14,646 research outputs found
Amplitude analysis and the nature of the Zc(3900)
The microscopic nature of the XYZ states remains an unsettled topic. We show
how a thorough amplitude analysis of the data can help constraining models of
these states. Specifically, we consider the case of the Zc(3900) peak and
discuss possible scenarios of a QCD state, virtual state, or a kinematical
enhancement. We conclude that current data are not precise enough to
distinguish between these hypotheses, however, the method we propose, when
applied to the forthcoming high-statistics measurements should shed light on
the nature of these exotic enhancements.Comment: 14 pages, 10 figures, 3 tables. Version accepted for publication on
Phys.Lett.
Exclusive tensor meson photoproduction
We study tensor meson photoproduction outside of the resonance region, at
beam energies of few GeVs. We build a model based on Regge theory that includes
the leading vector and axial exchanges. We consider two determinations of the
unknown helicity couplings, and fit to the recent a2 photoproduction data from
CLAS. Both choices give a similar description of the a2 cross section, but
result in different predictions for the parity asymmetries and the f2
photoproduction cross section. We conclude that new measurements of f2
photoproduction in the forward region are needed to pin down the correct
production mechanism. We also extend our predictions to the 8.5 GeV beam
energy, where current experiments are running.Comment: 13 pages, 7 figures, 3 tables. Version accepted for publication on
Phys.Rev.
Determination of the pole position of the lightest hybrid meson candidate
Mapping states with explicit gluonic degrees of freedom in the light sector
is a challenge, and has led to controversies in the past. In particular, the
experiments have reported two different hybrid candidates with spin-exotic
signature, pi1(1400) and pi1(1600), which couple separately to eta pi and eta'
pi. This picture is not compatible with recent Lattice QCD estimates for hybrid
states, nor with most phenomenological models. We consider the recent partial
wave analysis of the eta(') pi system by the COMPASS collaboration. We fit the
extracted intensities and phases with a coupled-channel amplitude that enforces
the unitarity and analyticity of the S-matrix. We provide a robust extraction
of a single exotic pi1 resonant pole, with mass and width 1564 +- 24 +- 86 MeV
and 492 +- 54 +- 102 MeV, which couples to both eta(') pi channels. We find no
evidence for a second exotic state. We also provide the resonance parameters of
the a2(1320) and a2'(1700).Comment: 6 pages + 3 pages of supplemental material. Version to appear on
Phys.Rev.Let
On orientational relief of inter-molecular potential and the structure of domain walls in fullerite C60
A simple planar model for an orientational ordering of threefold molecules on
a triangular lattice modelling a close-packed (111) plane of fullerite is
considered. The system has 3-sublattice ordered ground state which includes 3
different molecular orientations. There exist 6 kinds of orientational domains,
which are related with a permutation or a mirror symmetry. Interdomain walls
are found to be rather narrow.
The model molecules have two-well orientational potential profiles, which are
slightly effected by a presence of a straight domain wall. The reason is a
stronger correlation between neighbour molecules in triangular lattice versus
previously considered square lattice
A considerable reduction (up to one order) of orientational interwell
potential barrier is found in the core regions of essentially two-dimentional
potential defects, such as a three-domain boundary or a kink in the domain
wall. For ultimately uncorrelated nearest neighbours the height of the
interwell barrier can be reduced even by a factor of 100.Comment: 11 pages, 13 figures, LaTeX, to appear in Low Temperature Physic
- …