Single top production at LHC

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Single top production at LHC

• Zdenko van Kesteren

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LHC top factory

• Top quarks will be produced at LHC
• Mostly in pairs (via the strong process)
• g g ? t t and q q ? t t
• A significant number will be produced singly (via
  the electroweak process)

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Why interesting?

• Independent mass measurement
• Determination Vtb
• Single top events are background to other signals
  (i.e. some Higgs signals)
• Opportunity to measure t spin polarisation
• (test for V-A structure CC weak interaction)
• May probe FCNC
• New physics

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NIKHEF top

• ONETOP and TOPREX create single top events ?
  interfaces to PYTHIA (L.O.)
• M. Barisonzi, B. van Eijk
• Theory-department NIKHEF busy implementing single
  top in MC_at_NLO (summer 2005)
• E. Laenen, S. Frixione, P. Motylinski
• NIKHEF working on tt in commissioning phase
• S. Bentvelsen
• Expertise in D0
• P.de Jong, M. Vreeswijk, F. Blekman, G. Massaro

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Single top production diagrams

• W-gluon fusion (t-channel)
• W t production
• W (s-channel)

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Single top background

• Main background ?xBR(W?l?), le,µ
• tt s833 pb 246 pb
• Wbb s300 pb 66.7 pb
• Wjj s18103 pb 4103 pb
• W gluon fusion tt, Wbb, Wjj
• W t tt, Wbb
• W Wg fusion, Wt, tt, Wbb, Wjj

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Event selection

• Preselection
• 1 isolated lepton PT gt 20 GeV
• gt2 jets PT gt 30 GeV
• gt1 b-jet PT gt 50 GeV

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Example extra cut

• Invariant mass di-jet with mjj closest to mW
• Leaves only
• tt as back-
• ground for
• W t production

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Detector performance

• Fake lepton rate (p/e suppression 10-5)
• B-tagging efficiency
• Reconstruction and vetoing of low energy jets
• Identification of forward jets (? gt 2.5)

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Signal unambiguous (30 fb-1)
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Observing single top

• Assuming an integrated luminosity of
• 30 fb-1 ? possible to measure crossections of 3
  diagrams separately
• t-channel observable after 1 year
• LHC low luminosity (10 fb-1)

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Conclusions

• NIKHEF involved in single top physics
• Detector performance crucial
• Single top observable after one year LHC
• at low luminosity