2021-07-30T07:28:57Zhttps://tsukuba.repo.nii.ac.jp/oaioai:tsukuba.repo.nii.ac.jp:000453442021-03-01T13:55:19ZAnalysis of the Wtb vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the t-channel at √s=8 TeV with the ATLAS detector原, 和彦金, 信弘大川, 英希佐藤, 構二受川, 史彦ATLAS CollaborationHara, K.Kim, S.H.Okawa, H.Sato, K.Ukegawa, F.The electroweak production and subsequent decay of single top quarks in the t-channel is determined by the properties of the Wtb vertex, which can be described by the complex parameters of an effective Lagrangian. An analysis of a triple-differential decay rate in t-channel production is used to simultaneously determine five generalised helicity fractions and phases, as well as the polarisation of the produced top quark. The complex parameters are then constrained. This analysis is based on 20.2 fb−1 of proton-proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction of decays containing transversely polarised W bosons is measured to be f 1 = 0.30 ± 0.05. The phase between amplitudes for transversely and longitudinally polarised W bosons recoiling against left-handed b-quarks is measured to be δ − = 0.002π + 0.017π + 0.016π , giving no indication of CP violation. The fractions of longitudinal or transverse W bosons accompanied by right-handed b-quarks are also constrained. Based on these measurements, limits are placed at 95% CL on the ratio of the complex coupling parameters Re [g R/V L ∈ [−0.12, 0.17] and Im [g R/VL ∈ [−0.07, 0.06]. Constraints are also placed on the ratios |V R/V L| and |g L/V L|. In addition, the polarisation of single top quarks in the t-channel is constrained to be P > 0.72 (95% CL). None of the above measurements make assumptions about the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.journal articleSpringer2017-12application/pdfJournal of high energy physics122017171029-8479AA1188279Xhttps://tsukuba.repo.nii.ac.jp/record/45344/files/JHEP_2017-12-17.pdfeng10.1007/JHEP12(2017)017Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3.This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.