Abstract
Previous work has argued that, in the framework of plasma dark matter models, the DAMA annual modulation signal can be consistently explained with electron recoils. In the specific case of mirror dark matter, that explanation requires an effective low velocity cutoff, vc≳30,000km/s, for the halo mirror electron distribution at the detector. We show here that this cutoff can result from collisional shielding of the detector from the halo wind due to Earth-bound dark matter. We also show that shielding effects can reconcile the kinetic mixing parameter value inferred from direct detection experiments with the value favoured from small scale structure considerations, ϵ≈2×10−10.
Highlights
For over a decade, the DAMA collaboration have observed an annually modulating rate of scintillations in their NaI detector at Gran Sasso [1,2,3,4,5]
The DAMA collaboration have observed an annually modulating rate of scintillations in their NaI detector at Gran Sasso [1,2,3,4,5]. This annual modulation signal has properties consistent with dark matter interactions, but since there is no discrimination against electron recoils, both nuclear and electron scattering interpretations could be considered
Dark matter scattering off electrons is much less strongly constrained, and a consistent electron scattering interpretation of the DAMA annual modulation signal seems to be possible in the framework of plasma dark matter [10,11,12]
Summary
The DAMA collaboration have observed an annually modulating rate of scintillations in their NaI detector at Gran Sasso [1,2,3,4,5]. That experiment sees a small excess at low energies which can be interpreted as dark matter induced electron recoils, and in combination with the results from DAMA, indicates that the annual modulation amplitude is near maximal. The ionization of this layer would be due to the interactions of the halo mirror electrons with the Earth-bound dark matter.
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