Programme

I.1 -- Invited, VCTP-46

Date: Monday, 4 October 2021

Time: 08:50 - 09:20

Form-factor-independent test of lepton flavor universality in semileptonic heavy meson and baryon decays

Tran Chien Thang

HCMC University of Technology and Education

In semileptonic decays of heavy mesons and baryons, the lepton-mass dependence factors out in the quadratic $\cos^2\theta$ coefficient of the differential $\cos\theta$ 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 $\tau$ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three $(e,\mu,\tau)$ 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 $\bar{B}^0 \to D^{(\ast)+} \ell^- \bar\nu_\ell$ and $B_c^- \to J/\psi (\eta_c)\ell^- \bar\nu_\ell$, and semileptonic heavy baryon decays such as $\Lambda_b \to \Lambda_c \ell^- \bar\nu_\ell)$ for each $\ell=e,\mu,\tau$.

Presenter: Tran Chien Thang