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Register a new userObservation of the Helium 7 Lambda hypernucleus by the (e,eK+) reaction
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An experiment with a newly developed high-resolution kaon spectrometer (HKS) and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab (JLab). The ground state of a neutron-rich hypernucleus, He 7 Lambda, was observed for the first time with the (e,eK+) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The he 7 Lambda binding energy supplies the last missing information of the A=7, T=1 hypernuclear iso-triplet, providing a new input for the charge symmetry breaking (CSB) effect of Lambda N potential.
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The 3Lambda H and 4Lambda H hypernuclear bound states have been observed for the first time in kaon electroproduction on 3,4He targets. The production cross sections have been determined at Q**2= 0.35 GeV**2 and W= 1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the 3,4He(e,eK+)3,4Lambda H processes to the elementary cross section 1H(e,eK+) Lambda on the free proton, measured during the same experiment.
The missing mass spectroscopy of the $^{7}_{Lambda}$He hypernucleus was performed, using the $^{7}$Li$(e,e^{prime}K^{+})^{7}_{Lambda}$He reaction at the Thomas Jefferson National Accelerator Facility Hall C. The $Lambda$ binding energy of the ground state (1/2$^{+}$) was determined with a smaller error than that of the previous measurement, being $B_{Lambda}$ = 5.55 $pm$ 0.10(stat.) $pm$ 0.11(sys.) MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at $B_{Lambda}$ = 3.65 $pm$ 0.20(stat.) $pm$ 0.11(sys.) MeV was observed and assigned as a mixture of 3/2$^{+}$ and 5/2$^{+}$ states, confirming the gluelike behavior of $Lambda$, which makes an unstable state in $^{6}$He stable against neutron emission.
A double-$Lambda$ hypernucleus, ${}_{LambdaLambda}mathrm{Be}$, was observed by the J-PARC E07 collaboration in nuclear emulsions tagged by the $(K^{-},K^{+})$ reaction. This event was interpreted as a production and decay of $ {}_{LambdaLambda}^{;10}mathrm{Be}$, ${}_{LambdaLambda}^{;11}mathrm{Be}$, or ${}_{LambdaLambda}^{;12}mathrm{Be}^{*}$ via $Xi^{-}$ capture in ${}^{16}mathrm{O}$. By assuming the capture in the atomic 3D state, the binding energy of two $Lambda$ hyperons$,$($B_{LambdaLambda}$) 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, ${}_{LambdaLambda}^{;11}mathrm{Be}$ is the most likely explanation for the observed event.
We have determined the transparency of the nuclear medium to kaons from $A(e,e^{} K^{+})$ measurements on $^{12}$C, $^{63}$Cu, and $^{197}$Au targets. The measurements were performed at the Jefferson Laboratory and span a range in four-momentum-transfer squared Q$^2$=1.1 -- 3.0 GeV$^2$. The nuclear transparency was defined as the ratio of measured kaon electroproduction cross sections with respect to deuterium, ($sigma^{A}/sigma^{D}$). We further extracted the atomic number ($A$) dependence of the transparency as parametrized by $T= (A/2)^{alpha-1}$ and, within a simple model assumption, the in-medium effective kaon-nucleon cross sections. The effective cross sections extracted from the electroproduction data are found to be smaller than the free cross sections determined from kaon-nucleon scattering experiments, and the parameter $alpha$ was found to be significantly larger than those obtained from kaon-nucleus scattering. We have included similar comparisons between pion- and proton-nucleon effective cross sections as determined from electron scattering experiments, and pion-nucleus and proton-nucleus scattering data.
The production of neutron rich $Lambda$-hypernuclei via the ($K^-_stop$,$pi^+$) reaction has been studied using data collected with the FINUDA spectrometer at the DA$Phi$NE $phi$-factory (LNF). The analysis of the inclusive $pi^+$ momentum spectra is presented and an upper limit for the production of $^6_Lambda$H and $^7_Lambda$H from $^6$Li and $^7$Li, is assessed for the first time.
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