The search for dark matter weakly interacting massive particles with noble liquids has probed masses down and below a GeV/c^2. The ultimate limit is represented by the experimental threshold on the energy transfer to the nuclear recoil. Currently, the experimental sensitivity has reached a threshold equivalent to a few ionization electrons. In these conditions, the contribution of a Bremsstrahlung photon or a so-called Migdal electron due to the sudden acceleration of a nucleus after a collision might be sizable: I studied how these effects can be exploited in experiments based on liquid argon detectors and summarised the relevant results in a recent publication currently under review by the journal [1].
This project has the goal to further investigate the impact of Migdal effect and photon Bremsstrahlung in extending the search region for dark matter particles also for direct detection experiments based on different active materials. In this context it is crucial to develop a robust analysis framework which can provide new sensitivity bounds in the mass regions currently inaccessible by modeling the signal only with the traditional nuclear recoil interaction.
[1] G. Grilli di Cortona, A. Messina and S. Piacentini, "Migdal effect and photon Bremsstrahlung: improving the sensitivity to light dark matter of liquid argon experiments", arXiv:2006.02453
Despite the strong indirect evidence in support of the existence of the dark matter (DM) [1], a DM particle has not been discovered yet. Nowadays the experimental effort in the direction of a direct detection is therefore prodigious, and it currently focuses on the mass region beyond the GeV/c^2 scale.
However, taking into account the Migdal effect and photon Bremsstrahlung [2] is a powerful tool to improve the sensitivity bounds of direct detection experiments in terms of mass of the DM candidate as we showed in [3].
The project we intend to pursue with the present grant request is to set up an analysis framework using the Bayesian approach which, considering the Migdal effect and photon Bremsstrahlung contributions, has the aim of updating the current sensitivity bounds of DM direct detection experiments. We believe that this would push the sensitivity down to masses of O(100) MeV/c^2, improving by a factor of 10 the current results in terms of mass of the DM candidate. Moreover, the analysis will be performed in a statistical framework, the Bayesian approach, which is rarely employed by the experimental collaborations.
[1] N. Aghanim et al., "Planck 2018 results. VI. Cosmological parameters", arXiv:1807.06209.
[2] M. Ibe, W. Nakano, Y. Shoji, and K. Suzuki, "Migdal Effect in Dark Matter Direct Detection Experiments", JHEP 03(2018) 194
[3] G. Grilli di Cortona, A. Messina and S. Piacentini, "Migdal effect and photon Bremsstrahlung: improving the sensitivity to light dark matter of liquid argon experiments", arXiv:2006.02453