Phenomenology with Lattice NRQCD b Quarks

Abstract

The HPQCD collaboration has used radiatively-improved NonRelativistic QCD (NRQCD) for $b$ quarks in bottomonium to determine the decay rate of ${\rm Y}$ and ${{\rm Y}}^{\prime }$ mesons to leptons in lattice QCD. Using time-moments of vector bottomonium current-current correlators, we are also able to determine the $b$ quark mass in the $\overline{\mathrm{MS}}$ scheme. We use the same NRQCD $b$ quarks and Highly Improved Staggered Quark (HISQ) light quarks -- with masses down to their physical values -- to give a complete picture of heavy-light meson decay constants including those for vector mesons. We also study the semileptonic $B\to \pi \ell \nu$ decay at zero recoil to show that lattice QCD is consistent with the soft pion theorem for this decay: $f_0(q_{\max }^2)=f_B/f_{\pi }$ in the massless pion limit. Finally, we present preliminary results for the $B_c\to {\eta }_c\ell \nu$ semileptonic decay form factors. This is a showcase for the comparison of results for NRQCD $b$ quarks with those from HISQ $b$ quarks (both with HISQ $c$ quarks). We give the first 3-point results from our `heavy HISQ' programme, which will allow us to improve the normalisation of NRQCD-HISQ currents for other calculations.

Comments: 7 pages, 6 figures, Talk presented at the 33rd International Symposium on Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe International Conference Center, Kobe, Japan