90 research outputs found
Spectroscopy of the All-Charm Tetraquark
We use a non-relativistic model to study the mass spectroscopy of a
tetraquark composed by quarks in the
diquark-antidiquark picture. By numerically solving the Schr\"{o}dinger
equation with a Cornell-inspired potential, we separate the four-body problem
into three two-body problems. Spin-dependent terms (spin-spin, spin-orbit and
tensor) are used to describe the splitting structure of the spectrum
and are also extended to the interaction between diquarks. Recent experimental
data on charmonium states are used to fix the parameters of the model and a
satisfactory description of the spectrum is obtained. We find that the
spin-dependent interaction is sizable in the diquark-antidiquark system,
despite of the heavy diquark mass, and that the diquark has a finite size if
treated in analogy to the systems. We find that the lowest -wave
tetraquarks might be below their thresholds of spontaneous
dissociation into low-lying charmonium pairs, while orbital and radial
excitations would be mostly above the corresponding charmonium pair threshold.
These states could be investigated in the forthcoming experiments at LHCb and
Belle II.Comment: Presented at the XVII International Conference on Hadron Spectroscopy
and Structure - Hadron2017, 25-29 September, 2017, University of Salamanca,
Salamanca, Spai
Considerations on the Schmid theorem for triangle singularities
We investigate the Schmid theorem, which states that if one has a tree level
mechanism with a particle decaying to two particles and one of them decaying
posteriorly to two other particles, the possible triangle singularity developed
by the mechanism of elastic rescattering of two of the three decay particles
does not change the cross section provided by the tree level. We investigate
the process in terms of the width of the unstable particle produced in the
first decay and determine the limits of validity and violation of the theorem.
One of the conclusions is that the theorem holds in the strict limit of zero
width of that resonance, in which case the strength of the triangle diagram
becomes negligible compared to the tree level. Another conclusion, on the
practical side, is that for realistic values of the width, the triangle
singularity can provide a strength comparable or even bigger than the tree
level, which indicates that invoking the Schmid theorem to neglect the triangle
diagram stemming from elastic rescattering of the tree level should not be
done. Even then, we observe that the realistic case keeps some memory of the
Schmid theorem, which is visible in a peculiar interference pattern with the
tree level.Comment: 13 pages, 13 figure
Molecular states
Motivated by the recent finding of five states by the LHCb
collaboration, and the successful reproduction of three of them in a recent
approach searching for molecular states of meson-baryon with the quantum
numbers of , we extend these ideas and make predictions for the
interaction of meson-baryon in the beauty sector, searching for poles in the
scattering matrix that correspond to physical states. We find several
states: two states with masses 6405~MeV and 6465~MeV for ; two more states with masses 6427~MeV and 6665~MeV for
; and three states between 6500 and 6820~MeV, degenerate with
, stemming from the interaction of
vector-baryon in the beauty sector.Comment: 11 pages, 9 tables; v2: discussion added, version accepted for
publication in NP
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