  First results on the longitudinal asymmetry and its effect on the
pseudorapidity distributions in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ =
2.76 TeV at the Large Hadron Collider are obtained with the ALICE detector. The
longitudinal asymmetry arises because of an unequal number of participating
nucleons from the two colliding nuclei, and is estimated for each event by
measuring the energy in the forward neutron-Zero-Degree-Calorimeters (ZNs). The
effect of the longitudinal asymmetry is measured on the pseudorapidity
distributions of charged particles in the regions $|\eta| < 0.9$, $2.8 < \eta <
5.1$ and $-3.7 < \eta < -1.7 $ by taking the ratio of the pseudorapidity
distributions from events corresponding to different regions of asymmetry. The
coefficients of a polynomial fit to the ratio characterise the effect of the
asymmetry. A Monte Carlo simulation using a Glauber model for the colliding
nuclei is tuned to reproduce the spectrum in the ZNs and provides a relation
between the measurable longitudinal asymmetry and the shift in the rapidity
($y_{\mathrm{0}}$) of the participant zone formed by the unequal number of
participating nucleons. The dependence of the coefficient of the linear term in
the polynomial expansion, $c_{\rm 1}$, on the mean value of $y_{\mathrm{0}}$ is
investigated.
