Beam and SKS spectrometers at the K1.8 beam line

High-resolution spectrometers for both incident beams and scattered particles have been constructed at the K1.8 beam line of the Hadron Experimental Facility at J-PARC. A point-to-point optics is realized between the entrance and exit of QQDQQ magnets for the beam spectrometer. Fine-pitch wire chamber trackers and hodoscope counters are installed in the beam spectrometer to accept a high rate beam up to 107 Hz. The superconducting kaon spectrometer for scattered particles was transferred from KEK with modifications to the cryogenic system and detectors. A missing-mass resolution of 1.9 ± 0.1 MeV/c2 (FWHM) was achieved for the ∑ peaks of (π±, K+) reactions on a proton target in the first physics run of E19 in 2010

J-PARC E27 Experiment to Search for a K−pp Bound State

We have carried out an experimental search for the simplest kaonic nucleus, $K^{ - }pp$, by using the $d(\pi ^{ + },K^{ + })$ reaction at $p_{\pi ^{ + }}$ = 1.69 GeV/$c$. The differential cross section of this reaction with covering a wide missing-mass range from the $\Lambda$ production threshold to the $\Lambda (1405)/\Sigma (1385)$ region has been measured for the first time. The inclusive missing-mass shape of the $\Lambda$ and $\Sigma$ production region was understood with a simple quasi-free picture except for an enhancement at 2.13 GeV/$c^{2}$ due to a $\Sigma N$ cusp. An obtained peak attributed to $Y^{*}$ production was significantly shifted to the low mass side compared with the simulation by $- 22.4$ MeV/$c^{2}$

J-PARC E19 Experiment: Pentaquark Θ+ Search in Hadronic Reaction at J-PARC

A search for the Θ^+ pentaquark in the $\pi ^{ - }p \to K^{ - }X$ reaction was performed at the J-PARC Hadron Facility. Two data samples were collected in 2010 and 2012 at π beam momenta of 1.92 and 2.0 GeV/c, respectively. No peak structure was observed in the missing mass spectra obtained from either data set. The upper limit for the production cross section averaged over the scattering-angle range of 2° to 15° in the laboratory frame was found to be 0.28 µb/sr. The decay width of the Θ^+ can be directly connected to the production cross section through a theoretical calculation using an effective Lagrangian. The estimated upper limits of the width were 0.41 and 2.8 MeV for the spin-parities of 1/2^+ and 1/2^−, respectively

Strangeness physics programs by S-2S at J-PARC

In the K1.8 beam-line at Hadron Experimental Facility of J-PARC, a new magnetic spectrometer S-2S is being installed. S-2S was designed to achieve a high momentum resolution of Δp/p = 6 × 10−4 in FWHM. Several strangeness-physics programs which require the high resolution will be realized by S-2S. The present article introduces J-PARC E70 (missing-mass spectroscopy of Ξ12Be) and E94 (missing-mass spectroscopy of Λ7Li, Λ10B, and Λ12C) experiments

Measurement of KN scattering below the KN mass threshold

Abstract. We measured πE invariant mass spectra below and above the K¯N mass threshold in the K−d → NπE reaction in order to study the K¯N interaction and the Λ(1405) resonance. This reaction can be described by the two-step process: (i) K¯N1 → K¯N followed by (ii) K¯N2 → πΣ, where N1 and N2 are nucleons bound in the deuteron. We deduced the S -wave scattering amplitude of K¯N →K¯N in the framework of the K¯N πΣ coupled channel so as to reproduce the observed πΣ spectra in the I = 0 channel. We found a resonance pole at 1417.7-7.4+6.0 (fitting error)-1.0+1.1 (systematic error) - i[26.9-7.9+6.0 (fitting error)-2.0+1.7 (systematic error)]MeV/c2