Physicists working with the famous Large Hadron Collider (LHC) at CERN in Geneva, Switzerland, say recent experiments could point to undiscovered physics that challenge the Standard Model.
Long regarded as the dominant framework in modern physics for more than half a century, the Standard Model is now facing tantalizing hints from LHC experiments suggesting that the behavior of subatomic particles may be inconsistent with this long-held view of the universe.
The discoveries were detailed by William Barter, a physicist at the School of Physics and Astronomy at the University of Edinburgh, and Mark Smith, a Research Fellow in Collider Physics with the Faculty of Natural Sciences at Imperial College London, in a recent paper accepted for publication in Physical Review Letters, and in a piece featured at The Conversation.
The findings, if verified, could overturn the prevailing model on which physicists base most of our understanding of phenomena observed in the cosmos.
The Building Blocks of the Universe
According to the Standard Model, there are four fundamental forces that govern the phenomena we observe in the universe: gravity, electromagnetism, the weak force, and the strong force, all of which influence the behavior of particles down to their very smallest constituents, known as sub-atomic particles.
Although the Standard Model explains much about how these forces govern our universe, there are still missing pieces to this long-mysterious puzzle. The Standard Model, according to Barter and Smith, “is our best understanding of fundamental particles and forces, but we know it cannot be the whole story.” They argue—like a growing number of physicists today—that the current widely accepted model fails to explain gravity or dark matter, for instance.
Physicists currently use the LHC to smash particles together, producing conditions not unlike those near the beginning of the universe as we know it. Doing so allows researchers a rare glimpse at undiscovered physics through the production of unusual states of matter.
According to recent results from LHCb, the decay of subatomic particles called B mesons was investigated, and the results appear to disagree with most predictions of the Standard Model.
Such experiments fundamentally aim to test the theories first put forward by Einstein more than a century ago. “Physicists can compare measurements made at facilities such as the LHC with predictions based on the Standard Model to rigorously test the theory,” the authors write at The Conversation.
“Despite the fact that we know the Standard Model is incomplete, in over 50 years of increasingly rigorous testing, particle physicists are yet to find a crack in the theory,” they argue. However, that may be about to change.
Testing the Standard Model
Barter and Smith say that mounting evidence points to cracks in the Standard Model, specifically the results of an LHC experiment first reported in early 2025.
“Although the CMS results are not as precise as those from LHCb, they agree well, strengthening the case,” Barter and Smith note, adding that new results involving what is known as an “electroweak penguin decay” point to a specific kind of process where a transformation of short-lived particles occurs. In the case of the recent LHC experiments, the authors say this applies to the B meson decaying (or transforming) into four distinct subatomic particles. These include two muons, a kaon, and a pion.
By measuring the decay of the B meson in this way, physicists are able to study the way a particle known as a “beauty quark” is able to transform into another kind of fundamental particle: the enigmatic “strange quark.”
As Barter and Smith note, observing a penguin decay under such conditions is extremely rare in the Standard Model, since only one decay is expected to occur for roughly every million B mesons that exist. Yet the team’s recent measurements reveal the most precise figures to date for how often this process is expected to occur, and the numbers simply don’t match those predicted by the Standard Model.
“Penguin processes are uniquely sensitive to the effects of potentially very heavy new particles that cannot be created directly at the LHC,” the authors note, adding that these recent observations add to a growing number that have been observed by physicists over the last century, with an increasing number occurring in recent decades thanks to what can be achieved using the LHC.
“Our studies of rare processes let us explore parts of nature that may otherwise only become accessible using particle colliders planned for the 2070s,” Barter and Smith write, noting that such explorations in cutting-edge physics are suggestive of a need for new theories to help explain their findings. Some of these involve the incorporation of a variety of new particles known as “leptoquarks,” while another approach involves even heavier types of particles that conform to the Standard Model.
Although the findings are exciting, the researchers emphasize that there are still questions that prevent an open embrace of entirely new physics beyond the Standard Model, at least for now. Still, theoretical models combined with experimental LHCb data, they argue, still have a hard time accounting for the anomalies in their findings.
Going forward, physicists will hopefully be able to confirm findings like those reported by Barter and Smith, as the authors note that while their study looked at close to 650 billion B meson decays recorded between 2011 and 2018, revealing the presence of the so-called “penguin decays,” the recent LHCb experiment has already managed to record three times as many B mesons.
In the coming decades, upgrades to the LHC are expected to enable an even larger dataset, ultimately confirming whether unexplained factors are at work in our universe and potentially fundamentally reshaping our understanding of the physics behind how things work.
Barter and Smith reported the findings of the collaboration behind the recent experiments at The Conversation, and the paper announcing the results has been accepted for publication in Physical Review Letters.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.