Physics: the hunt for mysterious ‘dark photons’ intensifies

In the family of “dark matter candidates” I call “dark photon”. This hypothetical massive cousin of the photon, which would come from a type of particle called the “dark sector,” has been viewed by physicists for fifteen years as a role model in their search for answers to dark matter. Like all exotic particles put forward to explain the nature of this unknown and undetectable matter, which nevertheless makes up 26% of the contents of the universe, this dark photon, or “dark”, has never shown the slightest hint of its existence in space. experiments partly devoted to tracking it (this is the case of NA 64, started in 2016 at CERN, or the Hades collaboration for a high-acceptance di-electron spectrometer from GSI in Germany).

In a study published July 1 in the journal Physical Review Letters, a team of researchers led by Anthony Thomas, a physicist at the ARC Center of Excellence for Dark Matter Particle Physics at the University of Adelaide, nevertheless assures that a new experiment should begin soon. allow us to solve the problem of dark photons.

SABER, for sodium iodide with an active background suppression experiment, is currently under construction in a new laboratory located in a former gold mine in Victoria, one kilometer downstream from Stowell. The result of a collaboration between Australian, European and American researchers, it will provide “diffusion of parity-violating electrons, made possible by the modernization of the Thomas Jefferson National Accelerator Facility (JLab) in the United States,” explains Science and Future Anthony Thomas.

Invisible photon to explain anomalies

Dark matter, which was supposed to interfere due to the gravitational force, has become important in the theory of the standard model for explaining the clutch of galaxies and, more broadly, the large structures of the universe. For more than half a century, astrophysicists have unsuccessfully searched for it. Recent hypotheses indicate that it would rather be in the form of particles that interact very weakly with ordinary matter, hence the difficulty of detecting them, as indicated by their English abbreviation WIMPS for Weakly Interacting Massive Particles. Among the most suspected of these WIMPs are other hypothetical particles, called, for example, neutralinos or sneutrinos.

But black photons are still on the table. Endowed with mass, unlike Standard Model photons, those also called U-bosons have been speculated since the development of the great theories of supersymmetry, in particular superstring theory, in the 1980s and 1990s. , it’s possible that they combine with other dark particles to form dark atoms or even dark molecules, with a whole chemistry associated.

The existence of these particles has been, among other things, inferred from parity or mirror symmetry breaking (also called “spatial inversion”) in the weak interaction, which boils down to observing the differences between what happens within the experimental device and its exact replica obtained by capturing an image the specified device in the mirror. “The differences are very small, on the order of a few parts per million,” Anthony Thomas calculates. “But incredibly accurate measurements allow them to be observed and interpreted, for example, as a sign of the existence of this dark photon.”

lead core

Therefore, to preserve parity, including mirror symmetry, these “invisible” copies of the forces and particles of matter, including this dark twin of the photon, were created. This could more specifically explain the striking discrepancy found during the JLab PREX-II experiment between the neutron density in the lead nucleus and the predicted nuclear structure theory.

“We found a puzzling result for the size of the lead nucleus, which can be explained by the presence of a special new dark matter particle, the dark photon,” Anthony Thomas adds. “Given the progress in experimental capabilities over the past few years, it is possible to observe areas in which the sensitivity of the asymmetry of electron parity violation scattering (PVES) provides an opportunity to discover new physics in the near future,” says the researcher.

One of SABER’s tasks will be, first of all, to confirm or invalidate the results of another working group – the Gran Sasso laboratory in Italy – which claims that the DAMA/LIBRA experiment has identified potential clues to the presence of dark matter. FASER, named after the LHC detector, which is supposed to look for light particles with extremely weak interactions during the third launch of the Large Collider, also officially began collecting data on July 5, 2022, and this is until 2025. The same goes for the large LHCb. an experiment, one of the goals of which is to track these dark photons and, more broadly, all particles in the dark sector.

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