Reach and complementarity of $\hat{I}¼\to e$ searches

Abstract

In Effective Field Theory, we describe $\hat{I}¼\leftrightarrow e$ flavour changing transitions using an operator basis motivated by experimental observables. In a six-dimensional subspace probed by $\hat{I}¼\to e{\hat{I}}^3$, $\hat{I}¼\to 3e$ and $\hat{I}¼\to e$ conversion on nuclei, we derive constraints on the New Physics scale from past and future experiments, illustrating the complementarity of the processes in an intuitive way. We also recall that a precise determination of the scalar quark currents in the nucleon will be required to distinguish scalar $\hat{I}¼\to e$ interactions on u-quarks from those on d-quarks.

improved kappa definition, minor corrections, fig 3 replaced; corresponds to published version + erratum