Dark Matter (DM) accounts for 85% of the mass of the Universe, yet it has never traveled. Discovery of its nature would be one of the most significant scientific accomplishments of our time as it would tell us how the Universe that we know today has been formed.
My research has focused on enabling the discovery of galactic DM with cutting-edge, highly sensitive particle detectors located in deep underground laboratories. I have worked on several interconnected projects in this area and I am now part of the XENON1T experiment, currently the most sensitive DM experiment worldwide.
Weakly Interacting Massive Particles (WIMPs) are compelling candidates for DM but their expected scattering with terrestrial nuclei would be rare, and they would generate only extremely faint signals. Nonetheless, light and electrical charge from the collision can be identified and recorded using time projection chamber (TPC) detectors, operated under an electric field. These devices, that now dominate the international search for DM, are where my research is focussed. They consist of a chamber filled with noble gas, xenon or argon, in its liquid form at the bottom and its gaseous form at the top. This configuration allows accurate labeling of the type of particle that interacted in the detector, where Standard Model backgrounds that cannot account for the DM cause electrons to recoil in the detector, but WIMPs would impact the atomic nucleus. These signals are distinguished by the relative amount of light and charge liberated in the interaction.
Another big interest of mine is neutrinos, the second most abundant particles in the Universe after DM.
Although we now know a lot more about neutrinos compared to nearly 60 years ago when they were first discovered, many of their properties are still unknown. Neutrinos rarely interact, hereby travelling long distances undisturbed. In 1998, by studying on the Earth neutrinos emitted from the Sun, it was (surprisingly) discovered that neutrinos do have a very small, but nonzero, mass. We also know that neutrinos come in three flavors (electron, muon, and tau neutrino) and in three mass states, called 1, 2, and 3, whose values we do not know yet. For each flavor and mass neutrino states there exist a correspondent anti-neutrino state, hereby making neutrinos Dirac particles. Or at least that’s what we think for now. Several experiments around the world are trying to confirm whether neutrinos are indeed Dirac or Majorana particles (in this case the neutrino would be its own antiparticle).
Latest data-hints point to neutrinos violating charge-parity symmetry (CP). CP is the product of two symmetries: C, “which transforms a particle into its own antiparticle, and P, which creates the mirror image of a physical system” (Wikipedia docet). If a violation of CP is observed that implies that matter and anti-matter behave differently, which could explain why our Universe still exists today. In fact, according to the Bing Bang theory matter and anti-matter were created in equal amounts and when coming into contact, they should have annihilated producing photons… but we are here to tell this story, meaning that not all of the matter annihilated. Neutrinos could help us unravel this mystery.
The DUNE experiment, which I work on, will try to answer these questions—and other more, by firing neutrinos from Fermilab (Chicago, Illinois, U.S.A) to South Dakota (U.S.A). Neutrinos will travel 1,300 km through Earth and will reach four big liquid argon TPC detectors, each holding 10,000 tonnes of the noble gas in its state form. By detecting neutrinos when fired and when arriving in South Dakota, we can study many of their properties.
An exciting time for particle physics with potential for new discoveries is ahead of us, and I’m thrilled to be part of this journey.