Abstract
We study reported deviations between observations and theoretical predictions associated with the production of a pair of di-leptonically decaying top quarks at the LHC, and we examine the possibility that they reflect a signal of toponium formation. We investigate the production by gluon fusion of a color-singlet spin-0 toponium $\eta_t$ bound state of a top and anti-top quark, that then decays di-leptonically ($gg\to\eta_t \to \bar\ell \ell b \bar{b} \nu \bar{\nu}$). We find strong correlations favoring the production of di-lepton systems featuring a small angular separation in azimuth and a small invariant mass. Although toponium production only contributes to 0.8% of the total top-quark pair-production cross section at the 13 TeV LHC, there is a possibility that it can account for observed excesses in the narrow edges of phase space. We propose a method to discover toponium formation by `reconstructing' both its top and anti-top quark constituents in the di-lepton channel.
Highlights
Toponium systems consist of bound states of a top and an antitop quark and are predicted to impact top pairproduction near threshold
With threshold resummation at the next-to-next-to-leadinglogarithmic accuracy (NNLO þ NNLL) [14]. Whereas this significant excess led to a new physics interpretation through extra scalars [15], we show in this paper that it may be explained as a consequence of spin-0 toponium formation
We aim to find a clear signal of toponium formation among the 77,000 nonresonant and 2760 toponium events that survive this cut, as the signal-over-noise ratio (S=N) is still of 3.6%
Summary
Toponium systems consist of bound states of a top and an antitop quark and are predicted to impact top pairproduction near threshold. Because of this relative smallness, the properties of the toponium decay products have not yet been studied carefully. An excess of events featuring leptons emitted close to each other in azimuth and forming a system with a small invariant mass, i.e., with Δφll ≲ π=5 and mll ≲ 20 GeV, had been observed after a comparison with the best available QCD predictions. These relied on event generation at the next-to-leading-order matched with parton showers (NLO þ PS) [12,13] and accounted for a normalization at the next-to-next-to-leading order matched. Whereas this significant excess led to a new physics interpretation through extra scalars [15], we show in this paper that it may be explained as a consequence of spin-0 toponium formation
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