In this talk I present our recent work [1] on simulating the emergence of the Glasma in the early stages of heavy ion collisions in full 3+1 dimensions. Usually, in the color glass condensate framework incoming nuclei are assumed to be infinitely thin Lorentz-contracted pancakes which leads to boost-invariant rapidity profiles of the resulting energy density after the collision. We break boost invariance by allowing for a finite width of the incoming nuclei along the beam direction and obtain Gaussian-like rapidity profiles already at tree level. The profiles resemble strong coupling results and agree surprisingly well with experimental data of pion multiplicities as obtained at RHIC.
[1] AI, D. Müller, arXiv:1703.00017