Abstract
Abstract This paper presents measurements of the polarization of W bosons in top quark decays, derived from $ t\overline t $ events with missing transverse momentum, one charged lepton and at least four jets, or two charged leptons and at least two jets. Data from pp collisions at a centre-of-mass energy of 7 TeV were collected with the ATLAS experiment at the LHC and correspond to an integrated luminosity of 1.04 fb−1. The measured fractions of longitudinally, left- and right-handed polarization are F 0 = 0.67 ± 0.07, F L = 0.32 ± 0.04 and F R = 0.01 ± 0.05, in agreement with the Standard Model predictions. As the polarization of the W bosons in top quark decays is sensitive to the Wtb vertex Lorentz structure and couplings, the measurements were used to set limits on anomalous contributions to the Wtb couplings.
Highlights
A quark-antiquark pair or into a charged lepton and a neutrino
The uncertainty on the normalization of the small background contributions from single top quark and diboson production was estimated to be about 10% and 5%, respectively. The former estimate was based on the difference between the predictions from Monte Carlo (MC)@NLO and MCFM [49], whereas the latter comes from scale and parton distribution functions (PDFs) uncertainties evaluated with MCFM
A measurement of the polarization of the W bosons in top quark decays was presented, based on 1.04 fb−1 of data collected with the ATLAS detector in 2011
Summary
The ATLAS detector [14] at the LHC covers nearly the entire solid angle around the collision point. A three-level trigger system, designed to reduce the event rate from 40 MHz to about 200 Hz, is used to select events of interest
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