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Observation of Δ+→ pπ0 decay in heavy-ion collisions

Authors :: Matulewicz, T.
Aphecetche, L.
Charbonnier, Y.
Delagrange, H.
Gudima, K.K.
Martınez, G.
Płoszajczak, M.
Schutz, Y.
Toneev, V.D.
Appenheimer, M.
Averbeck, R.
Dıaz, J.
Döppenschmidt, A.
van Goethem, M.J.
Hlavač, S.
Hoefman, M.
Holzmann, R.
Lefèvre, F.
Kugler, A.
Löhner, H.
Marın, A.
Metag, V.
Novotny, R.
Ostendorf, R.W.
Siemssen, R.H.
Simon, R.S.
Stratmann, R.
Ströher, H.
Tlusty, P.
Vogt, P.H.
Wagner, V.
Weiss, J.
Wilschut, H.W.
Wissmann, F.
Wolf, A.R.
Wolf, M.
Source :: The European Physical Journal A - Hadrons and Nuclei; 20001001, Vol. 9 Issue: 1 p69-72, 4p
Publication Year :: 2000
Abstract: Abstract:: Proton-π<superscript>0</superscript> 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-π<superscript>0</superscript> invariant mass spectrum we observe a significant excess of strength above the background obtained by event mixing. We attribute this signal to the strength distribution N <subscript>Δ</subscript> of the Δ baryonic resonance. No correlation is observed in the case of deuteron-π<superscript>0</superscript> coincidences. Assuming isotropic emission of π<superscript>0</superscript> and Δ<superscript>+</superscript> from a midrapidity thermal source and isospin symmetry, we determined the global N <subscript>Δ</subscript>/N <subscript>π</subscript>ratio of 0.79 �0.30(stat) �0.2(syst). This value indicates that most pions produced at subthreshold energy in heavy-ion reaction are mediated by the Δ-resonance.