Physicists Measure Rare Particle Decay With Precision, Validating Standard Model
Researchers at the Large Hadron Collider have made the most precise measurement yet of how a B meson decays into a D* meson and tau lepton—a process that tests fundamental physics rules. The result aligns with theoretical predictions, bolstering confidence in the Standard Model and constraining theories of physics beyond it.
Originaltitel: Measurement of the <em>D</em>* longitudinal polarization in <em>B</em><sup>0</sup> â <em>D</em>*<sup>-</sup> Ï<sup>+</sup>Îœ<sub>t</sub> decays
<p>The longitudinal polarization fraction of the D* meson is measured in B-0 -> D*(-) tau(+)nu(t) decays, where the tau lepton decays to three charged pions and a neutrino, using proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV and corresponding to an integrated luminosity of 5 fb(-1). The D* polarization fraction F-L(D)* is measured in two q(2) regions, below and above 7 GeV2/c(4), where q(2) is defined as the squared invariant mass of the tau nu(tau) system. The F-L(D)*L values are measured to be 0.52 +/- 0.07 +/- 0.04 and 0.34 +/- 0.08 +/- 0.02 for the lower and higher q(2) regions, respectively. The first uncertainties are statistical and the second systematic. The average value over the whole q(2) range is F-L(D)* = 0.41 +/- 0.06 +/- 0.03. These results are compatible with the Standard Model predictions.</p>