Search

We have carried out an experiment to search for a neutron-rich hypernucleus, 6 H, by the 6 Li(π − , K + ) reaction at pπ− =1.2 GeV/c. The obtained missing-mass spectrum with an estimated energy resolution of 3.2 MeV (FWHM) showed no peak structure corresponding to the 6 H hypernucleus neither below nor above the 4 H+2n particle decay threshold. An upper limit of the production cross section for the bound 6 H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.

Study of exotic hadrons, which cannot be interpreted as ordinary three-quark baryons or quark-antiquark mesons, would offer us a good opportunity to investigate low-energy quark dyanmics. The pentaquark \(\varTheta ^+\) has a strangeness quantum number \(S=+1\) with its minimal quark configuration of \(uudd\bar{s}\). The distinct features of the \(\varTheta ^+\) are a light mass of about 1540 MeV and a narrow width of a few MeV or less. If such an exotic pentaquark exits, it is quite interesting from a viewpoint of the hadron structure. Many experiments searched for the \(\varTheta ^+\) so far, but the experimental situation was still controversial. For further investigation, a high-statistics and high-resolution experiment has been required. In this chapter, both theoretical and experimental studies of the \(\varTheta ^+\) pentaquark are reviewed. The present experiment is introduced in the last section.

We carried out an experiment to produce the neutron-rich hypernucleus H-6(Lambda) via the (pi(-), K+) reaction on Li-6 target at the pion beam momentum of 1.2 GeV/c (J-PARC E10). In order to calibrate the scale of the missing-mass or of the Lambda binding energy of the hypernucleus, we also measured the C-12(pi(+), K+)(12)(Lambda)12, p(pi(-), K+)Sigma(-) and p(pi(+), K+)Sigma(+) reactions. The experiment was performed at the J-PARC Hadron Hall K1.8 beam line in December 2012 and January 2013. The overall collected data sample corresponds to an integrated beam intensity of 1.65 x 10(12) pions

The ${\ensuremath{\Theta}}^{+}$ pentaquark baryon was searched for via the ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{\ensuremath{-}}X$ reaction with a missing mass resolution of $1.4\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ (FWHM) at the Japan Proton Accelerator Research Complex (J-PARC). ${\ensuremath{\pi}}^{\ensuremath{-}}$ meson beams were incident on the liquid hydrogen target with a beam momentum of $1.92\text{ }\text{ }\mathrm{GeV}/c$. No peak structure corresponding to the ${\ensuremath{\Theta}}^{+}$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2\ifmmode^\circ\else\textdegree\fi{} to 15\ifmmode^\circ\else\textdegree\fi{} in the laboratory frame is obtained to be $0.26\text{ }\text{ }\ensuremath{\mu}\mathrm{b}/\mathrm{sr}$ in the mass region of $1.51--1.55\text{ }\text{ }\mathrm{GeV}/{c}^{2}$. The upper limit of the ${\ensuremath{\Theta}}^{+}$ decay width is obtained to be 0.72 and 3.1 MeV for ${J}_{\ensuremath{\Theta}}^{P}=1/{2}^{+}$ and ${J}_{\ensuremath{\Theta}}^{P}=1/{2}^{\ensuremath{-}}$, respectively, using the effective Lagrangian approach.