1,459 research outputs found
Axial resonances a1(1260), b1(1235) and their decays from the lattice
The light axial-vector resonances and are explored in
Nf=2 lattice QCD by simulating the corresponding scattering channels
and . Interpolating fields and or
are used to extract the s-wave phase shifts for the first time. The and
are treated as stable and we argue that this is justified in the
considered energy range and for our parameters MeV and
fm. We neglect other channels that would be open when using
physical masses in continuum. Assuming a resonance interpretation a
Breit-Wigner fit to the phase shift gives the resonance mass
GeV compared to
GeV. The width is parametrized in terms of the
coupling and we obtain GeV compared to
GeV derived from
MeV. In the channel, we find energy levels related to
and , and the lowest level is found at
but is within uncertainty also compatible with an attractive interaction.
Assuming the coupling extracted from the experimental width
we estimate .Comment: 15 pages, 4 figures, updated to match published versio
Vector and scalar charmonium resonances with lattice QCD
We perform an exploratory lattice QCD simulation of scattering,
aimed at determining the masses as well as the decay widths of charmonium
resonances above open charm threshold. Neglecting coupling to other channels,
the resulting phase shift for scattering in p-wave yields the
well-known vector resonance . For MeV, the extracted
resonance mass and the decay width agree with experiment within large
statistical uncertainty. The scalar charmonium resonances present a puzzle,
since only the ground state is well understood, while there is
no commonly accepted candidate for its first excitation. We simulate
scattering in s-wave in order to shed light on this puzzle. The resulting phase
shift supports the existence of a yet-unobserved narrow resonance with a mass
slightly below 4 GeV. A scenario with this narrow resonance and a pole at
agrees with the energy-dependence of our phase shift. Further
lattice QCD simulations and experimental efforts are needed to resolve the
puzzle of the excited scalar charmonia.Comment: 24 pages, 8 figures, updated to match published versio
Excited light and strange hadrons from the lattice with two Chirally Improved quarks
Results for excited light and strange hadrons from the lattice with two
flavors of Chirally Improved sea quarks are presented. We perform simulations
at several values of the pion mass ranging from 250 to 600 MeV and extrapolate
to the physical pion mass. The variational method is applied to extract excited
energy levels but also to discuss the content of the states. Among others, we
explore the flavor singlet/octet content of Lambda states. In general, our
results agree well with experiment, in particular we confirm the Lambda(1405)
and its dominant flavor singlet structure.Comment: Contribution to the XV International Conference on Hadron
Spectroscopy "Hadron 2013", 4-8 November 2013, Nara, Japa
Predicting positive parity mesons from lattice QCD
We determine the spectrum of 1P states using lattice QCD. For the
and mesons, the results are in good agreement
with the experimental values. Two further mesons are expected in the quantum
channels and near the and thresholds. A
combination of quark-antiquark and meson-Kaon interpolating fields
are used to determine the mass of two QCD bound states below the
threshold, with the assumption that mixing with and
isospin-violating decays to are negligible. We predict a
bound state with mass GeV. With
further assumptions motivated theoretically by the heavy quark limit, a bound
state with GeV is predicted in the
channel. The results from our first principles calculation are compared to
previous model-based estimates.Comment: 5 pages, 2 figures; Final versio
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