Title screen

[References: 44 tit.]

In the semileptonic decays of heavy mesons and baryons, the lepton-mass dependence factors out in the quadratic cos2θ coefficient of the differential cosθ distribution. We call the corresponding normalized coefficient the convexity parameter. This observation opens the path to a test of lepton universality in semileptonic heavy meson and baryon decays that is independent of form-factor effects. By projecting out the quadratic rate coefficient, dividing out the lepton-mass-dependent factor, and restricting the phase space integration to the τ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three (e,μ,τ) modes in a given semileptonic decay process. We discuss how the identity is spoiled by new physics effects. We discuss semileptonic heavy meson decays such as ¯B0→D(*)+ℓ−¯νℓ and B−c→J/ψ(ηc)ℓ−¯νℓ and semileptonic heavy baryon decays such as Λb→Λcℓ−¯νℓ for each ℓ=e, μ, τ.