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

T. Matulewicz - et al.

doi:doi:10.1007/s100500070057

EPJ

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

T. Matulewicz^1,2 - L. Aphecetche¹ - Y. Charbonnier¹ - H. Delagrange¹ - K.K. Gudima¹ - G. Martínez¹ - M. P $\l$ oszajczak¹ - 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

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Observation of decay in heavy-ion collisions

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