# The 35th International Symposium on Lattice Field Theory

18-24 June 2017
Palacio de Congresos
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# Contribution Parallel

Andalucía I
Weak Decays and Matrix Elements

# The $B_s \rightarrow D_s$ decay with highly improved staggered quarks and NRQCD

## Speakers

• Mr. Euan MCLEAN

## Content

A number of anomalies (apparent inconsistencies with the standard model (SM)) in semileptonic decays involving a $b \rightarrow c$ transition, have surfaced over the years. For example there are persistent discrepancies between experimentally observed values and SM predictions for the ratios $\mathcal{B}(B \rightarrow D()\tau \nu)/\mathcal{B}(B->D() l \nu)$ ($l=e$ or $\mu$). This implies lepton universality violation, since it is most easily explained by the $\tau$ and $l$ leptons having different couplings to the $W^-$ that mediates the decay.

There will soon also be data for the $B_s \rightarrow D_s l\nu$ decay, and to make an analogous comparison we require a high precision theoretical determination. I will present a lattice QCD calculation of the form factors for $B_s \rightarrow D_s$, using a relativistic staggered action (HISQ) for light and charm quarks, and a non-relativistic (NRQCD) action for bottom, on HISQ ensembles provided by the MILC collaboration. We employ a new approach to the renormalization of the vector current, by exploiting it's relation to the easier normalized scalar current.