Forward-backward multiplicity correlations in proton-proton collisions from several GeV to LHC energies

Forward-backward multiplicity correlations in pp collisions at LHC energies are studied with the quark-gluon string model. Comparison with experimental data and with model calculations for lower energies is performed. The model correctly reproduces the linear slope of the correlations, $\left \langle n_{B} (n_{F})\right \rangle = a + b_{corr}n_{F}$, in the whole energy interval. Positive correlations arise because of mixing of sub-processes with different mean multiplicities. The increase of $b_{corr}$ with rising collision energy is linked to the increase of the variety of sub-processes going via the soft and hard multi-Pomeron exchanges. For the events with fixed amount of Pomerons the correlation slope $b_{corr}$ is shown to be essentially zero.