In 2018, the Large Hadron Collider ran a special data-taking campaign: the CMS detector captured proton collisions at breakneck speed to collect ten billion particles containing a beauty quark. These particles, B mesons, live for tiny fractions of a second and decay into lighter particles, like an overloaded train shedding cars on the move.
The Standard Model predicts how often different types of B mesons should be produced, but precise measurements are needed to check those predictions. Scientists from the CMS collaboration measured how many B+, B0, and B0s mesons are produced — three varieties that differ in which light quark sits next to the beauty quark. They found that the ratios of their yields change depending on the energy and angle at which the particle is emitted.
To obtain these numbers, physicists used two decay modes of B mesons: decays into particles with a charm quark (visible as showers of ordinary particles) and decays into particles containing J/ψ (which leave a clear signature of two muons). By comparing both modes, they also refined how often B mesons choose one decay path over the other.
A test of isospin symmetry, the idea that protons and neutrons should behave identically in strong interactions, showed that within measurement precision, the symmetry holds. This is another brick in the foundation of our understanding of how quarks assemble into particles.
as written by the authors arXiv:2602.10270
Production fraction ratios of B$$^+$$, B$$^0$$, and B$$^0_\mathrm{s}$$ mesons are measured in proton-proton collisions at $$\sqrt{s}$$ = 13 TeV using a special data set recorded in 2018 with high-rate triggers designed to collect an unbiased sample of $$10^{10}$$ b hadrons with the CMS experiment at the LHC. These data allow the study of the open-charm decays of B mesons (B$$_\mathrm{(s)}$$ $$\to$$ $$\pi$$D$$_\mathrm{(s)}$$) where the D meson decays into fully hadronic final states. By utilizing known branching fractions and precise theoretical calculations, production fraction ratios as functions of B meson transverse momentum ($$p_\mathrm{T}$$) and rapidity ($$y$$) are measured using the open-charm decays in the kinematic range of 8 $$\lt$$ $$p_\mathrm{T}$$ $$\lt$$ 60 GeV and $$\lvert y \rvert$$ $$\lt$$ 2.25. In addition, the same data set is used to measure the relative production fraction ratios with the charmonium decay channels (B$$_\mathrm{(s)}$$ $$\to$$ X$$\,$$J/$$\psi$$ with X indicating a K$$^+$$, K$$^*$$(892)$$^0$$, or $$\phi$$(1020) meson) where the J/$$\psi$$ meson decays into a pair of muons. The open-charm results are used to normalize the relative production fraction ratios obtained from the charmonium samples. Measurements of the ratios of branching fractions of B meson decays to charmonium and open-charm final states are also reported, which will improve the world-average values of these ratios. Finally, we test isospin invariance in B meson production in proton-proton collisions and observe that it holds within the experimental precision.
B mesons contain a beauty quark that is four times heavier than a proton, yet they live only about one and a half picoseconds — in that time, light travels less than a millimeter.
In the series 'Star Trek,' 'quark' technologies are mentioned, but real B mesons are too short-lived to fuel a warp drive.