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View of and from Lene Kristian's office window. The office mascot, a small pet pug, is sitting on top of a stack of books on the windowsill. Outside, there is a parking lot, trees and sky in the early dusk of a winter's day.

Lene Kristian Bryngemark

Researcher

View of and from Lene Kristian's office window. The office mascot, a small pet pug, is sitting on top of a stack of books on the windowsill. Outside, there is a parking lot, trees and sky in the early dusk of a winter's day.

Measurement of the W boson polarisation in tt¯ events from pp collisions at √s = 8 TeV in the lepton + jets channel with ATLAS

Author

  • M Aaboud
  • G. Aad
  • B Abbott
  • J. Abdallah
  • O Abdinov
  • B Abeloos
  • Torsten Åkesson
  • Simona Bocchetta
  • LENE BRYNGEMARK
  • Caterina Doglioni
  • Vincent Hedberg
  • Göran Jarlskog
  • Else Lytken
  • Ulf Mjörnmark
  • Oxana Smirnova
  • Oleksandr Viazlo
Show all

Summary, in English

This paper presents a measurement of the polarisation of W bosons from tt¯ decays, reconstructed in events with one high-pT lepton and at least four jets. Data from pp collisions at the LHC were collected at s = 8 TeV and correspond to an integrated luminosity of 20.2 fb- 1. The angle θ∗ between the b-quark from the top quark decay and a direct W boson decay product in the W boson rest frame is sensitive to the W boson polarisation. Two different W decay products are used as polarisation analysers: the charged lepton and the down-type quark for the leptonically and hadronically decaying W boson, respectively. The most precise measurement of the W boson polarisation via the distribution of cos θ∗ is obtained using the leptonic analyser and events in which at least two of the jets are tagged as b-quark jets. The fitted fractions of longitudinal, left- and right-handed polarisation states are F0=0.709±0.019, FL=0.299±0.015 and FR=-0.008±0.014, and are the most precisely measured W boson polarisation fractions to date. Limits on anomalous couplings of the Wtb vertex are set. © 2017, CERN for the benefit of the ATLAS collaboration.

Department/s

  • Particle and nuclear physics
  • eSSENCE: The e-Science Collaboration

Publishing year

2017

Language

English

Publication/Series

European Physical Journal C

Volume

77

Issue

4

Document type

Journal article

Publisher

Springer

Topic

  • Subatomic Physics

Status

Published

ISBN/ISSN/Other

  • ISSN: 1434-6044