413 research outputs found
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Efficient solution of the multichannel Lüscher determinant condition through eigenvalue decomposition
We present a method for efficiently finding solutions of L\"uscher's
quantisation condition, the equation which relates two-particle scattering
amplitudes to the discrete spectrum of states in a periodic spatial volume of
finite extent such as that present in lattice QCD. The approach proposed is
based on an eigenvalue decomposition in the space of coupled-channels and
partial-waves, which proves to have several desirable and simplifying features
that are of great benefit when considering problems beyond simple elastic
scattering of spinless particles. We illustrate the method with a toy model of
vector-vector scattering featuring a high density of solutions, and with an
application to explicit lattice QCD energy level data describing and
scattering in several coupled channels
Decays of an exotic 1-+ hybrid meson resonance in QCD
We present the first determination of the hadronic decays of the lightest
exotic resonance in lattice QCD. Working with SU(3) flavor
symmetry, where the up, down and strange quark masses approximately match the
physical strange-quark mass giving MeV, we compute
finite-volume spectra on six lattice volumes which constrain a scattering
system featuring eight coupled channels. Analytically continuing the scattering
amplitudes into the complex energy plane, we find a pole singularity
corresponding to a narrow resonance which shows relatively weak coupling to the
open pseudoscalar--pseudoscalar, vector--pseudoscalar and vector--vector decay
channels, but large couplings to at least one kinematically-closed
axial-vector--pseudoscalar channel. Attempting a simple extrapolation of the
couplings to physical light-quark mass suggests a broad resonance
decaying dominantly through the mode with much smaller decays into
, , and . A large total width is
potentially in agreement with the experimental candidate state,
observed in , , which we suggest may be heavily suppressed
decay channels
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B1 resonance in coupled πω, πφ scattering from lattice QCD
We present the first lattice QCD calculation of coupled and
scattering, incorporating coupled and -wave in
. Finite-volume spectra in three volumes are determined via a
variational analysis of matrices of two-point correlation functions, computed
using large bases of operators resembling single-meson, two-meson and
three-meson structures, with the light-quark mass corresponding to a pion mass
of MeV. Utilizing the relationship between the discrete
spectrum of finite-volume energies and infinite-volume scattering amplitudes,
we find a narrow axial-vector resonance (), the analogue of the
meson, with mass MeV and width
MeV. The resonance is found to couple dominantly to -wave , with
a much-suppressed coupling to -wave , and a negligible coupling
to consistent with the `OZI rule'. No resonant behavior is observed
in , indicating the absence of a putative low-mass analogue of
the claimed in . In order to minimally present the contents
of a unitary three-channel scattering matrix, we introduce an -channel
generalization of the traditional two-channel Stapp parameterization
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An a0 resonance in strongly coupled πη, K K scattering from lattice QCD a0 RESONANCE in STRONGLY COUPLED ⋯ DUDEK, EDWARDS, and WILSON
We present the first calculation of coupled-channel meson-meson scattering in
the isospin , -parity negative sector, with channels ,
and , in a first-principles approach to QCD. From
the discrete spectrum of eigenstates in three volumes extracted from lattice
QCD correlation functions we determine the energy dependence of the -matrix,
and find that the -wave features a prominent cusp-like structure in close to threshold coupled with a rapid turn
on of amplitudes leading to the final-state. This behavior is
traced to an -like resonance, strongly coupled to both and
, which is identified with a pole in the complex energy plane,
appearing on only a single unphysical Riemann sheet. Consideration of -wave
scattering suggests a narrow tensor resonance at higher energy.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevD.93.09450
Isoscalar ππ Scattering and the σ Meson Resonance from QCD
We present for the first time a determination of the energy dependence of the isoscalar ππ elastic scattering phase shift within a first-principles numerical lattice approach to QCD. Hadronic correlation functions are computed including all required quark propagation diagrams, and from these the discrete spectrum of states in the finite volume defined by the lattice boundary is extracted. From the volume dependence of the spectrum, we obtain the -wave phase shift up to the
threshold. Calculations are performed at two values of the , quark mass corresponding to MeV
, and the resulting amplitudes are described in terms of a σ meson which evolves from a bound state below the ππ threshold at the heavier quark mass to a broad resonance at the lighter quark mass.The research was supported in part under an Advanced Scientific Computing Research (ASCR), Advanced Leadership Computing Challenge (ALCC) grant, and used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. This research is also part of the Blue Waters sustained-petascale computing project, which is supported by the National Science Foundation (Grants No. OCI-0725070 and No. ACI-1238993) and the state of Illinois. Blue Waters is a joint effort of the University of Illinois at Urbana-Champaign and its National Center for Supercomputing Applications. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing computing resources. Gauge configurations were generated using resources awarded from the U.S. Department of Energy Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program at Oak Ridge National Lab and also resources awarded at NERSC. R. A. B., R. G. E., and J. J. D. acknowledge support from U.S. Department of Energy Contract No. DE-AC05-06OR23177, under which Jefferson Science Associates, LLC, manages and operates Jefferson Lab. J. J. D. acknowledges support from the U.S. Department of Energy Early Career Contract No. DE-SC0006765. D. J. W. acknowledges support from the Isaac Newton Trust/University of Cambridge Early Career Support Scheme [RG74916]
Glimpsing Colour in a World of Black and White
The past 40 years have taught us that nucleons are built of constituents that
carry colour charges with interactions governed by Quantum Chromodynamics
(QCD). How experiments (past, present and future) at Jefferson Lab probe
colourless nuclei to map out these internal colour degrees of freedom is
presented. When combined with theoretical calculations, these will paint a
picture of how the confinement of quarks and gluons, and the structure of the
QCD vacuum, determine the properties of all (light) strongly interacting
states.Comment: 8 pages, 9 figures. Invited talk at the Rutherford Centennial
Conference on Nuclear Physics, University of Manchester, 8-12 August 2011. To
appear in the Proceeding
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ππ →πγ∗ amplitude and the resonant ρ →πγ∗ 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.Science and Technology Facilities Council (Grant ID: ST/L000385/1)This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevD.93.11450
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