On a Possible Explanation of the DLS-Puzzle

Abstract

The enhancement in the dilepton spectrum observed in heavy-ion collisions for invariant electron-positron masses in the range 0.15 GeV/c${}^2<M_{e^{+}{e}^{-}}<$ 0.6 GeV/c${}^2$ has recently been traced back to a corresponding enhancement in $pn$ collisions relative to $pp$ collisions. Whereas the dilepton spectra in the latter are understood quantitatively, theoretical descriptions fail to describe the much higher dilepton rate in $pn$ collisions, in particular regarding the region $M_{e^{+}{e}^{-}}>$ 0.3 GeV/c${}^2$ at beam energies below 2 GeV. We show that the missing strength can be attributed to the $\rho$-channel ${\pi }^{+}{\pi }^{-}$-production, which is dominated by the $t$-channel $\Delta \Delta$ excitation and the recently found isoscalar dibaryonic resonance structure at 2.37 GeV.

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• The $d^{\ast }(2380)$ in neutron stars - a new degree of freedom?
• ABC Effect and Resonance Structure in the Double-Pionic Fusion to ${}^3$He
• Study of the quasi-free $np\to np{\pi }^{+}{\pi }^{-}$ reaction with a deuterium beam at 1.25 GeV/nucleon
• Dilepton Radiation from Strongly Interacting Systems
• Dibaryons: Molecular versus Compact Hexaquarks
• Analysis of the exclusive final state npe${}^{+}$e${}^{-}$ in quasi-free np reaction
• On the Production of an Isotensor Dibaryon in the $pp\to pp{\pi }^{+}{\pi }^{-}$ Reaction
• Resonance $d^{\ast }(2380)$ and higher isospin states
• Dibaryons at COSY