The LHC's most powerful collisions have still revealed no trace of the tiny black holes sought by physicists.
Some theories predict that microscopic black holes could appear during collisions between particles at extremely high energies. If they were produced in the Large Hadron Collider, or LHC, they would disappear almost immediately.
The LHC's CMS experiment
Image: CERN
Researchers analyzed proton collisions recorded between 2016 and 2018 by CMS, one of the LHC's major detectors. A possible micro black hole would immediately decay, producing numerous particles. These particles would travel in several directions with a very high total energy.
To identify these rare events, the team used a new method involving machine learning. It compares how particles are distributed after each collision. The goal is to distinguish a possible unusual signature from the large number of collisions explained by already-known physics.
No signal attributable to these black holes appeared. In the models tested, the results exclude microscopic black holes whose mass would be below a limit ranging from approximately 9.0 to 11.4 TeV. This unit is commonly used in particle physics to express energy and, by equivalence, mass.
Why search for such objects? Some theories propose the existence of extra dimensions of space, invisible at our scale. In these models, gravity could become much stronger over very small distances. LHC collisions could then reach the conditions needed to form micro black holes.
The absence of detection rules out some of the possibilities predicted by the models studied. The more domains experiments exclude, the more they narrow the space in which new physics could still be hiding.
The same study also searched for another hypothetical phenomenon called a sphaleron, without finding any trace of it. Future data may go further: the future high-luminosity LHC is expected to provide many more collisions, increasing the chances of detecting extremely rare phenomena, or even… micro black holes.