Top Quark Properties and Physics at LHC

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Top Quark Properties and Physics at LHC

• V imák
• CTU-FJFI, ASCR-FZU Prague
• (on behalf of ATLAS collaboration)

Weak Interactions and Neutrinos (WIN'05) 6-11
June 2005, Delphi, Greece

• Electroweak gauge bosons
• Top quark mass
• Physics with top quark

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p-p collisions at vs 14 TeV
bunch crossing every 25 ns (40MHz)

• low-luminosity L 2 x 1033cm-2s-1
• (L 20 fb-1/year)

• high-luminosity L 1034cm-2s-1
• (L 100 fb-1/year)

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Magnetic Field 2T solenoid plus air core
toroid Inner Detector s/pT 0.05 pT(GeV) ()
0.1 Tracking in range h lt 2.5 EM Calorimetry
s/E 10 / vE(GeV) () 1 Fine granularity up
to h lt 2.5 Hadronic Calorimetry s/E 50 /
vE(GeV) () 3 Muon Spectrometer s/pT 2-7
Covers h lt 2.7
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W - mass

• pp ? WX with W? ln and l e, m
• isolated charged lepton with
• pT gt 25 GeV inside h lt 2.4
• missing transverse energy
• ETmiss gt 25 GeV
• rejection of large pT Ws
• and plot the transverse mass, mT, given by

where Df is the azimuthal angle between the l
and the recoil X sensitivity is reduced by
detector smearing
LHC cross section is 30nb after selection
acceptance, reconstruction and identification
expect 60M Ws per low luminosity year gt
precision on mW is systematics limited
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Combining channels this reduces to 20MeV (15MeV
combined with CMS)
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stt(th)825150 pb
NNLO-NNNLL Kidonakis, Vogt, PRD 68 (03) 114014
8 millions tt pairs/year (1 pair/second) at low
luminosity!
Top decays classification di-lepton,
leptonjets, all jets
qq-gttt 13
gg-gttt 87
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Cross sections
1.96 TeV
14 TeV
hep-ph/9806332
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gg-gttt 87
Top decays classification di-lepton,
leptonjets, all jets
charge, mass, spin, decay, dynamics of production
Top quark properteis
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t coupling to photon can be probed via t tbar ?
events can also be used to confirm Q2/3
SM Br(t ?Wb) ? 99.9 Br(t ? Ws) ? 0.1, Br(t ?
Wd) ? 0.01 Many Beyond SM models involve
anomalous top couplings Several possible rare
decay modes (eg. FCNC) have clear experiment
signatures and, if observed at the LHC, would be
evidence for new physics
pT(?) GeV
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Semileptonic channel

• 0.2 efficiency
• Total background 5
• Mass extracted from jjb system
• (-gt large error from jet scale uncertainty)
• Stat. error 0.25 GeV
• Error from Pt(t) spectrum 0.4 GeV
• Jet scale DEj/Ej1 -gt DM0.3 GeV

• Require
• Isolated lepton with pT(l) gt 20 GeV
• Exactly 4 jets (?R0.4), each with pT(j) gt 40
  GeV
• No b-tagging used
• Plot m(jjj) of combo with max pT

?mt ? ? 1-2 GeV
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Dilepton channel
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• Unfeasible at low luminosity
• Independent from jet scale
• Promising at high luminosity
• Among main systematics
• b fragmentation

?mt ? ? 1 GeV
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W Polarization in Top Decays
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V-A weak interaction determines the top quark
decay in SM
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Polarization of Top
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Spin studies in tt pairs
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? 0
? -0.34 SM LO
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? -0.34 SM LO
? 0
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Neutral Higgs boson f with unspecified CP parity
W. Bernreuther, M. Flesch, P. Haberl Phys. Rev.
D58 (1998)
a, ã reduced scalar and pseudoscalar
couplings (SM Higgs boson a1, ã0)
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• top quark Yukawa coupling can be measured from t
  tbar H production
• for m(H) lt 130 GeV, H?bb is dominant decay
• ttH final state is WWbbbb)
• look for events with one W ? l?,
• the other W ? jj
• pT(lep) gt 20 GeV
• Njet ? 6 with pT(jet) gt 15 GeV
• Nbjet 4

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Single Top Production
3,000,000 events/yr
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• there are large bkgnds (eg. tt 830 pb, Wbb
  gt300 pb) with similar final states
• ability to extract signal depends critically on
  detector performance, including
• look at lepton, jet, bjet multiplicities, as well
  as kinematic distributions, to separate single
  top processes from ttbar, Wjj, Wbb, as well as
  from each other

Jet eta
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Each process is sensitive to possible new physics
in different ways Some examples heavy W ?
enhancement in s-channel W FCNC gu ? t ?
enhancement in Wg fusion It is important to
measure each process separately Also want to
measure W, top helicities Eg. sensitivity to VA,
anomalous couplings
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Phys.Rev. D70, p15015, 2004e-Print Archive
hep-ph/0409273
Helicity angle correlations in model with
graviton (MD 0.5 TeV, ? 1) A 0.97
The influence of extra-dimensions on the spin
correlations of top-antitop quarks could be
visible at the LHC in the case the effective
scale MD is lower than 1.5-2 TeV
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• One of the most urgent problems in HEP to
  identify the mechanism of EWSB and mass
  generation,
• in which the top quark may play a special
  role.
• The LHC has a large potential for discovery of
  New Physics effects e.g. heavy tt resonances,
  FCNC decays, etc

• Test some models beyond SM
• New type of interactions (resonant Higgs,
  extra-dimensions, )
• Modifications of SM couplings
• anomalous gtt couplings
• anomalous Wtb coupling

u d s c b t
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I would like to thank to my collegues from ATLAS
and CMS for most of pictures in this talk
Directly from Apollo If you switch on LHC you
will see what you have never seen

Pythia (Delphi. June 7,
2005)
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