Measurement of the W boson polarisation in t¯t events from pp collisions at √s = 8 TeV in the lepton + jets channel with ATLAS
This paper presents a measurement of the polarisation of W bosons from t¯t decays, reconstructed in events with one high-p<sub>T</sub> 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<s...
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| Autores principales: | , , , , , , , |
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| Formato: | Articulo |
| Lenguaje: | Inglés |
| Publicado: |
2017
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| Materias: | |
| Acceso en línea: | http://sedici.unlp.edu.ar/handle/10915/81860 |
| Aporte de: |
| Sumario: | This paper presents a measurement of the polarisation of W bosons from t¯t decays, reconstructed in events with one high-p<sub>T</sub> 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<sup>−1</sup>. 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 F<sub>0</sub> = 0.709 ± 0.019, F<sub>L</sub> = 0.299 ± 0.015 and F<sub>R</sub> = −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. |
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