Antiproton-nucleus electromagnetic annihilation as a way to access the proton timelike form factors |
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Authors: | H. Fonvieille and V. A. Karmanov |
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Affiliation: | 1.Laboratoire de Physique Corpusculaire,Université Blaise Pascal, IN2P3,Aubière Cedex,France;2.Lebedev Physical Institute,Moscow,Russia |
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Abstract: | Contrary to the reaction ( bar{{p}}) p ( rightarrow) e + e - with a high-momentum incident antiproton on a free target proton at rest, in which the invariant mass M of the e + e - pair is necessarily much larger than the ( bar{{p}}) p mass 2m , in the reaction ( bar{{p}}) d ( rightarrow) e + e - n the value of M can take values near or below the ( bar{{p}}) p mass. In the antiproton-deuteron electromagnetic annihilation, this allows to access the proton electromagnetic form factors in the timelike region of q2 near the ( bar{{p}}) p threshold. We estimate the cross-section (dsigma _{bar pd to e^ + e^ - n} /dmathcal{M}) for an antiproton beam momentum of 1.5GeV/c. We find that near the ( bar{{p}}) p threshold this cross-section is about 1pb/MeV. The case of heavy-nuclei target is also discussed. Elements of experimental feasibility are presented for the process ( bar{{p}}) d ( rightarrow) e + e - n in the context of the ( overline{{{rm P}}}) ANDA project. |
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