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Perspectives on single-top-quark production

Perspectives on single-top-quark production. Zack Sullivan Aspen Winter Conference 2007. What is single-top-quark production?. Tevatron. LHC (s-chan?). “ t -channel”. “ s -channel”. “Wt associated ”. For details see ZS, PRD70, 114012 (04).

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Perspectives on single-top-quark production

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  1. Perspectives on single-top-quark production Zack Sullivan Aspen Winter Conference 2007

  2. What is single-top-quark production? Tevatron LHC(s-chan?) “t-channel” “s-channel” “Wt associated” For details see ZS, PRD70, 114012 (04) 1 Harris, Laenen, Phaf, ZS, Weinzierl, PRD 66 (02) 054024 2 Tait, PRD 61 (00) 034001; Belyaev, Boos, PRD 63 (01) 034012 Zack Sullivan, Aspen 2007 January 10

  3. - - - æ 0 . 9730 0 . 9796 0 . 2174 0 . 2241 0 . 0030 0 . 0044 ö ç ÷ - - - 0 . 213 0 . 226 0 . 968 0 . 975 0 . 039 0 . 044 ç ÷ ç ÷ - - - 0 0 . 08 0 0 . 11 0.07 0 . 9993 è ø Learning about the Wtq vertex • Measuring B(tWb) only tells us Vtb » Vtd, Vts CDF, PRL 86 (01) 3233 • In the SM Vtb = 0.9991 ± 0.0001 (PDG 2004) Relax Unitarity of CKM matrix • Single-top cross section proportional to |Vtb|2 • Measure B(tWb) in tt, extract Vtb~ t/2 in each channel See polarization of top at production (~5 fb-1) Vtb Zack Sullivan, Aspen 2007 January 10 Stelzer, ZS, Willenbrock, PRD 58 (98) 094021

  4. Current evidence CDF results from: Note 8588 Note 8585 D0 results from: hep-ex/0612052 Twice as much data on tape. We will know better in summer. |Vtb|=1.30.2 New NN |Vtb|~0.3 Zack Sullivan, Aspen 2007 January 10

  5. FCNC Scalars (p+T) d,s Vector currents Vtd, Vts New phenomena affects- and t-channel separately Resonances New q-t-X verticies |Vtb|=1.30.2 Z KK-modes etc. New NN BR(tZc)<0.33 CDF, PRL80,2525(98) will soon change 4th generation? t-T mixing? Suppress t not s? |Vtb|~0.3 Zack Sullivan, Aspen 2007 January 10

  6. ZS, PRD 66, 075011 (2002) ZS, hep-ph/0306266 Model independent searches forWat Tevatron and LHC • LHC can test SM-like W bosons up to 5.5 TeV • Couplings of 10-1gSM up to 3 TeV Zack Sullivan, Aspen 2007 January 10

  7. The lasting importance ofsingle-top-quark production Theory Experiment A decade of intense collaboration and inspiration has led to a new or modified understanding of every aspect of the observable cross section. Zack Sullivan, Aspen 2007 January 10

  8. How to see the initial state “W-gluon fusion” (circa 1996) A “mathematical trick” let us resum large logs into a “b” PDF. Heavy-quark (b, c) PDFs are more than a trick: b & c are full-fledged components of the proton structure. • HERA is beginning to see evidence of intrinsic charm … stay tuned! • Leads to other processes: , Zb/Zc, Zbj/Zcj, Wbj … Gained new nomenclature “t-channel” production 1st testable need for a heavy-quark PDF Zack Sullivan, Aspen 2007 January 10

  9. D0 w&c HUGE Fully exclusive NLO calculations Required new methods to calculate fully exclusive cross sections with massive states • Worked out analytically in Harris, Laenen, Phaf, ZS, Weinzierl, PRD 66, 054024 (02) • Numerically studied using ZTOP ZS, PRD 70, 114012 (04) • Now in MCFM 5.1+ Campbell, K. Ellis New baseline NLO standard Cuts: ETj>15 GeV, |j|<2.5, no cuts on t Zack Sullivan, Aspen 2007 January 10

  10. bad idea • Choice of jet definition can have a larger effect than all theory uncertainties combined. Highest ET jet NLO “d” correct Paradigm of “jet calculations” How do we interpret fully differential NLO? • We are calculating jetsnotpartons • Calculations are not well defined w/o a jet definition • “Bad things” happen if you treat jets as partons dNLO = jets/hadrons  better partons Our language should evolve to recognize this Zack Sullivan, Aspen 2007 January 10 ZTOP

  11. Wbb NLO matching to event generators required for t-channel single-top • HERWIG/PYTHIA Wbb1/3 of LO prediction Both used • IS radiation is too soft and forward, miss hard b • Background to W-Higgs ~3 times larger as well • Feed LO events from MadEvent/CompHEP into HERWIG/PYTHIA and normalize to NLO tj, tb, tjj, tbj samples. • Other prescriptions: MLM, CKKW, etc. bad shapes ZTOP ZS, PRD 70, 114012 (04) Zack Sullivan, Aspen 2007 January 10

  12. ATLAS Stelzer,ZS,Willenbrock, PRD58(98)094021 O’Neil et al., hep-ph/0003033 Lessons of top-quark polarization d • The top quark decays before it hadronizes, and the pure V-A induce a 100% correlation between the d-jet in the event and the e+/m+ • The angular variable is a nice discriminant V-A V-A Zack Sullivan, Aspen 2007 January 10

  13. Angular correlations are important Many analyses do this (e.g. SUSY, HWW, etc.) Getting these right will be a big concern in a few years Zack Sullivan, Aspen 2007 January 10

  14. Use the correlated information ZS, PRD 72, 094034 (05) What is used now Why use these, when the primary information is in the well-measured angular correlations? Zack Sullivan, Aspen 2007 January 10

  15. Single-top-quark production forces us to reconsider our intuitions and develop new technologies that push the frontiers of perturbative QCD: We will have precision measurements of weak interaction structure. Single-top has changed how we think about the cross section. Things not covered 1st PDF uncertainties “Modifed Tolerance Method” (what you use for PDF errors) Kinematic uncertainties Push for “NN” b-tags and clever uses … Conclusions It will be vital to the success of the LHC to develop close interactions between theory and experiment of the type single-top-quark production has enjoyed. Zack Sullivan, Aspen 2007 January 10

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