Resonance-like coherent production of a pion pair in the reaction $pd \rightarrow pdππ$ in the GeV region

Abstract

The reaction $p + d \rightarrow p + d + X$ was studied at 0.8-2.0 GeV proton beam energies with the ANKE magnetic spectrometer at the COSY synchrotron storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8 GeV/$c$, were detected at small angles with respect to the proton beam. Distribution over the reaction missing mass $M_x$ reveals a local enhancement near the threshold of the pion pair production specific for the so-called ABC effect. The enhancement has a structure of a narrow bump placed above a smooth continuum. The invariant mass of the $dππ$ system in this enhancement region exhibits a resonance-like peak at $M_{dππ} \approx 2.36$ GeV/$c^2$ with the width $Γ\approx 0.10$ GeV/$c^2$. A possible interpretation of these features is discussed.

14 pages, 16 figures, submitted to Eur. Phys. J. A. v2: Added references [42,43] in section IV.A. v3: revised version according to referee remarks v4: revised version according to referee remarks