  The study of quark-gluon plasma (QGP) is hindered by our limited
understanding of its initial conditions, particularly its longitudinal
structure. We propose a novel approach that entails analyzing collisions
involving nuclei of similar masses but different deformations. This strategy
allows us to vary the initial conditions and collective expansion of the QGP,
while minimizing the influence of non-flow correlations. Using a dynamical
transport model, we have for the first time extracted the complete longitudinal
structure of elliptic flow ($v_2$). Our findings reveal that although
deformation significantly enhances the overall magnitude of $v_2$, it does not
alter its longitudinal profile. This approach not only enables the separation
of the rapidity dependence of flow from its rapidity decorrelations but also
prompts further investigation into other nuclear structural features, such as
nuclear skin thickness, to advance our understanding of the QGP's initial
conditions.
