Λb → pl-(v)over-barl form factors from lattice QCD with static b quarks

We present a lattice QCD calculation of form factors for the decay Lambda(b) -> p mu(-)(v) over bar (mu), which is a promising channel for determining the Cabibbo- Kobayashi-Maskawa matrix element vertical bar V-ub vertical bar 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 Lambda(b) -> p mu-(v) over bar (mu) differential decay rate in the range 14 GeV2 <= q(2) <= q(max)(2), and obtain the integral integral(q2max)(14 GeV2) [d Gamma/dq(2)]dq(2)/vertical bar V-ub vertical bar(2) = 15.3 +/- 4.2 ps(-1). Combined with future experimental data, this will give a novel determination of vertical bar V-ub vertical bar 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.