The LHCb collaboration at CERN report the first observation of the decay of one B meson into another. A meson is a quark–antiquark pair, and B mesons are so-called because they contain a bottom, or b, quark. In previous measurements of the decays of B mesons, it's been the b quark that decays to a charm quark through the weak interaction, with the other quark of the meson as a spectator. But LHCb has picked up the decay of Bc+ — a bound antibottom–charm pair — in which the antibottom quark is the spectator instead, and the charm quark undergoes a weak interaction to produce a strange quark, alongside two light quarks.
Specifically, the team have used 3 fb−1 of data from proton–proton collisions in the Large Hadron Collider at centre-of-mass energies of 7 TeV and 8 TeV to access distinct signatures of the Bc+ decay. It's a satisfying 'first', but these measurements will also serve to constrain models of the production and decay of particles, to better understand many of the interactions taking place inside the LHC.