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The Dilepton Spectrometer collaboration has reported a bump in the e⁺{e}^{{{-}}}$ mass distribution at around 2${m}_{{π}}$ in 4.9 GeV proton-Be collisions. Previous calculations have shown that this bump does not have its origin in nucleon-nucleon bremsstrahlung nor in the Dalitz decay of the {Δ} resonance. In this paper we estimate the contribution from two-pion annihilation based on relativistic kinetic theory, on the experimentally measured cross sections for the production of up to five pions, and on a phase space generator for the pion momentum distributions. The calculation fails to reproduce the data.. The origin of the bump remains unexplained.
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Kapusta et al. (1989) studied this question.
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