1 / 28

Bs Mixing & Measurement of Δms at CDF: Search for Bs-Bs Oscillations & Impact on UT Fit

This study explores Bs meson flavor oscillations and the measurement of oscillation frequency Δms at CDF Collaboration. It investigates Bs-Bs oscillations, their impact on the UT fit, and work in progress with a roadmap for measurement. The research delves into CKM elements, form factors, and experimental challenges in resolving oscillations at high frequency. Event selection techniques, flavor tagging, and decay time reconstruction methods are detailed to maximize sensitivity and control biases. Results show mixing asymmetry detected at a given Δms, impacting overall UT fit with small systematic uncertainty. Collaborative efforts and ongoing work towards Bs meson decay measurements are highlighted.

colt-hewitt
Download Presentation

Bs Mixing & Measurement of Δms at CDF: Search for Bs-Bs Oscillations & Impact on UT Fit

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related