PT Journal
AU ATLAS Collaboration (Aaboud, Mea
   Alvarez Piqueras, D
   Barranco Navarro, L
   Cabrera Urban, S
   Castillo Gimenez, V
   Cerda Alberich, L
   Costa, MJ
   Fernandez Martinez, P
   Ferrer, A
   Fiorini, L
   Fuster, J
   Garcia, C
   Garcia Navarro, JE
   Gonzalez de la Hoz, S
   Higon-Rodriguez, E
   Jimenez Pena, J
   King, M
   Lacasta, C
   Mamuzic, J
   Marti-Garcia, S
   Melini, D
   Mitsou, VA
   Pedraza Lopez, S
   Rodriguez Rodriguez, D
   Romero Adam, E
   Ros, E
   Salt, J
   Sanchez Martinez, V
   Soldevila, U
   Sanchez, J
   Valero, A
   Valls Ferrer, JA
   Vos, M
TI Measurement of the W boson polarisation in t(t)over-barevents from pp collisions at root s=8 TeV in the lepton plus jets channel with ATLAS
SO European Physical Journal C
JI Eur. Phys. J. C
PY 2017
BP 264
EP 28pp
VL 77
IS 4
DI 10.1140/epjc/s10052-017-4819-4
LA English
AB This paper presents a measurement of the polarisation of W bosons from t (t) over bar t decays, reconstructed in events with one high-p(T) lepton and at least four jets. Data from pp collisions at the LHC were collected at root s = 8 TeV and correspond to an integrated luminosity of 20.2 fb(-1). The angle theta* 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 theta* 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 F-0 = 0.709 +/- 0.019, F-L = 0.299 +/- 0.015 and F-R = – 0.008 +/- 0.014, and are the most precisely measured W boson polarisation fractions to date. Limits on anomalous couplings of the W tb vertex are set.
ER