1,367 research outputs found

### Search for pentaquarks at Belle

We search for the strange pentaquark $\Theta^+$ using kaon interactions in
the material of the Belle detector. No signal is observed in the $p K_S$ final
state, while in the $p K^-$ final state we observe $\sim 1.6 \cdot 10^4$
$\Lambda(1520) \to p K^-$ decays. We set an upper limit on the ratio of
$\Theta^+$ to $\Lambda(1520)$ yields $\sigma(\Theta^+) / \sigma(\Lambda(1520))
< 2%$ at 90% CL assuming that the $\Theta^+$ is narrow. We also report on
searches for strange and charmed pentaquarks in B meson decays. These results
are obtained from a 155$fb^{-1}$ data sample collected with the Belle detector
near the $\Upsilon(4S)$ resonance, at the KEKB asymmetric energy $e^+ e^-$
collider.Comment: 10 pages, 6 figures. To appear in the Proceedings of the PENTA04
conference in Kobe, Japan. These results were also presented by Belle at the
ICHEP04 conference in Beijing, China and at the FPCP04 conference in Daegu,
Korea. Minor correctio

### Small size pentaquark width: calculation in QCD sum rules

The pentaquark width is calculated in QCD sum rules. The higher dimension
operators contribution is accounted. It is shown, that $\Gamma_{\Theta}$ should
be very small, less than $1Mev$.Comment: 10 peges, 7 figure

### Model-independent Study of Electric Dipole Transitions in Quarkonium

The paper contains a systematic, model-independent treatment of electric
dipole (E1) transitions in heavy quarkonium. Within the effective field theory
framework of potential non-relativistic QCD (pNRQCD), we derive the complete
set of relativistic corrections of relative order v^2 both for weakly and
strongly-coupled quarkonia. The result supports and complements former results
from potential model calculations.Comment: 42 pages, 9 figure

### A practical parametrization for line shapes of near-threshold states

Numerous quarkonium(like) states lying near $S$-wave thresholds are observed
experimentally. We propose a self-consistent approach to these near-threshold
states compatible with unitarity and analyticity. The underlying
coupled-channel system includes a bare pole and an arbitrary number of elastic
and inelastic channels treated fully nonperturbatively. The resulting
analytical parametrization is ideally suited for a combined analysis of the
data available in various channels that is exemplified by an excellent overall
description of the data for the charged $Z_b(10610)$ and $Z_b(10650)$ states.Comment: LaTeX2e, 5 pages, 1 figure, typos corrected, version published in
Phys. Rev. Let

### Interplay of quark and meson degrees of freedom in near-threshold states: A practical parametrisation for line shapes

We propose a practical parametrisation for the line shapes of near-threshold
states compatible with all requirements of unitarity and analyticity. The
coupled-channel system underlying the proposed parametrisation includes bare
poles and an arbitrary number of elastic and inelastic channels treated fully
nonperturbatively. The resulting formulae are general enough to be used for a
simultaneous analysis of the data in all available production and decay
channels of the (system of) state(s) under consideration for a quite wide class
of reactions. As an example, we fit the experimental data currently available
for several decay channels for the charged $Z_b^{(\prime)}$ states in the
spectrum of bottomonia and find a good overall description of the data. We find
the present data to be consistent with the $Z_b(10610)$ as a virtual state and
with the $Z_b(10650)$ as a resonance, both residing very close to the
$B\bar{B}^*$ and $B^*\bar{B}^*$ threshold, respectively.Comment: LaTeX2e, 19 pages, 10 figures, version published in Phys.Rev.

### New hadronic spectroscopy

In the past few years the field of hadron spectroscopy has seen renewed interest due to the pubblication, initially mostly from B-Factories, of evidences of states that do not match regular spectroscopy, but are rather candidates for bound states with additional quarks or gluons (four quarks for tetraquarks and molecules and two quarks and gluons for hybrids). A huge effort in understanding the nature of this new states and in building a new spectroscopy is ongoing. This paper reviews the experimental and theoretical state of the art on heavy quarkonium exotic spectroscopy, with particular attention on the steps towards a global picture

### Effects of isospin violation in the $e^+e^- \rightarrow B^{(*)}\bar B^{(*)}$ cross sections

Model estimates are obtained for the influence of Coulomb effects on the
ratio of the cross sections for the production of charged and neutral $B\bar B$
and $B^*\bar B^*$ pairs in $e^+e^-$ annihilation. It is shown that the
difference between the masses of charged and neutral mesons obtained under the
assumption that this ratio is constant on a scale of the order of the beam
energy spread can differ from the true one by \delta M \sim 0.03\,\mbox{MeV}
at the energy of $\Upsilon (5S)$ and by \delta M \sim 0.4\,\mbox{MeV} at the
energy of $\Upsilon (4S)$. Thus, the errors given in the PDG for the difference
between the masses of charged and neutral $B$ mesons, based on the results
obtained at the energy of $\Upsilon (4S)$, are strongly underestimated. Similar
measurements at the energy of $\Upsilon (5S)$ will have an order of magnitude
smaller systematic shift for the mass difference. This circumstance should be
taken into account when planning future experiments at the $B$ factory in KEK.Comment: 6 pages, 2 figure

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