.0081 (theo) -0.0060 • compare to Belle bs (hep-ex/050679): |Vtd| / |Vts| = 0.199 +0.026 (stat) +0.018 (syst) -0.025 -0.015

  36. ms & CKM (CKMFitter)

  37. ms from Tevatron & BSM Limits Hep-ph/0509117 Agashe/Papucci/Perez/Pirjol Probability

  38. Conclusions PLB 186 (1987) 247, PLB 192 (1987) 245 PRL 62 (1989) 2233 Exciting times: • 1987 B0 mixing (UA1, Argus) • 1989 CLEO confirms B0 mixing • 1990s LEP B0 Mixing • 1993 • First time dependent md meas. (Aleph) • First lower limit on ms • 1999 CDF Run I lower limit (ms>5.8 ps-1) • 2005 • D0: ms>5.0 ps-1 • CDF: ms>7.9 ps-1 • 2006 • D0: ms [17,21] ps-1 @ 90% CL • CDF: ms=17.31+0.330.07 ps-1 • CDF: 5 observation, ms=17.77+0.100.07 ps-1 PLB 313 (1993) 498 PLB 322 (1994) 441 PRL 82 (1999) 3576 PRL 97 (2006) 021802 PRL 97 (2006) 0062003 -0.18

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