Search for the rare decays K(L)→π0π0μ+μ- and K(L)→π0π0X0→π0π0μ+μ-.

Area of Science:

• Particle Physics
• High Energy Physics
• Rare Decay Searches

Background:

• The HyperCP experiment reported a possible new neutral boson (X(0)) with a mass of 214.3 MeV/c².
• Rare kaon decays offer a window into new physics beyond the Standard Model.

Purpose of the Study:

• To search for the rare decays K(L)→π(0)π(0)μ(+)μ(-) and K(L)→π(0)π(0)X(0)→π(0)π(0)μ(+)μ(-).
• To investigate the nature of the X(0) boson and its potential role in HyperCP observations.

Main Methods:

• Analysis of data from the KTeV E799 experiment.
• Setting upper limits on branching ratios for the specified rare kaon decays.

Main Results:

• No evidence was found for the decay K(L)→π(0)π(0)X(0)→π(0)π(0)μ(+)μ(-).
• An upper limit of Br(K(L)→π(0)π(0)X(0)→π(0)π(0)μ(+)μ(-)) < 1.0 × 10⁻¹⁰ was established at 90% confidence level.
• An upper limit of Br(K(L)→π(0)π(0)μ(+)μ(-)) < 9.2 × 10⁻¹¹ was established at 90% confidence level.

Conclusions:

• The results exclude a pseudoscalar X(0) as an explanation for the HyperCP observation, assuming a real dsX(0) coupling.
• This study places stringent constraints on new physics scenarios involving rare kaon decays.