338 research outputs found
Can X(3915) be the tensor partner of the X(3872)?
It has been proposed recently (Phys. Rev. Lett. 115 (2015), 022001) that the
charmoniumlike state named X(3915) and suggested to be a scalar, is
just the helicity-0 realisation of the tensor state .
This scenario would call for a helicity-0 dominance, which were at odds with
the properties of a conventional tensor charmonium, but might be compatible
with some exotic structure of the . In this paper, we
investigate, if such a scenario is compatible with the assumption that the
is a molecular state - a spin partner of the
treated as a shallow bound state. We demonstrate that for a tensor
molecule the helicity-0 component vanishes for vanishing binding energy and
accordingly for a shallow bound state a helicity-2 dominance would be natural.
However, for the , residing about 100 MeV below the threshold, there is no a priori reason for a helicity-2 dominance and thus
the proposal formulated in the above mentioned reference might indeed point at
a molecular structure of the tensor state. Nevertheless, we find that the
experimental data currently available favour a dominant contribution of the
helicity-2 amplitude also in this scenario, if spin symmetry arguments are
employed to relate properties of the molecular state to those of the X(3872).
We also discuss what research is necessary to further constrain the analysis.Comment: LaTeX2e, 23 pages, 2 figures, version to appear in JHE
Charge symmetry breaking as a probe for the real part of eta--nucleus scattering lengths
We demonstrate that one can use the occurrence of charge symmetry breaking as
a tool to explore the eta--nucleus interaction near the eta threshold. Based on
indications that the cross section ratio of pi+ and pi0 production on nuclei
deviates from the isotopic value in the vicinity of the eta production
threshold, due to, e.g., pi0-eta mixing, we argue that a systematic study of
this ratio as a function of the energy would allow to pin down the sign of the
real part of the eta-nucleus scattering length. This sign plays an important
role in the context of the possible existence of eta-nucleus bound states.Comment: 4 pages, 1 figur
Spin partners of the and revisited
We study the implications of the heavy-quark spin symmetry for the possible
spin partners of the exotic states and in the
spectrum of bottomonium. We formulate and solve numerically the coupled-channel
equations for the states that allow for a dynamical generation of these
states as hadronic molecules. The force includes short-range contact terms and
the one-pion exchange potential, both treated fully nonperturbatively. The
strength of the potential at leading order is fixed completely by the pole
positions of the states such that the mass and the most prominent
contributions to the width of the isovector heavy-quark spin partner states
with the quantum numbers () come out as predictions.
Since the accuracy of the present experimental data does not allow one to fix
the pole positions of the 's reliably enough, we also study the pole
trajectories of their spin partner states as functions of the binding
energies. It is shown that, once the heavy-quark spin symmetry is broken by
means of the physical and masses, especially the pion tensor force
has a significant impact on the location of the partner states clearly
demonstrating the need of a coupled-channel treatment of pion dynamics to
understand the spin multiplet pattern of hadronic molecules.Comment: 21 pages, 5 figures, 1 tabl
Dispersive and absorptive corrections to the pion-deuteron scattering length
We present a parameter--free calculation of the dispersive and absorptive
contributions to the pion--deuteron scattering length based on chiral
perturbation theory. We show that once all diagrams contributing to leading
order to this process are included, their net effect provides a small
correction to the real part of the pion--deuteron scattering length.
At the same time the sizable imaginary part of the pion--deuteron scattering
length is reproduced accurately.Comment: Numerical error corrected. Results for dispersive corrections changed
- conclusions unchanged. Version as accepted by Phys. Lett.
Spin partners from the line shapes of the and
In a recent paper Phys.Rev. D98, 074023 (2018), the most up-to-date
experimental data for all measured production and decay channels of the
bottomonium-like states and were analysed in a
field-theoretical coupled-channel approach which respects analyticity and
unitarity and incorporates both the pion exchange as well as a short-ranged
potential nonperturbatively. All parameters of the interaction were fixed
directly from data, and pole positions for both states were determined.
In this work we employ the same approach to predict in a parameter-free way the
pole positions and the line shapes in the elastic and inelastic channels of the
(still to be discovered) spin partners of the states. They are
conventionally referred to as 's with the quantum numbers
(). It is demonstrated that the results of our most
advanced pionful fit, which gives the best for the data
in the channels, are consistent with all states being
above-threshold resonances which manifest themselves as well pronounced hump
structures in the line shapes. On the contrary, in the pionless approach, all
's are virtual states which can be seen as enhanced threshold cusps in
the inelastic line shapes. Since the two above scenarios provide different
imprints on the observables, the role of the one-pion exchange in the
systems can be inferred from the once available
experimental data directly.Comment: 24 pages, 12 figure
Precision calculation of the pi^- deuteron scattering length and its impact on threshold pi-N scattering
We present a calculation of the pi^- d scattering length with an accuracy of
a few percent using chiral perturbation theory. For the first time
isospin-violating corrections are included consistently. Using data on pionic
deuterium and pionic hydrogen atoms, we extract the isoscalar and isovector
pion-nucleon scattering lengths and obtain a^+=(7.6 +/- 3.1) x 10^{-3} mpi^{-1}
and a^-=(86.1 +/- 0.9) x 10^{-3} mpi^{-1}. Via the Goldberger-Miyazawa-Oehme
sum rule, this leads to a charged-pion-nucleon coupling constant g_c^2/4 pi =
13.69 +/- 0.20.Comment: 6 pages, 2 figures. Discussion of several points expanded, references
added in this version, which will appear in Physics Letters
Heavy-quark spin symmetry partners of the revisited
We revisit the consequences of the heavy-quark spin symmetry for the possible
spin partners of the . We confirm that, if the were a
molecular state with the quantum numbers , then in
the strict heavy-quark limit there should exist three more hadronic molecules
degenerate with the , with the quantum numbers , , and
in line with previous results reported in the literature. We
demonstrate that this result is robust with respect to the inclusion of the
one-pion exchange interaction between the mesons. However, this is true
only if all relevant partial waves as well as particle channels which are
coupled via the pion-exchange potential are taken into account. Otherwise, the
heavy-quark symmetry is destroyed even in the heavy-quark limit. Finally, we
solve the coupled-channel problem in the channel with nonperturbative
pions beyond the heavy-quark limit and, contrary to the findings of previous
calculations with perturbative pions, find for the spin-2 partner of the
a significant shift of the mass as well as a width of the order of 50
MeV.Comment: 17 pages, 3 figures, 1 table, version published in Phys.Lett.
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