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Abstract A double-$\\Lambda$ hypernucleus, _{\\Lambda\\Lambda}\\mathrm{Be}$, was observed by the J-PARC E07 Collaboration in nuclear emulsions tagged by the ($K^{-}, K^{+}$) reaction. This event was interpreted as the production and decay of $ {}_{\\Lambda\\Lambda}^{\\;10}\\mathrm{Be}$, _{\\Lambda\\Lambda}^{\\;11}\\mathrm{Be}$, or _{\\Lambda\\Lambda}^{\\;12}\\mathrm{Be}^{*}$ via $\\Xi^{-}$ capture in ^{16}\\mathrm{O}$. By assuming capture in the atomic 3D state, the binding energies of two $\\Lambda$ hyperons ($B_{\\Lambda\\Lambda}$) of these double-$\\Lambda$ hypernuclei are obtained to be $15.05 \\pm 0.11\\,\\mathrm{MeV}$, $19.07 \\pm 0.11\\,\\mathrm{MeV}$, and $13.68 \\pm 0.11\\,\\mathrm{MeV}$, respectively. Based on the kinematic fitting, _{\\Lambda\\Lambda}^{\\;11}\\mathrm{Be}$ is the most likely explanation for the observed event.

The Technical Design for the COMET Phase-I experiment is presented in this paper. COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into electrons in the field of an aluminum nucleus ($\\mu$–$e$ conversion, $\\mu^{-}N \\rightarrow e^{-}N$); a lepton flavor-violating process. The experimental sensitivity goal for this process in the Phase-I experiment is $3.1\\times10^{-15}$, or 90% upper limit of a branching ratio of $7\\times 10^{-15}$, which is a factor of 100 improvement over the existing limit. The expected number of background events is 0.032. To achieve the target sensitivity and background level, the 3.2 kW 8 GeV proton beam from J-PARC will be used. Two types of detectors, CyDet and StrECAL, will be used for detecting the $\\mu$–$e$ conversion events, and for measuring the beam-related background events in view of the Phase-II experiment, respectively. Results from simulation on signal and background estimations are also described.

In the J-PARC E27 experiment, we search for a K − pp bound state via the d ( π + , K + ) reaction at 1.7 GeV/ c at the K1.8 beam line. The binding energy and decay width of the K − pp bound state can be obtained in the missing mass measurement with a good energy resolution of 2 MeV/ c 2 . A range counter array (RCA) was constructed to detect the two high-momentum protons from the K − pp decay and to reduce the background such as quasi-free hyperon production. Recently, we have carried out a pilot run in June, 2012. The d ( π + , K + ) missing-mass spectrum has been obtained for the first time. In this report, an overview of the E27 experiment and a preliminary result on this pilot run are presented.

We have measured an inclusive missing-mass spectrum of the $d(\\pi ^+ , K^+ )$ reaction at a pion incident momentum of 1.69 GeV/$c$ at laboratory scattering angles between $2^\\circ$ and $16^\\circ$ with a missing-mass resolution of $2.7 \\pm 0.1$MeV/$c^{2}$ (FWHM) at the missing mass of 2.27 GeV/$c^{2}$. In this letter, we first try to understand the spectrum as a simple quasi-free picture based on several known elementary cross sections, considering the neutron/proton Fermi motion in the deuteron. While gross spectrum structures are well understood in this picture, we have observed two distinct deviations; one peculiar enhancement at 2.13 GeV/$c^{2}$ is due to the $\\Sigma N$ cusp, and the other notable feature is a shift of a broad bump structure, mainly originating from hyperon resonance productions of $\\Lambda (1405)$ and $\\Sigma (1385)^{+ /0}$, by about 22.4 $\\pm$ 0.4 (stat.) $^{+2.7}_{-1.7}$ (syst.) MeV/$c^{2}$ toward the low-mass side, which is calculated in the kinematics of a proton at rest as the target.

We have observed a “$K^{-}pp$”-like structure in the $d(\\pi ^{+ },K^{+ })$ reaction at 1.69 GeV$/c$. In this reaction, a $\\Lambda (1405)$ hyperon resonance is expected to be produced as a doorway to form $K^{-}pp$ through the $\\Lambda ^{\\ast }p\\rightarrow K^{-}pp$ process. However, most of the $\\Lambda (1405)$ produced would escape from the deuteron without secondary reactions. Therefore, coincidence of high-momentum ($>$250 MeV$/c$) proton(s) at large emission angles ($39^\\circ \\lt \\theta _{\\rm lab.} \\lt 122^\\circ$) was requested to enhance the signal-to-background ratio. A broad enhancement in the proton coincidence spectra is observed around the missing mass of 2.27 GeV$/c^2$, which corresponds to the $K^{-}pp$ binding energy of 95 ^{+18}_{-17}$ (stat.) ^{+30}_{-21}$ (syst.) MeV and the width of 162 ^{+87}_{-45}$ (stat.) ^{+66}_{-78}$ (syst.) MeV.

The first experiment at the J-PARC hadron facility, the J-PARC E19 experiment, aims at searching for the Theta super(+) pentaquark in the hadronic reaction pi super(-) p arrow right K super(-) X using the missing-mass technique. Based on a superconducting magnet excited at 2.5 T, the spectrometer achieved the high mass resolution of 1.4 MeV/c super(2) for the Theta super(+) production process. The first data taking was performed in the autumn of 2010. No significant structure was observed in the missing-mass spectrum. The upper limit obtained for the differential cross section is 0.26 mu b/sr in the laboratory frame at a 90 % CL.

The first experiment at the J-PARC hadron facility, the J-PARC E19 experiment, aims at searching for the Θ + pentaquark in the hadronic reaction π − p → K − X using the missing-mass technique. Based on a superconducting magnet excited at 2.5 T, the spectrometer achieved the high mass resolution of 1.4 MeV/c 2 for the Θ + production process. The first data taking was performed in the autumn of 2010. No significant structure was observed in the missing-mass spectrum. The upper limit obtained for the differential cross section is 0.26 μ b/sr in the laboratory frame at a 90 % CL.

In the J-PARC E27 experiment, we search for a K super(-) pp bound state via the d( pi super(+), K super(+)) reaction at 1.7 GeV/c at the K1.8 beam line. The binding energy and decay width of the K super(-) pp bound state can be obtained in the missing mass measurement with a good energy resolution of 2 MeV/c super(2). A range counter array (RCA) was constructed to detect the two high-momentum protons from the K super(-) pp decay and to reduce the background such as quasi-free hyperon production. Recently, we have carried out a pilot run in June, 2012. The d( pi super(+), K super(+)) missing-mass spectrum has been obtained for the first time. In this report, an overview of the E27 experiment and a preliminary result on this pilot run are presented.

Issue Title: FB20 Proceedings In the J-PARC E27 experiment, we search for a K ^sup -^ pp bound state via the d([pi] ^sup +^, K ^sup +^) reaction at 1.7 GeV/c at the K1.8 beam line. The binding energy and decay width of the K ^sup -^ pp bound state can be obtained in the missing mass measurement with a good energy resolution of 2 MeV/c ^sup 2^. A range counter array (RCA) was constructed to detect the two high-momentum protons from the K ^sup -^ pp decay and to reduce the background such as quasi-free hyperon production. Recently, we have carried out a pilot run in June, 2012. The d([pi] ^sup +^, K ^sup +^) missing-mass spectrum has been obtained for the first time. In this report, an overview of the E27 experiment and a preliminary result on this pilot run are presented.[PUBLICATION ABSTRACT]

Issue Title: FB20 Proceedings The first experiment at the J-PARC hadron facility, the J-PARC E19 experiment, aims at searching for the [Theta] ^sup +^ pentaquark in the hadronic reaction [pi] ^sup -^ p [arrow right] K ^sup -^ X using the missing-mass technique. Based on a superconducting magnet excited at 2.5 T, the spectrometer achieved the high mass resolution of 1.4 MeV/c^sup 2^ for the [Theta] ^sup +^ production process. The first data taking was performed in the autumn of 2010. No significant structure was observed in the missing-mass spectrum. The upper limit obtained for the differential cross section is 0.26 [mu]b/sr in the laboratory frame at a 90 % CL.[PUBLICATION ABSTRACT]