Towards a consistent understanding of the exotic nucleus $^{42}_{14}Si_{28}$

Abstract

The issue of whether $^{42}_{14}Si_{28}$ is doubly magical or not has been a contentious one. Fridmann {\it et al.} (Nature 435 (2005) 922) through studies of two-proton knockout reaction $^{44}_{16}S_{28} \rightarrow ^{42}_{14}Si_{28}$, presented a strong empirical evidence in support of magicity and sphericity of $^{42}_{14}Si_{28}$. However in complete conflict with this, Bastin {\it et al.} (Phys. Rev. Lett. 99 (2007) 022503) gave equally strong empirical evidences, to show that the N = 28 magicity had completely collapsed, and that $^{42}_{14}Si_{28}$ was a well deformed nucleus. At present the popular consensus (Gade {\it et al.}, Phys. Rev. Lett. 122 (2019) 222501) strongly supports the latter one and discards the former one. Here, while we accept the latter experiment as being fine and good, through a careful study of an RMF model calculation, we show that actually the experimental results of Fridmann are also independently good and consistent. As per the Fridmann experiment, the sphericity and magicity of $^{42}_{14}Si_{28}$ is manifested only through proton number Z=14 being a strong magic number, while the neutron magic number N=28 disappears (or goes into hiding); and still this nucleus is spherical. This is a new and amazing property manifesting itself in this exotic nucleus $^{42}_{14}Si_{28}$. In this paper we provide a consistent understanding of this novel reality within a QCD based model. This model, which has been successful in explanation of the halo phenomenon in exotic nuclei, comes forward to provide the physical reason as to why the Fridmann experiment is correct. This QCD based model shows that it is tritons, as elementary entity making up $^{42}_{14}Si_{28}$, which then provides consistency to the above amazing conclusions arising from the Fridmann experiment.