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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


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 $B \to D^*$.