The physics of K0-K0 mixing: BK and ΔMLS in the chiral quark model Original Research Article

We compute the BK parameter and the mass difference ΔMLS of the K0−K0 system by means of the chiral quark model. The chiral coefficients of the relevant ΔS = 2 and ΔS = 1 chiral Lagrangians are computed via quark-loop integration. We include the relevant effects of one-loop corrections in chiral perturbation theory. The final result is very sensitive to non-factorizable corrections of O(αSN) coming from gluon condensation. The size of the gluon condensate is determined by fitting the experimental value of the amplitude K+ → π+π0. By varying all the relevant parameters we obtain BK = 0.87 ± 0.33. We evaluate within the model the long-distance contributions to ΔMLS induced by the double insertion of the ΔS = 1 chiral Lagrangian and study the interplay between short- and long-distance amplitudes. By varying all parameters we obtain ΔMLSth/ΔMLSexp = 0.76−0.34+0.64. Finally, we investigate the phenomenological constraints on the the Kobayashi-Maskawa parameter Im λt entering the determination of ε′/ε.