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

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

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


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


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


Combining channels this reduces to 20MeV

(15MeV combined with CMS)

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


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


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


Cross sections

1.96 TeV

14 TeV

hep-ph/9806332]

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


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


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


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


Dilepton channel

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


  • 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


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


f0

t

t

t

b

W Polarization in Top Decays

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


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

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


Polarization of Top

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


« Spin studies in tt pairs »

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


κ= 0

κ= -0.34 SM LO

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


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


Atlas

κ= 0

κ= -0.34 SM LO

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


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 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


Single Top Production

3,000,000 events/yr

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


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


  • 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


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


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


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


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


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


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