Physicists pin down rare particle decay, refining test of Standard Model
Researchers have made the most precise measurement yet of how exotic charm particles decay, nailing down a fundamental constant that tests whether our best physics theory holds up. The finding could reveal cracks in the Standard Model or validate it—either way, it matters for understanding the universe's basic rules.
Originaltitel: Measurement of the branching fraction of <em>D<sub>s</sub></em><sup>+</sup> → <em>l</em><sup>+</sup>ν<sub><em>l</em></sub> via <em>e</em><sup>+</sup><em>e</em><sup>-</sup> → <em>D<sub>s</sub></em>*<sup>+</sup><em>D<sub>s</sub></em>*<sup>-</sup>
<p>Based on 10.64 fb<sup>-1</sup> of e<sup>+</sup>e<sup>-</sup> collision data taken at center-of-mass energies between 4.237 and 4.699 GeV with the BESIII detector, we study the leptonic D<sub>s</sub><sup>+</sup> decays using the e<sup>+</sup>e<sup>-</sup> → D<sub>s</sub><sup>*+</sup>D<sub>s</sub>*<sup>-</sup> process. The branching fractions of D<sub>s</sub><sup>+</sup> → <em>l</em><sup>+</sup>ν<sub><em>l</em></sub>(<em>l</em> = μ,τ) are measured to be B(D<sup>s+</sup> → μ<sup>+</sup>ν<sub>μ)</sub> = (0.547 ± 0.026(stat) ± 0.016(syst))% and B(D<sub>s</sub><sup>+</sup> → τ<sup>+</sup>ν<sub>τ</sub>)= (5.60 ± 0.16(stat) ± 0.20s(yst))%, respectively. The product of the decay constant and CabibboKobayashi-Maskawa matrix element |V<sub>cs</sub>| is determined to be f(D<sub>s</sub><sup>+</sup>)|V<sub>cs</sub>| = (246.5 ± 5.9(stat) ± 3.6(syst) ± 0.5<sub>input</sub>)<sub>μν</sub> and f(D<sub>s</sub><sup>+</sup>)|V<sub>cs</sub>|= 252.7 ± 3.6(stat) ± 4.5(syst) ± 0.6<sub>input</sub>)<sub>τν</sub> MeV, respectively. Taking the value of |V<sub>cs</sub>| from a global fit in the Standard Model, we obtain f(D<sub>s</sub><sup>+</sup>) = (253.2 ± 6.0(stat) ± 3.7(syst) ± 0.6<sub>input</sub>)<sub>μν</sub> and f(D<sub>s</sub><sup>+</sup>) = (259.6 ± 3.7(stat) ± 4.6(syst) ± 0.6<sub>input</sub>)<sub>τν</sub> MeV, respectively. Conversely, taking the value for f(D<sub>s</sub><sup>+</sup>) from the latest lattice quantum chromodynamics calculation, we obtain |V-cs| = (0.986 ± 0.023(stat) ± 0.014(syst) ± 0.003<sub>input</sub>)<sub>μν</sub> and |V<sub>cs</sub>| = (1.011 ± 0.014(stat) ± 0.018(syst) ± 0.003<sub>input</sub>)<sub>τν</sub>, respectively.</p><p></p>