Jozef J. Dudek

We study near-threshold D D ¯ scattering in S - and D -wave to determine whether or not resonances or bound states are present. Working in the approximation where charm annihilation is forbidden, with two degenerate light-quark flavors and a heavier strange quark, isospin is a good quantum number, and the only other channel that is kinematically open is η c η . Using lattice QCD we compute, as a function of varying light-quark mass, the S -matrix for coupled-channel η c η − D D ¯ scattering and find only weakly interacting meson pairs. In contrast to several other studies, we find no evidence for any bound-state or resonance singularity in the energy region between the deeply bound χ c 0 ( 1 P ) state and the D s D ¯ s threshold.

Invited talk in Mini-Symposium: New Results in Hadron Spectroscopy

We present a first principles calculation within quantum chromodynamics (QCD) of the radiative decays of the J / ψ into the light pseudoscalar mesons η and η ′ . Within a lattice computation we obtain the transition form factors as a function of photon virtuality from the timelike region, accessible experimentally via the “Dalitz” decay J / ψ → e + e − η ( ′ ) , through to the real photon point corresponding to J / ψ → γ η ( ′ ) . This is the first calculation in lattice QCD with two (heavier than physical) degenerate flavors of light quark and a heavier strange quark, in which the η ′ appears as the state with pseudoscalar isoscalar quantum numbers. We access it reliably by using variationally , the use of which also improves the purity of the J / ψ and η signals, reducing systematic uncertainties. High quality results at a large number of kinematic points are obtained in a typically noisy disconnected process by using a novel correlator averaging procedure. Our results show the expected enhanced production of the η ′ over the η in this process, and suggest that the demonstrated lattice technology is suitable for future calculations considering processes in which light meson are produced.

We report on the computation of amplitudes describing the radiative decay processes J / ψ → γ η and J / ψ → γ η ′ from first principles via lattice quantum chromodynamics (QCD). Using lattices with two heavier than physical degenerate flavors of light quark where m π ∼ 391 MeV , and a strange quark tuned to approximately the physical value, we compute three-point correlation functions using optimized meson operators with a range of momenta. The use of optimized operators allows access to the η ′ , even though it appears as an excited state, lying above the ground-state η in the isoscalar pseudoscalar channel. Statistically precise signals are obtained in this disconnected process by averaging over large numbers of kinematically equivalent correlators. We determine transition form factors as a function of photon virtuality across the timelike region, which describe also the Dalitz processes J / ψ → e + e − η ( ′ ) . Significantly lower magnitudes of transition form factor for both the η and η ′ are found than those extracted from experimental data, and possible explanations for this observation are presented.

We present a calculation of the vector-isovector timelike form factors of the pion and the kaon using lattice quantum chromodynamics. We calculate two-point correlation functions with m π ∼ 280 MeV , extracting both the finite-volume spectrum and matrix elements for these states created from the vacuum by a vector current. After determining the coupled-channel π π , K K ¯ scattering amplitudes, we perform the necessary correction for the significant finite-volume effects present in the current matrix elements, leading to the timelike form factors. We find these to be dominated by the presence of the ρ resonance, and we extract its decay constant by an analytic continuation of the amplitudes to the resonance pole. In addition, the spacelike pion form factor is determined on the same lattice configurations, and a dispersive parametrization is used to simultaneously describe the spacelike and elastic timelike regions. Published by the American Physical Society 2024