Lattice simulations (including a continuum limit extrapolation) were started and concluded, clarifying the spectrum of baryons containing two charm quarks and a strange quark, as a follow-up on preparatory work studying baryons with two charm quarks and a light quark. Subsequently, also the spectrum of mesons and baryons containing both a bottom quark and a charm (anti)quark was determined. Of these states only one has been discovered experimentally so far (and was confirmed in these new set of simulations). The results will guide future experimental searches, e.g. of the LHC experiments.
Another line of research was directed to the spectroscopy of charmonia. If these states become heavy, which is the case for radial excitations, these heavy-heavy mesons can decay into pairs of heavy-light mesons. Such short-lived resonances can be characterized by a pole in a complex Riemann sheet (rather than by just one real mass parameter). It is possible to extract the position of these poles from lattice simulations by varying the box size and also by varying the average momentum. Such scattering analyses had been carried out successfully in the past for hadronic ground states. In the charm sector several technical complications exist. One is the fact that radial excitations need to be resolved too, which requires a large basis of interpolators and novel methods (stochastic distillation). The other issue is a large number of decays into different pairs of mesons. For instance, an excited charmonium may not only decay into two heavy-light mesons but also into a lower lying charmonium state plus a light meson. Last but nor least, on the lattice the continuum symmetry is reduced and the spin identification becomes non-trivial, in particular at non-zero total momentum (in flight). All these was addressed and resolved in a string of publications and finally applied to a situation where the light quark masses are still unphysically heavy, to manage the computational cost.
The results were published in a number of scientific articles and presented at several international conferences and workshops. In particular, the Fellow was invited to present a plenary review talk on the research field at the annual conference of the Lattice Field Theory community, Lattice 2018 at Michigan State University.
