The top quark physics at the present colliders (Tevatron, LHC)

1
The top quark physics at the present colliders
(Tevatron, LHC)
E. Khramov
2
The top quark mass measurement
Leptonjets channel 30
Multi-jets channel 65
Di-lepton channel 5

• Tevatron
• Main methods TEMPLATE (fitting MC and Real data)
  and MATRIX ELEMENT (sensitivity of matrix element
  for production to Mtop)
• The most precise results obtained with
  leptonjets (
  ) decay channel
• 
  
• 
  Combination of D0 and CDF experiments
• Preliminary combined result of the CDF and D0
  experiments

3

• The top quark mass at ATLAS
• The leptonjets channel also the most favourite,
  the largest branching ratio65
• Expected precision of the top quark mass
  measurement 2 GeV

Leptonic decay
Hadronic decay
Signal background M(top) 175.2 0.6 GeV/c2
Signal only M(top) 175.4 0.6 GeV/c2
Signal only M(top) 176.1 0.6 GeV/c2
Signal background M(top) 176.2 0.6 GeV/c2
There is also possibility to reconstruct the top
quark mass through J/? from a b hadron in final
state. After 100 fb-1 about 1 GeV stat. error
expected.
4
Measurement of the production cross section
The measurements are carried out in all three
decay channels
Combined (topological) cross section for CDF
and D0 experiments
The NLO predicts And it is expected 8 M
pairs at low luminosity (1-21033 cm-2s-1) and
80 M pairs at high luminosity (1034 cm-2s-1)
5
Measurement of branching ratio
Tevatron D0 gives the most precise and Rgt0.64 at
95 C.L. CDF gives
and Rgt0.62 at 95 C.L.
W helicity in top quark decays
W
W
F0 F F -
CDF 0.740.22-0.34 lt0.27_at_95 CL (162pb-1) ---
D0 0.540.31 (Run I) 0.000.130.07 (ljet) ---
ATLAS 0.6770.015 0.0140.009 0.3090.009
t
t
b
b
Right-Handed W (f)
Logitudinal W (f0)
6
Spin correlations in events
Where k A?l1?l2 correlation coefficient.
A(2P-1), P fraction of events where top and
antitop has the same helicity. Only D0 measured
in di-lepton channel (Run I) k gt - 0.25 at 68
CL (SM k0.88)
ATLAS A0.450.06(stat.) (SM A0.42)
CMS shows accuracies for coefficient k after 30
fb-1 s(k)stat.0.035, s(k)syst. 0.028
7
Electroweak single top production

• Three different processes
• W (s-channel)
• W-t production
• (associated production)
• W-gluon fusion
• (t-channel)
• Two of them may be seen at the TeVatron (W-gluon,
  W)... but not yet!
• Upper limits after Run II
• CDF 10.1 (W-gluon) and 13.6 (W) pb _at_ 95 CL
• D0 5 (W-gluon) and 6.4 (W) pb _at_ 95 CL
• ATLAS
• All will be measured
• precisely at the LHC
• Expected errors on Vtb after 30 fb-1

8
Top quark Yukawa coupling

• Backgrounds
• top-antitop pair production
• top-antitopjj production
• top-antitopbb production

Preliminary estimate gives
Important channel for low-mass region (just above
the LEP mass exclusion limit mH 135 GeV)
9
Search for anomalous couplings

• Decay to charged Higgs t?Hb
• D0 set limit for M(H)75 GeV BR(t?Hb)lt0.36 _at_
  95 CL
• ATLAS is sensible BR(t?Hb)gt0.03
• X0?
• Ljets (D0)
• sBR(X0? ) ranges from
• 5 pb (MX400 GeV)
• to 1.5 pb (MX850 GeV),
• GX0.012MX at 95 CL.

Value of sBR required for a 5s discovery
potential for a narrow resonance decaying to
top-antitop, a function of mtt and for integrated
luminosity of either 30 or 300 fb-1
10
The top quark charge

• Latest results at D0 exclude exotic quark with
  charge 4e/3 _at_ 94 CL (leptjets channel).
• Weighting method of b-jet charge measurement was
  used
• k0.6
  (from full simulation)

Couple of week at low luminosity for verifying
the top quark charge at ATLAS