Y. Tajima

Experimental study of the decay KL0→π0νν̄

The first dedicated search for the rare neutral-kaon decay

Narrow Resonance at Eγ = 1020 MeV in the D(γ,η)pn Reaction

K_L^0\to\pi^0\nu\bar{\nu}

Development of silica aerogel with any density

has been carried out in the E391a experiment at the KEK 12-GeV proton synchrotron. The final upper limit of 2.6

Search for a light pseudoscalar particle in the decay K_{L};{0}-->pi;{0}pi;{0}X.

\times 10^{-8}

Search for the Decay K L-0 --> pi0nunu []

at the 90% confidence level was set on the branching ratio for the decay.

Search for a Light Pseudoscalar Particle in the DecayKL0→π0π0X

Differential and total cross sections of the D(γ, η)pn reaction have been measured for photon energies between 600 and 1150 MeV. The data provide the information of the γn → ηn reaction above Eγ ≥ 800 MeV. The total cross section shows a narrow resonance structure peaked at Eγ = 1020 MeV. The angular distribution coefficients together with the total cross section are compared with the calculation of the isobar model by using the impulse approximation. Although the spin and parity of the resonance cannot be determined unambiguously, a negative parity assignment gives better fit to the data.

Development of micro-gap wire chamber

New production methods of silica aerogel with high and low refractive indices have been developed. A very slow shrinkage of alcogel at room temperature has made possible producing aerogel with high refractive indices of up to 1.265 without cracks. Even higher refractive indices than 1.08, the transmission length of the aerogel obtained from this technique has been measured to be about 10 to 20 mm at 400 nm wave length. A mold made of alcogel which endures shrinkage in the supercritical drying process has provided aerogel with the extremely low density of 0.009 g/cm3, which corresponds to the refractive index of 1.002. We have succeeded producing aerogel with a wide range of densities

Development of a Neutral Beam Profile Monitor

We performed a search for a light pseudoscalar particle X in the decay K_{L};{0}-->pi;{0}pi;{0}X, X-->gammagamma with the E391a detector at KEK. Such a particle with a mass of 214.3 MeV/c;{2} was suggested by the HyperCP experiment. We found no evidence for X and set an upper limit on the product branching ratio for K_{L};{0}-->pi;{0}pi;{0}X, X-->gammagamma of 2.4x10;{-7} at the 90% confidence level. Upper limits on the branching ratios in the mass region of X from 194.3 to 219.3 MeV/c;{2} are also presented.

Search for the decay KL0→π0νν̄

We performed a search for the K L0-->pi0nu nu[over] decay at the KEK 12-GeV proton synchrotron. No candidate events were observed. An upper limit on the branching ratio for the decay was set to be 6.7 x 10(-8) at the 90% confidence level.We performed a search for the

Development of a low-mass and high-efficiency charged-particle detector

K^0_L \to \pi^0 \nu \bar{\nu}