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Half an hour outside of Rome, a sophisticated new experiment will try to answer one of the fundamental questions about the nature of reality. Does a fifth fundamental force exist in the universe? This force is connected to dark matter and dark energy, the (hypothetical) main components of the universe, and it would be carried by a small particle called the dark photon.
Just like photons carry electromagnetic radiation, dark photons would carry the fifth force and interact with dark matter. But unlike photons, they would have a small mass. The mysterious dark photon will be hunted by the Positron Annihilation into Dark Matter Experiment (PADME), which will start collecting data in the next couple of weeks.
PADME will use antimatter to try to locate the dark photon. A beam of positrons, or anti-electrons, will be shot at an artificial diamond wafer, 100 microns thick. They will interact with regular matter and release photons, but researchers think there is a chance they might emit dark photons too. Sophisticated detectors are there to study the regular photons in detail. Their properties will tell researchers if dark photons exist and, if they do, what they are like.
The experiment is an international collaboration and includes the Hungarian research group that first observed hints of a peculiar new particle, around 30 times the size of an electron. That experiment was conducted using unstable atoms of beryllium, which emits positrons and electrons when it decays. The experiment saw an anomaly in the data that was consistent with an unknown particle. Theoretical analysis suggested it could have been the dark photon.
While clearly exciting, we can't be certain what the particle is, or if it's even there at all. That’s PADME’s job. It will attempt to validate or refute these findings. No matter the results it will advance our understanding of dark matter. However, if it does confirm the existence of the dark photon, it will be revolutionary.
“The study of dark matter is one of the most fascinating frontiers of research in fundamental physics," spokesperson Mauro Raggi, from the Sapienza University of Rome, said in a statement. "We do not know what it is made of but we know it is made up of something different from the particles that make up ordinary matter like protons, neutrons or electrons.”
Dark matter and dark energy are proposed explanations for how the structures in the universe move and how the universe itself expands. All we see points strongly to their existence, but we are yet to find direct evidence. PADME could give us just that.
