Eur. Phys. J. C (2005) 44: 13-33
https://doi.org/10.1140/epjcd/s2005-02-009-9

Scientific Note

ATLAS sensitivity to top quark and W boson polarizationin events

¹ Centre de Physique des Particules de Marseille, CNRS/IN2P3 - Univ. Méditerranée, Marseille, France
² Institute of Experimental and Applied Physics, Czech Technical University, Prague, Czech Republic
³ Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Prague, Czech Republic
⁴ Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic

Abstract

Stringent tests on top quark production and decay mechanisms are provided by the measurement of the top quark and W boson polarization. This paper presents a detailed study of these two measurements with the ATLAS detector, in the semileptonic () and dileptonic () channels. It is based on leading-order Monte Carlo generators and on a fast simulation of the detector. A particular attention is paid to the systematic uncertainties, which dominate the statistical errors after one LHC year at low luminosity (10 fb^-1), and to the background estimate. Combining results from both channel studies, the longitudinal component of the W polarization (F ₀) can be measured with a 2% accuracy and the right-handed component (F _R , which is zero in the Standard Model) with a 1 precision with 10 fb^-1. Even though the top quarks in pairs are not polarized, a large asymmetry is expected within the Standard Model in the like-spin versus unlike-spin pair production. A 4% precision on this asymmetry measurement is possible with 10 fb^-1, after combining results from both channel studies. These promising results are converted in a sensitivity to new physics, such as tWb anomalous couplings, top decay to charged Higgs boson, or new s-channels (heavy resonance, gravitons) in production.