Control of SU(3) symmetry breaking effects in calculations of B meson decay constant.

Early B-physics experiments have left us with a number of puzzles in heavy flavour physics. New lattice calculations (with a greater understanding of QCD effects in the Standard Model) will be needed to support the increase in experimental precision to be achieved by upcoming experiments such as Belle II. We extend the CSSM/UKQCD/QCDSF studies of SU(3) flavour breaking effects by presenting new results for the decay constants $f_B$ and $f_{B_s}$.