A new measurement of the rare decay eta -> pi^0 gamma gamma with the Crystal Ball/TAPS detectors at the Mainz Microtron

TL;DR

This paper reports a precise measurement of the rare eta decay into pi^0 gamma gamma using advanced detectors at MAMI, providing new data on decay width and its dependence on photon invariant mass, aligning with theoretical predictions.

Contribution

It presents the first detailed measurement of the decay width dependence on m^2(gamma gamma) and a more accurate decay width value for eta->pi^0 gamma gamma.

Findings

Decay width Gamma(eta->pi^0 gamma gamma) = (0.33±0.03) eV.

Decay width dependence on m^2(gamma gamma) agrees with previous data.

Results match recent theoretical calculations.

Abstract

A new measurement of the rare, doubly radiative decay eta->pi^0 gamma gamma was conducted with the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. New data on the dependence of the partial decay width, Gamma(eta->pi^0 gamma gamma), on the two-photon invariant mass squared, m^2(gamma gamma), as well as a new, more precise value for the decay width, Gamma(eta->pi^0 gamma gamma) = (0.33+/-0.03_tot) eV, are based on analysis of 1.2 x 10^3 eta->pi^0 gamma gamma decays from a total of 6 x 10^7 eta mesons produced in the gamma p -> eta p reaction. The present results for dGamma(eta->pi^0 gamma gamma)/dm^2(gamma gamma) are in good agreement with previous measurements and recent theoretical calculations for this dependence.