51 research outputs found
Lattice QCD investigation of a doubly-bottom tetraquark with quantum numbers
We use lattice QCD to investigate the spectrum of the
four-quark system with quantum numbers . We use five different
gauge-link ensembles with flavors of domain-wall fermions, including one
at the physical pion mass, and treat the heavy quark within the
framework of lattice nonrelativistic QCD. Our work improves upon previous
similar computations by considering in addition to local four-quark
interpolators also nonlocal two-meson interpolators and by performing a
L\"uscher analysis to extrapolate our results to infinite volume. We obtain a
binding energy of , corresponding to the
mass , which confirms the existence of a
tetraquark that is stable with respect to the strong and
electromagnetic interactions.Comment: 27 pages, 13 figure
Search for Zc+(3900) in the 1+β channel on the lattice
AbstractRecently three experiments reported a discovery of manifestly exotic Zc+(3900) in the decay to J/ΟΟ+, while J and P are experimentally unknown. We search for this state on the lattice by simulating the channel with JPC=1+β and I=1, and we do not find a candidate for Zc+(3900). Instead, we only find discrete scattering states DDΒ―β and J/ΟΟ, which inevitably have to be present in a dynamical QCD. The possible reasons for not finding Zc+ may be that its quantum numbers are not 1+β or that the employed interpolating fields are not diverse enough. Simulations with additional types of interpolators will be needed to reach a more definite conclusion
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
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
scattering in the Roper channel
We present results from our recent lattice QCD study of scattering in
the positive-parity nucleon channel, where the puzzling Roper resonance
resides in experiment. Using a variety of hadron operators, that
include -like, in -wave and in -wave, we
systematically extract the excited lattice spectrum in the nucleon channel up
to 1.65 GeV. Our lattice results indicate that N scattering in the elastic
approximation alone does not describe a low-lying Roper. Coupled channel
effects between and seem to be crucial to render a low-lying
Roper in experiment, reinforcing the notion that this state could be a
dynamically generated resonance. After giving a brief motivation for studying
the Roper channel and the relevant technical details to this study, we will
discuss the results and the conclusions based on our lattice investigation and
in comparison with other lattice calculations.Comment: 8 pages, 5 figures, presented at the 35th International Symposium on
Lattice Field Theory, 18-24 June 2017, Granada, Spai
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