Near-threshold structures in seven e+e- annihilation channels are simultaneously described by a single chiral-EFT N Nbar final-state interaction plus slowly varying short-distance sources, without channel-specific narrow resonances.
Could the near-threshold $XYZ$ states be simply kinematic effects?
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abstract
We demonstrate that the spectacular structures discovered recently in various experiments and named as $X$, $Y$ and $Z$ states cannot be purely kinematic effects. Their existence necessarily calls for nearby poles in the $S$--matrix and they therefore qualify as states. We propose a way to distinguishing kinematic cusp effects from genuine $S$--matrix poles: the kinematic threshold cusp cannot produce a narrow peak in the invariant mass distribution in the elastic channel in contrast with a genuine $S$--matrix pole.
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Understanding the near-threshold structures in $e^+e^- $ annihilation from a unified $N \bar N$-interaction perspective
Near-threshold structures in seven e+e- annihilation channels are simultaneously described by a single chiral-EFT N Nbar final-state interaction plus slowly varying short-distance sources, without channel-specific narrow resonances.