Search for the Decay K_L -> pi^0 nu nubar using pi^0 -> e^+ e^- gamma

TL;DR

This paper reports a search for the rare decay K_L -> pi^0 nu nubar, crucial for understanding CP violation and CKM parameters, but found no events and set an upper limit on its branching ratio.

Contribution

First experimental search for K_L -> pi^0 nu nubar using pi^0 -> e^+ e^- gamma, establishing an upper limit on its branching ratio.

Findings

No decay events observed.

Set upper limit B(K_L -> pi^0 nu nubar) < 5.9 x 10^-7.

Supports constraints on CP violation and CKM parameters.

Abstract

We report on a search for the decay K_L -> pi^0 nu nubar, carried out as a part of E799-II, a rare K_L decay experiment at Fermilab. Within the Standard Model, the K_L -> pi^0 nu nubar decay is dominated by direct CP violating processes, and thus an observation of the decay implies confirmation of direct CP violation. Due to theoretically clean calculations, a measurement of B(K_L -> pi^0 nu nubar) is one of the best ways to determine the CKM parameter eta. No events were observed, and we set an upper limit B(K_L -> pi^0 nu nubar) < 5.9 times 10^-7 at the 90% confidence level.