.Box The bound-state levelstructures of the 16(cid:3) O and 15(cid:3) N hypernucleiwere studied by (cid:13) -ray spectroscopy using a germ anium detector array (H yperball) via the 16 O ( K (cid:0) ;(cid:25) (cid:0) (cid:13) ) reaction. A level schem e for 16(cid:3) O was determ ined from the observation ofthree (cid:13) -ray transitions from the doublet ofstates (2 (cid:0) ,1 (cid:0) ) at (cid:24) 6 : 7 M eV to the ground-state doublet (1 (cid:0) ,0 (cid:0) ). The 15(cid:3) N hypernucleiwere produced via proton em ission from unbound states in 16(cid:3) O .Three (cid:13) -rays were observed and the lifetim e ofthe 1 = 2 + ;1 state in 15(cid:3) N was m easured by the D oppler shift attenuation m ethod. By com paring the experim entalresults with shell-m odelcalculations,the spin-dependence ofthe (cid:3) N interaction isdiscussed.In particular,them easured 16(cid:3) O ground-statedoubletspacing of26.4 (cid:6) 1.6 (cid:6) 0.5 keV determ inesa sm allbutnonzero strength ofthe (cid:3) N tensorinteraction.

We measured the lifetime and the mesonic and non-mesonic decay rates of the 4He-Lambda hypernucleus. The hypernuclei were created using a 750 MeV/c momentum K- beam on a liquid 4He target by the reaction 4He(K-,pi-)4He-Lambda. The 4He-Lambda lifetime was directly measured using protons from Lambda p -> n p non-mesonic decay (also referred to as proton-stimulated decay) and was found to have a value of tau = 245 +/- 24 ps. The mesonic decay rates were determined from the observed numbers of pi-'s and pi0's as Gamma_pi-/Gamma_tot = 0.270 +/- 0.024 and Gamma_pi0/Gamma_tot = 0.564 +/- 0.036, respectively, and the values of the proton- and neutron-stimulated decay rates were extracted as Gamma_p/Gamma_tot = 0.169 +/- 0.019 and Gamma_n/Gamma_tot <= 0.032 (95% CL), respectively. The effects of final-state interactions and possible 3-body Lambda N N decay contributions were studied in the context of a simple model of nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and were used in the determination of the non-mesonic branching fractions. The implications of the results of this analysis were considered for the empirical Delta I = 1/2 rule and the decay rates of the 4H-Lambda hypernucleus.

We measured the lifetime and the mesonic and nonmesonic decay rates of the 4ΛHe hypemucleus. The hypemuclei were created using a 750 MeV/c momentum K - beam on a liquid 4 He target by the reaction 4 He(K - π - )4Λ He. The 4ΛHe lifetime was directly measured using protons from Ap → np nonmesonic decay (also referred to as proton-stimulated decay) and was found to have a value of T = 245 ± 24 ps. The mesonic decay rates were determined from the observed numbers of π - 's and π°'s as Γπ/ Γ tot = 0.270 ± 0.024 and Γπ°/ Γ tot = 0.564 ± 0.036, respectively, and the values of the proton- and neutron-stimulated decay rates were extracted as Fp/ r tot = 0.169 ± 0.019 and Γ n / Γ tot ≤0.032 (95% CL), respectively. The effects of final-state interactions and possible three-body ANN decay contributions were studied in the context of a simple model of nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and were used in the determination of the nonmesonic branching fractions. The implications of the results of this analysis were considered for the empirical ΔI = 1 2 rule and the decay rates of the 4ΛH hypemucleus.

Received 11 September 2007DOI:https://doi.org/10.1103/PhysRevC.76.039904©2007 American Physical Society

J.D. Parker, ∗ M.J. Athanas, † P.D. Barnes, ‡ S. Bart, B. Bassalleck, R. Chrien, G. Diebold, G.B. Franklin, K. Johnston, § P. Pile, B. Quinn, F. Rozon, R. Sawafta, ¶ R.A. Schumacher, R. Stearns, I. Sukaton, R. Sutter, J.J. Szymanski, ‡ and V.J. Zeps ∗∗ Carnegie Mellon University, Pittsburgh, PA 15213, USA Brookhaven National Laboratory, Upton, NY 11973, USA University of New Mexico, Albuquerque, NM 87131, USA University of Houston, Houston, TX 77004, USA Vassar College, Poughkeepsie, NY 12604, USA Indiana University Cyclotron Facility, Bloomington, IN 47408, USA (Revised September 13, 2007)

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

We present results from crystal spectroscopic analysis of silicon aero-gel foams heated by dynamic hohlraums on Z. The dynamic hohlraum on Z creates a radiation source with a 230-eV average temperature over a 2.4-mm diameter. In these experiments silicon aero-gel foams with 10 - mg / cm 3 densities and 1.7-mm lengths were placed on both ends of the dynamic hohlraum. Several crystal spectrometers were placed both above and below the z-pinch to diagnose the temperature of the silicon aero-gel foam using the K-shell lines of silicon. The crystal spectrometers were (1) temporally integrated and spatially resolved, (2) temporally resolved and spatially integrated, and (3) both temporally and spatially resolved. The results indicate that the dynamic hohlraum heats the silicon aero-gel to approximately 150-eV at peak power. As the dynamic hohlraum source cools after peak power the silicon aero-gel continues to heat and jets axially at an average velocity of approximately 50 - cm / μ s . The spectroscopy has also shown that the reason for the up/down asymmetry in radiated power on Z is that tungsten enters the line-of-sight on the bottom of the machine much more than on the top.

We have searched for neutrons from the three-body photon-induced reaction Be-9+gamma-->alpha+alpha+n using bremsstrahlung produced by electrons from a 2-MV Van de Graaff on a gold target. The target was located within a block of beryllium surrounded by an array of He-3 proportional counters embedded in paraffin. Based on energy and intensity calibrations of the accelerator and detector using the Be-9+gamma-->Be-8+n reaction, an upper limit of 93 nb (4sigma) was placed on the cross section for neutron production between the three-body and two-body thresholds. This value is substantially below a previous experimental result using photoexcitation by Pr-142 gamma rays and also below an earlier theoretical estimate. Bremsstrahlung spectra from the gold target were also measured in a NaI(Tl) detector at electron energies from 1.7 to 2.0 MeV and angles of 0degrees to 60degrees with respect to the beam axis. An analysis of photons above the 1665-keV two-body threshold shows that bremsstrahlung due to beta rays between 1665 keV and the 2160-keV end point of the Pr-142 beta-ray spectrum could account for the photoneutron yield in the three-body region that had previously been attributed to Pr-142 gamma rays.

High Resolution Spectroscopy of the 12 B Hypernucleus Produced by the e; e0K Reaction T. Miyoshi, M. Sarsour, L. Yuan, X. Zhu, A. Ahmidouch, P. Ambrozewicz, D. Androic, T. Angelescu, R. Asaturyan, S. Avery, O. K. Baker, I. Bertovic, H. Breuer, R. Carlini, J. Cha, R. Chrien, M. Christy, L. Cole, S. Danagoulian, D. Dehnhard, M. Elaasar, A. Empl, R. Ent, H. Fenker, Y. Fujii, M. Furic, L. Gan, K. Garrow, A. Gasparian, P. Gueye, M. Harvey, O. Hashimoto, W. Hinton, B. Hu, E. Hungerford, C. Jackson, K. Johnston, H. Juengst, C. Keppel, K. Lan, Y. Liang, V. P. Likhachev, J. H. Liu, D. Mack, A. Margaryan, P. Markowitz, J. Martoff, H. Mkrtchyan, S. N. Nakamura, T. Petkovic, J. Reinhold, J. Roche, Y. Sato, R. Sawafta, N. Simicevic, G. Smith, S. Stepanyan, V. Tadevosyan, T. Takahashi, K. Tanida, L. Tang, M. Ukai, A. Uzzle, W. Vulcan, S. Wells, S. Wood, G. Xu, H. Yamaguchi, and C. Yan

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.

The first Lambda-hypernuclear spectroscopy study using an electron beam has been carried out at Jefferson Lab. The hypernuclear spectrometer system (HNSS) was used to measure spectra from the C-12(e, e ' K+)(Lambda)B-12 reaction with close to 1 MeV resolution, the best energy resolution obtained so far in hypernuclear spectroscopy with magnetic spectrometers. This paper describes the HNSS and preliminary results for the B-12(Lambda) system. A program of hypernuclear physics experiments is planned for the future with much higher yield and even better energy resolution.

The (K-stopped(-), pi(0)) strangeness and charge changing reaction was investigated by producing a B-12(Lambda) hypernucleus from a carbon target. The branching ratio for K- capture to the ground and p-shell states of this hypernucleus was found to be (0.28+/-0.08) x 10(-3) and (0.35+/-0.09)x10(-3), respectively, which after correction for isospin was lower than a previously measured value for the C-12(K-stopped(-),pi(-)) C-12(Lambda) reaction, but still above the theoretical predictions for the ground state. The experiment obtained a missing-mass resolution comparable to in-flight reactions, however the higher background and lower selectivity of the K-stopped(-) reaction limits its usefulness in the study of new hypernuclear species.

The C-13(Lambda) hypernucleus was studied by measuring g rays in coincidence with the C-13(K-, pi(-)) reaction. g rays from the 1/2(-) and 3/2(-) states, which are the partners of the spin-orbit doublet states with a predominant configuration of [C-12(g.s.) (0(+))circle timesp(Lambda)], to the ground state were measured. The splitting of the states was found to be DeltaE(1/2(-) -3/2(-)) = 1152 +/- 54(stat) +/- 36(syst) keV. This value is 20-30 times smaller than that of single particle states in nuclei around this mass region. The j(Lambda) = l(Lambda) - 1/2[(p(1/2))(Lambda)] state appeared higher in energy, as in normal nuclei. The value gives new insight into the YN interaction. The excitation energies of the 1/2(-) and 3/2(-) states were obtained as 10.982 +/- 0.031(stat) +/- 0.056(syst) and 10.830 +/- 0.031(stat) +/- 0.056(syst) MeV, respectively. We also observed gamma rays from the 3/2(+) state, which has a [C-12(2(+))circle timess(Lambda)] configuration, to the ground state in C-13(Lambda). The excitation energy of the 3/2(+) state was obtained as 4.880 +/- 0.010(stat) +/-0.017(syst) MeV. Nuclear gamma rays with energies of 4.438 and 15.100 MeV had similar yields, which suggests that a quasifree knockout of a Lambda particle is dominant in highly excited regions.

An experiment demonstrating the production of double- Lambda hypernuclei in (K-, K+) reactions on Be-9 was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus H-4(Lambda Lambda) and the twin hypernuclei H-4(Lambda) and H-3(Lambda). The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the Lambda Lambda mass is unlikely.

We report a measurement of charge symmetry breaking in the NN eta system. We have measured the ratio of the differential cross sections of the charge-symmetric reactions pi (+) d-->pp eta and pi (-) d-->nn eta in the energy region of the eta threshold. Our result is R = d sigma(pi (+) d-->pp eta)/d sigma(pi (-) d-->nn eta) = 0.938+/-0.009 after a phase- space correction is made for the difference in the threshold energies of the two reactions. The deviation of R from unity is an indication of charge symmetry breaking, which is mostly due to pi (0)- eta mixing. A theoretical model for eta production which includes pi (0) - eta mixing was used to fit the data and yields a mixing angle of (1.5+/-0.4)degrees. Our result is consistent with the mixing angle determined in particle decay and isospin-forbidden processes as well as predictions by several theoretical analyses which yield approximate to1 degrees and another which yields approximate to2 degrees.

In the latest hg38 human genome assembly, centromeric gaps has been filled in by alpha satellite (AS) reference models (RMs) which are statistical representations of homogeneous higher-order repeat (HOR) arrays that make up the bulk of the centromeric regions. We analyzed these models to compose an atlas of human AS HORs where each monomer of a HOR was represented by a number of its polymorphic sequence variants. We combined these data and HMMER sequence analysis platform to annotate AS HORs in the assembly. This led to discovery of a new type of low copy number highly divergent HORs which were not represented by RMs. These were included in the dataset. The annotation can be viewed as UCSC Genome Browser custom track (the HOR-track) and used together with our previous annotation of AS suprachromosomal families (SFs) in the same assembly, where each AS monomer can be viewed in its genomic context together with its classification into one of the 5 major SFs (the SF-track). To catalog the diversity of AS HORs in the human genome we introduced a new naming system. Each HOR received a name which showed its SF, chromosomal location and index number. Here we present the first installment of the HOR-track covering only the 17 HORs that belong to SF1 which forms live functional centromeres in chromosomes 1, 3, 5, 6, 7, 10, 12, 16 and 19 and also a large number of minor dead HOR domains, both homogeneous and divergent. Monomer-by-monomer HOR annotation used for this dataset as opposed to annotation of whole HOR repeats provides for mapping and quantification of various structural variants of AS HORs which can be used to collect data on inter-individual polymorphism of AS.

The design, construction, and performance of a segmented-target, cathode-strip, tracking-detector is discussed. The chamber was made of low-Z materials in order to allow photons to leave the target region. It was used to determine the reaction vertex of stopping kaons, and was successfully operated in a high-intensity kaon beamline at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. The vertical and horizontal resolutions of the stopping kaon reaction positions were σX∼0.454mm and σY∼1.180mm, respectively. The uncertainty in the longitudinal (Z) direction is given by one-half the thickness of a target segment.

R. J. Sutter, 5 A. Švarc, and D. B. White University of California, Los Angeles, Los Angeles, California 90095-1547 Petersburg Nuclear Physics Institute, Gatchina, Leningrad District, 188350, Russia Rudjer Boskovic ́ Institute, Zagreb 10000, Croatia George Washington University, Washington, D.C. 20052 Brookhaven National Laboratory, Upton, New York 11973 Abilene Christian University, Abilene, Texas 79699 Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Forschungszentrum, Ju ̈lich D-52425, Ju ̈lich, Germany ~Received 16 June 2000; published 6 February 2001 !