Cross-Section Measurement of Virtual Photoproduction of Iso-Triplet Three-Body Hypernucleus, ⋀nn

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

Revealing the short-range structure of the "mirror nuclei" 3^3H and 3^3He

When protons and neutrons (nucleons) are bound into atomic nuclei, they are close enough together to feel significant attraction, or repulsion, from the strong, short-distance part of the nucleon-nucleon interaction. These strong interactions lead to hard collisions between nucleons, generating pairs of highly-energetic nucleons referred to as short-range correlations (SRCs). SRCs are an important but relatively poorly understood part of nuclear structure and mapping out the strength and isospin structure (neutron-proton vs proton-proton pairs) of these virtual excitations is thus critical input for modeling a range of nuclear, particle, and astrophysics measurements. Hitherto measurements used two-nucleon knockout or ``triple-coincidence'' reactions to measure the relative contribution of np- and pp-SRCs by knocking out a proton from the SRC and detecting its partner nucleon (proton or neutron). These measurementsshow that SRCs are almost exclusively np pairs, but had limited statistics and required large model-dependent final-state interaction (FSI) corrections. We report on the first measurement using inclusive scattering from the mirror nuclei $^3$H and $^3$He to extract the np/pp ratio of SRCs in the A=3 system. We obtain a measure of the np/pp SRC ratio that is an order of magnitude more precise than previous experiments, and find a dramatic deviation from the near-total np dominance observed in heavy nuclei. This result implies an unexpected structure in the high-momentum wavefunction for $^3$He and $^3$H. Understanding these results will improve our understanding of the short-range part of the N-N interaction

The Unsteady Wake of an Oscillating Cylinder at Low Reynolds Numbers

The pronounced distortion of a vortex core as it proceeds into the unstable region can be observed in Some hot-wire measurements were made in the wake of a cylinder at a Reynolds number of 220 to further investigate the unstable region of the vortex street. The vibration conditions were somewhat more extreme than those under which the flow visualization photographs were taken. The cylinder vibrated at 40 percent of a diameter and at a frequency 12 percent greater than the Strouhal frequency, for a vortex shedding parameter, St* = 0.295. Under these conditions, the formation region extended to about 1.4 dia downstream from the center of the cylinder. The mean velocity profiles recorded at four downstream positions are plotted in Conclusions The initiation of the unstable region of a vortex street wake has been studied at a Reynolds number of 220. The formation and stable regions that precede the unstable portion of the wake were stabilized by vibrating both smooth cylinders and stranded cables at frequencies near the Strouhal frequency of shedding for a stationary cylinder. These vibrations result in an essentially two-dimensional wake in the formation and stable regions, and suppress the initiation of instability. The stable and unstable regions of the vortex street have been observed at Reynolds numbers to 350 behind vibrating cylinders whereas they have been known to occur only at Reynolds numbers up to 120-150 behind a stationary cylinder. The results of both hot-wire measurements and flow visualization with injected aerosol tracers have shown that the initiation of the unstable region of the vortex wake is characterized by vortex elongation and distortion. These phenomena are accompanied by the reappearance of a substantial mean velocity deficit and an appreciable drop in velocity fluctuations. The author wishes to acknowledge the continuing support of the Naval Research Laboratory for the research program that resulted in this paper. The author is greatly indebted to his colleague, C, W. Votaw, with whom he worked during the flow visualization studies mentioned here