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Recently, the shift of the kaonic helium-4 2p state was precisely determined by the E570 and SIDDHARTA experiments. Prior to the experiment by E570, the average of three earlier experimental results showed - 43±8 eV, while most of the theoretical calculations give ∼ 0 eV. This five-sigma discrepancy between theory and experiment was known as the "kaonic helium puzzle". A recent theoretical model showed a possible resonance-like shift of maximum 10 eV for a certain value of a deep antikaon-nucleon interaction potential, which is different in helium 3 and helium 4. The E570 experiment determined the shift of the kaonic helium-4 2p state as +2±2 (stat)±2 (sys) eV in 2007. The SIDDHARTA experiment determined the shift as 0±6 (stat)±2 (sys) eV in 2009. The results of these experiments resolved the long-standing puzzle. A new experiment of the kaonic helium-3 X-ray measurement is being prepared by the J-PARC E17 collaborators, and the kaonic helium-3 X-ray data taken very recently by the SIDDHARTA experiment are on the way to be analyzed. The results of the E570, E17 and SIDDHARTA experiments examine the strong interaction for light nuclei with different isospin, and test furthermore recent theoretical predictions. © 2010 American Institute of Physics.

We have performed a γ spectroscopy experiment in 11 Λ B using a germanium detector array, Hyperball. In this experiment, we have observed six γ transitions from 11 Λ B. Among these transitions, the γ ray peak at 1482 keV is identified as E2 ( 1 / 2 + → 5 / 2 + ) . The result of this experiment indicates that the level structure seems quite different from a theoretical prediction based on the results of the previous experiments.

The present status of hypernuclear gamma-ray spectroscopy with Hyperball is summarized. We observed two gamma transitions of 16-Lambda-O(1- -> 1-,0-) and obtained the strength of the Lambda-N tensor force. In 10B(K-,pi- gamma) data, we did not observe the spin-flip M1 transition of 10-Lambda-B(2- -> 1-), but gamma rays from hyperfragments such as 7-Lambda-Li(7/2+ -> 5/2+) and 9-Lambda-Be(3/2+ ->1/2+) were observed. In 11B(pi+,K+ gamma) data, we observed six gamma transitions of 11_Lambda-B. We also attempted an inclusive gamma-ray measurement with stopped K- beam.

A new 3-axis magnetic field measurement system based on the Hall elements has been constructed at KEK. The new system was designed for the larger magnets of higher energy accelerator facilities such as J-PARC. We employed a 7 m long 2 m wide iron base, and the magnet and the field mapping machine were set on the same base. We set pivot fittings at intervals of 250 mm through the longer side of the base. Therefore the alignment accuracy between the mapping machine and the magnet is promised within 0.1 mm in total by simply putting the magnet on the base. In addition, by teaching the mapping-machine coordinates of the two separate points on the magnet axis to the mapping machine, the field measurement points on the magnet coordinates can automatically be calculated and positioned in software way. We used three single-axis Hall elements mass-produced by industry. 3 Hall elements could be mounted on a rectangular PEEK block. The distance between hall elements is approximately 3.3 mm. The accuracy of 3 directions of Hall elements is within 0.5 degrees. The temperature of Hall elements was controlled within 60 /spl plusmn/0.1 degrees centigrade. Owing to the light weight of the Hall sensor unit and the strong carbon fiber rod with one side support, the bend of the rod was less than 10 mm for 2200 mm rod length. Thus we have successfully measured the field of the big Q-magnet, whose bore diameter and length are 200 mm and 3 m.

A hybrid-emulsion experiment has been carried out at KEK-PS to study S = −2 nuclei. With the analysis of about 35% of total emulsion, we have successfully found three events of sequential weak decay of a double-hypernucleus. The results of these E373 events are summarized together with those of past experiments. The first experimental study of the branching ratios of weak decay modes of double-hypernuclei has been performed.

We will measure the x‐rays from kaonic 3He and 4He 3d→2p transition by using silicon drift detectors. Our precision goal is set to 1 eV to provide crucial information on the kaon‐nucleus strong interaction in the low energy limit. The experiment is to be performed as one of the first experiment in the J‐PARC hadron facility (J‐PARC E17). An overview and the present status of the experiment are presented.

We present an experimental study of Λ(1405) via the in‐flight (K−,n) reaction on the deuteron target (J‐PARC E31). We will measure all Σ+π−, Σ−π+ and Σ0π0 final states so that the isospin structure of the produced hyperon resonance state can be decomposed. In this report, we present an overview of the experiment and preparation status.

The KEK to Kamioka long-baseline neutrino experiment (K2K) has begun its investigation of neutrino oscillations suggested by atmospheric neutrino observations. Twenty-eight neutrino events have been detected in coincidence with the expected arrival time of the beam in the 22.5 kt fiducial volume of Super--Kamiokande, the far detector at 250 km distance. The expectation is 37.8+3.5-3.8, derived using measurements of neutrino interactions in a near detector and extrapolation using a beam simulation validated by a measurement of pion kinematics after production and focusing. The background is of order 10^-3 events., Comment: 6 pages, 3 embedded figures, LaTeX with RevTeX style, submitted to PRL. This version is As Submitted

A hybrid emulsion experiment was carried out to study double-strangeness nuclei produced via Ξ− hyperon capture at rest with the expectation of ten times larger statistics than previous experiments. We have analyzed 5% of the total emulsion and found one “twin-hypernuclei” event involving the emission of two single-Λ hypernuclei and a nuclear fragment from a Ξ− hyperon stopping point. The event is interpreted as the decay of a Ξ − + 14 N atomic system to 5 Λ He + 5 Λ He + 4 He + neutron . The species of the Ξ−-atom and the fragmentation products are uniquely identified for the first time for twin-hypernuclei events. Combined with the results from a past hybrid-emulsion experiment, one double-Λ hypernucleus and three twin-hypernuclei events have been found from Ξ− captures on light emulsion nuclei. The ratio of the detected rate of double-Λ hypernuclei to that of twin-hypernuclei is compared with theoretical estimates.

A high-intensity, high-resolution pion beam line has been proposed for the Japan Hadron Facility. An intensity of 109 and a momentum resolution of 10 -4 will be available. High-resolution, high-statistics, and high-sensitivity spectroscopic studies of hypernuclei will be possible.

High-quality excitation-energy spectra of Λ 7 Li, Λ 9 Be, Λ 13 C and Λ 16 O as well as Λ 12 C have been obtained with 2 MeV (FWHM) resolution and good statistics through the (π + ,K+) reaction. The spectra of Λ 12 C, Λ 16 0 and Λ 13 C are discussed in relation to the ΛN spindependent interaction, and those of Λ 9 Be and Λ 7 Li within the framework of the cluster structure of Λ hypernuclei. It is emphasized that Λ hypernuclear spectroscopy provides us with valuable information on Λ hypernuclear structure and the ΛN interaction.

We will measure the X‐rays from kaonic 3He 3d → 2p transition with a precision below 2 eV. It can provide crucial information on the kaon‐nucleus strong interaction. The experiment (J‐PARC E17) will be performed as Day‐1, which is one of the first experiments in the J‐PARC hadron facility in the year 2011. An overview and the present status of the J‐PARC E17 experiment are described.

The Theta+ was searched for via the K+p -> pi+X reaction using the 1.2 GeV/c K+ beam at the K6 beam line of the KEK-PS 12 GeV Proton Synchrotron. In the missing mass spectrum of the K+p -> pi+X reaction, no clear peak structure was observed. Therefore a 90 % C.L. upper limit of 3.5 ub/sr was derived for the differential cross section averaged over 2degree to 22degree in the laboratory frame of the K+p -> pi+Theta+ reaction. This upper limit is much smaller than the theoretical calculation for the t-channel process where a K0* is exchanged. From the present result, either the t-channel process is excluded or the coupling constant of g_{K*N\Theta} is quite small.

We have measured for the first time yields of both neutron‐proton and neutron‐neutron pairs emitted from the non‐mesonic weak decay of the Λ5He and Λ12C hypernuclei, produced via the (π+,K+) reaction. From the yields of both the back‐to‐back np‐pair events and nn‐pair events, we have directly determined the ratio of the neutron‐ and proton‐induced decay widths, Γn(Λn→nn)/Γp(Λp→np). Meanwhile, we have also determined the quenching of the observed numbers of single nucleons and coincident nucleon pairs compared with theoretical calculations. Our results suggest that contributions from the two‐nucleon‐induced three‐body process ΛNN→NNN are significant.

We have measured the angular correlation of the pair nucleons np and nn emitted from the nonmesonic weak decay (NMWD) of Λ12C produced via the (π+,K+) reaction in coincidence measurement. The Λp → np and Λn → nn modes were clearly identified by measuring the back‐to‐back correlation of the emitted nucleon pairs which is the characteristic of two‐body kinematics. From the measured nucleon pair numbers Nnn and Nnp, the ratio Γn/Γp of the partial decay widths Γn(Λn → nn) and Γp(Λp → np) of Λ12C was extracted to be 0.51 ± 0.13(stat)±0.04(syst); this result is almost free from the ambiguity due to the nuclear final state interaction and 3‐body decay process, which were inherent in the previous results. The obtained Γn/Γp ratio of Λ12C (p‐shell) is close to that of Λ5He (s‐shell). The results are consistent with those of recent theoretical calculations.

We have studied the residual gas beam profile monitor (RCBPM) for the J-PARC neutrino beamline, here the micro channel plate (MCP) is used as a read out device. We carried out the beam tests at the KEK-PS beamline to study the basic performance of the monitor. To check the capability of beam-profile measurement, we studied the properties of signal timing and the effect of electric field produced by the proton beam. We found that the ion collection is effective to avoid the beam induced background in a high beam background environment, and RGBPM works under the electric field produced by the beam itself of less than 20 kV/m. In addition, the gain calibration method of MCP has been developed using thermal electrons from the glowing wire. We found the gain of MCP is calibrated with an accuracy of better than 5%.

A technique using VHS high-fidelity equipment to record two different distinguishable signals on the same track is described. The first signal has to be recorded by a longer-gap-length head in order to obtain higher residual output after overwrite erasing by the second signal for coating-type materials. When the wavelength of the first signal is relatively short, the shorter the second signal wavelength, the greater is the erasure of the first signal. The azimuth angle should be chosen in such a way as to minimize the crosstalk between the first and second recorded signal. This phenomenon can be used for rotary erasing and overwrite erasing. >

We carried out an experiment to study asymmetric weak decays of polarized 5ΛHe produced via (π+,K+) reaction on 6Li. The experiment aims mainly at investigation of the ΛN weak interaction through the hypernuclear weak decays. We introduce the experiment and report current status of analysis.

This paper reports briefly recent works on asymmetries of weak decays from polarized Λ‐hypernuclei, weak decay branches of Λ12C and Λ11B hypernuclei, and production of Λ‐hypernuclei through compound hypernuclei through compound hypernuclei produced by (π+,K+) reactions at quasi‐free scattering region.