Progress in the determination of the $J/ψ-π$ cross section
Improving previous calculations, we compute the $J/ψπ\to {charmed mesons}$ cross section using QCD sum rules. Our sum rules for the $J/ψπ\to \bar{D} D^*$, $D \bar{D}^*$, ${\bar D}^* D^*$ and ${\bar D} D$ hadronic matrix elements are constructed by using vaccum-pion correlation functions, and we work up to twist-4 in the soft-pion limit. Our results suggest that, using meson exchange models is perfectly acceptable, provided that they include form factors and that they respect chiral symmetry. After doing a thermal average we get $<σ^{πJ/ψ} v>\sim 0.3$ mb at $T=150\MeV$.
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