Model-independent analysis of $b\to d$ processes

Abstract

We perform a model-independent analysis of $|\Delta b|=|\Delta d|=1$ processes to test the standard model and probe flavor patterns of new physics. Constraints on Wilson coefficients are obtained from global fits to $B^{+}\to {\pi }^{+}{\mu }^{+}{\mu }^{-}$, $B_s^0\to {\bar{K}}^{\ast 0}{\mu }^{+}{\mu }^{-}$, $B^0\to {\mu }^{+}{\mu }^{-}$, and radiative $B\to X_d\gamma$ decays data. The fits are consistent with the standard model but leave sizable room for new physics. Besides higher-statistics measurements and more data in theory-friendly bins of the dilepton mass, further complementary observables such as angular distributions of $B_s^0\to {\bar{K}}^{\ast 0}{\ell }^{+}{\ell }^{-}$, $B\to \rho {\ell }^{+}{\ell }^{-}$ or the baryonic modes ${\Xi }_b\to \Sigma {\ell }^{+}{\ell }^{-}$, ${\Omega }_b^{-}\to {\Xi }^{-}{\ell }^{+}{\ell }^{-}$ are necessary to resolve the significant degeneracy in the fit for the semileptonic four-fermion operators. Assuming minimal quark flavor violation, the $b\to s$ global fit implies tight constraints on the $b\to d$ couplings, and hence allows to test this paradigm with improved data. Another benefit from $|\Delta b|=|\Delta d|=1$ processes is to shed light on the $B$-anomalies in $|\Delta b|=|\Delta s|=1$ modes from a new angle. Specifically, studies of lepton flavor-specific and dineutrino modes are informative on the lepton flavor structure. Rare $b\to d\ell \ell ,\nu \bar{\nu }$ decays can be studied at high luminosity flavor facilities LHCb, Belle II, and a future $Z$-factory.

Comments: 16 pages, 5 figures, 8 tables. Adaptations of parametric and experimental fit input, corresponding tables and figures, minor clarifications added, conclusions unchanged