Top quark properties and physics at lhc
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Top Quark Properties and Physics at LHC. Weak Interactions and Neutrinos (WIN'05) 6-11 June 2005 , Delphi, Greece. V Šimák CTU-FJFI, ASCR-FZU Prague (on behalf of ATLAS collaboration). Electroweak gauge bosons Top quark mass Physics with top quark. Atlas.

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Top Quark Properties and Physics at LHC

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Top quark properties and physics at lhc

Top Quark Properties and Physics at LHC

Weak Interactions and Neutrinos

(WIN'05)

6-11 June 2005,

Delphi, Greece

V Šimák

CTU-FJFI, ASCR-FZU Prague

(on behalf of ATLAS collaboration)

  • Electroweak gauge bosons

  • Top quark mass

  • Physics with top quark


Top quark properties and physics at lhc

Atlas

p-p collisions at √s = 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)

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Magnetic Field

2T solenoid plus air core toroid

Inner Detector

s/pT ~ 0.05% pT(GeV) (+) 0.1%

Tracking in range |h| < 2.5

EM Calorimetry

s/E ~ 10% / √E(GeV) (+) 1%

Fine granularity up to |h| < 2.5

Hadronic Calorimetry

s/E ~ 50% / √E(GeV) (+) 3%

Muon Spectrometer

s/pT ~ 2-7 %

Covers |h| < 2.7

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

W - mass

pp → W+X with W→ ln and l = e, m

  • isolated charged lepton with

  • pT > 25 GeV inside |h| < 2.4

  • missing transverse energy

  • ETmiss > 25 GeV

  • rejection of large pT W’s

    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 => precision on mW is systematics limited…

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Combining channels this reduces to 20MeV

(15MeV combined with CMS)

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

stt(th)=825±150 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, lepton+jets, all jets

qq->tt: 13%

gg->tt: 87%

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Cross sections

1.96 TeV

14 TeV

hep-ph/9806332]

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

gg->tt: 87%

Top decays classification:

di-lepton, lepton+jets, all jets

charge,

mass,

spin,

decay,

dynamics of production

Top quark properteis:

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Qt = +2/3

Qt = -4/3

Atlas

  • t coupling to photon

    • can be probed via t tbar  events

    • can also be used to confirm Q=2/3

  • 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]

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Atlas

Semileptonic channel:

  • 0.2% efficiency

  • Total background 5%

  • Mass extracted from jjb system

  • (-> large error from jet scale uncertainty)

  • Stat. error: ±0.25 GeV

  • Error from Pt(t) spectrum: ±0.4 GeV

  • Jet scale: DEj/Ej~1% -> DM~±0.3 GeV

  • Require:

  • Isolated lepton with pT(l)> 20 GeV

  • Exactly 4 jets (R=0.4), each with pT(j) > 40 GeV

  • No b-tagging used

  • Plot m(jjj) of combo with max pT

mt  1-2 GeV

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Dilepton channel

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

  • Unfeasible at low luminosity

  • Independent from jet scale

  • Promising at high luminosity

  • Among main systematics:

  • b fragmentation

mt  1 GeV

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

f0

t

t

t

b

W Polarization in Top Decays

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

V-A weak interaction determines the top quark decay in SM

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Polarization of Top

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

« Spin studies in tt pairs »

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

κ= 0

κ= -0.34 SM LO

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Atlas

κ= 0

κ= -0.34 SM LO

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Neutral Higgs boson φ with

unspecified CP parity

W. Bernreuther, M. Flesch, P. Haberl – Phys. Rev. D58 (1998)

a, ã – reduced scalar and pseudoscalar couplings

(SM Higgs boson: a=1, ã=0)

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

top quark Yukawa coupling can be measured from t tbar H production

for m(H) < 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) > 20 GeV

    • Njet  6 with pT(jet) > 15 GeV

    • Nbjet = 4

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Single Top Production

3,000,000 events/yr

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Atlas

  • there are large bkgnds (eg. tt [830 pb], Wbb [>300 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

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

  • 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 V+A, anomalous couplings

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

Phys.Rev. D70, p15015, 2004e-Print Archive: hep-ph/0409273

Helicity angle correlations in model

with graviton (MD = 0.5 TeV, λ = 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


Top quark properties and physics at lhc

W helicity

Top Mass

l+

Top Width

Anomalous

Couplings

Production

cross-section

Top Spin

W+

CP violation

Top Charge

Resonance

production

n

Y

t

b

Production

kinematics

Top Spin

Polarization

_

t

Rare/non SM Decays

X

Branching Ratios

|Vtb|

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

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

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

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)

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


Top quark properties and physics at lhc

WIN05 Delphi 6-11 June 2005 V. Šimák, CTU Prague


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