460 research outputs found
Dynamically-coupled partial-waves in isospin-2 scattering from lattice QCD
We present the first determination of scattering, incorporating
dynamically-coupled partial-waves, using lattice QCD, a first-principles
numerical approach to QCD. Considering the case of isospin-2 , we
calculate partial-wave amplitudes with and determine the degree of
dynamical mixing between the coupled and -wave channels with .
The analysis makes use of the relationship between scattering amplitudes and
the discrete spectrum of states in the finite volume lattice. Constraints on
the scattering amplitudes are provided by over one hundred energy levels
computed on two lattice volumes at various overall momenta and in several
irreducible representations of the relevant symmetry groups. The spectra follow
from variational analyses of matrices of correlations functions computed with
large bases of meson-meson operators. Calculations are performed with
degenerate light and strange quarks tuned to the physical strange quark mass so
that MeV, ensuring that the is stable against strong
decay. This work demonstrates the successful application of techniques, opening
the door to calculations of scattering processes that incorporate the effects
of dynamically-coupled partial-waves, including those involving resonances or
bound states.Comment: Minor changes to match the published versio
The amplitude and the resonant transition from lattice QCD
We present a determination of the -wave
transition amplitude from lattice quantum chromodynamics. Matrix elements of
the vector current in a finite-volume are extracted from three-point
correlation functions, and from these we determine the infinite-volume
amplitude using a generalization of the Lellouch-L\"uscher formalism. We
determine the amplitude for a range of discrete values of the energy
and virtuality of the photon, and observe the expected dynamical enhancement
due to the resonance. Describing the energy dependence of the amplitude,
we are able to analytically continue into the complex energy plane and from the
residue at the pole extract the transition
form factor. This calculation, at MeV, is the first to
determine the form factor of an unstable hadron within a first principles
approach to QCD.Comment: 20 pages, 16 figures, 3 table
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Excited light meson spectroscopy from lattice QCD
I report on recent progress in calculating excited meson spectra using lattice QCD, emphasizing results and phenomenology. With novel techniques we can now extract extensive spectra of excited mesons with high statistical precision, including spin-four states and those with exotic quantum numbers. As well as isovector meson spectra, I will present new calculations of the spectrum of excited light isoscalar mesons, something that has up to now been a challenge for lattice QCD. I show determinations of the flavor content of these mesons, including the eta-eta' mixing angle, providing a window on annihilation dynamics in QCD. I will also discuss recent work on using lattice QCD to map out the energy-dependent phase shift in pi-pi scattering and future applications of the methodology to the study of resonances and decays
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Energy-Dependent π^{+}π^{+}π^{+} Scattering Amplitude from QCD.
Focusing on three-pion states with maximal isospin (), we
present the first non-perturbative determination of an energy-dependent
three-hadron scattering amplitude from first-principles QCD. The calculation
combines finite-volume three-hadron energies, extracted using numerical lattice
QCD, with a relativistic finite-volume formalism, required to interpret the
results. To fully implement the latter, we also solve integral equations that
relate an intermediate three-body K matrix to the physical three-hadron
scattering amplitude. The resulting amplitude shows rich analytic structures
and a complicated dependence on the two-pion invariant masses, represented here
via Dalitz-like plots of the scattering rate
Energy-Dependent π^{+}π^{+}π^{+} Scattering Amplitude from QCD.
Focusing on three-pion states with maximal isospin (π^{+}π^{+}π^{+}), we present the first nonperturbative determination of an energy-dependent three-hadron scattering amplitude from first-principles QCD. The calculation combines finite-volume three-hadron energies, extracted using numerical lattice QCD, with a relativistic finite-volume formalism, required to interpret the results. To fully implement the latter, we also solve integral equations that relate an intermediate three-body K matrix to the physical three-hadron scattering amplitude. The resulting amplitude shows rich analytic structure and a complicated dependence on the two-pion invariant masses, represented here via Dalitz-like plots of the scattering rate
Quark-Mass Dependence of Elastic πK Scattering from QCD.
We present a determination of the isospin-1/2 elastic πK scattering amplitudes in S and P partial waves using lattice quantum chromodynamics. The amplitudes, constrained for a large number of real-valued energy points, are obtained as a function of light-quark mass, corresponding to four pion masses between 200 and 400 MeV, at a single lattice spacing. Below the first inelastic threshold, the P-wave scattering amplitude is dominated by a single pole singularity that evolves from being a stable bound state at the highest quark mass into a narrow resonance that broadens as the pion and kaon masses are reduced. As in experiment, the S-wave amplitude does not exhibit an obviously resonant behavior, but instead shows a slow rise from threshold, which is not inconsistent with the presence of a κ/K_{0}^{⋆}(700)-like resonance at the considered quark masses. As has been found in analyses of experimental scattering data, simple analytic continuations into the complex energy plane of precisely determined lattice QCD amplitudes on the real energy axis are not sufficient to model-independently determine the existence and properties of this state. The spectra and amplitudes we present will serve as an input for increasingly elaborate amplitude analysis techniques that implement more of the analytic structure expected at complex energies
Tetraquark operators in lattice QCD and exotic flavour states in the charm sector
We present a general class of operators resembling compact tetraquarks which
have a range of colour-flavour-spin structures, transform irreducibly under the
symmetries of the lattice and respect other relevant symmetries. These
constructions are demonstrated in lattice QCD calculations with light quarks
corresponding to 391 MeV. Using the distillation framework,
correlation functions involving large bases of meson-meson and tetraquark
operators are computed in the isospin-1 hidden-charm and doubly-charmed
sectors, and finite-volume spectra are extracted with the variational method.
We find the spectra are insensitive to the addition of tetraquark operators to
the bases of meson-meson operators. For the first time, through using diverse
bases of meson-meson operators, the multiple energy levels associated with
meson-meson levels which would be degenerate in the non-interacting limit are
extracted reliably. The number of energy levels in each spectrum is found to be
equal to the number of expected non-interacting meson-meson levels in the
energy region considered and the majority of energies lie close to the
non-interacting levels. Therefore, there is no strong indication for any bound
state or narrow resonance in the channels we study
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