Λ[subscript b]→pℓ[superscript -]ν̅ [subscript ℓ] form factors from lattice QCD with static b quarks

Abstract

We present a lattice QCD calculation of form factors for the decay Λ[subscript b]→pμ[superscript -]ν̅[subscript μ], which is a promising channel for determining the Cabibbo-Kobayashi-Maskawa matrix element |V[subscript ub]| at the Large Hadron Collider. In this initial study we work in the limit of static b quarks, where the number of independent form factors reduces to two. We use dynamical domain-wall fermions for the light quarks, and perform the calculation at two different lattice spacings and at multiple values of the light-quark masses in a single large volume. Using our form factor results, we calculate the Λ[subscript b]→pμ[superscript -]ν̅[subscript μ] differential decay rate in the range 14 GeV[superscript 2]≤q[superscript 2]≤q[2 over max], and obtain the integral ∫[subscript 14 GeV]2[superscript qmax⁡2][dΓ/dq[superscript 2]]dq[superscript 2]/|V[subscript ub]|[superscript 2]=15.3±4.2 ps[superscript -1]. Combined with future experimental data, this will give a novel determination of |Vub| with about 15% theoretical uncertainty. The uncertainty is dominated by the use of the static approximation for the b quark, and can be reduced further by performing the lattice calculation with a more sophisticated heavy-quark action.