K. Shirotori

Observation of Spin-Dependent Charge Symmetry Breaking in

The energy spacing between the spin-doublet bound state of _{Λ}^{4}He(1^{+},0^{+}) was determined to be 1406±2±2  keV, by measuring γ rays for the 1^{+}→0^{+} transition with a high efficiency germanium detector array in coincidence with the ^{4}He(K^{-},π^{-})_{Λ}^{4}He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus _{Λ}^{4}H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in ΛN interaction. By combining the energy spacings with the known ground-state binding energies, it is also found that the CSB effect is large in the 0^{+} ground state but is vanishingly small in the 1^{+} excited state, demonstrating that the ΛN CSB interaction has spin dependence.

\Lambda N

The Θ(+) pentaquark baryon was searched for via the π(-)p→K(-)X reaction with a missing mass resolution of 1.4 MeV/c(2) (FWHM) at the Japan Proton Accelerator Research Complex (J-PARC). π(-) meson beams were incident on the liquid hydrogen target with a beam momentum of 1.92 GeV/c. No peak structure corresponding to the Θ(+) mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2° to 15° in the laboratory frame is obtained to be 0.26 μb/sr in the mass region of 1.51-1.55 GeV/c(2). The upper limit of the Θ(+) decay width is obtained to be 0.72 and 3.1 MeV for J(Θ)(P)=1/2(+) and J(Θ)(P)=1/2(-), respectively, using the effective Lagrangian approach.

Interaction: Gamma-Ray Spectroscopy of

We have carried out an experiment to search for a neutron-ric h hypernucleus, 6 Λ H, by the6Li(π−,K+) reaction atpπ− =1.2 GeV/c. The obtained missing-mass spectrum with an estimated energy re solution of 3.2 MeV (FWHM) showed no peak structure correspo nding to the6 Λ H hypernucleus neither below nor above the 4 Λ H+2n particle decay threshold. An upper limit of the production c ross section for the bound6 Λ H hypernucleus was estimated to be 1.2 nb /sr at 90% confidence level.

^4_{\Lambda }

In this paper, a preliminary result from the latest hypernuclear γ-ray spectroscopy experiment (KEK-E566) is presented together with a short discussion. The experiment was performed at the KEK-PS K6 beam line in 2005. In this experiment, the 12C(π +,K +) Λ 12 C reaction was employed to populate Λ 12 C/ Λ 11 B hypernuclei. A germanium detector array, Hyperball2, was constructed to detect γ-rays emitted from the hypernuclei produced. Three hypernuclear γ-ray peaks were observed and assigned.

He

We have been conducting an experimental program to study strangeness photoproduc‐tions on the deuteron by measuring K0 and Λ in the threshold energy region. The π−π+ from K0 and π−p from Λ are detected by use of large acceptance magnetic spectrometers. At the first stage of the program, we started with Neutral Kaon Spectrometer (NKS), which consisted of timing counters and tracking devices in the magnetic field. The NKS spectrometer was employed to measure K0 photoproductions from deuteron and carbon target for the first time. A newly constructed spectrometer (NKS2) has been employed for the second stage experiment. It consists of a 110 ton dipole magnet and a combination of detectors. The momentum distributions of K0 and A from γ+d process were observed, and compared with the calculations based on the isobar models. The NKS2 spectrometer has been upgraded by installing a three dimensional tracking device in the central region. This improvement enables to explore the simultaneous measurement of the K0‐A w...

Search for the Θ+ pentaquark via the π(-)p→K(-)X reaction at 1.92 GeV/c.

The energy of tagged photons, which were provided from the internal photon tagging system of the Laboratory of Nuclear Science, Tohoku University, has been calibrated using the d(γ,π−pp) reaction. Charged pions and protons in the final state were detected with the Neutral Kaon Spectrometer (NKS2). Photon energies were obtained from the reaction of d(γ,π−pp). The derived photon energy was consistent with the design of the tagger system and the previous measurement using electron-positron pair production. The consistency demonstrates the performance of NKS2 and the capability of the photon energy calibration using d(γ,π−pp).

Search for HΛ6 hypernucleus by the Li6(π−,K+) reaction at pπ−=1.2GeV/c

The next generation hypernuclear γ-ray spectrometer, Hyperball-J, is described. Three of the key aspects in the array construction, namely geometrical configurations, cooling mechanism of Ge detectors, and Compton suppressors, are discussed. Results of simulation for planar and spherical arrangements are compared. Progresses in the development of pulse tube cooling system and PWO background suppression counters are reported.

γ-ray spectroscopy study of 11ΛB and 12ΛC

We report on the first observation of γ rays emitted from an sd-shell hypernucleus, _{Λ}^{19}F. The energy spacing between the ground state doublet, 1/2^{+} and 3/2^{+} states, of _{Λ}^{19}F is determined to be 315.5±0.4(stat)_{-0.5}^{+0.6}(syst)  keV by measuring the γ-ray energy of the M1(3/2^{+}→1/2^{+}) transition. In addition, three γ-ray peaks are observed and assigned as E2(5/2^{+}→1/2^{+}), E1(1/2^{-}→1/2^{+}), and E1(1/2^{-}→3/2^{+}) transitions. The excitation energies of the 5/2^{+} and 1/2^{-} states are determined to be 895.2±0.3(stat)±0.5(syst) and 1265.6±1.2(stat)_{-0.5}^{+0.7}(syst)  keV, respectively. It is found that the ground state doublet spacing is well described by theoretical models based on existing s- and p-shell hypernuclear data.

Neutral Kaon Photo‐Production in the Threshold Energy Region

We have carried out a pilot data taking of the J-PARC E05 experiment to search for the bound state peaks of

Energy calibration of tagged photons by the d(γ,π−pp) reaction

^{12}_\Xi