Physicists observe rare particle decays, refining model of matter
Researchers at China's BESIII detector have directly observed two previously undetected particle decay processes, measuring their probability for the first time. The findings strengthen our understanding of the fundamental particles that make up matter and validate theoretical physics models used to explain the universe's behavior.
Originaltitel: Observation of the semileptonic decays D<sup>0 </sup>→ K<sup>0</sup><sub>S</sub>π<sup>−</sup>π<sup>0</sup>e<sup>+</sup>ν<sub>e</sub> and D<sup>+</sup>→ K<sup>0</sup><sub>S</sub>π<sup>+</sup>π<sup>−</sup>e<sup>+</sup>ν<sub>e</sub>
<p>By analyzing <em>e</em><sup>+</sup><em>e</em><sup><em>−</em></sup> annihilation data corresponding to an integrated luminosity of 2.93 fb<sup><em>−</em>1</sup> collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, the first observation of the semileptonic decays D0→K0Sπ−π0e+νe and D+→K0Sπ+π−e+νe is reported. In the hypothesis that all events correspond to <em>K</em><sub>1</sub>(1270) decays, the branching fractions are measured to be B(D0→K1(1270)−(→K0Sπ−π0)e+νe)=(1.69+0.53−0.46±0.15)×10−4 and B(D+→¯¯¯¯¯K1(1270)0(→K0Sπ+π−)e+νe)=(1.47+0.45−0.40±0.14)×10−4 with statistical significance of 5.4<em>σ</em> and 5.6<em>σ</em>, respectively. When combined with measurements of the <em>K</em><sub>1</sub>(1270) <em>→ K</em><sup>+</sup><em>π</em><sup><em>−</em></sup><em>π</em> decays, the absolute branching fractions are determined to be B(D0→K1(1270)−e+νe)=(1.08+0.14+0.08−0.13−0.10±0.21)×10<sup>−3</sup> and B(D+→¯¯¯¯¯K1(1270)0e+νe)=(1.70+0.26−0.23±0.13±0.35)×10<sup>−3</sup>. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainties originate from the assumed branching fractions of the <em>K</em><sub>1</sub>(1270) <em>→ Kππ</em> decays.</p>