Observation of the charge symmetry breaking d+d-->4He+pi(0) reaction near threshold |
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Authors: | Stephenson E J Bacher A D Allgower C E Gårdestig A Lavelle C M Miller G A Nann H Olmsted J Pancella P V Pickar M A Rapaport J Rinckel T Smith A Spinka H M van Kolck U |
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Institution: | Indiana University Cyclotron Facility, Bloomington, Indiana 47408, USA. |
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Abstract: | We report the first observation of the charge symmetry breaking d+d-->4He+pi(0) reaction near threshold. Measurements using a magnetic channel (gated by two photons) of the 4He scattering angle and momentum (from time of flight) permitted reconstruction of the pi(0) "missing mass," the quantity used to separate 4He+pi(0) events from the continuum of double radiative capture 4He+gamma+gamma events. We measured total cross sections for neutral pion production of 12.7+/-2.2 pb at 228.5 MeV and 15.1+/-3.1 pb at 231.8 MeV. The uncertainty is dominated by statistical errors. These cross sections arise fundamentally from the down-up quark mass difference and quark electromagnetic effects that contribute in part through meson mixing (e.g., pi(0)-eta) mechanisms. |
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