πNNform factor for explaining sea-quark distributions in the nucleon

Abstract

We reinvestigate a soft πNN form factor with a monopole cutoff parameter ${\mathrm{\Lambda }}_1$<0.5 GeV obtained by Frankfurt, Mankiewicz, and Strikman for explaining sea-quark distributions in the nucleon. It is found that their estimate is small in comparison to the limit ${\mathrm{\Lambda }}_1$<0.65–0.7 GeV estimated in this investigation. Studying processes involving πNN and πNΔ vertices, we find that the limit for the dipole form factor is ${\mathrm{\Lambda }}_2$<0.95 GeV (which corresponds to ${\mathrm{\Lambda }}_1$<0.6 GeV). Therefore, a typical πNN form factor with ${\mathrm{\Lambda }}_1$∼0.6 GeV in quark models could be consistent with deep-inelastic experimental data at this stage. However, it is softer than a πNN form factor with ${\mathrm{\Lambda }}_1$∼1 GeV widely used in nuclear physics. Using the cutoff ${\mathrm{\Lambda }}_2$=0.95 GeV, we investigate pionic contributions to a SU(2${)}_{\mathit{f}}$-breaking distribution u¯(x)-d¯(x) in the nucleon. We find that the pionic contributions to u¯(x)-d¯(x) are negative and a contribution to the deviation from the Gottfried sum rule is estimated to be -0.041, which could explain a part of the discrepancies indicated by recent New Muon Collaboration experiments.