Our set of rules describing particle physics may be under threat, according to results published by CERN. Read more: Large Hadron Collider discovers five hidden subatomic particles
The Standard Model of particle physics is a set of laws that describes everything we currently know about the most fundamental building blocks of nature. Now, data from the Large Hadron Collider is testing its boundaries.
While the Standard Model works incredibly well for describing things like how atoms stick together, how radioactivity works, why the proton is stable and how the Universe formed, it has a few limitations. It can't explain gravity, for example, because it is incompatible with our best explanation of how gravity works (general relativity) nor does it explain dark matterparticles.
Additionally, the quantum theory used to describe the small particles in the world, and the general theory of relativity used to describe the larger objects world, are difficult to reconcile. It has not yet been possible to make the two mathematically compatible in the context of the Standard Model.
For years, physicists have been trying to find ways to break the rules and find new theories and the latest experiments from LHC beauty, or LHCb, identified hints that extend beyond this Standard Model.
The results could lead to the discovery of new particles or even new forces, that could one day help explain the Universe's mysteries, like dark matter.
"Deviations such as what we see now are very exciting in the sense that if there are new particles, it means we can eventually use those new building blocks," Freya Blekman, CERN physicist and professor at the Vrije Universiteit in Brussels, told WIRED.
The latest data originated from studying the decay of one particle, called a B meson, which is made up of a bottom quark and an up quark. "Such a particle is quite common," says Blekman. "Due to the nature of particle physics, any unstable particles like the B meson fall apart to more stable particles in a very similar way as chemical and radioactive reactions," she says. "We call this the decay of a particle."
The Standard Model predicts many of the ways this meson can decay. When the B meson decays through one particular route, it ends up as a K meson, which is made up of a strange quark and an up quark, plus a pair of leptons – either electrons or muons.
"Now here it gets interesting," Blekman says. For this specific decay, the Standard Model predicts the chances the decay will result in a pair of electrons is about the same as the chances it will end up as with a pair of muons. This is known as lepton universality. Read more: A dark matter 'bridge' holding galaxies together has been captured for the first time
If you measure the ratio of the number of times two muons appear over the number of times two electrons appear, and correct for any difference in the way they are detected, the ratio should be 1, or very close to 1. Instead, LHCb’s results show muons are produced much less frequently than electrons.
"LHCb does not measure 1, they measure a number much closer to 0.7," says Blekman. "The difference is about 2.2-2.5 standard deviations, meaning there is a chance of one in 80 or so that this measurement is still consistent with 1."
In particle physics, results need to reach at least three standard deviations before they are considered a discovery. "For particle physicists, this result is tantalising but not evidence for anything," Blekman says.
While not statistically significant enough to be conclusive yet, physicists are excited because another experiment has shown hints of a similar behaviour. If it does turn out to be true, it could mean two different things.
"Either lepton universality is not true, or there is something extra happening, for example, a new extra intermediate particle," Blekman says. "Proving and explaining, either way, would be amazing and would completely change the way we understand how matter sticks together," she continues, "particularly if there are new particles, new forces that can explain things like dark matter in the galaxy or how the Universe formed."
The LHC will start up again next month after a winter hibernation, and physicists are expecting to see more results from the next set of experiments.
“More data and more observations of similar decays are needed in order to clarify whether these hints are just a statistical fluctuation or the first signs for new particles that would extend and complete the Standard Model of particles physics,” a CERN statement said.
This article was originally published by WIRED UK
