Proton-\pi0 coincidences have been measured at the beam energy of 180A MeV in the reaction Ar+Ca studied by TAPS at SIS/GSI. In the proton-\pi0 invariant mass spectrum we evidence a significant excess of counts above the background obtained by event mixing. We assign this signal to the strength distribution of the \Delta baryonic resonance. From the measured yields we deduce a \pi\Delta ratio of 0.9 \pm 0.3 (preliminary value), pointing that most (if not all) pions produced in subthreshold energy heavy-ion reaction are mediated by the \Delta-resonance.
PACS numbers: 14.40.--n, 25.90.+k
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