Dr Benoit Blossier (CNRS/Laboratoire de Physique Théorique d'Orsay)
Understanding the composition of final states in B --> Xc l nu could help to get a feedback on the persisting disagreement between exclusive and inclusive determinations of Vcb. In particular the series of orbital excitations D** and radial excitations (D', D*') has received a lot of attention; a misinterpretation as a scalar state of the (D' --> D pi) spectrum tail could have induced an experimental overestimate of the broad states contribution to the total B --> Xc l nu width with respect to theoretical expectations, all of them made however in the infinite mass limit: it is the so-called 1/2 vs 3/2 puzzle. We will describe first attempts to measure on the lattice form factors of B --> D** l nu at realistic quark masses. Cleaner processes, like hadronic decays B --> D** pi and semileptonic decays Bs --> Ds** l nu in the strange sector have recently been examined by phenomenologists, putting new interesting ideas on those issues with, again, the need of lattice inputs.