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Register a new userSpectroscopy of Lambda-9Li by electroproduction
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In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei can provide information on the details of the effective hyperon-nucleon interaction. Electroproduction of the hypernucleus Lambda-9Li has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a 9Be target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. The cross section to low-lying states of Lambda-9Li is concentrated within 3 MeV of the ground state and can be fitted with four peaks. The positions of the doublets agree with theory while a disagreement could exist with respect to the relative strengths of the peaks in the doublets. A Lambda separation energy of 8.36 +- 0.08 (stat.) +- 0.08 (syst.) MeV was measured, in agreement with an earlier experiment.
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An experiment measuring electroproduction of hypernuclei has been performed in Hall A at Jefferson Lab on a $^{12}$C target. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. An unprecedented energy resolution of less than 700 keV FWHM has been achieved. Thus, the observed lam{12}{B} spectrum shows for the first time identifiable strength in the core-excited region between the ground-state {it s}-wave $Lambda$ peak and the 11 MeV {it p}-wave $Lambda$ peak.
An experimental study of the 16O(e,eK^+)16N_Lambda reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e,eK^+)Lambda,Sigma_0 exclusive reactions and a pre
cise calibration of the energy scale. A ground-state binding energy of 13.76 +/- 0.16 MeV was obtained for 16N_Lambda with better precision than previous measurements on the mirror hypernucleus 16O_Lambda. Precise energies have been determined for peaks arising from a Lambda in s and p orbits coupled to the p_{1/2} and p_{3/2} hole states of the 15N core nucleus.
We have measured the induced polarization of the ${Lambda}(1116)$ in the reaction $eprightarrow eK^+{Lambda}$, detecting the scattered $e$ and $K^+$ in the final state along with the proton from the decay $Lambdarightarrow ppi^-$.The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy $W$ ($1.6leq W leq 2.7$ GeV) and covered the full range of the kaon production angle at an average momentum transfer $Q^2=1.90$ GeV$^2$.In this experiment a 5.50 GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the $W$ and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially $Q^2$ independent in our kinematic domain, suggesting that somewhere below the $Q^2$ covered here there must be a strong $Q^2$ dependence. Along with previously published photo- and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved $s$-channel resonances.
An instrument of central importance for the strangeness photo- and electroproduction at the 1.5-GeV electron beam of the MAMI accelerator at the Institut fur Kernphysik in Mainz, Germany, is the newly installed magnetic spectrometer Kaos that is operated by the A1 collaboration in $(e,eK)$ reactions on the proton or light nuclei. Its compact design and its capability to detect negative and positive charged particles simultaneously complements the existing spectrometers. The strangeness program performed with Kaos in 2008-9 is addressing some important issues in the field of elementary kaon photo- and electroproduction reactions. Although recent measurements have been performed at Jefferson Lab, there are still a number of open problems in the interpretation of the data and the description of the elementary process using phenomenological models. With the identification of $Lambda$ and $Sigma^0$ hyperons in the missing mass spectra from kaon production off a liquid hydrogen target it is demonstrated that the extended facility at MAMI is capable to perform strangeness electroproduction spectroscopy at low momentum transfers $Q^2$ < 0.5 (GeV/c)$^2$. The covered kinematics and systematic uncertainties in the cross-section extraction from the data are discussed.
Level structure of the $^{12}_{Lambda}$C hypernucleus was precisely determined by means of $gamma$-ray spectroscopy. We identified four $gamma$-ray transitions via the $^{12}$C$(pi^{+},K^{+}gamma)$ reaction using a germanium detector array, Hyperball2. The spacing of the ground-state doublet $(2^{-}_{1},1^{-}_{1})$ was measured to be $161.5pm0.3text{(stat)}pm0.3text{(syst)}$,keV from the direct $M1$ transition. Excitation energies of the $1^{-}_{2}$ and $1^{-}_{3}$ states were measured to be $2832pm3pm4$,keV and $6050pm8pm7$,keV, respectively. The obtained level energies provide definitive references for the reaction spectroscopy of $Lambda$ hypernuclei.
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