The goal of this research project is to contribute to the search for low mass Dark Matter (DM) candidates. In particular I'm interested in the direct detection experimental effort, that is the direct observation of nuclear recoils in underground detectors induced by the DM.
The search for Dark Matter weakly interacting massive particles with noble liquids has probed masses down and below a GeV/c^2, corresponding to an experimental threshold equivalent to a few ionization electrons. In these conditions, the energy taken by the so-called Migdal electron could be sizable compared to the energy of the induced nuclear recoil. In a recent publication [1], we showed how such an effect allows us to push the experimental sensitivity of liquid argon experiments down to masses of 0.1 GeV/c^2, extending the search region for dark matter particles of previous results. The Migdal effect [2] is then a promising handle to improve the sensitivity of the DM direct detection experiments to light DM candidates, but it has not been measured yet. This has been the subject of my PhD studies [1], which, in the context of the two international collaborations DarkSide-20k and CYGNO, were focused both on phenomenological and experimental aspects of the search for low mass DM. I will therefore further extend my work, and in particular in the context of the CYGNO collaboration I will have the opportunity to contribute to the measurement of the Migdal effect using the CYGNO prototypes with neutrons. This measurement is crucial for the low mass DM searches, allowing us to safely exploit the Migdal effect to extend the sensitivity of direct detection experiments.
[1] G. G. di Cortona, A. Messina, and S. Piacentini, "Migdal effect and photon bremsstrahlung: improving the sensitivity to light dark matter of liquid argon experiments", JHEP 11 (2020) 034
[2] M. Ibe, W. Nakano, Y. Shoji, and K. Suzuki, "Migdal Effect in Dark Matter Direct Detection Experiments", JHEP 03 (2018) 194
Although there are strong indirect purely gravitational evidences of the existence of the dark matter (DM)[1], no new DM particle has been discovered yet. A prodigious effort for the direct detection of a DM particle has been deployed by many experimental collaborations, whose program has been mainly focused on the DM mass region beyond the GeV/c^2 scale. To overcome the limits set by the current energy experimental thresholds, and to test therefore a lower DM mass window, new signal contributions can be taken into account. A promising handle for this purpose can be the Migdal effect: in [2] we showed how it is possible to extend the sensitivity of LAr direct detection experiments up to masses below 0.1 GeV/c^2.
The project we intend to pursue with the present grant request is therefore twofold: to demonstrate in the real case of the DarkSide-50 experiment that including the Migdal effect 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; contributing to the first known measurement of the Migdal effect induced by neutrons using the CYGNO prototypes, which would have a central role in the context of the DM direct detection.
[1] N. Aghanim et al., "Planck 2018 results. VI. Cosmological parameters", arXiv:1807.06209.
[2] G. G. di Cortona, A. Messina, and S. Piacentini, "Migdal effect and photon bremsstrahlung: improving the sensitivity to light dark matter of liquid argon experiments", JHEP 11 (2020) 034