Model-independent measurement of the transversity amplitudes of the $B^0\to K^{\ast 0}{\mu }^{+}{\mu }^{-}$ decay

An analysis of the decay amplitudes of $B^0\to K^{\ast 0}(\to K^{+}{\pi }^{-}){\mu }^{+}{\mu }^{-}$ is presented, using proton-proton collision data recorded by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 8.4 fb${}^{-1}$. The amplitudes are constructed from Legendre polynomials in the ${\mu }^{+}{\mu }^{-}$ invariant mass squared region $1.1<q^2<8.0$ GeV${}^2\mathrm{/}{c}^4$. $C\text{\hspace{0.17em}⁣}P$-averaged observables are obtained from the amplitudes. Some of these observables present deviations with respect to the Standard Model, which can be interpreted as shifts in the effective Wilson coefficients. This model-independent approach enables tests of theoretical predictions that can help disentangle hadronic effects from potential contributions from physics beyond the Standard Model. This allows flexibility in the choice of $q^2$ binning for global analyses. Depending on the binning scheme, the deviation of the Wilson coefficient $C_9$ from its Standard Model expectation varies from $4.3\sigma$ to $4.8\sigma$.