String breaking by light and strange quarks in QCD

Abstract

The energy spectrum of a system containing a static quark anti-quark pair is computed for a wide range of source separations using lattice QCD with N f = 2 + 1 dynamical flavours. By employing a variational method with a basis including operators resembling both the gluon string and systems of two separated static mesons, the first three energy levels are determined up to and beyond the distance where it is energetically favourable for the vacuum to screen the static sources through light-or strange-quark pair creation, enabling both these screening phenomena to be observed. The separation dependence of the energy spectrum is reliably parameterised over this saturation region with a simple model which can be used as input for subsequent investigations of quarkonia above threshold and heavy-light and heavy-strange coupled-channel meson scattering.

String breaking with 2+1 dynamical fermions using the stochastic LapH method

“…The full mixing analysis with an enhanced spatial resolution as well as higher statistics is underway [20], utilizing a set of off-axis distances between 17a and 21.8a to ensure that we are able to map out the first as well as the second expected avoided level crossing.…”

Diabatic description of charmoniumlike mesons

“…with σ, χ and β standing for the string tension, the color Coulomb strength, and a constant fixing the origin of the potential respectively. On the other hand, unquenched (with gluon and lightquark fields) lattice QCD calculations [17,18] have shown that due to string breaking the association of the light field ground state with a QQ configuration holds only for small values of the relative QQ distance r ≡ jrj. When increasing r the QQ configuration mixes significantly with mesonmeson configurations.…”

“…In Fig. 1 we have represented graphically this situation for QQ and one meson-meson threshold (the representation for two meson-meson thresholds can be seen in [17,18]).…”

“…An intermediate step in this direction was taken in [16] by identifying the unquenched lattice energy for static Q and Q sources, when the QQ configuration mixes with one or two open flavor meson-meson ones [17,18], with a QQ potential. This unquenched approximation allows for some physical understanding of threshold effects beyond hadron loops.…”

Bottomonium resonances with I=0 from lattice QCD correlation functions with static and light quarks

“…The boundary conditions of the solutions (u(r), χ(r)) of the Schrödinger equation (50) can be read of from Eqs. (40), (41), (46) and (47) and are u(r) ∝ r for r → 0 (64) u(r) = 0 for r → ∞ (65) χ(r) ∝ r 2 for r → 0 (66)…”