Dark matter: CERN goes in search of “dark photons”

Dark matter could interact with normal matter not only with gravitational force, but also with currently invisible « dark photons ». CERN is looking for these hypothetical particles and could well revolutionize our vision of the Universe.

In our universe, galaxies spin so fast that the gravity produced by the observable matter they contain cannot hold them together. Thus, they should logically have been undone a long time ago. This is why the researchers are convinced of the presence of an invisible element, for the moment undetectable, which gives these galaxies an additional mass producing the surplus of gravity which they need to maintain themselves. This mysterious presence is called “dark matter”.

There would thus exist in space a large quantity of this dark matter. It would compose about 85% of the observable universe. Invisible, astrophysicists have suspected its existence through its interactions with « normal » matter, but it could also be that these enigmatic particles also interact with something else: dark photons which are suspected of acting as a mediator between matter black and visible.

“To use a metaphor, imagine an impossible dialogue between two people who do not speak the same language (visible and dark matter). The black photon would then act as a kind of mediator understanding one language and speaking the other”, illustrates one of the researchers and spokesperson for the mission Sergei Gninenko.

To hunt the dark photon, CERN launched the NA 64 experiment last July. Usually, particles are hunted with collisions of proton beams at the Large Hadron Collider (LHC), but this year physicists bombarded the nuclei of atoms with electron beams. The method of detecting dark photons is based on the principle of conservation of energy. We begin by precisely determining the energy of the electrons used to bombard the nuclei. The Standard Model tells us how much energy must be emitted by collisions in the form of ordinary photons. The dark photon theory tells us that part of this energy must in fact be in the form of these exotic particles and that we must therefore measure a precise deficit of energy in the form of ordinary photons betraying the existence of black photons.

Note that for the moment no trace of black photons has yet been discovered, but we are however only at the beginning of this experiment. Matter and hypothetical photons remain in the shadows for the moment, but in the event of future success, the experiment could well revolutionize our vision of the Universe.


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