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  1. Free, publicly-accessible full text available March 1, 2023
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  4. null (Ed.)
  5. Missing mass spectroscopy with the (e,e′K+) reaction was performed at Jefferson Laboratory's Hall C for the neutron rich Λ hypernucleus 9ΛLi. The ground state energy was obtained to be Bg.s.Λ=8.84±0.17stat.±0.15sys. 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 [8Li(3+)⊗sΛ=3/2+2,1/2+] and [8Li(1+)⊗sΛ=5/2+2,7/2+] were observed at EΛ(no. 2)=1.74±0.27stat.±0.11sys. MeV and EΛ(no. 3)=3.30±0.24stat.±0.11sys. MeV, respectively. The EΛ(no. 3) is larger than shell model predictions by a few hundred keV, and the difference would indicate that a 5He+t structure is more developed for the 3+ state than those for the 2+ and 1+ states in a core nucleus 8Li as a cluster model calculation suggests.
  6. The explicit breaking of the axial symmetry by quantum fluctuations gives rise to the so-called axial anomaly. This phenomenon is solely responsible for the decay of the neutral pion π0into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of theπ0 γγprocess. The differential cross sections for π0photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yieldingΓ(π0 γγ)=7.798±0.056(stat.)±0.109(syst.) eV, where stat. denotes the statistical uncertainty and syst. the systematic uncertainty. We combined the results of this and an earlier experiment to generate a weighted average ofΓ(π0 γγ)=7.802±0.052(stat.)±0.105(syst.) eV. Our final result has a total uncertainty of 1.50% and confirms the prediction based on the chiral anomaly in quantum chromodynamics.