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Experimental results for mesonic $b \to s \mu^+ \mu^-$ decays show a patternof deviations from Standard-Model predictions, which could be due to newfundamental physics or due to an insufficient understanding of hadroniceffects. Additional information on the $b \to s \mu^+ \mu^-$ transition can beobtained from $\Lambda_b$ decays. This was recently done using the process$\Lambda_b \to \Lambda \mu^+ \mu^-$, where the $\Lambda$ is the lighteststrange baryon. A further interesting channel is $\Lambda_b \to p^+ K^- \mu^+\mu^-$, where the $p^+ K^-$ final state receives contributions from multiplehigher-mass $\Lambda$ resonances. The narrowest and most prominent of these isthe $\Lambda(1520)$, which has $J^P=\frac32^-$. Here we present an ongoinglattice QCD calculation of the relevant $\Lambda_b \to \Lambda(1520)$ formfactors. We discuss the choice of interpolating field for the $\Lambda(1520)$,and explain our method for extracting the fourteen $\Lambda_b \to\Lambda(1520)$ helicity form factors from correlation functions that arecomputed in the $\Lambda(1520)$ rest frame. We present preliminary numericalresults at a pion mass of 340 MeV and a lattice spacing of 0.11 fm. Thiscalculation uses a domain-wall action for the $u$, $d$, and $s$ quarks and arelativistic heavy-quark action for the $b$ quark, and is based on gauge-fieldconfigurations generated by the RBC and UKQCD Collaborations.

Lattice QCD calculation of form factors for $\Lambda_b \to \Lambda(1520) \ell^+ \ell^-$ decays