Search for low-mass exotic mesonic structures. I. Experimental results

Recently, several papers have discussed the existence of a new low-mass structure at a mass close to M = 214.3 MeV. It was suggested that the Σ⁺ disintegration Σ⁺ → pP ⁰, P ⁰ → μ⁻μ⁺ proceeds through an intermediate particle P ⁰ having such a mass. The present work intends to look at the other new or available data, in order to observe the eventual existence of small narrow peaks or shoulders in very low mesonic masses. Indeed, narrow structures were already extracted from various data in dibaryons, baryons, and mesons (at larger masses than those studied here). The text was submitted by the authors in English.