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Exploring Top Physics and Higgs Searches: DOE Site Visit Insights from Harvard's Aug. 2006 Presentation

This summary outlines key findings from the DOE Site Visit on August 21, 2006, led by João Guimarães da Costa from Harvard University. It covers advancements in top quark searches, the significance of B-tagging efficiency, and ongoing analysis techniques for Higgs production and rare decays. The challenges posed by W+heavy flavor backgrounds are discussed, alongside proposed improvements in systematic uncertainties and data estimations. The presentation emphasizes the search for new physics through top samples and elaborates on collaborative efforts to analyze kinematics and heavy particles.

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Exploring Top Physics and Higgs Searches: DOE Site Visit Insights from Harvard's Aug. 2006 Presentation

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Presentation Transcript

  1. The Next Step DOE Site Visit Aug 21, 2006 João Guimarães da Costa Harvard University The Next Steps ---- DOE Visit 2006

  2. tt+X Search tt+ET Search Top Cross Section Higgs Search Top Rare Decays (FCNC) (see Ingyin’s talk) Top sample kinematics Little Higgs SUSY: Stop

  3. Improvements in Top Cross Section Relative Uncertainty (%) Luminosity (pb-1) • Reduce major systematic uncertainties • B-tagging efficiency (see Daniel’s talk) • Background: W + heavy flavor • Smaller improvements • Better treatment of mistags • Improvements in Non-W background estimation • Complementary B-tagging technique • Soft Electron Tagger (see John Paul’s talk) Systematic limited Projections

  4. B-tagging Efficiency Systematic (see Daniel’s talk) Similar technique will be used at LHC

  5. Background: W + Heavy Flavor ~35% of top background is W+HF W+bbX W+cX W+ccX Current uncertainty: ~30%

  6. Cross Section using Jet Spectrum Fit Checking the W + heavy flavor prediction in W+jets data Fit Results W + HF underestimated by 26%

  7. Background: W + Heavy Flavor W+bbX W+cX W+ccX • Difficult to model • W+heavy flavor cross section has large uncertainties • Depend on PDF, hadronization and fragmentations scales and mass of b,c quarks • Heavy flavor fractions cancel most uncertainties Get these from Monte Carlo

  8. Background: W + Heavy Flavor • Calibrate using generic jet data • In Run I, the MC underestimated the gluon splitting component • Measure gluon splitting in data Distance between dijets in ,  space Double Tagged Direct production Gluon splitting Flavor excitation

  9. W+HF Fractions Measurement Run II: • Run 2: Measurement was done with low Et sample ~ 27% uncertainty Gluon splitting Work in Progress Distance between dijets in ,  space

  10. Top Cross Section with Soft Electron Tags Lifetime b-tagger Most decays happen quickly Probability to remain(t) (see John Paul’s talk) e,μ ~ 60% of top events gbct 940 m 470 • Advantages: • Recover b-tagging efficiency • SecVtx: 48% efficient per b-jet • SLT: Extra ~10% per b-jet in top events • Sensitive to different new physics • Discrepancy on cross section would be indication of new physics • Interesting events seen in run I (superjets) • Excess of SecVtx + SLT tagged events ~ 1 mm b P.V. secondary vertex Soft Lepton Tagger primary vertex impact parameter

  11. tt + X: Is there new physics in the top sample? “The most likely place to find new physics is in the tt + X sample……” Nima Arkani-Hamed Top Sample: 408 single tag events 119 double tag events Heavy objects decaying into tt+X would distort the kinematics distributions Event Kinematics Analysis: Double Tag Sample

  12. New Physics in the Large Top Sample? Event Kinematics Analysis KS Probabilities

  13. Heavy Tops: Generic Analysis Heavy pair-produced particles decaying into tt + ET • Heavy Top “T”: • Little Higgs theories • Fermionic particle • Cross Section: ~1pb at 300 GeV • Stop: • Small cross section • Collaborating: • With our colleagues in the theory group • With Kevin and Verena on ATLAS • Massive particle: T • More central events SM top • Larger acceptance Same final state as tt but different kinematics

  14. Heavy Top Search: Kinematics • No killer variable • Large correlations Advance analysis technique Missing Energy (GeV) HT (GeV) W Transverse Mass (GeV)

  15. Heavy Top Search: Neural Net Technique Takes care of correlations automatically • Work in progress: • Cover full range of possible masses • Investigate MC sample with TT production • Look at data Expected Limit

  16. Search for the SM Higgs Measurement done in the W+Jets sample

  17. W+jets Background (W+HF) • W + heavy flavor is major background for Higgs W+HF

  18. Search for the SM Higgs

  19. Conclusions • Top Physics • Transition from statistics limited analysis to systematic limited analysis • Explore new large top sample searching for new physics • Soft electron tagger • Kinematics studies • Search for heavy particles decaying into tt • Higgs Physics • Too early to see SM Higgs at CDF • However, we can establish the ground work for a possible discovery Lots of exciting things to do at CDF

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