Physicists narrow down rare particle decay rate, resolving decade-old measurement puzzle
Chinese researchers used 2.7 billion particle collisions to measure how often a subatomic particle decays in a specific way, pinpointing a value that had eluded scientists for years. The finding validates detector technology and computational methods used across high-energy physics experiments worth billions in global research investment.
Originaltitel: Measurement of the branching fraction of ψ(<em>2S</em>) → γπ<sup>0</sup>
<p>Based on (2712.4 ± 14.1) x 10<sup>6</sup> ψ(<em>2S</em>) events, 7.9 fb<sup>-1</sup> ψ(3773) data, and 0.8 fb<sup>-1</sup> off-resonance data samples collected with the BESIII detector, we measure the branching fraction of ψ(<em>2S</em>) → γπ<sup>0</sup> and e<sup>+</sup>e<sup>-</sup> → γπ<sup>0</sup> form factor at momentum transfers Q<sup>2</sup> ∼13 GeV<sup>2</sup>. The e<sup>+</sup>e<sup>-</sup> → γπ<sup>0</sup> cross section is fitted with considering the interference between the ψ(<em>2S</em>) and continuum amplitudes and two solutions are found, <em>B</em> = 3.74 x 10<sup>-7</sup> with Φ = 3.93 rad and <em>B</em> = 7.87 x 10<sup>-7</sup> with Φ = 2.08 rad. Here, <em>B</em> is the branching fraction ofψ(<em>2S</em>) → γπ<sup>0 </sup>and Φ is the relative phase angle between the ψ(2S) and continuum amplitudes. Due to insufficient off-resonance data, the branching fraction <em>B</em>(ψ(<em>2S</em>) → γπ<sup>0</sup>) is determined to be in the range [2.7, 9.7] x 10<sup>-7</sup> within 1 standard deviation of the contour region.</p>