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 $Lambda$ 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 spectro
meter 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.
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.
Spectroscopy of a $^{10}_{Lambda}$Be hypernucleus was carried out at JLab Hall C using the $(e,e^{prime}K^{+})$ reaction. A new magnetic spectrometer system (SPL+HES+HKS), specifically designed for high resolution hypernuclear spectroscopy, was used
to obtain an energy spectrum with a resolution of 0.78 MeV (FWHM). The well-calibrated spectrometer system of the present experiment using the $p(e,e^{prime}K^{+})Lambda,Sigma^{0}$ reactions allowed us to determine the energy levels, and the binding energy of the ground state peak (mixture of 1$^{-}$ and 2$^{-}$ states) was obtained to be B$_{Lambda}$=8.55$pm$0.07(stat.)$pm$0.11(sys.) MeV. The result indicates that the ground state energy is shallower than that of an emulsion study by about 0.5 MeV which provides valuable experimental information on charge symmetry breaking effect in the $Lambda N$ interaction.
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.
Since the pioneering experiment, E89-009 studying hypernuclear spectroscopy using the $(e,e^{prime}K^+)$ reaction was completed, two additional experiments, E01-011 and E05-115, were performed at Jefferson Lab. These later experiments used a modified
experimental design, the tilt method, to dramatically suppress the large electromagnetic background, and allowed for a substantial increase in luminosity. Additionally, a new kaon spectrometer, HKS (E01-011), a new electron spectrometer, HES, and a new splitting magnet were added to produce precision, high-resolution hypernuclear spectroscopy. These two experiments, E01-011 and E05-115, resulted in two new data sets, producing sub-MeV energy resolution in the spectra of ${}^{7}_{Lambda}text{He}$, ${}^{12}_{Lambda}text{B}$ and ${}^{28}_{Lambda}text{Al}$ and ${}^{7}_{Lambda}text{He}$, ${}^{10}_{Lambda}text{Be}$, ${}^{12}_{Lambda}text{B}$ and ${}^{52}_{Lambda}text{V}$. All three experiments obtained a ${}^{12}_{Lambda}text{B}$, spectrum, which is the most characteristic $p$-shell hypernucleus and is commonly used for calibration. Independent analyses of these different experiments demonstrate excellent consistency and provide the clearest level structure to date of this hypernucleus as produced by the $(e,e^{prime}K^+)$ reaction. This paper presents details of these experiments, and the extraction and analysis of the observed ${}^{12}_{Lambda}text{B}$ spectrum.
Aerogel and water Cerenkov detectors were employed to tag kaons for a lambda hypernuclear spectroscopic experiment which used the (e,eK+) reaction in experimental Hall C at Jefferson Lab (JLab E05-115). Fringe fields from the kaon spectrometer magnet
yielded ~5 Gauss at the photomultiplier tubes (PMT) for these detectors which could not be easily shielded. As this field results in a lowered kaon detection efficiency, we implemented a bucking coil on each photomultiplier tubes to actively cancel this magnetic field, thus maximizing kaon detection efficiency.
We report a comprehensive x-ray scattering study of charge density wave (stripe) ordering in $rm La_{2-x}Ba_xCuO_4 (x approx 1/8)$, for which the superconducting $T_c$ is greatly suppressed. Strong superlattice reflections corresponding to static ord
ering of charge stripes were observed in this sample. The structural modulation at the lowest temperature was deduced based on the intensity of over 70 unique superlattice positions surveyed. We found that the charge order in this sample is described with one-dimensional charge density waves, which have incommensurate wave-vectors (0.23, 0, 0.5) and (0, 0.23, 0.5) respectively on neighboring $rm CuO_2$ planes. The structural modulation due to the charge density wave order is simply sinusoidal, and no higher harmonics were observed. Just below the structural transition temperature, short-range charge density wave correlation appears, which develops into a large scale charge ordering around 40 K, close to the spin density wave ordering temperature. However, this charge ordering fails to grow into a true long range order, and its correlation length saturates at $sim 230AA$, and slightly decreases below about 15 K, which may be due to the onset of two-dimensional superconductivity.
