Proposing Institution

Fakultät für Mathematik und Naturwissenschaften, Theoretische Teilchenphysik, Uni Wuppertal
Project Manager

Prof. Dr. Francesco Knechtli
Gaussstr. 20
42119 Wuppertal
Abstract
The goal of this project is to study the impact of a dynamical charm quark in Quantum Chromodynamics (QCD). Up to date many simulations of QCD are carried out using $N_f = 2 + 1$ dynamical light quarks (up, down, strange). This model has so far provided important results and predictions in Particle Physics and can be considered an excellent approximation of the full theory at energies much below the charm quark mass. However, a more complete setup would include a dynamical charm quark ($N_f = 2 + 1 + 1$ QCD), since it eliminates systematic effects due to the “quenching” of the charm quark in $N_f = 2 + 1$ QCD simulations and also leads to a better understanding of charm physics. To give a first reliable estimate of the effects of a dynamical charm quark in QCD, we compare results for physical observables obtained with: i) measurements on gauge ensembles generated using a simplified setup, namely QCD with two degenerate charm quarks; ii) measurements on pure gauge ensembles ($N_f = 0$ QCD). The advantage of our simplified model relies on the fact that the absence of light quarks allows to reach extremely fine lattice spacings (down to 0.02 fm) and this is crucial for reliable continuum extrapolations.For this allocation, our first objective is to compute the decay constants of the two lightestparticles of the charmonium spectrum, namely the pseudo-scalar meson $\eta_c$ and the vector meson $J/\psi$. The charmonium system, frequently characterized as the “hydrogen atom” of meson spectroscopy owing to the fact that it is non-relativistic enough to be reasonably well described by certain potential models, is the perfect testing ground for a comparison of theory with experiment.Finally, we also plan to study the charm sea effects on the hyperfine splitting of a $B_c$ meson made of a bottom quark (antiquark) and a charm antiquark (quark). At the LHC, with its higher luminosity, the spectroscopy and decay of $B_c^{\star}$ mesons can now be experimentally measured with much better confidence such that on the theory side complementary precision studies of these meson states by means of lattice QCD become increasingly important.

Impressum, Conny Wendler