Physicists discover three new particle resonances in rare charm interactions
Researchers have identified three previously unknown resonance states in electron-positron collisions, including one observed for the first time. The findings advance understanding of exotic hadron behavior and could refine particle physics models used in detector design and high-energy research facilities.
Originaltitel: First Observation of a Three-Resonance Structure in <em>e</em><sup>+</sup><em>e</em><sup>-</sup> → Nonopen Charm Hadrons
<p>We report the measurement of the inclusive cross sections for e<sup>+</sup>e<sup>-</sup> → nOCH (where nOCH denotes non-open charm hadrons) with improved precision at center-of-mass (c.m.) energies from 3.645 to 3.871 GeV. We observe three resonances: <em>R</em>(3760), <em>R</em>(3780), and <em>R</em>(3810) with significances of 8.1σ, 13.7σ, and 8.8σ, respectively. The <em>R</em>(3810) state is observed for the first time, while the <em>R</em>(3760) and <em>R</em>(3780) states are observed for the first time in the nOCH cross sections. Two sets of resonance parameters describe the energy-dependent line shape of the cross sections well. In set I [set II], the <em>R</em>(3810) state has mass (3805.7 ± 1.1 ± 2.7) [(3805.7 ± 1.1 ± 2.7)] MeV/c<sup>2</sup>, total width (11.6 ± 2.9 ± 1.9) =[(11.5 ± 2.8 ± 1.9)] MeV, and an electronic width multiplied by the nOCH decay branching fraction of (10.9 ± 3.8 ± 2.5) [(11.0 ± 3.4 ± 2.5)] eV. In addition, we measure the branching fractions <em>B</em>=<em>R</em>(3760) → nOCH] = (25.2 ± 16.1 ± 30.4)% [(6.4 ± 4.8 ± 7.7)%] and <em>B</em>[<em>R</em>(3780) → nOCH] = (12.3 ± 6.6 ± 8.3)% [10.4 ± 4.8 ± 7.0)%] for the first time. The <em>R</em>(3760) state can be interpreted as an open-charm (OC) molecular state, but containing a simple four-quark state component. The <em>R</em>(3810) state can be interpreted as a hadrocharmonium state.</p>