3,295 research outputs found
Two Photon Decays of Charmonia from Lattice QCD
We make the first calculation in lattice QCD of two-photon decays of mesons.
Working in the charmonium sector, using the LSZ reduction to relate a photon to
a sum of hadronic vector eigenstates, we compute form-factors in both the
space-like and time-like domains for the transitions and . At the on-shell point we find
approximate agreement with experimental world-average values.Comment: Replaced with version to be published in PRL. Expanded discussion of
possible systematic error
Charmonium excited state spectrum in lattice QCD
Working with a large basis of covariant derivative-based meson interpolating
fields we demonstrate the feasibility of reliably extracting multiple excited
states using a variational method. The study is performed on quenched
anisotropic lattices with clover quarks at the charm mass. We demonstrate how a
knowledge of the continuum limit of a lattice interpolating field can give
additional spin-assignment information, even at a single lattice spacing, via
the overlap factors of interpolating field and state. Excited state masses are
systematically high with respect to quark potential model predictions and,
where they exist, experimental states. We conclude that this is most likely a
result of the quenched approximation.Comment: Fixed typos: normalisation of chi-squared, some operator projections
in appendix, missing lattice irrep tabl
Isoscalar scattering and the mesons from QCD
We present the first lattice QCD study of coupled isoscalar
- and -wave scattering extracted from
discrete finite-volume spectra computed on lattices which have a value of the
quark mass corresponding to MeV. In the sector we find
analogues of the experimental and states, where the
appears as a stable bound-state below threshold, and, similar
to what is seen in experiment, the manifests itself as a dip in the
cross section in the vicinity of the threshold. For
we find two states resembling the and ,
observed as narrow peaks, with the lighter state dominantly decaying to
and the heavier state to . The presence of all these
states is determined rigorously by finding the pole singularity content of
scattering amplitudes, and their couplings to decay channels are established
using the residues of the poles
Excited state baryon spectroscopy from lattice QCD
We present a calculation of the Nucleon and Delta excited state spectrum on
dynamical anisotropic clover lattices. A method for operator construction is
introduced that allows for the reliable identification of the continuum spins
of baryon states, overcoming the reduced symmetry of the cubic lattice. Using
this method, we are able to determine a spectrum of single-particle states for
spins up to and including J = 7/2, of both parities, the first time this has
been achieved in a lattice calculation. We find a spectrum of states
identifiable as admixtures of SU(6) x O(3) representations and a counting of
levels that is consistent with the non-relativistic constituent quark
model. This dense spectrum is incompatible with quark-diquark model solutions
to the "missing resonance problem" and shows no signs of parity doubling of
states.Comment: 29 pages, 18 figure
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