Authors: Y. Yan, K. Khosonthongkee, C. Kobdaj, P. Suebka
Title: Electron-positron annihilation to nucleon-antinucleon pairs at low energies
Keywords: quark model, quark-antiquark pair, vector meson
Abstract:
It is indicated, by experimental data on the reaction of electron-positron to neutron-antineutron from the FENICE collaboration, earlier data on the reaction lectron-positron to proton-antiproton from the FENICE and DM2 collaborations, data collected at the LEAR antiproton ring at CERN on the time-reversed reaction of proton-antiproton to electron-positron, and also recent measurements from the BES Collaborations and the BaBar Collaborations, that the ratio of the cross section of electron-positron annihilation to neutron-antineutron to the one of electron-positron to proton-antiproton is larger than 1 at energies around the nucleon-antinucleon threshold.
In a naive perturbative description of electron-positron annihilation into baryons the virtual time-like photon first decays into a quark-antiquark pair, then the quark-antiquark pair is dressed by two additional quark-antiquark pairs excited out of the vacuum to form a baryon pair. The dressing process does not distinguish between u and d quarks at high momentum transfers since in the description of perturbative QCD the gluon couplings are flavor blind. In the conventional perturbative picture the only difference between the proton and neutron production arises from the different electric charges of the primary quark-antiquark
pairs. One expects that the ratio of the cross section of electron-positron annihilation to neutron-antineutron to the one of electron-positron to proton-antiproton is well smaller than 1 at large momentum transfers where the u quark contribution dominates in the proton and the d quark in the neutron.
The reaction electron-positron to nucleon-antinucleon at energies around the nucleon-antinucleon threshold is highly nonperturbative, hence the problem must be tackled in a nonperturbative manner. We study the reactions nucleon-antinucleon in the nonperturbative 3P0 quark dynamics which describes quark-antiquark annihilation and creation. It was shown that the 3P0 approach is phenomenologically successful in the description of hadronic couplings. |