Normalization and shape of the ηt toponium signal component near threshold

Determine the normalization and shape of the pseudoscalar toponium ηt contribution to top-quark pair production near threshold (for invariant masses 345–400 GeV and relative longitudinal velocity βz<0.9) at √s=13 TeV, so that this component need not be treated as unknown via systematic uncertainties.

Background

The combined signal model includes a pseudoscalar toponium ground state (ηt) to improve threshold-region modeling. However, the authors explicitly state that the ηt component’s normalization and shape are unknown and are therefore handled via dedicated systematic uncertainties and smearing procedures.

Resolving this uncertainty would refine the modeling of entanglement-sensitive observables (such as the cosφ distribution) and reduce systematic impacts attributed to the ηt signal component.