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Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13 TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb⁻¹. The search uses two observables,$$ \mathcal{O} $$$O$₁and$$ \mathcal{O} $$$O$₃, which are Lorentz scalars. The observable$$ \mathcal{O} $$$O$₁is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while$$ \mathcal{O} $$$O$₃consists of the four-momenta of the charged leptons and the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model.

 

Measurements of the associated production of a W boson and a charm ($${\text {c}}$$$\text{c}$) quark in proton–proton collisions at a centre-of-mass energy of 8$$\,\text {TeV}$$$\text{TeV}$are reported. The analysis uses a data sample corresponding to a total integrated luminosity of 19.7$$\,\text {fb}^{-1}$$${\text{fb}}^{-1}$collected by the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm quark jets are selected using distinctive signatures of charm hadron decays. The product of the cross section and branching fraction$$\sigma (\text {p}\text {p}\rightarrow \text {W}+ {\text {c}}+ \text {X}) {\mathcal {B}}(\text {W}\rightarrow \ell \upnu )$$$\sigma (\text{pp}\to \text{W}+\text{c}+\text{X})B(\text{W}\to \ell \nu )$, where$$\ell = \text {e}$$$\ell =\text{e}$or$$\upmu $$$\mu$, and the cross section ratio$$\sigma (\text {p}\text {p}\rightarrow {{\text {W}}^{+} + \bar{{\text {c}}} + \text {X}}) / \sigma (\text {p}\text {p}\rightarrow {{\text {W}}^{-} + {\text {c}}+ \text {X}})$$$\sigma (\text{pp}\to {\text{W}}^{+}+\overline{\text{c}}+\text{X})/\sigma (\text{pp}\to {\text{W}}^{-}+\text{c}+\text{X})$are measured in a fiducial volume and differentially as functions of the pseudorapidity and of the transverse momentum of the lepton from the W boson decay. The results are compared with theoretical predictions. The impact of these measurements on the determination of the strange quark distribution is assessed.

 

A bstract A search is presented for single production of a vector-like T quark with charge 2 / 3 e , in the decay channel featuring a top quark and a Z boson, with the top quark decaying hadronically and the Z boson decaying to neutrinos. The search uses data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb − 1 recorded at the CERN LHC in 2016–2018. The search is sensitive to a T quark mass between 0.6 and 1.8 TeV with decay widths ranging from negligibly small up to 30% of the T quark mass. Reconstruction strategies for the top quark are based on the degree of Lorentz boosting of its final state. At 95% confidence level, the upper limit on the product of the cross section and branching fraction for a T quark of small decay width varies between 15 and 602 fb, depending on its mass. For a T quark with decay widths between 10 and 30% of its mass, this upper limit ranges between 16 and 836 fb. For most of the studied range, the results provide the best limits to date. This is the first search for single T quark production based on the full Run 2 data set of the LHC.