Precise determination of the electromagnetic form factor of the proton in the time-like region up to s = 4.2 GeV2

The process $$\bar p$$ p?e ? e + with polarized initial particles and proton form factors in time-like region

“…Starting from the seventies some informations on the electromagnetic form factors of the proton in the time-like region have been obtained. Recently rather accurate measurements of the proton form factors in the time-like region, from q 2 = 4M 2 up to q 2 = 4.2 GeV 2 , have been done at LEAR [1,2]. Some informations on the electromagnetic form factor of the proton at high time-like q 2 were also obtained at Fermilab [3].…”

Nucleon electromagnetic form factors in the timelike region

“…The discovery of this reaction was finally possible using an antiproton beam at PS/CERN in 1976 [22]. Antiproton experiments were later continued with great success at LEAR/CERN with the PS170 experiment [10,23,24] and at FNAL [25,26,27].…”

Nucleon form factors and final state radiative corrections toe+e−→p¯Czyż1, Kühn2, Tracz3 2014Phys. Rev. D150140View full textAdd to dashboardCite

“…The model parameters, namely, the complex VNN couplings, were fitted to the following experimental data: e þ e − →pp cross section [12,[17][18][19][20][21][22][23],pp → e þ e − cross section [24][25][26][27][28][29], e þ e − →nn cross section [21], ratio of the proton electric and magnetic form factors in the spacelike [30][31][32][33] and timelike [12,24] regions, and ratio of the neutron electric and magnetic form factors in the spacelike region [34,35]. The cross sections of the reaction ep → ep, which depend also on the form factors we model, contain also nonnegligible contributions from two-photon exchange diagrams [7].…”

“…The reason is that the PS170 [24][25][26] and DM2 [17,18]) data are in conflict with the BABAR data [12]. It is quite implausible that any model can accommodate PS170 and BABAR data sets at the same time, as the ratio of the form factors is in evident conflict and, even more important, both e þ e − → pp andpp → e þ e − cross sections are proportional to the same combination of the magnetic and electric form factors …”