C. Ciobanu, page 1

Top Quark Properties

Catalin CiobanuLPNHE, Pierre and Marie Curie University / IN2P3-CNRS

for the CDF and D Collaborations

Hadron Collider Physics Symposium 2008, Galena ILMay 27, 2008

C. Ciobanu, page 2

Top Quarks Strong (pair) production – main

channel (ttX) ~ 7 pb

qqtt :85%

gg tt :15%

Top decay: SM: t Wb almost 100% of the time Classified according to W decays

Lepton+jets, dilepton, all hadronic

e-e (1/ 81)

mu-mu (1/ 81)

tau-tau (1/ 81)

e -mu (2/ 81)

e -tau (2/ 81)

mu-tau (2/ 81)

e+j ets (12/ 81)

mu+j ets (12/ 81)

tau+j ets (12/ 81)

j ets (36/ 81)

5% Tau dilepton e, 5% Dilepton (ee, , e) 30% Lepton+jets (e+j, +j) 45% All hadronic

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Top Properties2. Top Production• Mechanism• Forward-backward asymmetry• Resonances decaying to top• stop production

2. Top Production• Mechanism• Forward-backward asymmetry• Resonances decaying to top• stop production

3. Top Decays• W helicity (V-A)• Branching ratios

•FCNC• Top to Higgs

3. Top Decays• W helicity (V-A)• Branching ratios

•FCNC• Top to Higgs

1. Top Properties• Top Quark mass (prev)

• Charge, width

1. Top Properties• Top Quark mass (prev)

• Charge, width

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1. Top Properties: Charge

Standard Model: Qtop = 2/3 e Exotic model: doublet (–1/3e,–4/3e) ?

D. Chang et al., Phys. Rev. D59 (1999) 091503 D0 Phys Rev Lett. 98, 041801 (2007)

Fraction of exotic quark pairs < 0.80  (90% CL) CDF result with 1.5/fb

Hypotheses tested: 2/3e (null) or 4/3e (test) P-value 0.31 Exotic charge model XM of -4/3 excluded with

87% C.L.

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2. Top Production Mechanism

Top pair production via: qqtt and gg tt (theoretical uncertainties ~10%) Other production mechanisms?

Two approaches to test this at CDF: Using a neural network based on event kinematics Using multiplicity of low PT tracks Both approaches statistics limited

Result: (gg->tt)/(qq->tt)<0.38 at 95% C.L. (gg->tt)/(qq->tt)=0.07-0.07

+0.15

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Forward-Backward Asymmetry in Top Production at D0

Test of discrete symmetries of strong interaction at high PT Asymmetry:

LO – no asymmetry At NLO, a few percent (4-7%) asymmetry predicted Higher order corrections may be important

AFB measured in parton rest frame: AFB = 0.12 ± 0.08 (stat) ± 0.01(syst) Consistent with expectation

Also probing new physics; leptophobic Z’

)(

)(

ttpp

ttZppf

Phys. Rev. Lett. 100, 142002 (2008)

> >

00

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AFB measured in both the parton rest frame and the lab rest frame AFB

tt ~ 1.3 AFBpp

Unfolding to go from reconstructed to parton level Results:

AFBtt = 0.24± 0.13(stat) ± 0.04(syst)

AFBpp = 0.17± 0.07(stat) ± 0.04(syst)

AFB Higher , but consistent with expectation

Forward-Backward Asymmetry in Top Production at CDF

)( 04.0)( 07.017.0, syststatA ppobsFB

CDF II

tt frame

pp frame

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tt Resonance Searches at D0

New heavy particles could couple strongly with 3rd generation fermions A narrow-width leptophobic Z’ is such

a case technicolor model (Hill and Parke,

Phys. Rev. D 49 (1994) 4454) Analyze the high-mass region of the

reconstructed Mtt spectrum

MZ’<760 GeV for Z’/MZ’ =1.2%

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tt Resonance Searches at CDF

Measurement of the tt Differential Cross Section, dσ/dMtt

Lepton+4jets sample Measure top pair cross-section in

bins of Mtt

Indirectly probing for new phyiscs Data consistent with SM

P-value = 0.45

CDF latest result in search of Gtt

Test:0.05≤ Γ/M ≤0.5

Dynamical Likelihood Method used for the Mt

measurement

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t’ Resonance Search

Fourth generation heavy quark: Pair-produced via strong interaction Heavier than the top Decays to Wb, Ws, Wd

Two-variable search: Reconstructed Mt’

HT (total transverse energy) P-value 2.8%

Mt’ < 284GeV

at 95%C.L.

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Scalar top search at D0

SUSY searches? Search for stop pair production

If the stop is lighter than top Final state similar to the SM tt

Likelihood discriminant: 11 variables, depending on M(t) point

First search of this kind at the Tevatron Limits ~7-12 theory values

stop mass     175  175  175  160  160  145    GeV

χ1± mass     135  120  105  120  105  105    GeV

σ(t1~ t1~) <     5.6  6.6  5.6  7.5  9.7  12.3    pb  (95% CL)

+jets +jets

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Scalar Top Search at CDF

Search for tt pair production Dilepton channel

Assumptions:

Theoretical cross sections

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3. Top Decays - W Helicity at D0

Fit for f- and f+ gives:F0 = 0.42 0.17(stat) 0.10(sys)

F+= 0.12 0.09(stat) 0.05(sys)

The V-A nature of the weak current t Wb requires the following helicity fractions: F0 = 0.7, F = 0.3, F+ = 0.0 (longitudinal, left-handed, right-handed

One can simultaneously fit for F0 and F+

Phys Rev Lett 100, 062004 (2008)

* angle between lepton and top in W rest frame

dilepton

l+jets

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W Helicity at CDF CDF used three approaches for this measurement Using the fully reconstructed decay chain:

F0= 0.38 ± 0.21(stat) ± 0.07(syst) F+= 0.15 ± 0.10(stat) ± 0.04(syst)

Template method with similar results Using a matrix element-based technique

Likelihood based on differential cross-sections of signal and background

Matrix Element - based methodF0 = 0.64 ± 0.08(stat)± 0.07(syst)

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FCNC search Flavor changing Neutral Currents

Highly suppressed in SM Fit to a mass 2

Tag and anti-tag(zero-tag)

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Charged Higgs Searches at D0

R

Standard Model predicts: R = (tt->X)l+jets / (tt->X)ll = 1

D0 measurement:R=1.21+0.27-0.26 (stat+syst)

In the context of a general multi-Higgs-doublet model in which H± cs only: (tt->X)l+jets enhanced, (tt->X)ll stays the same Expect BR(t Hb) <0.25 at 95%C.L. Measure BR(t Hb) = 0.13+0.12

-0.11Observe BR(t Hb) < 0.35 at 95%C.L.

BR(t Hb)

Feldman Cousins contours

For R and BR(t Hb)

Assumptions: MH+ = 80 GeV

and Hcs exclusive decays

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Charged Higgs Searches at CDF

In the context of a general multi-Higgs-doublet model in which H± cs only Reconstruct the dijet system Higher invariant mass than the W qq Sharpen peak by adding the FSR jet to mother jet

ΔR < 1.0

No signal observed: Exclusion contour BR versus MH+

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Other Measurements Simultaneous measurement of R and

ttbar cross-section R=BR(tWb)/B(t Wq) with q = d,s,b Extract (tt) without setting BR(tWb)=1 Simultaneous fit

R = 0.97 +0.09 –0.08 (stat+syst) ,  R > 0.79  (95% CL)|Vtb| > 0.89  (95% CL)  (if 3x3 CKM is unitary)

(tt)=8.18+0.90-0.84 ± 0.5 (lumi)

For Mtop=175 GeV

Phys Rev Lett 100 , 192003 (2008 )

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Conclusions Presented several top quark results from 1-2.3 fb-1

Properties (charge) Production mechanism:

gg/qqZ’/G searchesAFB measurement

Other searches in top-related samples:Differential M(tt) cross-section Fourth generation t’Scalar top quarks

Tevatron top properties sector very rich and mature No new phenomena uncovered yet, but: New data crucial, with many New Physics analyses statistics limited

Very dynamic CDF and D0 groups, please visit: http://www-d0.fnal.gov/Run2Physics/top/top_public_web_pages/top_public.html http://www-cdf.fnal.gov/physics/new/top/top.html

Decay of top quarksW helicity

FCNC search

Charged Higgs

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Top Width Check the consistency of our

data with MC generated with different top widths (but same mass Mt =175 GeV)

Parameterize the reconstructed top mass distribution as function of width. Perform pseudoexperiments to check sensitivity.

t < 12.7 @ 95% CLt < 12.7 @ 95% CL