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Register a new userSearch for $^6_Lambda$H hypernucleus by the $^6$Li$(pi^-,K^+)$ reaction at $p_{pi^-}$ = 1.2 GeV/$c$
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We have carried out an experiment to search for a neutron-rich hypernucleus, $^6_{Lambda}$H, by the $^6$Li($pi^-,K^+$) reaction at $p_{pi^-}$ =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 $^6_{Lambda}$H hypernucleus neither below nor above the $^4_{Lambda}$H$+2n$ particle decay threshold. An upper limit of the production cross section for the bound $^6_{Lambda}$H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.
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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*NTheta} is quite small.
We searched for the bound state of the neutron-rich $Lambda$-hypernucleus ${}^{6}_{Lambda}$H, using the ${}^{6}$Li($pi^{-}, K^{+}$)X double charge-exchange reaction at a $pi^{-}$ beam momentum of 1.2 GeV/c at J-PARC. A total of $1.4 times 10^{12}$ $pi^{-}$ was driven onto a ${}^{6}$Li target of 3.5-g/$rm cm^2$ thickness. No event was observed below the bound threshold, i.e., the mass of ${}^{4}_{Lambda}$H + 2n, in the missing-mass spectrum of the ${}^{6}$Li($pi^{-}, K^{+}$)X reaction in the $2^{circ}$ < $theta_{pi K}$ < $20^{circ}$ angular range. Furthermore, no event was found up to 2.8 MeV/$c^2$ above the bound threshold. We obtained the the double-differential cross section spectra of the ${}^{6}$Li($pi^{-}, K^{+}$)X reaction in the angular range of $2^{circ}$ < $theta_{pi K}$ < $14^{circ}$. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the ${}^{6}_{Lambda}$H hypernucleus bound state. In addition, not only the bound state region, but also the $Lambda$ continuum region and part of the $Sigma^{-}$ quasi-free production region of the ${}^{6}$Li($pi^{-}, K^{+}$)X reaction, were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the $Sigma^{-}$-nucleus optical potential for $Sigma^{-}$-${}^{5}$He through spectrum shape analysis.
The $Theta^+$ pentaquark baryon was searched for via the $pi^-pto K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $pi^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $Theta^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{circ}$ to 15$^{circ}$ in the laboratory frame was obtained to be 0.26 $mu$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $Theta^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_{Theta}=1/2^+$ and $J^P_{Theta}=1/2^-$, respectively.
We have measured an inclusive missing-mass spectrum of the $d(pi^+, K^+)$ reaction at the pion incident momentum of 1.69 GeV/$c$ at the laboratory scattering angles between 2$^circ$ and 16$^circ$ with the 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 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 studied the reaction K+ p -> K+ n pi+ using an 11 GeV/c K+ beam and the Large Acceptance Superconducting Solenoid (LASS) multiparticle spectrometer facility at SLAC. We put limits on the production of narrow theta+ baryons in this reaction.
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