In lattice QCD, colour confinement manifests in flux tubes. We compute in detail the quarkantiquark flux tube for pure gauge SU(3) dimension D = 3 + 1 for quark-antiquark distances R ranging from 0.4 fm to 1.4 fm. To increase the signal over noise ratio, we apply the improved multihit and extended smearing techniques. We detail the gauge invariant squared components of the colour electric and colour magnetic fields both in the mediator plane between the static quark and static antiquark and in the planes of the sources. We fit the field densities with appropriate ansatze and we observe the screening of the colour fields in all studied planes together with the quantum widening of the flux tube in the mediator plane. All components squared of the colour fields are non-vanishing and are consistent with a penetration length λ ∼ 0.22 to 0.24 fm and an effective screening mass µ ∼ 0.8 to 0.9 GeV. The quantum widening of the flux tube is well fitted with a logarithmic law in R.PACS11.15. Ha, 12.38.Gc,74.25.Uv,

We study tetraquark resonances with lattice QCD potentials computed for a staticbb pair in the presence of two lighter quarks ud, the Born-Oppenheimer approximation and the emergent wave method. As a proof of concept we focus on the system with isospin I = 0, but consider different relative angular momenta l of the heavy quarksbb. For l = 0 a bound state has already been predicted with quantum numbers I(J P ) = 0(1 + ). Exploring various angular momenta we now compute the phase shifts and search for S and T matrix poles in the second Riemann sheet. We predict a tetraquark resonance for l = 1, decaying into two B mesons, with quantum numbers I(J P ) = 0(1 − ), mass m = 10 576 +4 −4 MeV and decay width Γ = 112 +90 −103 MeV.

We discuss, how to study I = 0 quarkonium resonances decaying into pairs of heavy-light mesons using static potentials from lattice QCD. These static potentials can be obtained from a set of correlation functions containing both static and light quarks. As a proof of concept we focus on bottomonium with relative orbital angular momentum L = 0 of thebb pair corresponding to J P C = 0 −+ and J P C = 1 −− . We use static potentials from an existing lattice QCD string breaking study and compute phase shifts and T matrix poles for the lightest heavy-light meson-meson decay channel. We discuss our results in the context of corresponding experimental results, in particular for Υ(10860) and Υ(11020).

We argue that three-quark excited states naturally group into quartets, split into two parity doublets, and that the mass splittings between these parity partners decrease higher up in the baryon spectrum. This decreasing mass difference can be used to probe the running quark mass in the midinfrared power-law regime. A measurement of masses of high-partial-wave Á Ã resonances should be sufficient to unambiguously establish the approximate degeneracy. We test this concept with the first computation of excited high-j baryon masses in a chirally invariant quark model. DOI: 10.1103/PhysRevLett.103.092003 PACS numbers: 12.39.Ki, 11.30.Fs, 12.38.Aw Quantum chromodynamics (QCD) has been thoroughly tested in high-energy physics, through hadron jets, DrellYan processes, e À e þ annihilation, and deep inelastic scattering. Low-energy QCD manifests chiral symmetry breaking ( SB) that enhances quark masses in the infrared (IR), generating most of the visible mass in our Universe, and that removes the degeneracy from the ground states of light hadron spectra (so light hadrons do not come in parity doublets). The excited light-quark baryon spectrum, with masses above that of the Á resonance (1232 MeV), has not been accessible to any form of perturbation theory, effective or fundamental.Insensitivity to chiral symmetry breaking, recently stressed by Glozman and co-workers [1,2] and Swanson [3], and retrospectively present in chirally invariant quark models [4,5] has led many hadron physicists to accept that spontaneous SB, the salient feature of the low hadron spectrum, becomes less important for highly excited resonances. For these, chiral symmetry is asymptotically realized in Wigner mode, arranging hadrons in degenerate chiral multiplets [6]. We have realized that a formalization of this statement is that the ratio of the quark mass to its momentum h m k i provides a new perturbative parameter to study some aspects of the excited hadron spectrum when the typical momentum becomes higher than the running mass. Reasoning in reverse, we propose employing a cancellation in mass differences of very excited resonances, to access this small parameter, and hence the quark mass. We also show analytically and numerically that three-quark states naturally group into quartets with two states of each parity. Diagonalizing the chiral charge in terms of quarks, the quartet is split into two parity doublets, and all mass splittings tend to decrease when going higher in the spectrum. For simplicity and to minimize the impact of molecular meson-nucleon configurations [7], we study the maximum-spin excitations Á Ã of the Delta baryon.The u or d quark mass [8] (understood as taken from the full two-point function of the field theory) is theorized to vary from m ' 1-6 MeV at a high, perturbative momentum k scale (typically )Ã QCD $ 210 MeV) to a constituent mass of circa 300 MeV at vanishing momentum k ' Ã QCD . This IR enhancement of 2 orders of magnitude is shown in Fig. 1. The simplest constituent quark model considers a constant mass [9]...