Measurement of top quark pair production in association with a Z boson in proton-proton collisions at √s = 13 TeV

Abstract

A measurement of the inclusive cross section of top quark pair production in association with a Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC is performed. The data sample corresponds to an integrated luminosity of 77.5 fb⁻¹, collected by the CMS experiment during 2016 and 2017. The measurement is performed using final states containing three or four charged leptons (electrons or muons), and the Z boson is detected through its decay to an oppositely charged lepton pair. The production cross section is measured to be σ( (t\overline{t}Z) ) = 0.95 ± 0.05 (stat) ± 0.06 (syst) pb. For the first time, differential cross sections are measured as functions of the transverse momentum of the Z boson and the angular distribution of the negatively charged lepton from the Z boson decay. The most stringent direct limits to date on the anomalous couplings of the top quark to the Z boson are presented, including constraints on the Wilson coefficients in the framework of the standard model effective field theory.

Description
Keywords
High Energy Physics - Experiment, Hadron-Hadron scattering (experiments), Top physics
Citation
Sirunyan, A. M., Tumasyan, A., Adam, W., Ambrogi, F., Bergauer, T., Brandstetter, J., Dragicevic, M., Erö, J., Escalante Del Valle, A., Flechl, M., Frühwirth, R., Jeitler, M., Krammer, N., Krätschmer, I., Liko, D., Madlener, T., Mikulec, I., Rad, N., … Woods, N. (2020). Measurement of top quark pair production in association with a Z boson in proton-proton collisions at $ \sqrt{\mathrm{s}} $ = 13 TeV. In Journal of High Energy Physics (Vol. 2020, Issue 3). Springer Science and Business Media LLC. https://doi.org/10.1007/jhep03(2020)056