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

Abstract

Experimental results for mesonic $b\to s{\mu }^{+}{\mu }^{-}$ 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 $b\to s{\mu }^{+}{\mu }^{-}$ transition can be obtained from ${\Lambda }_b$ decays. This was recently done using the process ${\Lambda }_b\to \Lambda {\mu }^{+}{\mu }^{-}$, where the $\Lambda$ is the lightest strange baryon. A further interesting channel is ${\Lambda }_b\to p^{+}{K}^{-}{\mu }^{+}{\mu }^{-}$, where the $p^{+}{K}^{-}$ final state receives contributions from multiple higher-mass $\Lambda$ resonances. The narrowest and most prominent of these is the $\Lambda (1520)$, which has $J^P={\frac{3}{2}}^{-}$. Here we present an ongoing lattice QCD calculation of the relevant ${\Lambda }_b\to \Lambda (1520)$ form factors. 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 are computed in the $\Lambda (1520)$ 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.

7 pages, 3 figures