2018 Impact factor 2.481
Hadrons and Nuclei
Eur. Phys. J. A 9, 69-72

Observation of $\mathsf\Delta^+\rightarrow p\pi^{0}$ decay in heavy-ion collisions

T. Matulewicz1,2 - L. Aphecetche1 - Y. Charbonnier1 - H. Delagrange1 - K.K. Gudima1 - G. Martínez1 - M. P\loszajczak1 - Y. Schutz1 - V.D. Toneev1 - M. Appenheimer3 - R. Averbeck4 - J. Díaz5 - A. Döppenschmidt4 - M.J. van Goethem6 - S. Hlavac7 - M. Hoefman6 - R. Holzmann4 - F. Lefèvre4 - A. Kugler8 - H. Löhner6 - A. Marín5 - V. Metag3 - R. Novotny3 - R.W. Ostendorf6 - R.H. Siemssen6 - R.S. Simon4 - R. Stratmann4 - H. Ströher3 - P. Tlusty8 - P.H. Vogt6 - V. Wagner8 - J. Weiss3 - H.W. Wilschut6 - F. Wissmann4 - A.R. Wolf3 - M. Wolf3

1 Grand Accélérateur National d'Ions Lourds, CEA/DSM - CNRS/IN2P3, F-14076 Caen, France
2 Institute of Experimental Physics, Warsaw University, PL-00-681 Warszawa, Poland
3 II Physikalisches Institut, Universität Gießen, D-35392 Gießen, Germany
4 Gesellschaft für Schwerionenforschung, D-64291 Darmstadt, Germany
5 Instituto de Fisica Corpuscular, E-46100 Burjasot, Spain
6 Kernfysisch Versneller Instituut, NL-9747 AA Groningen, The Netherlands
7 Slovak Academy of Science, SK-84228 Bratislava, Slovak Republic
8 Nuclear Physics Institute, CZ-25068 Rez, Czech Republic

Received: 7 April 2000 / Revised version: 20 July 2000
Communicated by W. Henning

Abstract
Proton-$\pi^0$ 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-$\pi^0$ 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 $N_{\Delta^+}$ of the $\Delta^+$ baryonic resonance. No correlation is observed in the case of deuteron-$\pi^0$ coincidences. Assuming isotropic emission of $\pi^0$ and $\Delta^+$ from a midrapidity thermal source and isospin symmetry, we determined the global $N_\Delta/N_\pi \,$ratio of 0.79 $\pm$0.30(stat) $\pm$0.2(syst). This value indicates that most pions produced at subthreshold energy in heavy-ion reaction are mediated by the $\Delta$-resonance.

PACS
25.70.-z Low and intermediate energy heavy-ion reactions - 25.75.Dw Particle and resonance production - 14.20.Gk Baryon resonances with S = 0


Copyright Società Italiana di Fisica, Springer-Verlag 2000