Rare b→sℓ+ℓ− decays provide some of the most sensitive tests of the Standard Model and require precise and systematically improvable hadronic input from lattice QCD. For the phenomenologically important channel B→K∗ℓ+ℓ− this entails a first-principles treatment of a resonant Kπ final state together with controlled heavy-quark dynamics. We present the status of a new exploratory lattice calculation that combines a variational determination of finite-volume Kπ states with the 1+J→2 finite-volume formalism to access the relevant matrix elements. The computation is carried out on an RBC/UKQCD domain-wall fermion ensemble with a−1≈2.7GeV and employs a dual heavy-quark strategy, using both a relativistic heavy-quark action tuned to the physical b mass and domain-wall heavy masses extrapolating from charm. All correlation functions are computed using (stochastic) distillation, providing a versatile setup that supports a broad range of heavy-to-light transitions into resonant final states. We show first two-point results for the K∗↔Kπ system and discuss the accessible kinematic region, which allows for a controlled study at high q2. The outlook for extending the calculation to lower q2 and for incorporating effects from charmonium resonances is outlined.
@article{arxiv.2603.17900,
title = {$K \pi$ scattering as a step towards $B \to K^* \ell^+ \ell^-$ from Lattice QCD},
author = {Felix Erben and Matthew Black and Peter Boyle and Matteo Di Carlo and Vera Gülpers and Maxwell T. Hansen and Nelson Pitanga Lachini and Rajnandini Mukherjee and Antonin Portelli and J. Tobias Tsang},
journal= {arXiv preprint arXiv:2603.17900},
year = {2026}
}