New Measurement of the π0 [pi superscript 0] Radiative Decay Width

Abstract

High precision measurements of the differential cross sections for π0 [pi superscript 0] photoproduction at forward angles for two nuclei, 12C [superscript 12 C] and 208Pb [superscript 208 Pb], have been performed for incident photon energies of 4.9–5.5 GeV to extract the π0→γγ [pi superscript 0 → gamma gamma] decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0→γγ [pi superscript 0 → 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 Γ(π0→γγ)[Gamma (pi superscript 0 → gamma gamma)] =7.82±0.14(stat)±0.17(syst) eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.