How open charm production and scaling violations probe the rightmost hard BFKL pole exchange

In 1994 Zakharov and the present authors argued that in color dipole (CD) BFKL approach to DIS excitation of open charm at moderately large Q2 is dominated by hard BFKL exchange. In view of the rapid accumulation of the experimental data on small-x charm structure function of the proton F2c from HERA, we subject the issue of dominance of the rightmost hard BFKL pole exchange to further scrutiny. Based on CD BFKL-Regge factorization we report parameter-free predictions for the charm structure function F2c and show that the background to the dominant rightmost hard BFKL exchange from subleading hard BFKL and soft-pomeron exchanges is negligible small from real photo-production to DIS at Q2≲50–100 GeV2. The agreement with the experiment is good and lends strong support for the intercept of the rightmost hard BFKL pole ΔP=αP−1=0.4 as found in 1994 in the color dipole approach. We comment on the related determination of ΔP from the x-dependence of the longitudinal structure function FL(x,Q2) and of the scaling violation ∂F2/∂logQ2 taken at a suitable value of Q2.