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Helicity amplitudes and crossing relations for one-photon exchange antiproton proton reactions

  • Regular Article - Nuclear Structure and Reactions
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Abstract.

Antiproton proton annihilation reactions allow unique access to the moduli and phases of nucleon electromagnetic form factors in the time-like region. We present the helicity amplitudes for the unequal-mass single-photon reaction p¯ → l + l - in the s channel including the lepton mass. The relative signs of these amplitudes are determined using simple invariance properties. Helicity amplitudes for one-photon exchange annihilation reaction p¯ → B¯ are also given, where B is any spin-one-half particle with structure. Crossing relations between the ep → ep scattering and the p¯ → l + l - annihilation channels are discussed and the crossing matrix for the helicity amplitudes is given. This matrix may be used to verify known expressions for the space-like helicity amplitudes due to one-photon exchange.

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Authors and Affiliations

  1. School of Mathematics, Trinity College, Dublin, Ireland

    N. H. Buttimore & E. Jennings

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  1. N. H. Buttimore
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  2. E. Jennings
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Correspondence to E. Jennings.

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Xiangdong Ji

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Buttimore, N.H., Jennings, E. Helicity amplitudes and crossing relations for one-photon exchange antiproton proton reactions. Eur. Phys. J. A 33, 21–27 (2007). https://doi.org/10.1140/epja/i2007-10393-6

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  • DOI: https://doi.org/10.1140/epja/i2007-10393-6

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