A search is presented for top quark-antiquark ($\mathrm{t\bar{t}}$) quasi-bound ``toponium''states, near the kinematic $\mathrm{t\bar{t}}$ production threshold in final states with a single electron or muon and jets. The study uses proton-proton collision data at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 138 fb$^{-1}$. The analysis examines the relative velocity between the top quark and antiquark, along with two angular observables sensitive to the parity and spin of the $\mathrm{t\bar{t}}$ system. A significant excess of events is observed relative to the standard model prediction for $\mathrm{t\bar{t}}$ production calculated at next-to-next-to-leading order in perturbative quantum chromodynamics (QCD). The excess corresponds to an observed total cross section of 5.1$\pm$0.9 pb and is consistent with a simplified model of a color singlet pseudoscalar toponium motivated by nonrelativistic QCD, with a resulting observed significance of 6.1 standard deviations. The result provides an independent confirmation of the excess reported in the dilepton channel.
The first single-experiment observation of single top-quark production in the $s$-channel is presented. Measurements of this process are essential to fully characterize the electroweak interactions of the top quark and probe for new physics, however its highly suppressed cross-section has so far caused it to evade dire...
We present an empirical determination of the threshold excess $\Delta$ in top-quark pair production, taking full account of correlated uncertainties with PDFs, the top-quark mass $m_t$ and the strong coupling $\alpha_s(m_Z)$. We extract $\Delta$ from a variety of differential $t\bar{t}$ cross-section measurements by AT...
A search for new high-mass phenomena in events with a high-transverse-momentum photon and a jet is performed using data collected by the ATLAS experiment from proton-proton collisions at the LHC, with a centre-of-mass energy of 13 TeV. The analysis is based on a total integrated luminosity of 140 fb$^{-1}$. The $\gamma...
We investigate the discovery potential of a singly produced vector-like top quark $T$ via the $T\to tZ$ decay channel at future muon-proton ($\mu p$) colliders, considering three benchmark center-of-mass energies: $\sqrt{s}=5.29$, $6.48$, and $9.16$~TeV. The baseline signal final state consists of a semileptonic top...
Ying-Hao Gao, Yao-Bei Liu· Chinese Physics C, High Ener...· 0 citations
A search for a new top-philic vector boson ($Z'$) produced in association with a top-quark or a pair of top quarks, and decaying into a top quark pair is presented. The search uses $pp$ collision data collected by the ATLAS detector at the Large Hadron Collider at centre-of-mass energies of $\sqrt{s} =$ 13 TeV and 13.6...
The $t$-channel production of a top quark in association with a $Z$ boson, $tZq$, is measured in the trilepton channel. The measured $pp \rightarrow t\ell^+\ell^-q$ process is defined for $m_{\ell\ell}>30\,\text{GeV}$ and includes both resonant $Z$-boson production and non-resonant dilepton production. The data collect...
A. Collaboration· 0 citations
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