On a possible explanation of the DLS puzzle
Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 14, D-72076, Tübingen, Germany
2 Kepler Center for Astro and Particle Physics, University of Tübingen, Tübingen, Germany
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Accepted: 6 June 2014
Published online: 4 July 2014
The enhancement in the dilepton spectrum observed in heavy-ion collisions for invariant electron-positron masses in the range has recently been traced back to a corresponding enhancement in np 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 np collisions at beam energies below 2GeV, in particular regarding the region . We show that the missing strength can be attributed to ρ 0-channel π + π − production, which is dominated by the t-channel ΔΔ excitation and the recently found isoscalar dibaryonic resonance structure at 2.37 GeV. These processes do not contribute in pp collisions, but only in np collisions.
© SIF, Springer-Verlag Berlin Heidelberg, 2014