Extraction of bare Form Factors for $\mathrm B_\mathrm s \to \mathrm K \ell \nu$ Decays in non-perturbative HQET

Understand

We discuss the extraction of the ground state $\langle \mathrm{K} ({\bf p})|V_\mu(0)|\mathrm{B} ({\bf 0})\rangle$ matrix elements from Euclidean lattice correlation functions.

• The emphasis is on the elimination of excited state contributions.
• Two typical gauge-field ensembles with lattice spacings $0.075, \; 0.05$ fm and pion masses $330,\;270$ MeV are used from the O($a$)- improved CLS 2-flavour simulations and the final state momentum is $|{\bf p}|=0.5\,{\rm GeV}$.
• The b-quark is treated in HQET including the $1/m_\mathrm{b}$ corrections.