Rare two-body decays of the top quark into a bottom meson plus an up or charm quark

Abstract

Rare two-body decays of the top quark into a neutral bottom-quark meson plus an up- or charm-quark: tto {overline{B}}^0+u,kern0.5em c;tto {overline{B}}_s^0+c,kern0.5em u ; and t → ϒ(nS) + c, u, are studied for the first time. The corresponding partials widths are computed at leading order in the non-relativistic QCD framework. The sums of all two-body branching ratios amount to mathrm{mathcal{B}}left(tto {overline{B}}^0+mathrm{jet}right)approx mathrm{mathcal{B}}left(tto {overline{B}}_s^0+mathrm{jet}right)approx 4.2cdot {10}^{-5} and ℬ(t → ϒ(nS) + jet) ≈ 2 ⋅ 10−9, respectively. The feasibility to observe the tto {overline{B}}_{(s)}^0+ jet decay is estimated in top- pair events produced in proton-proton collisions at sqrt{s} = 14, 100 TeV at the LHC and FCC, respectively. Combining many exclusive hadronic {overline{B}}_{(s)}^0 decays, with J/ψ or D0,± final states, about 50 (16 000) events are expected in 3 (20) ab−1 of integrated luminosity at the LHC (FCC), after typical selection criteria, acceptance, and efficiency losses. An observation of the two-body top-quark decay can also be achieved in the interesting t → b(jet) + c(jet) dijet final state, where the {overline{B}}_{(s)}^0 decay products are reconstructed as a jet, with 5 300 and 1.4 million signal events above backgrounds expected after selection criteria at the LHC and FCC, respectively. Such unique final states provide a new direct method to precisely measure the top-quark mass via simple 2-body invariant mass analyses.