Search

RI-RICH, a ring-imaging Cherenkov counter for radioactive ions, has been developed to measure the velocity of the ions at intermediate energies. Our RI-RICH system consists of six multi-anode photomultiplier tubes covered with 360-nm bandpass filters and a radiator made of quartz or BK7. For the primary 132Xe beam with a velocity of β = 0 . 712 , a velocity resolution of Δ β ∕ β = 4 . 9 × 1 0 − 4 (one standard deviation σ ) and a detection efficiency of more than 99.99% were achieved. For the secondary beams with Z = 44 – 55 and β ≃ 0 . 70 , we successfully performed particle identification using the B ρ - Δ E - β method. The velocity resolutions of RI-RICH for these nuclides were equivalent to a more than 6 σ separation for the mass number.

The ΛN interaction is able to be studied with Λ hypernuclei. A missing mass spectroscopy with the (e, e′K+) reaction was developed and established at Jefferson Lab. The (e, e′K+) experiment achieved the best precision and accuracy in reaction spectroscopy of hypernuclei. In this article, we introduce the latest results of JLab E05-115 with a discussion of the ΛN charge symmetry breaking in p-shell hypernuclei. In addition, an analysis status of the nnΛ search experiment (JLab E12-17-003) is presented. An overview of one of future plans in which we aim to accurately measure the hypertriton binding energy (JLab C12-19-002) is also shown.

We present a precise measurement of the cross section, proton and $\rm ^3He$ analyzing powers, and spin correlation coefficient $C_{y,y}$ for $p$-$\rm ^3He$ elastic scattering near 65 MeV, and a comparison with rigorous four-nucleon scattering calculations based on realistic nuclear potentials and a model with $\Delta$-isobar excitation. Clear discrepancies are seen in some of the measured observables in the regime around the cross section minimum. Theoretical predictions using scaling relations between the calculated cross section and the $\rm ^3 He$ binding energy are not successful in reproducing the data. Large sensitivity to the $NN$ potentials and rather small $\Delta$-isobar effects in the calculated cross section are noticed as different features from those in the deuteron-proton elastic scattering. The results obtained above indicate that $p$-$\rm ^3He$ scattering at intermediate energies is an excellent tool to explore nuclear interactions not accessible by three-nucleon scattering., Comment: 22 pages, 6 figures

We present acoustic signatures of the electric quadrupolar degrees of freedom in the honeycomb-layer compound UNi$_4$B. The transverse ultrasonic mode $C_{66}$ shows softening below 30 K both in the paramagnetic phase and antiferromagnetic phases down to $\sim0.33$ K. Furthermore, we traced magnetic field-temperature phase diagrams up to 30 T and observed a highly anisotropic elastic response within the honeycomb layer. These observations strongly suggest that $\Gamma_6$(E$_{\rm 2g}$) electric quadrupolar degrees of freedom in localized $5f^2$ ($J = 4$) states are playing an important role in the magnetic toroidal dipole order and magnetic-field-induced phases of UNi$_4$B, and evidence some of the U ions remain in the paramagnetic state even if the system undergoes magnetic toroidal ordering., Comment: 6 pages, 4 figures + Supplemental Materials (11 pages, 9 figures)

We measured the cross section and the proton analyzing power A_yAy for pp–^33He elastic scattering at the angles \theta = 26.9^{\circ}θ=26.9∘–170.1^{\circ}170.1∘ in the center of mass system with a 65 MeV polarized proton beam. We compared the data with the rigorous numerical calculations based on the various nucleon–nucleon potentials. For the cross section, clear discrepancy is seen at the angles where the cross section takes minimum. For the proton analyzing power A_yAy, the calculations have moderate agreements with the data. In this proceedings, we show only the experimental results.

We performed the measurement of the cross section and the proton analyzing power \(A_y\) for p–\(^3\)He elastic scattering with a 65 MeV polarized proton beam at Research Center for Nuclear Physics (RCNP), Osaka University. The proton analyzing power \(A_y\) data are compared with the theoretical calculations based on the nucleon–nucleon potential (INOY04).

Missing-mass spectroscopy with the 3H(e, e′K+) reaction was carried out at Jefferson Lab’s (JLab) Hall A in Oct–Nov, 2018. The differential cross section for the 3H(γ∗, K+)Λnn was deduced at ω = Ee − Ee′ = 2.102 GeV and at the forward K+-scattering angle (0° ≤ θγ∗K ≤ 5°) in the laboratory frame. Given typical predicted energies and decay widths, which are (BΛ, Γ) = (−0.25, 0.8) and (−0.55, 4.7) MeV, the cross sections were found to be 11.2 ± 4.8(stat.)+4.1−2.1(sys.) and 18.1 ± 6.8(stat.)+4.2−2.9(sys.) nb/sr, respectively. The obtained result would impose a constraint for interaction models particularly between Λ and neutron by comparing to theoretical calculations.

JLab E12-19-002 Experiment is planned to measure the Λ-binding energies of 3ΛH [Jπ = 1/2+ or 3/2+(T = 0)] and 4ΛH (1+) at JLab Hall C. The expected accuracy for the binding-energy measurement is |ΔBtotal Λ | ≃ 70 keV. The accurate spectroscopy for these light hypernuclei would shed light on the puzzle of the small binding energy and short lifetime of 3ΛH, and the chargesymmetry breaking in the ΛN interaction. We aim to perform the experiment in 2025.

The hyperon puzzle, the observation that the two-solar-mass neutron stars existence is hardly explained by all models predicting the appearance of hyperons in the neutron star core is currently one of the unsolved key issues in the physics of compact stars. An experimental study of the reaction (e,e′K) on 40Ca 48Ca nuclei to study the isospin dependence of hyperon dynamics has been proposed, by the Jefferson lab hypernuclear collaboration, and approved by the Jefferson Lab (JLab) PAC. This paper describes a proposal to make a complementary study by extending it to 208Pb, whose properties largely reflects those of the uniform nuclear matter present in the interior of the neutron stars making it the ideal one for this task.

International audience; α-clustering strength at the surface of tin isotopes ^112,116,120,124Sn was measured by using quasi-free (p, pα) reaction at RCNP. By measuring the scattered protons and α particles in coincidence, formation of α clusters at the surface of tin isotopes was clearly evidenced. Surface α-clustering in heavy nuclei provides a natural explanation for the origin of α particles in α decay, and may also impact the neutron-skin thickness which plays an important role in constraining the nuclear symmetry energy.

"Why are the tin isotopes soft?" has remained, for the past decade, an open problem in nuclear structure physics: models which reproduce the isoscalar giant monopole resonance (ISGMR) in the "doubly-closed shell" nuclei, $^{90}$Zr and $^{208}$Pb, overestimate the ISGMR energies of the open-shell tin and cadmium nuclei, by as much as 1 MeV. In an effort to shed some light onto this problem, we present results of detailed studies of the ISGMR in the molybdenum nuclei, with the goal of elucidating where--and how--the softness manifests itself between $^{90}$Zr and the cadmium and tin isotopes. The experiment was conducted using the $^{94,96,98,100}$Mo($\alpha,\alpha^\prime$) reaction at $E_\alpha = 386$ MeV. A comparison of the results with relativistic, self-consistent Random-Phase Approximation calculations indicates that the ISGMR response begins to show softness in the molybdenum isotopes beginning with $A=92$., Comment: Accepted for publication to Physics Letters B

Beam helicity asymmetries in the $\overrightarrow{e}p \rightarrow e' K^{+} \Lambda $ reaction have been measured at unprecedentedly low four-momentum transfers $\langle Q^{2} \rangle = 0.05$ (GeV/c)2. At the Mainz Microtron (MAMI), the experiment was performed with a longitudinally polarized beam and an out-of-plane detection of the scattered electron. This experiment probed the associated helicity-dependent structure function ${\rm d} \sigma_{LT'}/{\rm d} \Omega_K^{c.m.}$ , which is sensitive to the details of resonances of the proton. The results were compared to models for kaon electroproduction using effective Lagrangians. The MAMI data is not supporting the Kaon-Maid isobar model, which uses strong longitudinal couplings of the virtual photon to nucleon resonances and predicts a strong peaking of the structure function at forward angles and low $Q^{2}$ . The data is also in disagreement with a Regge-plus-resonance model that predicts the incorrect sign of the structure function. The combination of the MAMI results wih data taken at higher four-momentum transfers measured at Jefferson Lab indicates a smooth transition in $Q^{2}$ without significant changes of the interference pattern in the electroproduction process.

The missing mass spectroscopy of the HeΛ7 hypernucleus was performed using the Li7(e, e ′K+)HeΛ7 reaction at the Thomas Jefferson National Accelerator Facility Hall C. The Λ- binding energy of the ground-state (1/2+) was determined with a smaller error than that of the previous measurement, being BΛ=5.55±0.10stat.±0.11sys.MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at BΛ=3.65±0.20stat. ±0.11sys.MeV was observed and assigned as a mixture of 3/2+ and 5/2+ states, confirming the "gluelike" behavior of Λ, which makes an unstable state in He6 stable against neutron emission.

T. Gogami1 ∗, P. Achenbach2, A. Ahmidouch3, I. Albayrak4, D. Androic5, A. Asaturyan6, R. Asaturyan6, O. Ates4, P. Baturin7, R. Badui7, W. Boeglin7, J. Bono7, E. Brash8, P. Carter8, C. Chen4, A. Chiba1, E. Christy4, S. Danagoulian3, R. De Leo10, D. Doi1, M. Elaasar11, R. Ent9, Y. Fujii1, M. Fujita1, M. Furic5, M. Gabrielyan7, L. Gan12, F. Garibaldi13, D. Gaskell9, A. Gasparian3, O. Hashimoto1, T. Horn9, B. Hu14, Ed. V. Hungerford21, M. Jones9, H. Kanda1, M. Kaneta1, S. Kato19, M. Kawai1, D. Kawama1, H. Khanal7, M. Kohl4, A. Liyanage4, W. Luo14, K. Maeda1, A. Margaryan6, P. Markowitz7, T. Maruta1, A. Matsumura1, V. Maxwell7, A. Mkrtchyan6, H. Mkrtchyan6, S. Nagao1, S. N. Nakamura1, A. Narayan15, C. Neville7, G. Niculescu16, M. I. Niculescu16, A. Nunez7, Nuruzzaman15, Y. Okayasu1, T. Petkovic5, J. Pochodzalla2, X. Qiu14, J. Reinhold7, V. M. Rodriguez17, C. Samanta18, B. Sawatzky9, T. Seva5, A. Shichijo1, V. Tadevosyan6, L. Tang4, N. Taniya1, K. Tsukada1, M. Veilleux8, W. Vulcan9, F. R. Wesselmann20, S. A. Wood9, T. Yamamoto1, L. Ya4, Z. Ye4, K. Yokota1, L. Yuan4, S. Zhamkochyan6 and L. Zhu4

International audience; The first observation of \({}_{\Lambda }^{4}\text{H}\) fragments by means of decay-pion spectroscopy with a high resolution magnetic spectrometer was achieved in 2012 at the Mainz Microtron MAMI. The extracted Λ binding energy was consistent with older nuclear emulsion data, but almost one order of magnitude higher in precision, while being limited by systematic uncertainties. This paper gives details on the kaon tagging at 0° forward angle which was indispensable for the success of the experiment. In addition, a re-analysis of the data collected in 2012 is presented, including an improved a posteriori spectrometer calibration and a more robust fitting of the decay-pion peak in the momentum spectrum.

We investigate magnetotransport properties in a single crystal of pyrochore-type ${\mathrm{Nd}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$. The metallic conduction is observed on the antiferromagnetic domain walls of the all-in--all-out-type Ir $5d$ moment ordered insulating bulk state that can be finely controlled by an external magnetic field along [111]. On the other hand, an applied field along [001] induces the bulk phase transition from insulator to semimetal as a consequence of the field-induced modification of the Nd $4f$ and Ir $5d$ moment configurations. A theoretical calculation consistently describing the experimentally observed features suggests a variety of exotic topological states as functions of electron correlation and Ir $5d$ moment orders, which can be finely tuned by the choice of rare-earth ion and magnetic field, respectively.

The giant acceleration (GA) of diffusion is a universal phenomenon predicted by the theoretical analysis given by Reimann et al. [Phys. Rev. Lett. 87, 010602 (2001)]. Here we apply the theory of the GA of diffusion to a single-molecule experiment on a rotary motor protein, ${\mathrm{F}}_{1}$, which is a component of ${\mathrm{F}}_{\mathrm{o}}{\mathrm{F}}_{1}$ adenosine triphosphate synthase. We discuss the energetic properties of ${\mathrm{F}}_{1}$ and identify a high energy barrier of the rotary potential to be $20{k}_{B}T$, with the condition that the adenosine diphosphates are tightly bound to the ${\mathrm{F}}_{1}$ catalytic sites. To conclude, the GA of diffusion is useful for measuring energy barriers in nonequilibrium and single-molecule experiments.

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a ^9B

International audience; Negatively charged pions from two-body decays of stopped _Lambda^4H hypernuclei were studied in 2012 at the Mainz Microtron MAMI, Germany. The momenta of the decay-pions were measured with unprecedented precision by using high-resolution magnetic spectrometers. A challenge of the experiment was the tagging of kaons from associated K^+∧ production off a Be target at very forward angles. In the year 2014, this experiment was continued with a better control of the systematic uncertainties, with better suppression of coincident and random background, improved particle identification, and with higher luminosities. Another key point of the progress was the improvement in the absolute momentum calibration of the magnetic spectrometers.

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a (^9)Be target in order to study the Λ binding energy of light hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at 0° forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. Coincidentally, negatively charged decay pions were detected by two independent high-resolution spectrometers. About 10^3 pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at p_π ≈ 133 MeV/c, corresponding to the unique signature for the two-body decay of hyperhydrogen (_Λ^4)H→(^4)H+π^-, stopped inside the target. Its Λ binding energy was determined to be B_Λ = 2.12 ± 0.01 (stat) ± 0.09 (syst) MeV with respect to the (^3)H + Λ mass.

An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, (Λ)(7)He, was observed for the first time with the (e, e'K+) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The (Λ)(7)He binding energy supplies the last missing information of the A = 7, T = 1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the ΛN potential.

The binding energy of 7He-Lambda has been obtained for the first time with reaction spectroscopy using the (e, e'K+) reaction at Jefferson Lab's Hall C. A comparison among the binding energies of the A=7 T=l iso-triplet hypernuclei, 7He-Lambda, 7Li*-Lambda and 7Be-Lambda, is made and possible charge symmetry breaking (CSB) in the Lambda-Nucleon potential is discussed. For 7He-Lambda and 7Be-Lamnda, the shifts in binding energies are opposite to those predicted by a recent cluster model calculation, which assumes that the unexplained part of the binding energy difference between 4H-Lambda and 4He-Lambda, is due to the CSB of the Lambda-Nucleon potential. Further examination of CSB in light hypernuclear systems is required both experimentally and theoretically.

The third generation spectroscopic study of Lambda hypernuclei using (e, e'K+) reaction (JLab E05-115) was performed at JLab Hall-C in 2009. The experiment introduced the newly developed high-resolution electron spectrometer (HES) with the existing high-resolution kaon spectrometer (HKS). Experimental configuration, conditions, spectrometer designs and current status of analysis are presented.

We have been conducting an experimental program to study strangeness photoproduc‐tions on the deuteron by measuring K0 and Λ in the threshold energy region. The π−π+ from K0 and π−p from Λ are detected by use of large acceptance magnetic spectrometers. At the first stage of the program, we started with Neutral Kaon Spectrometer (NKS), which consisted of timing counters and tracking devices in the magnetic field. The NKS spectrometer was employed to measure K0 photoproductions from deuteron and carbon target for the first time. A newly constructed spectrometer (NKS2) has been employed for the second stage experiment. It consists of a 110 ton dipole magnet and a combination of detectors. The momentum distributions of K0 and A from γ+d process were observed, and compared with the calculations based on the isobar models. The NKS2 spectrometer has been upgraded by installing a three dimensional tracking device in the central region. This improvement enables to explore the simultaneous measurement of the K0‐A with reasonable statistics.

We describe the design considerations and construction techniques of a large cylindrical transition radiation detector (TRD), 296 cm long and 311.4 cm in diameter, for the VENUS experiment at the e+e+ storage ring, TRISTAN. The design is based on measurements by using test chambers with e/π beams and X-ray sources. The test results will be fully described. The TRD contains four modules of radiators, each followed by an X-ray chamber with 8192 (2688) total (sense) wires. The gain calibration of all sense wires has been completed with an accuracy of 5%. The TRD is expected to provide a pion rejection ratio of 15±3 with an electron efficiency of 90% for isolated tracks with momenta above 1 GeV/c.

We have measured the branching ratio of the three-body process in the nonmesonic weak decay of {sub {Lambda}{sup 12}}C to be 0.29+-0.13. This result was obtained by reproducing the nucleon and the nucleon pair yields introducing a measured final state interaction. At the same time, we have determined the absolute decay widths, GAMMA{sub n} and GAMMA{sub p}, along with GAMMA{sub 2N}, whose relative ratio has been a long-standing puzzle. Including the three-body process, we have successfully reproduced the nucleon energy distribution, the coincidence two-nucleon angular correlation, and the momentum sum distribution simultaneously.

We have measured the branching ratio of the three-body process in the nonmesonic weak decay of Lambda12C to be 0.29+/-0.13. This result was obtained by reproducing the nucleon and the nucleon pair yields introducing a measured final state interaction. At the same time, we have determined the absolute decay widths, Gamma(n) and Gamma(p), along with Gamma2N, whose relative ratio has been a long-standing puzzle. Including the three-body process, we have successfully reproduced the nucleon energy distribution, the coincidence two-nucleon angular correlation, and the momentum sum distribution simultaneously.

We have measured for the first time yields of both neutron‐proton and neutron‐neutron pairs emitted from the non‐mesonic weak decay of the Λ5He and Λ12C hypernuclei, produced via the (π+,K+) reaction. From the yields of both the back‐to‐back np‐pair events and nn‐pair events, we have directly determined the ratio of the neutron‐ and proton‐induced decay widths, Γn(Λn→nn)/Γp(Λp→np). Meanwhile, we have also determined the quenching of the observed numbers of single nucleons and coincident nucleon pairs compared with theoretical calculations. Our results suggest that contributions from the two‐nucleon‐induced three‐body process ΛNN→NNN are significant.

We report unusual evolution of the conduction-electron state in the localized f electron system CexLa1-xB6 from normal electron state to heavy Fermi liquid (FL) state through local FL and non-FL states with increasing Ce concentration and/or with increasing magnetic field. The effective mass of quasiparticle or the coefficient A of T2 term of resistivity is found to increase divergently near the boundary between FL state and non-FL state. The features of the non-FL state are also different from those of the typical non-FL systems previously observed or theoretically predicted.

We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay (NMWD) of ^{5}_{\Lambda}He formed via the ^{6}Li(\pi^+,K^+) reaction. The energies of two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body decay of \Lambda p --> n p and \Lambda n --> n n, respectively. The ratio of the nucleon pair numbers was N_{nn}/N_{np}=0.45 \pm 0.11(stat)\pm 0.03(syst) in the kinematic region of cos(theta_{NN}) np)/\Gamma(\Lambda n --> nn). The ratio is consistent with recent theoretical calculations based on the heavy meson/direct quark exchange picture.

In a \ensuremath{\gamma}-ray spectroscopy experiment with the $({K}^{\ensuremath{-}},{\ensuremath{\pi}}^{\ensuremath{-}})$ reaction on a $^{10}\mathrm{B}$ target, we have observed the $7/{2}^{+}\ensuremath{\rightarrow}5/{2}^{+}$ spin-flip $M1$ transition in ${}_{\ensuremath{\Lambda}}^{7}\text{Li}$ via \ensuremath{\gamma}-\ensuremath{\gamma} coincidence with the $5/{2}^{+}\ensuremath{\rightarrow}1/{2}^{+}E2$ transition. This is the first successful $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurement for hypernuclei. The measured $M1 \ensuremath{\gamma}$-ray energy is $470.8\ifmmode\pm\else\textpm\fi{}1.9$(stat)$\ifmmode\pm\else\textpm\fi{}0.6$(syst) keV. The spacing of the $7/{2}^{+},5/{2}^{+}$ doublet is consistently explained using the strengths of the spin-spin, \ensuremath{\Lambda}-spin-orbit, and tensor interactions obtained from previous \ensuremath{\gamma}-spectroscopy experiments.

We have measured the angular correlation of the pair nucleons np and nn emitted from the nonmesonic weak decay (NMWD) of Λ12C produced via the (π+,K+) reaction in coincidence measurement. The Λp → np and Λn → nn modes were clearly identified by measuring the back‐to‐back correlation of the emitted nucleon pairs which is the characteristic of two‐body kinematics. From the measured nucleon pair numbers Nnn and Nnp, the ratio Γn/Γp of the partial decay widths Γn(Λn → nn) and Γp(Λp → np) of Λ12C was extracted to be 0.51 ± 0.13(stat)±0.04(syst); this result is almost free from the ambiguity due to the nuclear final state interaction and 3‐body decay process, which were inherent in the previous results. The obtained Γn/Γp ratio of Λ12C (p‐shell) is close to that of Λ5He (s‐shell). The results are consistent with those of recent theoretical calculations.

We performed a coincidence measurement of two nucleons emitted from the nonmesonic weak decay of lambda(5)He formed via the 6Li(pi+, K+) reaction. The energies of the two nucleons and the pair number distributions in the opening angle between them were measured. In both np and nn pairs, we observed a clean back-to-back correlation coming from the two-body weak reactions of lambda p --np and lambda n --nn, respectively. The ratio of the nucleon pair numbers was N(nn)/N(np) = 0.45 +/- 0.11(stat) +/- 0.03(syst) in the kinematic region of cos theta(NN)-0.8. Since each decay mode was exclusively detected, the measured ratio should be close to the ratio of gamma(lambda p --np)/gamma(lambda n --nn). The ratio is consistent with recent theoretical calculations based on the heavy meson and/or direct-quark exchange picture.

We have observed two $\ensuremath{\gamma}$-ray transitions in $_{\ensuremath{\Lambda}}^{16}\mathrm{O}$ from the 6.6 MeV excited ${1}_{2}^{\ensuremath{-}}$ state to both ground-state spin-doublet members (${1}_{1}^{\ensuremath{-}},{0}^{\ensuremath{-}}$) by the (${K}^{\ensuremath{-}},{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$) reaction. We have obtained the ground-state doublet spacing to be $26.4\ifmmode\pm\else\textpm\fi{}1.6(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\ifmmode\pm\else\textpm\fi{}0.5(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$ and the excitation energy of the ${1}_{2}^{\ensuremath{-}}$ state to be $6561.7\ifmmode\pm\else\textpm\fi{}1.1(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\ifmmode\pm\else\textpm\fi{}1.7(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$. The ground-state doublet spacing provides a small but nonzero strength of the tensor interaction between a $\ensuremath{\Lambda}$ and a nucleon. This is the first experimental result on the $\ensuremath{\Lambda}N$ tensor interaction.

High energy CW electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the usefulness of the (e,e'K+) reaction. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed resolution, ~900 keV, of the 12B(hypernuclear) spectrum is the best yet attained using magnetic spectrometers. The positions of the major excitations are in agreement with theoretical predictions and the previous binding energy measurements.

High-energy, cw electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the potential of the (e,e'K+) reaction for hypernuclear spectroscopy. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed energy resolution was found to be approximately 900 keV for the (12)(Lambda)B spectrum, and is substantially better than any previous hypernuclear experiment using magnetic spectrometers. The positions of the major excitations are found to be in agreement with a theoretical prediction and with a previous binding energy measurement, but additional structure is also observed in the core excited region, underlining the future promise of this technique.

FIRST PREFACE - 'The most important experiment to be carried out in low energy K-meson physics today is the definitive determination of the energy level shift in the K-p atoms, because of their direct connection with the physics of KN interaction and their complete independence from all other kinds of measurements which bear on this interaction'.

The binding energy of 7ΛHe has been obtained for the first time with reaction spectroscopy using the (e, e'K+) reaction at Jefferson Lab's Hall C. A comparison among the binding energies of the A = 7 T = l iso-triplet hypernuclei, 7ΛHe, 7ΛLi*and 7ΛBe, is made and possible charge symmetry breaking (CSB) in the ΛN potential is discussed. For 7ΛHe and 7ΛBe, the shifts in binding energies are opposite to those predicted by a recent cluster model calculation, which assumes that the unexplained part of the binding energy difference between 4ΛH and 4ΛHe, is due to the CSB of the ΛN potential. Further examination of CSB in light hypernuclear systems is required both experimentally and theoretically.