COLLOQUIUM: "First joint measurement of 𝑅(𝐷∗) and 𝑅(𝐷0) at LHCb" by Greg Ciezarek (CERN)


Previous measurements of the ratio of semileptonic decays 𝑅(𝐷∗)=𝐵(𝐵→𝐷∗tau nu)/𝐵(𝐵→𝐷∗ mu nu) and 𝑅(𝐷0)=𝐵(𝐵→𝐷0 tau nu)/𝐵(𝐵→𝐷0 mu nu) from Babar, Belle, and LHCb hint at a deviation from lepton universality. This colloquium presents the first joint measurement of both 𝑅(𝐷∗) and 𝑅(𝐷0) at LHCb, reconstructed with the tau→mu nu nubar decay mode in the [𝐷∗ mu] and [𝐷0 mu] final states and assuming isospin symmetry. This pathfinder analysis is based on Run 1 data. This result supersedes the previous LHCb measurement of 𝑅(𝐷(∗+)) alone with the muonic decay of the tau.