Search

We have successfully measured neutral kaons, bombarding a liquid deuterium target with a photon beam in the threshold region from 0.8 to 1.1GeV. It was the first data for K^0 photoproduction on the deuteron in this energy region. The momentum spectra of K^0 production were compared with theoretical spectra calculated assuming isobar models for the elementary process and a realistic deuteron wave function for the target The present experiment has demonstrated a usefulness of the neutral kaon measurement for the investigation of photo strangeness production reactions.

A quasi-free photo-production of neutral kaons on ^C has been measured in the threshold region. Neutral kaons were identified by the invariant mass of two charged pions after K_s →π^+π^- decay outside the target. The obtained cross section is almost the same magnitude as that of K^+. The data are also compared with the calculation using the elementary kaon photo-production model. The results are the first information on n(γ, K^0)Λ reaction which is necessary to improve the models.

We have developed a liquid deuterium target system to be used with the Neutral Kaon Spectrometer (NKS). We designed the system with attention to yield, background and safety. For maximizing the K^0 yield, target thickness was optimized and the density of the liquid was kept as high as possible. For minimizing the background, we tried to reduce the amount of material around the target region. For the safety operation, we adopted the LabVIEW on Linux which enabled the remote monitoring and controlling. The target cell is made of aluminum outer shell with a thickness of 1mm and beam windows of 75μm thick polyimide film. We adopted the carbon fiber reinforced plastic (CFRP) with a thickness of 1.5mm for the material of the wall of the vacuum chamber covering the target cell. We succeeded in suppressing the boiling of the liquid deuterium and keeping the state as long as 2 weeks. The density of the liquid deuterium throughout the beam time in May 2004 was 0.1731±0.00007g/cm^3 including long term stability and short term fluctuation. The total error of the number of the target is 0.63%, which is much less than the statistical error.

The (e, e'p_0) cross section of ^O was measured at an energy transfer of 60 MeV and a momentum transfer of 105.2 MeV/c, using a 199.53 MeV continuous electron beam. The result is compared with theoretical calculations based on the relativistic distorted-wave impulse approximation (RDWIA). The theoretical values overestimate the experimental ones by a factor of two. The contribution of meson exchange current (MEC) effects is important in the high missing momentum region.

The (e, e'p_0) cross section of ^C previously measured using a 197.5 MeV continuous electron beam is compared with theoretical calculations based on the relativistic distorted-wave impulse approximation (RDWIA). The theoretical values overestimate the experimental ones by a factor of two. The contribution of meson exchange current (MEC) effects is important in the high missing momentum region.

We performed the ^C(γ, pn) experiment using tagged photons in an energy range from 30 to 120 MeV. Protons and neutrons were detected by a range telescope and NE213 liquid scintillators, respectively. Missing energy spectra of the ^C(γ, pn) reaction were deduced to search for the two nucleon excited states. In this report, we show the experimental setup for the ^C(γ, pn) reaction using the tagged photon beams. The preliminary results are shown and discussed. The data analysis is in progress.

The (e, e' n) cross sections have been measured in the giant resonance region at three momentum transfers. The E1 cross section shows a shallow minimum at 22 MeV. It is believed that the reaction mechanism is different from each other in the both sides of the minimum. The angular distribution of emitted neutrons and the momentum-transfer dependence of the cross section suggest that the E2 component is distributed over a wide energy region. About 40% of branching-ratio is observed to leave the residual ^8Be nucleus at levels of 16.6 and 16.9 MeV.

A 1.2 GeV booster electron synchrotron (STB ring) with combined use of pulse-beam stretcher at Laboratory of Nuclear Science (LNS) [1], Tohoku University was constructed for study of nuclear physics, which is also supposed to be an injector for a planned future 3rd generation light source. Currently the STB ring is routinely operated with a booster-storage mode to supply high energy γ-rays for nuclear study produced via bremsstrahlung using an internal target wire. Since finite range of a tagging counter array mounted in a bending section, the booster has to be also operated at another flat-top energy lower than 1.2 GeV to extend the γ-ray energy toward lower side. Because characteristics of the STB ring have not been well understood, various beam properties such as betatron tunes and instabilities are not completely controlled at the moment. In order to improve performance of the machine and to study the beam dynamics in a circular accelerator, fundamental properties of the STB ring is now being measured.

Acoustic detectors were developed using a piezo ceramic compound PZT. A shape of the PZT detector was essential to obtain a high sensitivity. A detector of a spherically shaped shell structure, whose size was 50 mm in diameter and 2 mm thick, was fabricated. Its sensitivity was calibrated to be about 40 mV/Pa at 54 kHz. Using the hydrophone, acoustic signals generated by an electron-induced cascade shower in water were detected. Experimental results were compared with simulation data and confirmed a consistency in between.

The (e, e' a) cross section has been measured at energy transfers from 10.0 to 28.4 MeV and a momentum transfer of 99 MeV/c, using a 197 MeV continuous electron beam. The cross section rapidly increases with decreasing energy at angles smaller than 25°, while it appears flat at larger angles. The forward-peaked angular distribution was observed below 18 MeV, and the forward peak shrinks at higher energies. An amount of αparticles from decay of ^5He is estimated.

We describe the 200-MeV bremsstrahlung photon tagging system, which was installed in the experimental Hall-1 at the Laboratory of Nuclear Science, Tohoku University. This system produces tagged photons from high duty electron beams supplied by Stretcher Booster Ring. The tagged photon energies are over a range from 20% to 80% of the incident electron energy. We carried out commissioning to examine the performance of the tagged photon beams produced by the 198 MeV electron beam. We demonstrated that the tagged photons can be employed for photonuclear reaction experiments with a momentum resolution Δp/p～1% at the tagged photon intensity I≤5×10^6.

The (e, e' p) cross section has been measured at an energy transfer of 60 MeV and a momentum transfer of 104.1 MeV/c, using a 197 MeV continuous electron beam. The reduced cross section at missing momenta between 81.3 and 321.2 MeV/c obtained from the experiment is compared with a distorted-wave impulse approximation (DWIA) in a reasonable agreement. This result demonstrates a high reliability of the DWIA calculation in this energy region, and supports the discussion that a large difference between the experimental data and the DWIA calculation in the (γ, p) reaction is related to the non-nucleonic degrees of freedom such as meson exchange currents.