Lattice QCD calculation of form factors for Λ_b → Λ (1520)ℓ+ℓ- decays

Experimental results for mesonic b→sμ⁺μ- decays show a pattern of deviations from Standard- Model predictions, which could be due to new fundamental physics or due to an insufficient understanding of hadronic effects. Additional information on the b → sμ⁺μ- transition can be obtained from Λ_b decays. This was recently done using the process Λ_b → Λμ⁺μ-, where the L is the lightest strange baryon. A further interesting channel is Λ_b → p+K-μ+ μ-, where the p⁺K^- final state receives contributions from multiple higher-mass L resonances. The narrowest and most prominent of these is the Λ (1520), which has J^P = 3/2 -. Here we present an ongoing lattice QCD calculation of the relevant Λ_b → Λ (1520) form factors. We discuss the choice of interpolating field for the L(1520), and explain our method for extracting the fourteen Λ_b → Λ (1520) helicity form factors from correlation functions that are computed in the L(1520) rest frame. We present preliminary numerical results at a pion mass of 340 MeV and a lattice spacing of 0:11 fm. This calculation uses a domain-wall action for the u, d, and s quarks and a relativistic heavy-quark action for the b quark, and is based on gauge-field configurations generated by the RBC and UKQCD Collaborations.