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Abstract

It is evident that the current Standard Model of particle physics fails to decode the enigma of dark matter. Amongst dark matter candidates, a promising contender is a hypothetical fifth-force coupling between atom constituents, which is key to establishing a New Physics (NP) model. To prove its existence, isotope shifts are investigated with the King plot method to detect its coupling effect between neutrons and electrons in an atom. Although this effect is weak, it may be resolved with quantum logic spectroscopy of highly charged ions, which offers high precision measurements of isotope shifts, but this method requires ground-state transitions.

In this thesis, I measured ground-state transitions in isotope-rich elements, Ca and Xe, using an electron beam ion trap. Furthermore, I theoretically investigated these transitions in their sensitivity to a hypothetical fifth-force, using the generalized King plot method. My results predicted an improvement of sensitivity by at least four orders of magnitude, compared to previous King plot analyses. This sensitivity would constrain the NP parameter space more stringently than prior imposed restrictions.

This work lays the theoretical foundation of searching for a fifth force and, ultimately, validating an NP model better suited to decipher our universe's mysteries.