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Evidence for B s Mixing and measurement of m s at CDF

Evidence for B s Mixing and measurement of m s at CDF. S. Giagu and CDF Collaboration University of Rome “La Sapienza” INFN Sezione di Roma 1. Outline. Introduction Search for B s -B s oscillations in CDF Impact on the overall UT fit Work in progress and Outlook. CDF Collaboration,

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Evidence for B s Mixing and measurement of m s at CDF

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  1. Evidence for Bs Mixing and measurement of msat CDF S. Giagu and CDF Collaboration University of Rome “La Sapienza” INFN Sezione di Roma 1

  2. Outline • Introduction • Search for Bs-Bs oscillations in CDF • Impact on the overall UT fit • Work in progress and Outlook CDF Collaboration, “Measurement of the Bs-Bs Oscillation Frequency” hep-ex/0606027 – accepted by Physical Review Letters S.Giagu - ICHEP 2006, Moscow

  3. s, s, s, s, B Meson Flavor Oscillations Neutral B mesons can spontaneously transform in the corresponding antiparticle In the SM generated via F=2 2nd order weak interactions, dominated by the exchange of a top quark Mixing involves CKM elements, measuring Δmq constraints the unitarity triangle New exotic particles may run in the loop  mixing sensitive to NP Form factors and B-parameters from Lattice calculations are known at ~15% level S.Giagu - ICHEP 2006, Moscow

  4. ms and the side of UT md  f2BBB [(1-r)2+h2] circle centered in (r,h)=(1,0) f2BBB known at 15% from LQCD • many theoretical uncertainties cancel in the ratio • |Vts|/|Vtd| can be determined at ~4% (hep-lat/0510113) Experimental challenge: |Vts| >> |Vtd|  ms >> md  needs to resolve > 2.3 THz oscillations Status of Dms measurements: LEP/SLD/CDF-I: ms > 14.4 ps-1 @ 95% CL HFAG Average for PDG 2006 D0 Run-II: ms  [17,21] ps-1 @ 90% CL Phys. Rev. Lett. 97, 021802 (2006)

  5. vertexing (same) side e,,Jet 4 2 4 1 “opposite” side 3 Road map to ms measurement 5 • Collect as many Bs as possible • Tevatron, Trigger (SVT) • Extract Signal • Bs flavor at decay inferred from decay products • Measure proper decay time of the Bs meson • L00, per event primary vertex, candidate specific decay time resolution • Determine Bs flavor at production (flavor tagging) • PID (TOF, dE/dx) • Flavor tag quantified by Dilution: D=1-2w, w = mistag probability • Measure asymmetry between unmixed and mixed events • In practice: perform likelihood fit to expected unmixed and mixed distributions

  6. Event Selection: Fully Hadronic Bs used in this analysis • Bs momentum completely reconstructed • Excellent decay time resolution, good S/N • Small BR  low statistic • Good sensitivity at high values of ms Cleanest decay mode: BsDs[] [KK] 

  7. Event Selection: Semileptonic Bs Ds Mass • Missing momentum () • Poorer decay time resolution • Large BR  high statistic • Good sensitivity at low values of ms l+Ds Mass 48000 l+Ds candidates, 75% are from Bs decay • Minv(l+Ds) helps reject BG • BG Sources: • Ds + fake lepton from PV • Bs,dDsDX (DslnX) • cc

  8. p p  D decay B decay Lxy RUN 304720 EVENT 109026 Proper decay time reconstruction PV Detector length scale and proper treatment of detector/selection biases controlled by performing lifetime measurements

  9. Decay time resolution • Finite resolution dilutes the amplitude of mixing asymmetry: • Sensitivity maximized by making full use of all available information: • layer-00, candidate specific primary vertex and decay time resolution • Resolution measured in data in large samples of prompt D meson decays • D+ combined with prompt tracks to mimic B0-like topologies oscillation period @ ms=18 ps-1 M(lDs) > 3.3 GeV/c first bin of ct 4 sampling per cycle Hadronic decays gives CDF sensitivity at much larger values of ms than previous experiments

  10. Flavor Tagging Performances Two types of flavor tags used in CDF • OST: produce bb pairs: find 2nd b, determine flavor, infer flavor of 1st b • calibrated on large samples of B0 ad B+ decays • SST: use charge correlation between the b flavor and the leading product of b hadronization • performances (D) evaluated in MC, after extensive comparison data VS MC Same-side kaon tag increases effective statistics  ~4

  11. k k k k = Sst D isolation K-factor ct [cm] pT [GeV/c] Courtesy of J.Kroll Likelihood Data fitted with an unbinned likelihood function to the expected unmixed and mixed distributions Procedure checked on B0 by fitting for md for each event: k=sig,bg k sig pdg (*) H-G.Moser, A.Roussarie, NIM A384 (1997) Amplitude method(*): scan ms space: fix msfit for A: A consistent with 1  mixing detected at the given ms

  12. A/A (17.3 ps-1) = 3.7 +0.047 -0.035 Inputs from PDG 06 andξ=1.210 (hep-lat/0510113) Results Likelihood ratio: A=1 VS A=0 hypothesis hep-ex/0606027 – accepted by PRL P-value = 0.2% (>3) small systematic uncertainty dominated by knowledge of the absolute scale of the decay-time measurement

  13. Impact on the overall UT Fit SM fit SM+NP fit CDF measurement CBs = 0.97 ± 0.27 CKM fit (no Δms) (21.5 ± 2.6) ps-1 no angles angles only UTfit Coll.: hep-ph/0605213 and Vincenzo’s talk Similar results from CKMfitter group: http://ckmfitter.in2p3.fr and Stephane T’Jampens talk

  14. CDF Run II Preliminary L=1 fb-1 Work in progress BsDs+-+ (Ds +--) • Collecting new integrated luminosity • Squeezing maximum information from the data • we already have: • Systematic use of Neural Networks in signal extraction: • use decays modes previously discarded cause high BG • more signal in already used modes • Use partially reconstructed BsDs*/K and Ds: • large BR • good momentum resolution • Improve Flavor taggers: • OST: +15% D2 • NN to combine OS taggers • OSKT • SSKT: ~+10% D2 • better use of combined PID and kinematics NBs = 220 BsDs+ (Ds-)

  15. Summary and Outlook • CDF finds evidence for flavor oscillations in the Bs sector • Probability of a random fluctuation 0.2% • Measurement of the mixing frequency with <2% precision • Most precise measurement of |Vtd/Vts| An important and precise experimental input for the overall test of the SM and the end of a very long effort to measure ms … but not the end of the CDF B-physics programme

  16. Random Slides S.Giagu - ICHEP 2006, Moscow

  17. Decay Vertex PV d0 = impact parameter Data Sample • Bs candidates collected by SVT trigger • TTT: two displaced tracks • L+SVT: lepton + displaced track(s) used in this analysis Typical inst. Luminosity 1032 cm-2 s-1 ~1.4 fb-1 collected by CDF ~1 fb-1 (good runs) used in this analysis S.Giagu - ICHEP 2006, Moscow

  18. Other results on ms LEP, SLD, CDF-I Recent from D0 collaboration 1st direct single experiment upper bound ms  [17,21] ps-1 @ 90% CL Null hypothesis probability: 5% ms > 14.4 ps-1@ 95% CL D0 Coll.: Phys. Rev. Lett. 97, 021802 (2006) HFAG Average for PDG 2006 S.Giagu - ICHEP 2006, Moscow

  19. Decay Vertex PV d0 = impact parameter Example of Specific Trigger for B Physics Level 1 - 2 XFT tracks with pT > 1.5 GeV - opposite charge -  < 135o - |pT1| + |pT2| > 5.5 GeV Level 2 - confirm L1 requirements - both XFT tracks - SVT 2<15 - 120 m< |d0| <1mm - 2o <  < 90o - Decay length Lxy > 200m Level 3 - confirm L2 with COT & SVX “offline” quality track reco. S.Giagu - ICHEP 2006, Moscow

  20. Correction Factor (MC) Decay Time Reconstructed quantity Semileptonics: Correction for Missing Momentum oscillation period @ ms=18 ps-1 S.Giagu - ICHEP 2006, Moscow

  21. PID Separartion Power Combined PID: TOF + dE/dx  K S.Giagu - ICHEP 2006, Moscow

  22. Systematic Uncertainties Hadronic Semileptonic • related to absolute value of amplitude, relevant only when setting limits • cancel in A/A, folded in in confidence calculation for observation • systematic uncertainties are very small compared to statistical S.Giagu - ICHEP 2006, Moscow

  23. systematic uncertainties from fit model evaluated on toy Monte Carlo have negligible impact only relevant systematic: knowledge of lifetime scale Incertezze sistematiche su ms All relevant systematic uncertainties are common between hadronic and semileptonic samples S.Giagu - ICHEP 2006, Moscow

  24. Amplitude Scan: Hadronic decays data period 1 data period 2 data periodo 3 S.Giagu - ICHEP 2006, Moscow

  25. Amplitude Scan: Semileptonic decays data period 1 data period 2 data period 3 S.Giagu - ICHEP 2006, Moscow

  26. ptrel  Parameterization of the tagging decision • Exploit peculiarity of each tagger to minimize mistag probability • example: soft muon tag  from b decay jet axis  from c decay S.Giagu - ICHEP 2006, Moscow

  27. SSKT Calibration • Dilution measured in high statistic samples of light B meson decays and compared with the results of simulation Dominant source of systematic uncertainty: Data/MC agreement ~O(14%) S.Giagu - ICHEP 2006, Moscow

  28. Negative log likelihood ratio S.Giagu - ICHEP 2006, Moscow

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