Jul 6 – 13, 2022
Bologna, Italy
Europe/Rome timezone

Modified HQET power counting for constrained second-order power corrections in $B \to D^{(*)}l\nu$: $R(D^{(*)})$, $|V_{cb}|$ and New Physics

Jul 8, 2022, 5:00 PM
Room 9 (Indaco)

Room 9 (Indaco)

Parallel Talk Quark and Lepton Flavour Physics Quark and Lepton Flavour Physics


Markus Prim (Bonn University)


We develop a modified power-counting within the heavy quark effective theory (HQET),
that results in a highly constrained set of second-order power corrections in the heavy quark expansion, compared to the standard approach. We implement this modified expansion to determine all $\bar{B} \to D^{(*)}$ form factors, both within and beyond the Standard Model, to $\mathcal{O}(\alpha_s, \alpha_s/m_{c,b}, 1/m_{c,b}^2)$. Using measured $\bar{B} \to D^{(*)} \ell \bar\nu$ differential branching fractions for light leptons ($\ell = e$, $\mu$), we constrain not only leading and subleading Isgur-Wise functions, but also the $1/m_{c,b}^2$ corrections from subsubleading terms. We provide updated precision predictions for $\bar{B} \to D^{(*)} \tau \bar\nu$ decay rates, lepton universality ratios, and the CKM matrix element $|V_{cb}|$.

In-person participation Yes

Primary authors

Florian Bernlochner (University of Bonn) Chenglu Xiong (University of Bonn) Dean Robinson (LBNL) Michele Papucci (Caltech) Zoltan Ligeti (LBNL) Markus Prim (Bonn University)

Presentation materials