Study of a Narrow pi+ pi- Peak at about 755 MeV/c**2 in pbar n --> 2 pi+ 3 pi- Annihilation at Rest

TL;DR

This paper reanalyzes a previously overlooked narrow pi+ pi- peak at about 755 MeV/c² in pbar n annihilation at rest, confirming its existence with high statistical significance and suggesting a possible JP=0+ quantum number.

Contribution

The study provides the first detailed reanalysis of the peak, establishing its mass, width, and statistical significance, and discusses its possible quantum numbers.

Findings

Peak mass: 757.4 MeV/c² with uncertainties

Peak significance: 5.2 standard deviations

Estimated production rate: about 1% of annihilations

Abstract

A narrow peak in the pi+ pi- mass distribution was seen by the Rome-Syracuse Collaboration in pbar n --> 2 pi+ 3 pi- annihilation at rest in 1970. It was ignored for 40 years. The reanalysis of this peak finds that it has the mass 757.4 +- 2.8_stat +- 1.1_sys MeV/c**2 and a width consistent with the experimental resolution. The evidence of the peak is 5.2 standard deviations. The peak is generated in (1.03 +- 0.21_stat +- 0.21_sys)% of the pbar n annihilations at rest. No spin analysis is possible with the statistics of the experiment but there are arguments suggesting that it has JP = 0+.