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Register a new userExperimental techniques and performance of $Lambda$-hypernuclear spectroscopy with the $(e,e^{prime}K^{+})$ reaction
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The missing-mass spectroscopy of $Lambda$ hypernuclei via the $(e,e^{prime}K^{+})$ reaction has been developed through experiments at JLab Halls A and C in the last two decades. For the latest experiment, E05-115 in Hall C, we developed a new spectrometer system consisting of the HKS and HES; resulting in the best energy resolution ($E_{Lambda} simeq0.5$-MeV FWHM) and $B_{Lambda}$ accuracy ($B_{Lambda}leq0.2$ MeV) in $Lambda$-hypernuclear reaction spectroscopy. This paper describes the characteristics of the $(e,e^{prime}K^{+})$ reaction compared to other reactions and experimental methods. In addition, the experimental apparatus, some of the important analyses such as the semi-automated calibration of absolute energy scale, and the performance achieved in E05-115 are presented.
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Experimental studies of hypernuclear dynamics, besides being essential for the understanding of strong interactions in the strange sector, have important astrophysical implications. The observation of neutron stars with masses exceeding two solar masses poses a serious challenge to the models of hyperon dynamics in dense nuclear matter, many of which predict a maximum mass incompatible with the data. In this article, it is argued that valuable new insight may be gained extending the experimental studies of kaon electro production from nuclei to include the $isotope[208][]{rm Pb}(e,e^prime K^+) isotope[208][Lambda]{rm Tl}$ process. The connection with proton knockout reactions and the availability of accurate $isotope[208][]{rm Pb}(e,e^prime p) isotope[207][]{rm Tl}$ data can be exploited to achieve a largely model-independent analysis of the measured cross section. A framework for the description of kaon electro production based on the formalism of nuclear many-body theory is outlined.
Missing mass spectroscopy with the $(e,e^{prime}K^{+})$ reaction was performed at Jefferson Laboratorys Hall C for the neutron rich $Lambda$ hypernucleus $^{9}_{Lambda}{rm Li}$. The ground state energy was obtained to be $B_{Lambda}^{rm g.s.}=8.84pm0.17^{rm stat.}pm0.15^{rm sys.}~{rm MeV}$ by using shell model calculations of a cross section ratio and an energy separation of the spin doublet states ($3/2^{+}_1$ and $5/2^{+}_1$). In addition, peaks that are considered to be states of [$^{8}{rm Li}(3^{+})otimes s_{Lambda}=3/2^{+}_{2}, 1/2^{+}$] and [$^{8}{rm Li}(1^{+})otimes s_{Lambda}=5/2^{+}_{2}, 7/2^{+}$] were observed at $E_{Lambda}({rm no.~2})=1.74pm0.27^{rm stat.}pm0.11^{rm sys.}~{rm MeV}$ and $E_{Lambda}({rm no.~3})=3.30pm0.24^{rm stat.}pm0.11^{rm sys.}~{rm MeV}$, respectively. The $E_{Lambda}({rm no.~3})$ is larger than shell model predictions by a few hundred keV, and the difference would indicate that a ${rm ^{5}He}+t$ structure is more developed for the $3^{+}$ state than those for the $2^{+}$ and $1^{+}$ states in a core nucleus $^{8}{rm Li}$ as a cluster model calculation suggests.
The missing mass spectroscopy of $Xi^{-}$ hypernuclei with the $(K^{-},K^{+})$ reaction is planned to be performed at the J-PARC K1.8 beam line by using a new magnetic spectrometer, Strangeness $-2$ Spectrometer (S-2S). A $v{C}$cerenkov detector with a radiation medium of pure water (refractive index of 1.33) is designed to be used for on-line proton rejection for a momentum range of 1.2 to 1.6 GeV/$c$ in S-2S. Prototype water $v{C}$erenkov detectors were developed and tested with positron beams and cosmic rays to estimate their proton-rejection capability. We achieved an average number of photoelectrons of greater than 200 with the latest prototype for cosmic rays, which was stable during an expected beam time of one month. The performance of the prototype in the cosmic-ray test was well reproduced with a Monte Carlo simulation in which some input parameters were adjusted. Based on the Monte Carlo simulation, we expect to achieve $>90%$ proton-rejection efficiency while maintaining $>95%$ $K^{+}$ survival ratio in the whole S-2S acceptance. The performance satisfies the requirements to conduct the spectroscopic study of $Xi^{-}$ hypernuclei at J-PARC.
The interpretation of the signals detected by high precision experiments aimed at measuring neutrino oscillations requires an accurate description of the neutrino-nucleus cross sections. One of the key element of the analysis is the treatment of nuclear effects, which is one of the main sources of systematics for accelerator based experiments such as the Long Baseline Neutrino Experiment (LBNE). A considerable effort is currently being made to develop theoretical models capable of providing a fully quantitative description of the neutrino-nucleus cross sections in the kinematical regime relevant to LBNE. The approach based on nuclear many-body theory and the spectral function formalism has proved very successful in explaining the available electron scattering data in a variety of kinematical conditions. The first step towards its application to the analysis of neutrino data is the derivation of the spectral functions of nuclei employed in neutrino detectors, in particular argon. We propose a measurement of the coincidence $(e,e^prime p)$ cross section on argon. This data will provide the experimental input indispensable to construct the argon spectral function, thus paving the way for a reliable estimate of the neutrino cross sections. In addition, the analysis of the $(e,e^prime p)$ data will help a number of theoretical developments, like the description of final-state interactions needed to isolate the initial-state contributions to the observed single-particle peaks, that is also needed for the interpretation of the signal detected in neutrino experiments.
Experiment 865 at the Brookhaven AGS obtained 410 K+ -> e+ nu e+e- and 2679 K+ -> mu+ nu e+e- events including 10% and 19% background. The branching ratios were measured to be (2.48+-0.14(stat.)+-0.14(syst.))x10^-8 (m_ee>150 MeV) and (7.06+-0.16+-0.26)x10^-8 (m_ee>145 MeV), respectively. Results for the decay form factors are presented.
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