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CDF での Top Flavor の物理

CDF での Top Flavor の物理. 戸村 友宣 ( 筑波大学 ). Introduction. Top quark is the heaviest known fundamental particle. Is this large mass related to electroweak symmetry breaking? Relationship between m t , m W , and m H Top quark has very short lifetime Decay before hadronization

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CDF での Top Flavor の物理

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  1. CDFでのTop Flavorの物理 戸村 友宣 (筑波大学) 特定領域「フレーバーの物理の新展開」研究会 2008

  2. Introduction • Top quark is the heaviest known fundamental particle. • Is this large mass related to electroweak symmetry breaking? • Relationship between mt, mW, and mH • Top quark has very short lifetime • Decay before hadronization • Momentum and spin are transferred to decay products 特定領域「フレーバーの物理の新展開」研究会 2008

  3. Tevatron Run II • Proton-Antiproton Collider with CM energy of 1.96 TeV • Peak luminosity: 2.91032 cm-2s-1 • Delivered luminosity: > 3.5 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  4. CDF II Detector • General Purpose solenoidal detector • Efficiency: ~85% • Recorded >2.9 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  5. Top Pair Production • Top pair production through strong interaction ~85% ~15% 特定領域「フレーバーの物理の新展開」研究会 2008

  6. Top Pair Production Cross Section • Measured using many different techniques • Good agreement • Between measurements • Between data and theory dilepton l+jets all hadronic 特定領域「フレーバーの物理の新展開」研究会 2008

  7. Forward Backward Asymmetry • Forward-backward asymmetry arises from interference between LO and higher order diagrams 1.9 fb-1 • Lab (ppbar-rest) frame • ttbar (parton) rest frame (NLO Theory: Afb = 0.04±0.01) (NLO Theory: Afb = 0.04—0.07) 特定領域「フレーバーの物理の新展開」研究会 2008

  8. ttbar Production Mechanism • Measure fraction of gg vs. qq top production • SM prediction: ~85% qq, ~15% gg • Large theoretical uncertainty (~10%) • Two complementary approaches • NN with production and decay kinematics • Track multiplicity distributions • Combine two methods: ~6% improvement 1 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  9. ttbar Differential Cross Section • Measure d/dMtt and test consistency with SM • Spectrum is sensitive to many BSM resonances (Z′, coloron, etc.) • ttbar invariant mass is reconstructed for l+jets events • Subtract background and correct the distribution using a regularized unfolding technique • Data is consistent with SM • p-value = 0.45 1.9 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  10. qgs Qgs gs gs + g G q Q q Q Search for Massive Gluon • Search for heavy gluon-like particle, Gttbar(color-octet model, etc.) • 3 parameters • Mass(M), Width(), coupling() • Event-by-event ttbar invariant mass reconstruction for l+jets with a Matrix Element technique (DLM) • Data is consistent with SM (<1.7) within 400M800, 0.05/M0.5 • Set upper/lower limit for massive gluon coupling • Coloron model (=1, /M0.2) is excluded in the range, /M0.5 and M800 1.9 fb-1 SM  interfere  MG 特定領域「フレーバーの物理の新展開」研究会 2008

  11. Top Quark Mass • Many techniques were deployed for top mass measurements • Tevatron combination calculated 1 year ago 特定領域「フレーバーの物理の新展開」研究会 2008

  12. New Mass Measurements (1) • Template Method • Reconstruct top mass event-by-event and generate templates • Use dijet mass from W daughters for in-situ jet energy calibration 1.9 fb-1 • all-hadronic • Combined for dilepton and l+jets Apply NN event-selection to improve S/B 特定領域「フレーバーの物理の新展開」研究会 2008

  13. New Mass Measurement (2) • Matrix Element Method • Calculate event-probability from the kinematics of decay products using Matrix Element 1.9 fb-1 • dilepton • lepton+jets Apply NN event-selection to optimize S/B Cut lower tail of log-likelihood distribution 特定領域「フレーバーの物理の新展開」研究会 2008

  14. Top Quark Width • Measure width of top quark directly using template method • Use 1-tag and 2-tag l+jets data • Calculate upper limit using Feldman-Cousin prescription 1 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  15. Top Quark Charge • Measure the charge of “top” quark • SM top charge: +2/3 • XM top charge: −4/3 • D. Chang et. al. Phys. Rev. D59 (1999) 091503 • tW+b or tW−b • Charge of W (lepton charge) • Pairing between W and b • Flavor of b-jet • Use dilepton and l+jets data 1.5 fb-1 Measured f+=0.87 p-value=0.31 Exclude XM @87% CL 特定領域「フレーバーの物理の新展開」研究会 2008

  16. l+ q* b W+ nl W Helicity • V−A character of the top decay makes the helicity of W onlyF0=0.70, F−=0.30, F+=0.00(longitudinal, left-handed, right-handed) • cosq* Method • Matrix Element Technique If F+ fixed to 0: If F0 fixed to 0.7: 1.9 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  17. Search for FCNC Decay tZq • Top FCNC is extremely rare • In SM, BR(tZq)=O(10-14) • BSM, up to O(10-4) • Calculate 2 for FCNC top decay 1.9 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  18. W,H+ Single Top Production • Single top production through weak interaction • single top |Vtb|2 • Sensitive to: • 4-th generation • H+ • W′ • FCNC • Etc. • Background for WHlbb ? t-channel NLO = 1.98±0.21 pb Z c t s-channel NLO = 0.88±0.07 pb 特定領域「フレーバーの物理の新展開」研究会 2008

  19. Multivariate Likelihood Function 7 input variables (kinematics, kinematic solver and ANN b-tag outputs) Matrix Element Technique Ratio of event probability densities for signal and bkg Evidence for Single Top 1.5 fb-1 2.7 significance (2.9 expected) 3.1 significance (3.0 expected) 特定領域「フレーバーの物理の新展開」研究会 2008

  20. Direct Measurement of |Vtb| 1.5 fb-1 • CKM Matrix Element |Vtb| • Describes strength of Wtb vertex • single top |Vtb|2 • Assumes |Vtb|2+|Vtb|2<<|Vtb|2 • Measured with Matrix Element Technique • Theory uncertainty arises from the cross-section dependence on • Top quark mass • Factorization and renormalization scales • PDFs and s • (Z. Sullivan, Phys. Rev. D70 (2004) 114012) 特定領域「フレーバーの物理の新展開」研究会 2008

  21. Search for W′ Resonance • Search for resonance in tb channel using MWJJ • Many theories include new gauge boson • Extensions to the SM (GUT) • Extra Dimensions (Kaluza-Klein) • Use massive W boson with SM-like couplings • Z. Sullivan, arXiv:hep-ph/0207290 • Large branching fraction to tb 1.9 fb-1 @95%CL 特定領域「フレーバーの物理の新展開」研究会 2008

  22. Summary • CDF entered era of precision top measurements. • Mass and cross section • No longer stat. dominant. Need revisit syst. Uncertainty. • New measurements for the properties of top quark. • Some of them are measurable only at Tevatron. • Many improvements in analysis techniques. • Top is a good probe for new physics. • Good agreement with Standard Model, so far. • New results will be coming! • CDF/Tevatron combination for top mass,including recent 2 /fb results. • Single top: 4~5 sigma w/ >2 /fb 特定領域「フレーバーの物理の新展開」研究会 2008

  23. Backups 特定領域「フレーバーの物理の新展開」研究会 2008

  24. Dilepton Lepton+Jets Background Table @1.9 fb-1 特定領域「フレーバーの物理の新展開」研究会 2008

  25. Example of Syst. Err. for Mtop • Combined Template Method for dilepton and lepton+jets 特定領域「フレーバーの物理の新展開」研究会 2008

  26. b-jet Flavor Tagging • Jet Charge • Performance PTrel Soft m Jet axis b tagged (x=0.5) Away Jet b tagged Dil: e=87%, P=61%, eD2=0.10 L+J: e=98%, P=61%, eD2=0.13 特定領域「フレーバーの物理の新展開」研究会 2008

  27. W Helicity 特定領域「フレーバーの物理の新展開」研究会 2008

  28. Forward-Backward Asymmetry • Interference between LO and NLO diagrams 特定領域「フレーバーの物理の新展開」研究会 2008

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