Partial-wave analysis of the eta pi+ pi- system produced in the reaction pi-p --> eta pi+ pi- n at 18 GeV/c

TL;DR

This paper presents a detailed partial-wave analysis of eta pi+ pi- events produced in pi- p reactions at 18.3 GeV/c, identifying key resonances and their properties, and comparing results with previous measurements to refine branching fraction estimates.

Contribution

It provides the first comprehensive partial-wave analysis of eta pi+ pi- system at this energy, determining resonance parameters and updating branching fractions using amplitude analysis.

Findings

Resonance eta(1295) mass 1282 MeV, width 66 MeV

Resonance eta(1440) mass 1404 MeV, width 80 MeV

Significant differences in f1(1285) branching fractions from previous data

Abstract

A partial-wave analysis of 9082 eta pi+ pi- n events produced in the reaction pi- p --> eta pi+ pi- n at 18.3 GeV/c has been carried out using data from experiment 852 at Brookhaven National Laboratory. The data are dominated by J^{PC} = 0^{-+} partial waves consistent with observation of the eta(1295) and the eta(1440). The mass and width of the eta(1295) were determined to be 1282 +- 5 MeV and 66 +- 13 Mev respectively while the eta(1440) was observed with a mass of 1404 +- 6 MeV and width of 80 +- 21 MeV. Other partial waves of importance include the 1++ and the 1+- waves. Results of the partial wave analysis are combined with results of other experiments to estimate f1(1285) branching fractions. These values are considerably different from current values determined without the aid of amplitude analyses.