Mark Vagins

The final result of Brookhaven Experiment 845 is discussed. This experiment was a dedicated search for decays of the long-lived neutral kaon, $K\sb{L}$, into electromagnetic final states, and was conducted at Brookhaven National Laboratory; data were taken between February and May of 1989. Neutral kaons produced by 24 GeV/c protons striking a copper target were allowed to decay in vacuum. Their decay products then passed through various detector elements: charged particle tracking and momentum information were provided by four drift chambers and a spectrometer magnet; particle identification was performed by a threshold Cerenkov counter; a lead glass calorimeter provided energy and position information; and several arrays of scintillators were used for triggering the electronics and vetoing uninteresting events.

We report here on a search for the rare, flavor-changing neutral current decay $K\sb{L}\to e\sp+e\sp-e\sp+e\sp-$, known as the double Dalitz decay of the $K\sb{L}$, and a determination of its branching ratio. This decay is of theoretical interest due to its potential to allow a direct determination of the neutral kaon’s intrinsic parity and to provide inputs to an estimation of the mass of the as-yet undiscovered top quark.
A total of six events were observed with negligible background, tripling the previous world sample of two observed events. The double Dalitz decay’s branching ratio was measured to be BR($K\sb{L}\to e\sp+e\sp-e\sp+e\sp-) = (3.07 \pm 1.25$ (stat) $\pm$ 0.26 (sys)) $\times$ 10$\sp{-8}$, in good agreement with the theoretically predicted branching ratio of 3.4 $\times$ 10$\sp{-8}$.