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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Shallow Bound States and Hints for Broad Resonances with Quark Content b ¯ c ¯ u d in B − D ¯ and B * − D ¯ Scattering from Lattice QCD

We present the first determination of the energy dependence of the B − D ¯ and B * − D ¯ isospin-0, S -wave scattering amplitudes both below and above the thresholds using lattice QCD, which allows us to investigate rigorously whether mixed bottom-charm b ¯ c ¯ u d tetraquarks exist as bound states or resonances. The scattering phase shifts are obtained using Lüscher’s method from the energy spectra in two different volumes. To ensure that no relevant energy level is missed, we use large, symmetric 7 × 7 and 8 × 8 correlation matrices that include, at both source and sink, B ( * ) − D ¯ scattering operators with the lowest three or four possible back-to-back momenta in addition to local b ¯ c ¯ u d operators. We fit the energy dependence of the extracted scattering phase shifts using effective-range expansions. We observe sharp peaks in the B ( * ) − D ¯ scattering rates close to the thresholds, which are associated with shallow bound states, either genuine or virtual, a few MeV or less below the B ( * ) − D ¯ thresholds. In addition, we find hints for resonances with masses of order 100 MeV above the thresholds and decay widths of order 200 MeV. Published by the American Physical Society 2024

Alexandrou, Constantia↗
DOE OSTI2025

Generalized parton distributions from lattice QCD with asymmetric momentum transfer: Unpolarized quarks at nonzero skewness

We extend the formalism of asymmetric frames of reference for generalized parton distributions (GPDs) to the case of nonzero skewness, i.e., including longitudinal momentum transfer. The framework, based on Lorentz-invariant amplitudes and previously developed and numerically implemented for unpolarized, helicity and transversity GPDs at zero skewness, gives efficient access to a broad range of kinematics, making full mapping of GPDs from the lattice realistic. The general-skewness formalism is tested using lattice data with both transverse and longitudinal or only longitudinal momentum transfer, the latter being a special case with a reduced number of independent amplitudes. We extract the amplitudes in coordinate space and express the GPDs 𝐻 and 𝐸 in terms of these amplitudes. This is followed by reconstruction of quasidistributions and their matching to the light cone. We further identify and discuss the principal challenges for nonzero skewness GPDs.

Lattice QCD↗