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Highlights from Top Quark Physics

Highlights from Top Quark Physics. Suyong Choi Korea University. Introduction Measurement of Production C ross S ections Properties of the Top Quark Summary and Outlook. Contents. CDF. D Ø. CDF. D Ø. Top Quark. Run 2 results. Top Mass Distributions from 1995 observation paper.

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Highlights from Top Quark Physics

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  1. Highlights from Top Quark Physics Suyong Choi Korea University

  2. Introduction • Measurement of Production Cross Sections • Properties of the Top Quark • Summary and Outlook Contents

  3. CDF DØ CDF DØ Top Quark Run 2 results Top Mass Distributions from 1995 observation paper

  4. Success of the SM

  5. Top quark is special • Most massive • Interaction only within 3rd generation • top-Higgs coupling ~ 1 • Boundary between metastabilityand stability The Top Quark

  6. 5 fb-1 @ 7 TeV 20 fb-1 @ 8 TeV LHC and Experiments

  7. Properties • Mass • Decay width • Spin • Coupling • Cross section measurements • Production and decays Physics with Top Quarks

  8. Higher cross sectionand higher luminosity at LHC • Top quark factory • Rare processes with top quarks • New physics with top quarks • Tevatron and LHC are complementary Cross Sections at Tevatron and LHC

  9. Production

  10. Strongly produced • Contribution of andchanges as Pair production diagams Pair Production

  11. Lepton+jets per lepton flavor Multijet– Highest statistics, but large backgrounds and combinatorics Lepton+jets – Highest statistics and usually yields best measurement Dilepton – Smaller statistics but clean, less combinatoric, solving for 2 neutrino momenta not trivial channels

  12. Experimental error comparable to theory error • QCD explains well the inclusive pair production Pair Production Cross Section

  13. Lepton asymmetry reflects • Asymmetry in production • Polarization of : vs • SM predicts small asymmetry in production and no polarization Lepton Forward-Backward Asymmetry

  14. SM prediction @ NLO: Lepton AFB in

  15. s and t channel • Electroweak production • Cross section of the sameorder as pair production • Sensitive probe of withoutthe assumption of 3 generationof quarks W associated Single Top Production

  16. Single Top Production t-channel

  17. Signal Region Control Region significance Observation of Wt Single Top Production

  18. From single top quark production cross section, we can measure directly without assuming 3 generation of quarks • Current best direct measurement: Measurement of

  19. Properties

  20. Tevatron: GeV– 0.5% accuracy Mass of Top Quark

  21. CPT violated if • and distinguished by electric charged of lepton Mass Difference of and

  22. In SM, top quark width at NLO is • 1.29 GeV/c2 • Lifetime of • Decay width reflected in reconstructed mass distribution • CDF measures Decay Width of Top Quark

  23. B-jet charge calculatedfrom tracks associatedwith b-jet Electric Charge of Top Quark

  24. W from top decays are either left-handed or longitudinal W Polarization from Top

  25. and the spins of top quarks are correlated • Due to , spin state of top at production reflected in decay products • Lepton is the most sensitive probe of top spin polarization • Tevatron and LHC has different contributions of and • ATLAS observed spin correlations at 5.1 s.d. Spin Correlation

  26. Top Coupling with Vector Bosons with and

  27. Major background to • Number of b-tagged jets distribution Production

  28. Approaching 20 years of rich physics program at hadron colliders with top quark events • Top quark production and properties consistent with SM • Many measurements systematics limited. What can you do with millions of top quark events? Summary and Outlook

  29. When was discovered in 1977, it was considered as a bound state of quarks. Hence extra quark was thought to exist. • It took a long time until top quark was discovered in 1995 by CDF and D-Zero experiments using FermilabTevatron accelerators • Being the most massive quark, it may hold the key. • With the luminosity and energy reach of the LHC at CERN, top quarks can be studied with unprecedented precision. • 1.96 TeV→ 8 TeV Introduction

  30. is a function of and Strong Coupling Constant

  31. Searches with Top Quarks

  32. Search for Resonances Decaying into

  33. Anomalous Single Top Search for Search for FCNC

  34. Top-Higgs coupling almost 1 • Consistent with backgrounds • Cross section limits at Search for

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