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Similar to the electrons in the atom, the atomic nucleus can be described by protons and neutrons occupying quantum levels (shells) separated by energy gaps. The number of nucleons that completely fill each shell define the so called nuclear ‘magic’ numbers, known in stable nuclei as 2, 8, 20, 28, 50, 82, 126 (black double lines in the figure). A fundamental understanding of how these magic configurations emerge from the underlying theory of the strong interaction, quantum chromodynamics (QCD),  and how they impact different nuclear properties, is one of the main challenges of modern nuclear physics.

Of particular interest are the properties of doubly-magic nuclei (purples circles in the figure) as their "simple" structures make them accessible to different many-body methods. Hence they form the cornerstone in our understanding of nuclear structure and nuclear matter. However, as several of these nuclei do not occur naturally and only live for a fraction of a second, they have to be produced artificially at specialized facilities such as FRIB (US), TRIUMF (Canada), RIKEN (Japan) and ISOLDE, CERN (Switzerland).

Our group has contributed with development of sensitive and precise laser spectroscopy techniques for nuclear structure and fundamental physics research. 

Nuclei at the extreme of stability are produced in very low quantities (1000 nuclei/s).

Thanks to the advances in chiral effective field theory [Epel09,Ham13], and the  development of powerful many-body methods [Carl15,Herg16], low-energy nuclear physics has found a  route towards the long sought connection with the underlying theory of the strong-interaction, QCD. The complex interactions between quark and gluons can be approximated by a systematic expansion of many-body interactions among nucleons, whose parameters can be constrained by selected properties of nuclear systems. As these parameters are not uniquely defined, the comparison between theoretical calculations and  select experimental properties is an essential step to disentangle the subtle components that define these  inter-nucleon interactions. Observables such as the nuclear charge radius have shown to be particularly sensitive to the details of the nuclear force [Ekst15,Gar16a, Hage16,Lona18]. Remarkably, the charge radii  of finite nuclei can also provide direct constraints to the properties of nuclear matter such as the radii of  neutron stars and parameters of the equation of state [Hage16,Brow17]. Complementary observables such as nuclear electromagnetic moments have been shown to be key to understand the role of electro-weak  processes in nuclei [Carl15,Past13].

[Brow17] Brown, Phys Rev Lett 119, 122502 (2017). 

[Carl15] Carlson et al. Rev Mod Phys 87, 1067 (2015).  

[Ekst15] Ekström et al. Phys Rev C 91, 051301(R) (2015).  

[Epel09] Epelbaum et al. Rev Mod Phys 81, 1773 (2009).  

[Gar16a] Garcia Ruiz et al. Nature Physics 12, 594 (2016).  

[Hage16] Hagen et al. Nature Physics 12, 186 (2016). 

[Past13] Pastore et al. Phys Rev C 87, 035503 (2013).  

[Lona18] Lonardoni et al. Phys Rev Lett 120, 122502 (2018).  

[Ham13] Hammer et al. Rev Mod Phys 85, 197 (2013). 
[Herg16] Hergert et al. Phys. Rep. 621, 165 (2016). 

[Lona18] Lonardoni et al. Phys Rev Lett 120, 122502 (2018).  

[Past13] Pastore et al. Phys Rev C 87, 035503 (2013).  

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