Probing Flavor Physics in BSM Scenarios with SM Null Tests (original) (raw)

2019, Springer Proceedings in Physics

As direct searches for new physics (NP) beyond the standard model (SM) at the LHC and other colliders have so far come up empty, increasingly attention has been paid to the intensity frontier, where high-precision measurements can probe rare processes which are possibly sensitive to indirect signals of NP. An important tool in the quest for NP effects on rare processes is the null tests of the SM. These are observables which vanish or are very small in the SM and which therefore could receive potentially large contributions from NP. Among such tests are, to be discussed here, asymmetries in the charm-meson decays D → P 1 P 2 + − (P = π, K and = e, μ), direct C P asymmetries in Cabibbo-favored nonleptonic charm-meson decays, muon asymmetries in the hyperon decay Σ + → pμ + μ − , and searches for the rare transitions b → ssd, dds and for nonleptonic B s-meson decays which fully break isospin symmetry. These are under ongoing or near-future investigations in the LHCb and other experiments. Observables which are predicted to be very small or vanish within the standard model (SM) serve, at least in principle, as its (approximate or exact) null tests [1]. They are potentially good places to look for indications of new physics (NP) beyond the SM (BSM), as any unambiguous nonnegligible result of the measurement of such an observable would be a compelling hint of NP BSM. If an experiment performing this kind of test produces no positive result, the null outcome will, on the flip side, translate into a constraint on the NP scenario under consideration. Over the years there have already been numerous efforts to conduct SM null tests with various flavor-changing neutral current (FCNC) transitions. Examples are the searches for processes manifesting charged-lepton-flavor violation, such as μ → eγ and B 0 → μ ± τ ∓ , which have so far come up negative [2]. Since they are forbidden in the SM, their observation would be clear evidence for NP. Another instance of SM null test is the deviation of the ratio R K (*) of the branching fractions of the decays