DREB Conference 2024

The intrinsic view of quadrupole deformed nuclear rotors is
still prevalent in the community. In it, the shape is characterised by the
$\beta$ and $\gamma$ parameters. A lot of discussions have taken place
about the existence of "rigid" triaxial nuclei, i.e. having a well
defined value of $\gamma$. However, the only invariant quantities
that are physically relevant in the laboratory frame are the
Kumar invariants Q${}^2$ and Q${}^3$, from which $\beta$ and $\gamma$
can be deduced. We have been able to compute recently, without any
approximation, the higher order invariants (up to Q${}^6$) that make it
possible to evaluate the variances of $\beta$ and $\gamma$. The conclusions
are that $\beta$ is softer that usually assumed, and that the $\gamma$ span at
1$\sigma$ is typically of 20-30º, at odds with the image of rigid triaxiallity.
I will touch upon as well some issues related to the extraction of these
shape parameters by means of ultra relativistic heavy ion collisions.