From Hadrons at Unphysical Quark Masses to Coupled-Channel Reaction Dynamics

by Prof. Matthias Lutz (GSI Darmstadt)

Monday 14 May 2018, 14:15 → 16:45 Europe/Berlin

3344 (TUM - Physics Department - Garching)

In this talk I discuss recent progress on how to study QCD in its regime where non-perturbative structures emerge. While QCD

lattice-simulations are available for masses of hadrons in their ground state, reliable computations of the excitation spectra are still far in

the future. Nevertheless, the current lattice data at unphysical quark masses are helpful to access the QCD excitation spectrum. Such data

can be used to determine the low-energy constants of effective chiral Lagrangians, and coupled-channel

approaches can then provide the missing link to the empirical data. The obtained low-energy constants are found to be compatible with the

hierarchy of sum rules from large$-N_c$ QCD, and the implications on the baryon sigma terms are eluded on. As a second case we discuss mesons

involving a charm quark. A quantitative reproduction of the masses of D-mesons in the $J^P = 0^-$ and $J^P = 1^-$ ground states on all

available QCD-lattice ensembles is achieved. The resulting low-energy constants are used in a coupled-channel approach and predictions for the

s-wave scattering phase-shifts and inelasticity parameters are made.

These results are scrutinized against first QCD-lattice computations of the $\pi D$ scattering phase shifts by HSC at unphysical quark masses.

A striking dependence on the choice of quark masses is predicted. At physical quark masses, a clear signal of an exotic flavour sextet in the

$\eta D$ invariant mass distribution is foreseen.