In the last years, several discrepancies between observables in b->c quark transitions and the SM predictions have been found by the Belle, BaBaR, and LHCb collaborations. An interesting channel to investigate lepton flavor universality violations is the semileptonic decay of the Bc meson, which is accessible at the LHC. The ratio of the branching fractions of the Bc meson decaying to a J/psi and leptons of different generations (taus and muons) was measured by the LHCb collaboration to be  compatible with the SM within two standard deviations.

In this blackboard cross-talk, Camilla Galloni, an experimental physicist, will describe the principles and challenges of the recent measurement of lepton flavor universality violation with the R(J/psi) ratio with the CMS Run 2 data. Judd Harrison, a lattice theorist, will then outline the status of predictions for R(J/psi) made using lattice QCD, as well as prospects for future calculations.

 

 

 

Camilla Galloni (CMS) is an experimental particle physicist at the University of Wisconsin that she joined with a postdoctoral position after her PhD in particle physics at the University of Zurich. She has worked on CMS analyses with final states involving tau leptons. Since 2019 she has joined the CMS GEM Muon group working on the data acquisition system, operations, and commissioning of the GEM detector.

 

Judd Harrison (TH) joined the University of Glasgow in 2018 after completing his PhD at the University of Cambridge. In 2021 he secured a Stephen Hawking research fellowship and has since led various form factor calculations for B decays to vector final states for the HPQCD lattice collaboration, including B to D*, Bs to Ds* and Bc to J/psi.