**B_c decays from highly improved staggered quarks and NRQCD**

*A. Lytle, B. Colquhoun, C. Davies, J. Koponen, C. McNeile, HPQCD Collaboration*

in 34th annual International Symposium on Lattice Field Theory

Contribution: pdf

**Abstract**

We calculate semileptonic form factors for the decays

$B_c \to \eta_c \, l \nu$ and $B_c \to J/\psi \, l \nu$

over the entire $q^2$ range, using

a highly improved lattice

quark action for charm at several lattice spacings down to $a=0.045$~fm.

We have two ways of treating the $b$ quark:

either with an $\O(\alpha_s)$ improved NRQCD formalism or

by extrapolating a heavy

mass $m_h$ to $m_b$ in the relativistic formalism.

Comparison of the two approaches

provides an important cross-check of methodologies in lattice QCD.

Nonperturbative renormalisation of the currents in the relativistic

theory also allows us then to fix NRQCD-charm normalisation

for $b$ to $c$ decays such as $B \to D$

and $B \to D^*$.