A recent study published on arXiv explores the validity of the classical interpretation of nuclear deformation in ultra-relativistic ion collisions. These collisions, which generate a quark-gluon plasma, are a key tool for investigating many-body correlations in the ground states of nuclei. In particular, the observed azimuthal hadronic flow is sensitive to intrinsic nuclear deformation, an effect traditionally analyzed using a classical rigid rotor model, despite the intrinsically quantum nature of nuclei.

The researchers systematically compared the quantum quadrupolar rotor model with its classical rigid rotor limit, evaluating its validity in different nuclei. They found that quantum contributions, linked to the fermionic nature of nucleons, are largely independent of shell effects and, therefore, of intrinsic deformation. These quantum contributions account for almost the entirety of the effective quadrupolar rotor deformation in light or spherical nuclei. However, their importance drastically decreases in heavy, intrinsically well-deformed nuclei, where they fall below 10%.

This work underscores the need to move beyond the classical rigid rotor paradigm for an accurate quantitative interpretation of nuclear structure effects on collision final-state observables. The results suggest that, in addition to the quantum contributions quantified in this study, it is crucial to include and characterize correlations associated with collective vibrations and non-collective nucleonic motion to obtain a complete and accurate description of these phenomena. This opens new avenues for refining our understanding of nuclear matter under extreme conditions.