Beyond Colours and Flavours on Supercomputers

ended

We propose precision lattice QCD computations aiding the search for new physics beyond the Standard Model. In particular, we will address currently observed anomalies such as those displayed in the anomalous magnetic moment of the muon and lepton flavour universality tests in semi-leptonic B meson decays. We will further supplement searches for new physics through the computation of hadronic inputs, which combined with experimental results allow the determination of elements of the Cabibbo-Kobayashi-Maskawa matrix, thereby providing precision tests of the standard model. We will compute a large set of hadronic form factors of semi-leptonic B(s) and D(s) meson decays including pseudo-scalar and vector final states. State-of-the-art computations of these have two major shortcomings: the use of effective theories for the b-quark, and the treatment of vector final states as QCD-stable particles. We will eliminate the former of these by utilising very fine lattices which allow for the direct simulation of the b-quark near its physical mass. The latter will be addressed by merging specialist expertise in the computation of such form factors with that of hadronic scattering processes. This will result in the first calculation that takes the unstable nature of the vector final states in QCD into account. This is of paramount importance in order to address the observed anomalies in the B to D* and B to K* decays. We will compute the full basis of possible currents thereby providing standard model predictions as well as inputs for tests of beyond the standard model theories. Further, we will use the approach of massive QED in lattice QCD computations to provide an independent cross check of the electromagnetic corrections to the hadronic vacuum polarisation. This work will provide vital inputs in searches for physics beyond the standard model which are needed to fully exploit large ongoing experiments at the Large Hadron Collider and at facilities in Japan and the US.