Public Analysis Web Page

Measurement of W-Boson Helicity Fractions in Top-Quark Decays using 955pb^-1.

Shulamit Moed (Geneva)
Markus Klute (MIT)
D.Glenzinski, A.Hocker (Fermilab)

E-mail W-Boson Helicity Group

Abstract:
We peresent a first simultaneous measurement of the fractions of longitudinally (f_0) and right-handed (f_+) W bosons produced in top-quark decays. The W boson helicity fractions are extracted through an analysis of the angular distribution of cos(theta*) - the angle between the lepton and the W boson in the top rest frame.
This analysis is based on an integrated luminosity of 955 pb^-1, out of which we select and fully reconstruct 220 event in the lepton+jets channel of the top decay. Fitting the longitudinal and right-handed fractions simultaneously we find f_0 = 0.74 ± 0.25 ± 0.06 and f_+ = -0.06 ± 0.10 ± 0.03 .
We also perform 1D measurements - while fitting to extract the fraction of the longitudinal W helicity (f_0) with f_+ fixed to 0, we find f_0 = 0.61 ± 0.12 ± 0.06, and fitting the right-handed W fraction while fixing f_0 to its SM value expectation with a top mass of 175 GeV, we find f_+ = -0.06 ± 0.06 ± 0.03 Using a bayesian method we set an upper limit on the fraction on the right-handed W bosons f_+ < 0.11 at 95% CL.
Public Note ( CDF 8449 ) First results of simultaneous longitudinal and right-handed W fractions using 955pb^-1

Public Note ( CDF 8368 ) for Analysis using 955pb^-1

Private Webpage for W Boson Helicity Analysis ( CDF Password )

Private W Boson Helicity Analysis TWIKI ( CDF Password )

Blessed first simultaneous fit - longitudinal and right-handed fraction:

cos(theta*) distribution in data with longitudinal fraction and right handed fraction fit results.
The observed cos(theta*) distribution in the data (points) overlaid with the background (dotted), background + right-handed (dash-dot), background + right-handed + left-handed (dashed) and background + right-handed + left-handed + longitudinal (solid) distributions as determined by the fit for F+ (the right handed fraction).

2D likelihood
Contours of constant ln likelihood in the (f0,f+) plane from the fit to the data. The X shows the minimum of the ln likelihood, i.e our result.

Limit on right handed fraction - exclusion plot
The area of the (f+,f0) plane excluded by the data is shown as the hatched region. The unhatched region on the upper right is unphysical.

Blessed Figures and Results using 955pb^-1:

cos theta* distribution in data with the longitudinal fraction fit result.
The observed cos(theta*) distribution in the data (points) overlaid with the background (dotted), background + left-handed (dashed), background + left-handed + longitudinal (solid) distributions as determined by the fit for F0 (the longitudinal fraction).

cos theta* distribution in data with right-handed fraction fit result.
The observed cos(theta*) distribution in the data (points) overlaid with the background (dotted), background + right-handed (dash-dot), background + right-handed + left-handed (dashed) and background + right-handed + left-handed + longitudinal (solid) distributions as determined by the fit for F+ (the right handed fraction).

parametrisation of signal and background shape.
A comparison ofthe parameterizations of the reconstructed cos(theta*) distributions for signal and the dominant backgroud sources. The parameterizations are extracted from fitting out template MC samples to a 3rd order polinomial function times an exponent.

likelihood distribution for f0 and f+ fit.

likelihood for right-handed fraction fit w/ and w/o systematic
The f+ likelihood returned by the fit is multiplied by a prior constant between 0 and 1 to arrive to a posterior probablility distribution for f+. This posterior probability is hown with (blue) and without (black) folding in systematic uncertainties.

limit on right handed fraction.
Posterior probability for and 95% C.L limit on f+.

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The analysis has been performed in spring'06 using 695pb^-1:

Blessed Figures and Results using 695pb^-1:

cos theta* distribution in data with longitudinal fraction fit result.
The observed cos(theta*) distribution in the data (points) overlaid with the background (dotted), background + left-handed (dashed), background + left-handed + longitudinal (solid) distributions as determined by the fit for F0 (the longitudinal fraction).

cos theta* distribution in data with longitudinal fraction fit result.
The observed cos(theta*) distribution in the data (points) overlaid with the background (dotted), background + right-handed (dash-dot), background + right-handed + left-handed (dashed) and background + right-handed + left-handed + longitudinal (solid) distributions as determined by the fit for F+ (the longitudinal fraction).

parametrisation of signal and background shape.
A comparison ofthe parameterizations of the reconstructed cos(theta*) distributions for signal and the dominant backgroud sources. The parameterizations are extracted from fitting out template MC samples to a 3rd order polinomial function times an exponent .

likelihood distribution for f0 and f+ fit.

likelihood for right-handed fraction fit w/ and w/o systematic
The f+ likelihood returned by the fit is multiplied by a prior constant between 0 and 1 to arrive to a posterior probablility distribution for f+. This posterior probability is hown with (blue) and without (black) folding in systematic uncertainties.

limit on right handed fraction
Posterior probability for and 95% C.L limit on f+.

Public Analysis Web Page

Measurement of W-Boson Helicity Fractions in Top-Quark Decays using 955pb-1.

Shulamit Moed (Geneva)Markus Klute (MIT) D.Glenzinski, A.Hocker (Fermilab)

Abstract:

Public Note ( CDF 8449 ) First results of simultaneous longitudinal and right-handed W fractions using 955pb-1

Public Note ( CDF 8368 ) for Analysis using 955pb-1

Private Webpage for W Boson Helicity Analysis ( CDF Password )

Private W Boson Helicity Analysis TWIKI ( CDF Password )

Blessed first simultaneous fit - longitudinal and right-handed fraction:

Blessed Figures and Results using 955pb-1:

The analysis has been performed in spring'06 using 695pb-1:

Blessed Figures and Results using 695pb-1:

Measurement of W-Boson Helicity Fractions in Top-Quark Decays using 955pb^-1.

Shulamit Moed (Geneva)
Markus Klute (MIT)
D.Glenzinski, A.Hocker (Fermilab)

Public Note ( CDF 8449 ) First results of simultaneous longitudinal and right-handed W fractions using 955pb^-1

Public Note ( CDF 8368 ) for Analysis using 955pb^-1

Blessed Figures and Results using 955pb^-1:

The analysis has been performed in spring'06 using 695pb^-1:

Blessed Figures and Results using 695pb^-1: