Effective models of WIMP Direct Detection in DAMA/LIBRA-phase2

TL;DR

This paper explores various effective interaction models of WIMPs to interpret DAMA/LIBRA-phase2 data, finding some models fit better than standard ones but remain in tension with other experimental constraints.

Contribution

It systematically analyzes a broad set of effective WIMP-nucleus interactions, identifying models that better fit DAMA data with less parameter fine-tuning.

Findings

Most non-relativistic effective couplings improve fit over standard spin-independent interactions.

Velocity-dependent cross sections can better fit high-mass WIMP data.

All best-fit models are in tension with XENON1T and PICO60 exclusion limits.

Abstract

Since the DAMA/LIBRA collaboration released updated results from their search for the annual modulation signal expected from Dark Matter (DM) scattering in their NaI detectors, we have fitted the updated DAMA result for the modulation amplitudes for a Weakly Interacting Massive Particle (WIMP) signal, parameterizing the interaction with nuclei in terms of the most general effective Lagrangian for a WIMP particle spin 1/2, systematically assuming dominance of one of the 14 possible interaction terms and a standard Maxwellian for the WIMP velocity distribution. We find that most of the couplings of the non-relativistic effective Hamiltonian can provide a better fit compared to the standard Spin Independent interaction case, and with a reduced fine-tuning of the three parameters (WIMP mass, WIMP-nucleon effective cross-section and ratio between the WIMP-neutron and the WIMP-proton couplings). In addition, effective models for which the cross section depends explicitly on the WIMP incoming velocity can provide a better fit of the DAMA data at large values of $m_{\chi}$ compared to the standard velocity-independent cross-section due to a different phase of the modulation amplitudes. All the best fit solutions are in tension with exclusion plots of both XENON1T and PICO60.