Current Projects of the HPQCD Collaboration
$B$ and $\Upsilon$ physics using the Nonrelativistic QCD action for $b$ quarks
- Analysis of $B$ and $B_s$ meson mixing for comparison to experiment, to determine CKM elements and constrain new physics.
- Calculation of $B$, $B_s$ and $B_c$ semileptonic form factors for comparison to experiment to determine CKM elements from a variety of processes.
- Calculation of electromagnetic transition rates in bottomonium systems for stringent tests of NRQCD/QCD.
- Extension of our calculations of bottomonium spectroscopy to include studies of possible exotic states with non-standard quark content, following experimental evidence for such states in the charmonium spectrum.
Light, charmed and $B$ meson physics using the Highly Improved Staggered Quark action
- Calculation of the Hadronic Vacuum Polarisation contribution to the anomalous magnetic moment of the muon. This quantity currently shows a 3$\sigma$ discrepancy between experiment and Standard Model expectations with improved experimental results on the horizon.
- Calculation of form factors for weak and electromagnetic decays for a range of mesons. This includes determinations using HISQ quarks with masses heavier than charm, that can be extrapolated up to the $b$. Comparison with NRQCD results can then test/improve our understanding of systematic uncertainties.
- Determination of quark masses and strong coupling constant. Further improvements are planned so that these QCD parameters can be pinned down even more accurately from lattice QCD results combined with experiment.
We work on gluon field configurations that use our improved (through $\alpha_s a^2$) discretisation of the gluon action and include $u$, $d$, $s$ and $c$ quarks in the sea using our Highly Improved Staggered Quark action. These configurations are generated by the MILC collaboration. They include $u$, $d$ sea quarks with a range of masses going down to their physical value for a very realistic picture of the QCD vacuum. We use computer time on the STFC's DiRAC facility and at Fermilab.