top quark properties and physics at lhc v Šimák ctu-fjfi, ascr-fzu prague (on behalf of atlas...

Top Quark Properties and Physics at LHC

V ŠimákCTU-FJFI, ASCR-FZU Prague

(on behalf of ATLAS collaboration)

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

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

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

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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)

Atla

s


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Magnetic Field2T solenoid plus air core toroidInner Detector/pT ~ 0.05% pT(GeV) (+) 0.1% Tracking in range || < 2.5EM Calorimetry /E ~ 10% / √E(GeV) (+) 1%Fine granularity up to || < 2.5Hadronic Calorimetry/E ~ 50% / √E(GeV) (+) 3%Muon Spectrometer/pT ~ 2-7 %Covers < 2.7


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pp → W+X with W→ l and l = e,

• isolated charged lepton with • pT > 25 GeV inside || < 2.4• missing transverse energy • ET

miss > 25 GeV• rejection of large pT W’s and plot the transverse mass, mT, given by

)cos1(2 TTWT ppM l

LHC cross section is 30nb: after selection acceptance, reconstruction and identification expect 60M Ws per low luminosity year => precision on mW is systematics limited…

where is the azimuthal angle between the l and the recoil X

sensitivity is reduced by detector smearing

W - mass


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ProcessRate

[Hz]Events/

YearEvents

(total)

Z→e+e- 1.5 ~107 ~107 LEP

W→ev 15 ~108 ~104 LEP

t anti-t 800 ~107 104 Tevatron

At low luminosity

Combining channels this reduces to 20MeV

(15MeV combined with CMS)

Source MW

(Me)

Statistics 2

E-p scale 15

Energy resolution 5

Recoil model 5

Lepton identification 5

pTW 5

Parton distribution functions

10

W width 7

Radiative decays 10

Background 5

Total 25


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tt(th)=825±150 pb

qq->tt: 13% gg->tt: 87%

8 millions tt pairs/year(1 pair/second)

at low luminosity!

NNLO-NNNLL: Kidonakis, Vogt, PRD 68 (03) 114014

Top decays classification: di-lepton, lepton+jets, all jets


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ttbar pairs 6.70+0.71-0.88 pb 825±150 pb

Single top

(s-channel)0.75±0.12 pb 10±1 pb

Single top

(t-channel)1.47±0.22 pb 245±17 pb

Single top

(Wt channel)0.15±0.04 pb 60±10 pb

Wjj ~1200 pb ~7500 pb

bb+other jets ~2.4x105 pb ~5x105 pb

1.96 TeV 14 TeV

hep-ph/9806332]

Cross sections

http://xxx.lanl.gov/abs/hep-ph/9806332


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% e qq

e 1.2 2.5 2.5 14.8

1.2 2.5 14.8

1.2 14.8

qq 44.4

Top decays classification: di-lepton, lepton+jets, all jets

gg->tt: 87%

charge,mass,spin, decay,dynamics of production

Top quark properteis:


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Atla

sQt = +2/3

Qt = -4/3

t coupling to photoncan be probed via t tbar eventscan also be used to confirm Q=2/3

pT() [GeV]

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


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• 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: Ej/Ej~1% -> M~±0.3 GeV

mt 1-2 GeV

Semileptonic channel:

Atla

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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


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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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t t

W Polarization in Top Decays

bt

f0


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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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κ= -0.34 SM LOκ= 0


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Atla

s

κ= -0.34 SM LOκ= 0


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Neutral Higgs boson φ with unspecified CP parity

a, ã – reduced scalar and pseudoscalar couplings(SM Higgs boson: a=1, ã=0)

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


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

for m(H) < 130 GeV, Hbb 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

12 vev

my t

t


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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 [>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

Atla

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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 helicitiesEg. sensitivity to V+A, anomalous couplings

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

1.2

1.4

cos

1/

d

/

d (c

os

)

cos of top quark in CMS of t-tbar (s = 1 TeV2, MD = 1 TeV, = 1)

q+qbar->t+tbar,RR+LL,Standard Modelq+qbar->t+tbar,RL+LR,Standard Modelq+qbar->t+tbar,RR+LL,Graviton Effectq+qbar->t+tbar,RL+LR,Graviton Effect

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

cos

1/

d

/

d (c

os

)

cos of top quark in CMS of t-tbar (s = 1 TeV2, MD = 1 TeV, = 1)

g+g->t+tbar,RR+LL,Standard Modelg+g->t+tbar,RL+LR,Standard Modelg+g->t+tbar,RR+LL,Graviton Effectg+g->t+tbar,RL+LR,Graviton Effect

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

MD [TeV]

A

Dependence of t-tbar spin correlations on MD (p-p at 14 TeV)

= 1=-1

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

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


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tY

X

t b

W+

l

Production cross-section

Resonance production

Production kinematics

Top Spin Polarization

Top MassW helicity

|Vtb|

Branching Ratios

Rare/non SM Decays

Anomalous Couplings

CP violation

Top Spin

Top Charge

Top Width

_


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Test some models beyond SM : New type of interactions (resonant Higgs, extra-dimensions, …) Modifications of SM couplings :

anomalous gtt couplings anomalous Wtb coupling

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…

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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top quark properties and physics at lhc v Šimák ctu-fjfi, ascr-fzu prague (on behalf of atlas...

Documents

ctu prague

win05 delphi

p t gev

t solenoid

w mass slide

atlas q t

muon spectrometer p

t tbar events