Improved determination of the electroweak penguin contribution to ϵ′/ϵ in the chiral limit

AbstractWe perform a finite energy sum rule analysis of the flavor ud two-point V–A current correlator, ΔΠ(Q2). The analysis, which is performed using both the ALEPH and OPAL databases for the V–A spectral function, Δρ, allows us to extract the dimension six V–A OPE coefficient, a6, which is related to the matrix element of the electroweak penguin operator, Q8, by chiral symmetry. The result for a6 leads directly to the improved (chiral limit) determination ϵ′/ϵ=(−15.0±2.7)×10−4. Determination of higher dimension OPE contributions also allows us to perform an independent test using a low-scale constrained dispersive analysis, which provides a highly nontrivial consistency check of the results