New determination of the mass of the eta meson at COSY-ANKE

TL;DR

This paper reports a high-precision measurement of the eta meson mass at COSY-ANKE using a novel method involving polarized deuteron beams and detailed analysis of the reaction kinematics, achieving results consistent with recent measurements.

Contribution

The study introduces a new high-precision method for determining the eta meson mass using polarized beams and missing-mass techniques at COSY-ANKE.

Findings

Measured eta meson mass as 547.873 ± 0.005(stat) ± 0.027(syst) MeV/c^2

Achieved a relative precision of 3 x 10^-5 in beam momentum measurement

Demonstrated the effectiveness of detailed final-state momentum analysis for high-precision mass determination

Abstract

A value for the mass of the eta meson has been determined at the COSY-ANKE facility through the measurement of a set of deuteron laboratory beam momenta and associated 3He center-of-mass momenta in the d+p -> 3He+X reaction. The eta was then identified by the missing-mass peak and the production threshold determined. The individual beam momenta were fixed with a relative precision of 3 x 10^-5 for values around 3 GeV/c by using a polarized deuteron beam and inducing an artificial depolarizing spin resonance, which occurs at a well-defined frequency. The final-state momenta in the two-body d+p -> 3He+eta reaction were investigated in detail by studying the size of the 3He momentum ellipse with the forward detection system of the ANKE spectrometer. Final alignment of the spectrometer for this high precision experiment was achieved through a comprehensive study of the 3He final-state momenta as a function of the center-of-mass angles, taking advantage of the full geometrical acceptance. The value obtained for the mass, m(eta)=(547.873 +- 0.005(stat) +- 0.027(syst)) MeV/c^2, is consistent and competitive with other recent measurements, in which the meson was detected through its decay products.