Abstract
In the leading paradigm of modern cosmology, about 80% of our Universe's matter content is in the form of hypothetical, as yet undetected particles. These do not emit or absorb radiation at any observable wavelengths, and therefore constitute the so-called Dark Matter (DM) component of the Universe. Detecting the particles forming the Milky Way DM component is one of the main challenges for astroparticle physics and basic science in general. One promising way to achieve this goal is to search for rare DM-electron interactions in low-background deep underground detectors. Key to the interpretation of this search is the response of detectors' materials to elementary DM-electron interactions defined in terms of electron wave functions' overlap integrals. In this work, we compute the response of atomic argon and xenon targets used in operating DM search experiments to general, so far unexplored DM-electron interactions. We find that the rate at which atoms can be ionized via DM-electron scattering can in general be expressed in terms of four independent atomic responses, three of which we identify here for the first time. We find our new atomic responses to be numerically important in a variety of cases, which we identify and investigate thoroughly using effective theory methods. We then use our atomic responses to set 90% confidence level (C.L.) exclusion limits on the strength of a wide range of DM-electron interactions from the null result of DM search experiments using argon and xenon targets.
Highlights
One of the major unsolved mysteries in modern physics is the elusive nature of dark matter (DM) [1]
Motivated by recent experimental efforts in the field of astroparticle physics [10], here we focus on DM particles of mass in the 1–1000 MeV/c2 range and on their interactions with the electrons in materials used in direct detection experiments
Dual-phase argon and xenon targets are used in direct detection experiments searching for signals of nonrelativistic interactions between Milky Way DM particles and electrons in the target materials
Summary
One of the major unsolved mysteries in modern physics is the elusive nature of dark matter (DM) [1]. They do not apply to scenarios where incoming DM particles induce collective excitations, such as magnons or plasmons [41,42] Within this general theoretical framework, we find that the rate of DM-induced electronic transitions in a given target material can be expressed in terms of four, independent material response functions. They depend on scalar and vectorial combinations of electron momenta and wave functions.
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