13,076 research outputs found

### Radiative decay of the X(3872) as a mixed molecule-charmonium state in QCD Sum Rules

We use QCD sum rules to calculate the width of the radiative decay of the
meson X(3872), assumed to be a mixture between charmonium and exotic molecular
$[c\bar{q}][q\bar{c}]$ states with $J^{PC}=1^{++}$. We find that in a small
range for the values of the mixing angle, $5^0\leq\theta\leq13^0$, we get the
branching ratio $\Gamma(X\to J/\psi\gamma)/\Gamma(X\to
J/\psi\pi^+\pi^-)=0.19\pm0.13$, which is in agreement, with the experimental
value. This result is compatible with the analysis of the mass and decay width
of the mode $J/\psi(n\pi)$ performed in the same approach.Comment: 7 pages, 9 figures; revised version accepted for publication in Phys.
Rev.

### Production of the Y(4260) State in B Meson Decay

We calculate the branching ratio for the production of the meson $Y(4260)$ in
the decay $B^- \to Y(4260)K^-$. We use QCD sum rules approach and we consider
the $Y(4260)$ to be a mixture between charmonium and exotic tetraquark,
$[\bar{c}\bar{q}][qc]$, states with $J^{PC}=1^{--}$. Using the value of the
mixing angle determined previously as: $\theta=(53.0\pm0.5)^\circ$, we get the
branching ratio $\mathcal{B}(B\to Y(4260)K)=(1.34\pm0.47)\times10^{-6}$, which
allows us to estimate an interval on the branching fraction $3.0 \times 10^{-8}
< {\mathcal B}_{_Y} < 1.8 \times 10^{-6}$ in agreement with the experimental
upper limit reported by Babar Collaboration.Comment: 5 pages, 2 figures, 1 table. arXiv admin note: text overlap with
arXiv:1105.134

### Y(4260) as a mixed charmonium-tetraquark state

Using the QCD sum rule approach we study the Y(4260) state assuming that it
can be described by a mixed charmonium-tetraquark current with $J^{PC}=1^{--}$
quantum numbers. For the mixing angle around $\theta \approx (53.0\pm
0.5)^{0}$, we obtain a value for the mass which is in good agreement with the
experimental mass of the Y(4260). However, for the decay width we find the
value \Ga_Y \approx (1.0\pm 0.2) MeV which is not compatible with the
experimental value \Ga \approx (88\pm 23) MeV. Therefore, we conclude that,
although we can explain the mass of the Y(4260), this state cannot be described
as a mixed charmonium-tetraquark state since, with this assumption, we can not
explain its decay width.Comment: 9 pages, 6 figure

### The small $x$ behavior of the gluon structure function from total cross sections

Within a QCD-based eikonal model with a dynamical infrared gluon mass scale
we discuss how the small $x$ behavior of the gluon distribution function at
moderate $Q^{2}$ is directly related to the rise of total hadronic cross
sections. In this model the rise of total cross sections is driven by
gluon-gluon semihard scattering processes, where the behavior of the small $x$
gluon distribution function exhibits the power law $xg(x,Q^2)=
h(Q^2)x^{-\epsilon}$. Assuming that the $Q^{2}$ scale is proportional to the
dynamical gluon mass one, we show that the values of $h(Q^2)$ obtained in this
model are compatible with an earlier result based on a specific nonperturbative
Pomeron model. We discuss the implications of this picture for the behavior of
input valence-like gluon distributions at low resolution scales.Comment: 19 pages, 3 figures; revised version; to appear in Int. J. Mod. Phys.

### A QCD sum rule calculation of the $X^\pm(5568) \to B_{s}^0\pi^\pm$ decay width

To understand the nature of the $X(5568)$, recently observed in the mass
spectrum of the $B_{s}^0\pi^\pm$ system by the D0 Collaboration, we have
investigated, in a previous work, a scalar tetraquark (diquak-antidiquark)
structure for it, within the two-point QCD sum rules method. The result found
for its mass agrees well with the experimental value. Encouraged by this
finding we now extend our calculations to obtain the decay width of $X(5568)$
to $B_{s}^0\pi^\pm$ using the three-point QCD sum rule. We obtain a value of
(20.4\pm8.7)\MeV, which, on comparing with the experimental value of
21.9\pm6.4 (\mbox{sta})^{+5.0}_{-2.5}(\mbox{syst}) \MeV/c^2, reinforces the
scalar four quark nature of $X(5568)$.Comment: Minor modifications made. Some new discussions and references adde

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