A precision determination of the mass of the $\eta$ meson

TL;DR

This paper reports a precise measurement of the eta meson mass using proton-deuteron collision data, employing a calibrated spectrograph to achieve high accuracy and resolve discrepancies with previous measurements.

Contribution

It introduces a new high-precision determination of the eta meson mass, utilizing simultaneous measurements of multiple meson production processes with a calibrated magnetic spectrograph.

Findings

Measured eta meson mass: 547.311 ± 0.028 (stat) ± 0.032 (syst) MeV/c^2

Result is significantly lower than the NA48 measurement

Consistent with earlier counter experiments

Abstract

Several processes of meson production in proton-deuteron collisions have been measured simultaneously using a calibrated magnetic spectrograph. Among these processes, the $\eta$ meson is seen clearly as a sharp missing--mass peak on a slowly varying background in the $p+d\to ^3\textrm{He} +X$ reaction. Knowing the kinematics of the other reactions with well determined masses, it is possible to deduce a precise mass for the $\eta$ meson. The final result, $m(\eta)=547.311\pm 0.028 \textrm{(stat)} \pm 0.032 \textrm{(syst) MeV/c}^2$, is significantly lower than that found by the recent NA48 measurement, though it is consistent with values obtained in earlier counter experiments.