The Physics of $K^0 -\bar K^0$ Mixing: $\widehat{B}_K$ and $\Delta M_{LS}$ in the Chiral Quark Model

TL;DR

This paper calculates the $K^0-ar K^0$ mixing parameters $\widehat{B}_K$ and $\Delta M_{LS}$ using the chiral quark model, incorporating one-loop corrections and gluon condensate effects, to compare with experimental data and constrain CKM parameters.

Contribution

The paper provides a novel computation of $\widehat{B}_K$ and $\Delta M_{LS}$ within the chiral quark model, including non-factorizable corrections and long-distance effects.

Findings

$\widehat{B}_K= 0.87 \, ext{±} \, 0.33$

$\Delta M_{LS}^{th}/ ext{exp} = 0.76^{+0.64}_{-0.34}$

Gluon condensate effects significantly influence the results.

Abstract

We compute the $\widehat B_K$ parameter and the mass difference $\Delta M_{LS}$ of the $K^0-\bar K^0$ system by means of the chiral quark model. The chiral coefficients of the relevant $\Delta S=2$ and $\Delta S=1$ 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 $O(\alpha_S N)$ coming from gluon condensation. The size of the gluon condensate is determined by fitting the experimental value of the amplitude $K^+ \to \pi^+\pi^0$. By varying all the relevant parameters we obtain $\widehat{B}_K= 0.87 \pm 0.33\ .$ We evaluate within the model the long-distance contributions to $\Delta M_{LS}$ induced by the double insertion of the $\Delta S = 1$ chiral lagrangian and study the interplay between short- and long-distance amplitudes. By varying all parameters we obtain $\Delta M_{LS}^{th}/\Delta M_{LS}^{exp} = 0.76 ^{+0.64}_{-0.34} .$ Finally, we investigate the phenomenological constraints on the Kobayashi-Maskawa parameter Im $\lambda _t$ entering the determination of $\epsilon'/\epsilon$.