Phenomenology of near-threshold states: a practical parametrisation for the line shapes

Abstract

Abstract. In the last decade many states in the spectrum of charmonium and bottomonium have been observed experimentally above the lowest open-flavour threshold. Most of these states reside in the vicinity of strong thresholds and show properties that cannot be captured by simple quark models. Description and understanding of such exotic states is a challenge for the phenomenology of strong interactions, since it requires building adequate theoretical tools and approaches. In this work, a practical parametrisation for the line shapes of near threshold resonance(s) is derived in the framework of a coupledchannel model which includes an arbitrary number of elastic and inelastic channels as well as of bare pole terms. Parameters of the distribution have a direct relation to phenomenology and the resulting analytical parametrisation is therefore ideally suited to harvest the full information content provided by the measurements and to establish a link between the experimental data and their theoretical interpretation.

Study of the doubly charmed tetraquark $${{{{{{\rm{T}}}}}}}_{{{{{{\rm{c}}}}}}{{{{{\rm{c}}}}}}}^{+}$$

“…That function, while sufficient to reveal the existence of the state, does not account for the resonance being in close vicinity of the D * D threshold. To assess the fundamental properties of resonances that are close to thresholds, advanced parametrisations ought to be used [80][81][82][83][84][85][86][87][88][89][90] . A unitarised Breit-Wigner profile F U , described in Methods Eq.…”

Study of the doubly charmed tetraquark $T_{cc}^+$

“…That function, while sufficient to reveal the existence of the state, does not account for the resonance being in close vicinity of the D * D threshold. To assess the fundamental properties of resonances that are close to thresholds, advanced parametrisations ought to be used [93][94][95][96][97][98][99][100][101][102][103]. A unitarised Breit-Wigner profile F U , described in Methods Eq.…”