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RESEARCH PRODUCT

Charge symmetry breaking inA= 4 hypernuclei

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Charge symmetry breaking in the A = 4 hypernuclear system is reviewed. The data on binding energies of the mirror nuclei and hypernuclei are examined. At the Mainz Microtron MAMI the high-resolution spectroscopy of decay-pions in strangeness electro-production is used to extract the Λ hyperon ground state binding energy in 4 Λ H. This binding energy is used together with the 4 Λ He ground state binding energy from nuclear emulsion experiments and with energy levels of the 1 + excited state for both hypernuclei from γ-ray spectroscopy to address the charge symmetry breaking in the strong interaction. The binding energy difference of the ground states in the mirror pair is reduced from its long accepted value Δ B 4 Λ (0 + g.s. ) ≈ 0.35MeV to ≈ 0.24MeV. The energy difference of the excited states becomes Δ B 4 Λ (1 + exc ) ≈ −0.08MeV, for the first time with opposite sign. These values were not reproduced by theoretical calculations with the exception of very recent approaches, although with a large systematic dependence. The full understanding of the charge symmetry breaking in the A = 4 hypernuclei still remains one of the open issues of hypernuclear physics.