Hydrodynamic simulations together with models for the fluctuating initial conditions lead to a good description of experimental data on all flow harmonics. To complement these analyses which allow to constrain initial fluctuations, one can use rapidity-odd directed flow to unravel the global initial geometry. We discuss what properties of the tilt of the initial state is necessary to reproduce data on v1(y) and v1(b). We argue that skewness (asymmetry in the transverse overlap region) of the initial state is needed to reproduce data on v1(pt). We conclude by computing tilt and skewness of various initial conditions and showing which are consistent with data on rapidity-odd directed flow.
Fernando Gardim (USP) Dr Jean-Yves Ollitrault (CNRS)