  Two-particle pseudorapidity correlations of hadrons produced in Pb+Pb
collisions at 2.76 TeV at the CERN Large Hadron Collider are analyzed in the
framework of a model based on viscous 3+1-dimensional hydrodynamics with the
Glauber initial condition. Based on our results, we argue that the correlation
from resonance decays, formed at a late stage of the evolution, produce
significant effects. In particular, their contribution to the event averages of
the coefficients of the expansion in the Legendre basis explain 60-70% of the
experimental values. We have proposed an accurate way to compute these <a_n
a_m> coefficients, independent of the binning in pseudorapidity, and tested a
double expansion of the two-particle correlation function in the azimuth and
pseudorapidity, which allows us to investigate the pseudorapidity correlations
between harmonics of the collective flow. In our model, these quantities are
also dominated by non-flow effects from the resonance decays. Finally, our
method can be used to compute higher-order cumulants for the expansion in
orthonormal polynomials which offers a suitable way of eliminating the non-flow
effects from the correlation analyses.
