TY - JOUR
T1 - Measurement of the W boson polarisation in tt¯tt¯ events from pp collisions at s√s = 8 TeV in the lepton + jets channel with ATLAS
AU - Barnes, Sarah
AU - Bielski, Rafal
AU - Cox, Brian
AU - Da Via, Cinzia
AU - Dann, Nick
AU - Forcolin, Giulio
AU - Forti, Alessandra
AU - Iturbe Ponce, Julia
AU - Li, Xingguo
AU - Loebinger, Frederick
AU - Marsden, Stephen
AU - Masik, Jiri
AU - Menary, Stephen
AU - Munoz Sanchez, Francisca
AU - Neep, Thomas
AU - Oh, Alexander
AU - Ospanov, Rustem
AU - Pater, Joleen
AU - Peters, Yvonne
AU - Pilkington, Andrew
AU - Pin, Arnaud
AU - Price, Darren
AU - Qin, Yang
AU - Raine, John
AU - Roberts, Rhys
AU - Shaw, Savanna
AU - Tomlinson, Lee
AU - Watts, Stephen
AU - Wilk, Fabian
AU - Woudstra, Martin
AU - Wyatt, Terence
AU - The ATLAS Collaboration,
PY - 2017/4/26
Y1 - 2017/4/26
N2 - This paper presents a measurement of the polarisation of W bosons from tt¯tt¯ decays, reconstructed in events with one high- p T p T lepton and at least four jets. Data from pp collisions at the LHC were collected at s√s = 8 TeV and correspond to an integrated luminosity of 20.2 fb −1−1 . The angle θ∗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 cosθ∗cosθ∗ 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 ± 0.019F0= 0.709 ± 0.019 , FL= 0.299 ± 0.015FL= 0.299 ± 0.015 and FR= −0.008 ± 0.014FR= −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.
AB - This paper presents a measurement of the polarisation of W bosons from tt¯tt¯ decays, reconstructed in events with one high- p T p T lepton and at least four jets. Data from pp collisions at the LHC were collected at s√s = 8 TeV and correspond to an integrated luminosity of 20.2 fb −1−1 . The angle θ∗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 cosθ∗cosθ∗ 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 ± 0.019F0= 0.709 ± 0.019 , FL= 0.299 ± 0.015FL= 0.299 ± 0.015 and FR= −0.008 ± 0.014FR= −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.
U2 - 10.1140/epjc/s10052-017-4819-4
DO - 10.1140/epjc/s10052-017-4819-4
M3 - Article
SN - 1434-6044
VL - 77
JO - European Physical Journal C. Particles and Fields
JF - European Physical Journal C. Particles and Fields
IS - 264
M1 - 264
ER -