Strongly intensive quantities for rapidity correlations of multiplicities

Studies of the phase diagram of strongly interacting matter created in nuclear collisions are typically carried out using event-by-event fluctuations. Well-known way to disentangle statistical and dynamical fluctuations is to construct special observables named strongly intensive which are free from trivial volume fluctuations. Within the color string model behavior of the second-order strongly intensive quantity $\Sigma$ is completely determined by the two-particle correlation function from a single string and the string fusion mechanism. In this paper, we analyze third-order strongly intensive observable for forward-backward rapidity correlations and test its behavior within the PYTHIA8 model.