A New Measurement of the $\pi^0$ Radiative Decay Width

TL;DR

This paper reports a highly precise measurement of the neutral pion's two-photon decay width using photoproduction data at Jefferson Lab, significantly improving the accuracy over previous measurements and confirming theoretical expectations.

Contribution

It provides the most precise experimental determination of the $ o ext{pi}^0 o ext{gamma} ext{gamma}$ decay width to date, using updated theoretical models and high-resolution detectors.

Findings

Decay width measured as 7.82 eV with 2.8% total uncertainty

Result is 2.5 times more precise than previous averages

Measurement is consistent with theoretical predictions

Abstract

High precision measurements of the differential cross sections for $\pi^0$ photoproduction at forward angles for two nuclei, $^{12}$C and $^{208}$Pb, have been performed for incident photon energies of 4.9 - 5.5 GeV to extract the ${\pi^0 \to \gamma\gamma}$ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The ${\pi^0 \to \gamma\gamma}$ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is $\Gamma{(\pi^0 \to \gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm eV}$. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current PDG average of this fundamental quantity and it is consistent with current theoretical predictions.