Physicists Measure Rare Particle Decay to Test Fundamental Forces
Researchers have precisely measured how a charm quark decays into lighter particles—a rare process never directly observed before. The measurement reveals the internal structure of these transformations and tests predictions from the Standard Model of physics, potentially revealing gaps in our understanding of nature's most basic rules.
Originaltitel: Analysis of the dynamics of the decay <em>D</em><sup>+</sup>→ <em>K</em><sup>0</sup><em><sub>S</sub></em> π<sup>0</sup><em>e</em><sup>+</sup>ν<em><sub>e</sub></em>
<p>The branching fraction of D+ -> K-S(0)pi(0)e(+)nu(e) is measured for the first time using 7.93 fb(-1) of e(+)e(-) annihilation data collected at the center-of-mass energy root s = 3.773 GeV with the BESIII detector operating at the BEPCII collider, and is determined to be B(D+ -> K-S(0)pi(0)e(+)nu(e)) = (0.881 +/- 0.017(stat.) +/- 0.016(syst.))%. Based on an analysis of the D+ -> K-S(0)pi(0)e(+)nu(e) decay dynamics, we observe the S-wave and P-wave components with fractions of f(S-wave) = (6.13 +/- 0.27(stat.) +/- 0.30(syst.))% and f((K) over bar*(892)0) = (93.88 +/- 0.27(stat.) +/- 0.29(syst.))%, respectively. From these results, we obtain the branching fractions B(D+ -> (K-S(0)pi(0))(S-wave) e(+)nu(e)) = (5.41 +/- 0.35(stat.) +/- 0.37(syst.)) x 10(-4) and B(D+ -> (K) over bar*(892)(0)e(+)nu(e)) = (4.97 +/- 0.11(stat.) +/- 0.12(syst.))%. In addition, the hadronic form-factor ratios of D+ -> (K) over bar*(892)(0)e(+)nu(e) at q(2) = 0, assuming a single-pole dominance parameterization, are determined to be r(V) = V(0)/A(1)(0) = 1.43 +/- 0.07(stat.) +/- 0.03(syst.) and r(2) = A(2)(0)/A(1)(0) = 0.72 +/- 0.06(stat.) +/- 0.02(syst.).</p>