Study of a narrow pi+ pi- peak at about 755 MeV/c^2 in bar-p n --> 2 pi+ 3 pi- annihilation at rest

TL;DR

This paper reanalyzes a 39-year-old experimental peak in the pi+ pi- mass distribution from antiproton-neutron annihilation, confirming its existence with improved precision and statistical significance.

Contribution

It provides a refined measurement of a narrow pi+ pi- resonance at about 757 MeV/c^2, with increased statistical significance and updated production rate.

Findings

Mass of the peak: 757.4 ± 2.6 MeV/c^2

Significance: 5.2 standard deviations

Production in 12.4 ± 2.4% of annihilations

Abstract

A narrow peak in the pi+ pi- mass distribution was seen by the Rome-Syracuse Collaboration in bar-p n --> 2 pi+ 3 pi- annihilation at rest 39 years ago. The reanalysis of this peak finds a mass of 757.4 +- 2.6 MeV/c^2 and a width slightly narrower than the experimental resolution. The evidence of the peak is 5.2 standard deviations. This state is generated in (12.4 +- 2.4)% of the bar-p n --> 2 pi+ 3 pi- annihilations at rest. No spin analysis is possible with the statistics of the experiment.