B- K and D- K form factors from fully relativistic lattice QCD

We present the result of lattice QCD calculation of the scalar, vector and tensor form factors for the B -Ke thorn e- decay, across the full physical range of momentum transfer. We use the highly improved staggered quark (HISQ) formalism for all valence quarks on eight ensembles of gluon-field configurations generated by the MILC collaboration. These include four flavors of HISQ quarks in the sea, with three ensembles having the light u=d quarks at physical masses. In the first fully relativistic calculation of these form factors, we use the heavy-HISQ method. This allows us to determine the form factors as a function of heavy-quark mass from the c to the b, and so we also obtain new results for the D -K tensor form factor. The advantage of the relativistic formalism is that we can match the lattice weak currents to their continuum counterparts much more accurately than in previous calculations; our scalar and vector currents are renormalized fully nonperturbatively and we use a well-matched intermediate momentum-subtraction scheme for our tensor current. Our scalar and vector B -K form factors have uncertainties of less than 4% across the entire physical q2 range and the uncertainty in our tensor form factor is less than 7%. Our heavy-HISQ method allows us to map out the dependence on heavy-quark mass of the form factors and we can also see the impact of changing spectator quark mass by comparing to earlier HPQCD results for the same quark weak transition but for heavier mesons.

Automated summary

We present the lattice QCD calculation results of the scalar, vector, and tensor form factors for the B-Ke- decay, covering the entire physical range of momentum transfer. Using the high-improved staggered quark (HISQ) formalism, we calculate the form factors with heavy-quark mass variation from c to b. The relativistic formalism allows us to accurately match the lattice weak currents to the continuum counterparts, resulting in form factors with uncertainties less than 4% for scalar and vector currents, and less than 7% for the tensor current. By comparing with previous results, we analyze the impact of changing the spectator quark mass.