  We compile information from low-energy observables sensitive to
flavor-conserving 4-fermion operators with two or four leptons. Our analysis
includes data from e+e- colliders, neutrino scattering on electron or nucleon
targets, atomic parity violation, parity-violating electron scattering, and the
decay of pions, neutrons, nuclei and tau leptons. We recast these data as
tree-level constraints on 4-fermion operators in the Standard Model Effective
Field Theory (SMEFT) where the SM Lagrangian is extended by dimension-6
operators. We allow all independent dimension-6 operators to be simultaneously
present with an arbitrary flavor structure. The results are presented as a
multi-dimensional likelihood function in the space of dimension-6 Wilson
coefficients, which retains information about the correlations. In this form,
the results can be readily used to place limits on masses and couplings in a
large class of new physics theories.
