N. Ishibashi

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

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.

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

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.

Missing-mass spectroscopy with the Li6(π−,K+)X reaction to search for HΛ6

We searched for the bound state of the neutron-rich Lambda-hypernucleus H-6(Lambda), using the Li-6(pi(-), K+)X double charge-exchange reaction at a pi-beam momentum of 1.2 GeV/c at J-PARC. A total of 1.4 x 10(12) pi(-) was driven onto a Li-6 target of 3.5-g/cm(2) thickness. No event was observed below the bound threshold, i.e., the mass of H-4(Lambda) + 2n, in the missing-mass spectrum of the Li-6(pi(-), K+) X reaction in the 2 degrees < theta(pi K) < 20 degrees angular range. Furthermore, no event was found up to 2.8 MeV/c(2) above the bound threshold. We obtained the double-differential cross section spectra of the Li-6(pi(-), K+)X reaction in the angular range of 2 degrees < theta(pi K) < 14 degrees. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the H-6(Lambda) hypernucleus bound state. In addition, not only the bound state region, but also the Lambda continuum region and part of the Sigma(-) quasifree production region of the Li-6(pi(-), K+) reaction were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the Sigma(-) -nucleus optical potential for Sigma(-) -He-5 through spectrum shape analysis.

Missing-mass spectroscopy with the

We searched for the bound state of the neutron-rich Lambda-hypernucleus H-6(Lambda), using the Li-6(pi(-), K+)X double charge-exchange reaction at a pi-beam momentum of 1.2 GeV/c at J-PARC. A total of 1.4 x 10(12) pi(-) was driven onto a Li-6 target of 3.5-g/cm(2) thickness. No event was observed below the bound threshold, i.e., the mass of H-4(Lambda) + 2n, in the missing-mass spectrum of the Li-6(pi(-), K+) X reaction in the 2 degrees < theta(pi K) < 20 degrees angular range. Furthermore, no event was found up to 2.8 MeV/c(2) above the bound threshold. We obtained the double-differential cross section spectra of the Li-6(pi(-), K+)X reaction in the angular range of 2 degrees < theta(pi K) < 14 degrees. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the H-6(Lambda) hypernucleus bound state. In addition, not only the bound state region, but also the Lambda continuum region and part of the Sigma(-) quasifree production region of the Li-6(pi(-), K+) reaction were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the Sigma(-) -nucleus optical potential for Sigma(-) -He-5 through spectrum shape analysis.

{}^{6}

Exotic hadron study is key role to investigate the hadron structure and dynamics of the low energy QCD. In 2003, the evidence of the pentaquark Θ + , a light baryon with strangeness S=+1, was reported as the first candidate for the multi-quark system by LEPS group [1]. After the first report, there have been many both theoretical and experimental works. However, since the existence of Θ + is not yet established, an experiment with higher sensitivity is required. The J-PARC E19 experiment was performed to search for pentaquark Θ + in the π p→K X reaction at the K1.8 beam line as the first experiment in the J-PARC Hadron Experimental Facility. The unique features of E19 are as follows;  Less ambiguity: A meson induced reaction is desirable to understand the production mechanism of Θ + . In addition, a liquid hydrogen target was used in E19 to reduce the background contribution.  High statistics and high resolution: High intensity π beam is available at J-PARC K1.8 beam line. The spectrometer for the beam and the scattered particle provided a mass resolution better than 2 MeV/c 2 (FWHM), which is useful to determine the narrow width. Physics runs were carried out in 2010 and 2012. In the first (second) run, 7.8×10 10 (8.7×10 10 ) π beam with the momentum of 1.92 (2.0) GeV/c was irradiated on the liquid hydrogen target. No peak structure was observed in the missing mass spectra of both data. The 90% confidence level upper limit of the production cross section was estimated to be 0.26 μb/sr [2] for the first run, which are averaged over 2-15 deg. in the laboratory frame. With a theoretical calculation using the effective Lagrangian approarch [3], the upper limit of the Θ + decay width was estimated to be 0.72 and 3.1 MeV/c 2 for J P =1/2 + and 1/2 for the first run. The analysis on the second run is ongoing. The contribution will review the result of E19 experiment including analysis update.

Li(

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.

\pi^{-}, K^{+}

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.

)X reaction to search for

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.

{}^{6}_{\Lambda}

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.

H

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.