We present a measurement of the fractions F0 and F+ of longitudinally polarized and right-handed W bosons in top-quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 318  pb-1. We select tt̅ candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle θ*, which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W momentum in the top-quark rest frame. The cos⁡θ* distribution in the data is determined by full kinematic reconstruction of the tt̅ candidates. We find F0=0.85-0.22+0.15(stat)±0.06(syst) and F+=0.05-0.05+0.11(stat)±0.03(syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F+<0.26 at the 95% confidence level.

Measurement of the helicity fractions of W bosons from top quark decays using fully reconstructed t(t)over-bar events with CDF II

BISELLO, DARIO;BUSETTO, GIOVANNI;CORTIANA, GIORGIO;LUCCHESI, DONATELLA;ROSSIN, ROBERTO;
2007

Abstract

We present a measurement of the fractions F0 and F+ of longitudinally polarized and right-handed W bosons in top-quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 318  pb-1. We select tt̅ candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle θ*, which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W momentum in the top-quark rest frame. The cos⁡θ* distribution in the data is determined by full kinematic reconstruction of the tt̅ candidates. We find F0=0.85-0.22+0.15(stat)±0.06(syst) and F+=0.05-0.05+0.11(stat)±0.03(syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F+<0.26 at the 95% confidence level.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2473747
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