3,838 research outputs found
Novel insights into the transition form factor
BaBar's observation of significant deviations of the pion transition form
factor (TFF) from the asymptotic expectation with GeV has brought a
serious crisis to a fundamental picture established for such a simplest
system by perturbative QCD, i.e. the dominance of collinear
factorization at high momentum transfers for the pion TFF. We show that
non-factorizable contributions due to open flavors in
could be an important source that contaminates the pQCD asymptotic limit and
causes such deviations with GeV. Within an effective Lagrangian
approach, the non-factorizable amplitudes can be related to intermediate hadron
loops, i.e. and etc, and their corrections to the
and TFFs can be estimated.Comment: Revtex, 6 pages and 4 eps figures; Extended version accepted by Eur.
Phys. J.
Study of the anomalous cross-section lineshape of e^+e^-\to D\bar D at \psi(3770) with an effective field theory
We study the anomalous cross-section lineshape of
with an effective field theory. Near the threshold, most of the pairs
are from the decay of . Taking into account the fact that the
nonresonance background is dominated by the transition, the produced
pair can undergo final-state interactions before the pair is
detected. We propose an effective field theory for the low-energy
interactions to describe these final-state interactions and find that the
anomalous lineshape of the cross section observed by the BESII
collaboration can be well described.Comment: 10 pages,6 figures, redo the calculation with PDS scheme and more
discussions added, accepted by Phys.Lett.
Employing spin symmetry to disentangle different models for the XYZ states
In order to test different models proposed for some states discovered
recently in the charmonium mass range that do not fit into the pattern
predicted by the conventional quark model, we derive predictions for the
spectrum within the hadro-charmonium picture, the tetraquark picture as well as
the hadronic molecular approach. We exploit heavy quark spin symmetry for the
hadro-charmonium and hadronic molecule scenarios. The patterns that emerge from
the different models turn out to be quite distinct. For example, only within
the hadro-charmonium picture a pseudoscalar state emerges that is lighter than
the Y(4260). Possible discovery channels of these additional states are
discussed.Comment: 22 pages, 4 figures, version accepted by PR
Production of the X(3872) in charmonia radiative decays
We discuss the possibilities of producing the X(3872), which is assumed to be
a D \bar D^* bound state, in radiative decays of charmonia. We argue that the
ideal energy regions to observe the X(3872) associated with a photon in e^+e^-
annihilations are around the Y(4260) mass and around 4.45 GeV, due to the
presence of the S-wave D \bar D_1(2420) and D^* \bar D_1(2420) threshold,
respectively. Especially, if the Y(4260) is dominantly a D \bar D_1 molecule
and the X(3872) a D \bar D^* molecule, the radiative transition strength will
be quite large.Comment: 15 pages, 3 figures. Typos fixed, to appear in Phys. Lett.
Confirming the molecular nature of the and the
The decays of the and the to ,
and (, and ) are
investigated within a nonrelativistic effective field theory. It is argued
that, while the decays to suffer from potentially large
higher order corrections, the -wave transitions of the states offer
the best possibility to confirm the nature of the states as molecular
states and to further study their properties. We give nontrivial and
parameter-free predictions for the ratios of various partial widths for final
states with and . In addition, the branching
fractions for the neutral -states to are predicted to be
of order --. This provides a fine test of the molecular
nature in future high-luminosity experiments.Comment: 18 pages, 2 figure
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