Search for Heavy Pseudoscalar and Scalar Bosons Decaying to a Top Quark Pair in Proton-Proton Collisions at √s = 13 TeV

Abstract

This article has 2,424 authors. A search for pseudoscalar or scalar bosons decaying to a top quark pair (t ̄t) in final states withone or two charged leptons is presented. The analyzed proton–proton collision data wasrecorded at√s=13TeV by the CMS experiment at the CERN LHC and corresponds to anintegrated luminosity of 138 fb−1. The invariant massmt ̄tof the reconstructed t ̄t system andvariables sensitive to its spin and parity are used to discriminate against the standard model t ̄tbackground. Interference between pseudoscalar or scalar boson production and the standardmodel t ̄t continuum is included, leading to peak-dip structures in themt ̄tdistribution. An excessof the data above the background prediction, based on perturbative quantum chromodynamics(QCD) calculations, is observed near the kinematic t ̄t production threshold, while goodagreement is found for highmt ̄t. The data are consistent with the background prediction if thecontribution from a simplified model of a color-singlet1S[1]0t ̄t quasi-bound stateηt, inspired bynonrelativistic QCD, is added. Upper limits at 95% confidence level are set on the couplingbetween the pseudoscalar or scalar bosons and the top quark for boson masses in the range365–1000GeV, relative widths between 0.5% and 25%, and two background scenarios with orwithoutηtcontribution.