The CP-conserving contribution to KL→π0νν̄

The rare decay KL→π0νν̄ is dominated by direct CP violation and can be computed with extraordinarily high precision. In principle, also a CP-conserving contribution to this process can arise within the Standard Model. We clarify the structure of the CP-conserving mechanism, analysing both its short-distance and long-distance components. It is pointed out that the calculation of the CP-conserving amplitude, although sensitive in part to non-perturbative physics, is quite well under control. The resulting CP-conserving contribution to the rate for KL→π0νν̄ turns out to be very strongly suppressed because of several factors, which we discuss in detail.