Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at s $$ \sqrt{s} $$
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Received: May 7, 2020 Accepted: June 29, 2020 Published: August 12, 2020
The ATLAS and CMS collaborations E-mail: [email protected], [email protected] Abstract: The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0 ), left-handed (FL ), or right-handed (FR ) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL ) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR ), and left- and right-handed tensor (gL , gR ) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR , [−0.08, 0.05] for gL , and [−0.04, 0.02] for gR , at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived. Keywords: Hadron-Hadron scattering (experiments), Top physics ArXiv ePrint: 2005.03799
Open Access, Copyright CERN, for the benefit of the ATLAS-CMS Collaboration. Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP08(2020)051
JHEP08(2020)051
Combination of the W boson polarization measurements in top quark decays using ATLAS and √ CMS data at s = 8 TeV
Contents 1 Introduction
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2 The 2.1 2.2 2.3
3 3 4 5
ATLAS and CMS measurements The ATLAS measurement The CMS measurements The W boson polarization values from the input measurements
6 7 11
4 Correlations and uncertainties in the ATLAS and CMS measurements 4.1 Correlations 4.2 Correlation choices for the partially correlated uncertainties 4.3 Summary of the uncertainties and correlations of the input measurements
13 13 16 17
5 Results 5.1 Stability tests 5.2 Limits on anomalous couplings
17 20 21
6 Summary
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The ATLAS collaboration
30
The CMS collaboration
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1
6
Introduction
The large number of top quarks produced at the CERN LHC provides an excellent laboratory for the study of their production and decay properties. Precise predictions of some of these properties are available in the standard model (SM) of particle physics, and are tested through detailed comparisons to data. Potential deviations between data and predictions could reveal important information on the existence of new physics beyond the SM. The properties of the top quark decay vertex tWb are governed
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