A. Masaike

Search for the H dibaryon in (K−, K+) reaction with scintillating fiber active target

Abstract We have studied ( K − , K + ) reactions at P K − = 1.66 GeV/c by using a newly developed active target made of plastic scintillating fibers. The H dibaryon ( S = −2, I ( J π ) = 0(0 + )) has been searched for through the direct process, K − + C → K + + H + X , by the analysis of the K + momentum spectrum with the help of visual data of the scintillating fiber target. No evidence for the H production was observed. Upper limits for the differential cross section for the H production in the forward direction of the K + is 0.04–0.6 μb/sr at the 90% confidence level for the H mass range from 1850 to 2215 MeV/c 2 .

High proton polarization in crystalline naphthalene by dynamic nuclear polarization with laser excitation at room temperature and liquid nitrogen temperature

Abstract We have successfully polarized protons in naphthalene doped with pentacene at room temperature and liquid nitrogen temperature. Pentacene molecules have been excited with a laser beam and protons have been polarized dynamically in the triplet state of pentacene. We have obtained a polarization of about 13% at liquid nitrogen temperature in a field of about 3 kG with an N2 laser of about 150 mW. We expect to obtain a polarization higher than 30% with another type of laser.

Neutron spin rotation and P-violation

A new apparatus to measure the neutron spin rotation due to interaction with matter has been developed at KEK. The present apparatus enables us to measure the parity violating neutron spin rotation in the p-wave resonance in the energy region of eV.

Study of parity and time‐reversal violation in neutron‐nucleus interactions

The parity and time‐reversal symmetries can be studied in neutron‐nucleus interactions. Parity non‐conserving asymmetries have been observed for many p‐wave resonances in a compound nucleus and measurements were performed on several nuclei in the mass region of A∼100 and A∼230. The statistical model of the compound nucleus provides a theoretical basis for extracting mean‐squared matrix elements from the experimental asymmetry data, and for interpreting the mean‐squared matrix elements. The constraints on the weak meson‐exchange couplings calculated from the compound‐nucleus asymmetry data agree qualitatively with the results from few‐body and light‐nuclei experiments. The tests of time‐reversal invariance in various experiments using thermal, epithermal, and MeV neutrons are being developed.

Test of parity violation and time reversal invariance in slow neutron absorption reactions

Abstract Measurements of helicity asymetries in slow neutron absorption reactions have been performed by detecting capture γ-rays. Large enhancements of parity-violation effect observed in these reactions are explained by interference between s- and p-wave resonances. The weak matrix element in hadronic reaction has been deduced from the results. Violation of time reversal invariance is being searched for in reactions in which large enhancement of the parity violation effect occurs. The same order of enhancement is expected in violation of time reversal invariance. The difference between the probability for helicity flip (+ → −) and that for (− → +) during transmission through a transversely polarized target is being measured. Recently, 139 La nuclei in LaAlO 3 crystal have been polarized successfully. The crystal is useful for the target, since the highest enhancement of the parity violation effect has been found for the 139 La target. The perspective of the experiment is shown.

Proton polarization at room temperature

We have polarized protons in naphthalene doped with pentacene at higher temperature (≥77 K) and lower magnetic field (∼3 kG) than those for ordinary polarized proton targets. Pentacene molecules have been excited with a laser beam. Protons in naphthalene have been polarized dynamically on the intermediate state of pentacene. We obtain about 13% polarization at liquid nitrogen temperature in about 3kG with a N2‐laser of about 150 mW. It has been found to be also possible to obtain high polarization at room temperature.

Neutron polarization for P- and T-violation experiments

The polarization of neutron spin, target nucleus spin and He nuclear spin was developed at KEK for measuring the T-odd term in polarized neutron transmission through a polarized nuclear target. A method to measure the neutron spin rotation was developed for the T-violation experiment. This apparatus has been found to be quite useful for the P-violating neutron spin rotation experiment. The angular distribution of neutron-capture γ-rays was measured for the study of the enhancement mechanism of the P-violation. The results are also discussed.