Update (March 24, 2021): The Large Hadron Collider (LHCb) beauty experiment continues to insist that there is a flaw in our best model of particle physics.
As explained below, previous results comparing the collider data to what we might expect from the standard model yielded a curious discrepancy of around 3 standard deviations, but we needed a lot more information to be sure it really reflected something new in physics. .
The newly published data has brought us closer to that confidence, putting the results at 3.1 sigma; there’s still a 1 in 1,000 chance that what we’re seeing is the result of physics being just messy, and not a new law or particle. Read our original coverage below for all the details.
Original (August 31, 2018): Previous experiments using CERN’s large particle smasher, the Large Hadron Collider (LHC), hinted at something unexpected. A particle called the beauty meson was breaking down in ways that just didn’t match predictions.
That means one of two things: our predictions are wrong or the numbers are out of place. And a new approach makes the observations less likely to be a mere coincidence, which makes it almost enough to get scientists excited.
A small group of physicists took data from the collider on the disintegration of the beauty meson (or meson b for short) and investigated what might happen if they swapped an assumption regarding its disintegration for one that assumed that interactions continued to occur after that were transformed.
The results were more than surprising. The alternative approach duplicates the idea that something strange is really happening.
In physics, anomalies are generally seen as good things. Fantastic things. Unexpected numbers could be the window into a whole new way of looking at physics, but physicists are conservative too: you I have be when the fundamental laws of the Universe are at stake.
So when the experimental results don’t quite agree with the theory, it is first presumed to be a random error in the statistical chaos of a complicated test. If a follow-up experiment shows the same thing, it is still presumed to be ‘one of those things’.
But after enough experiments, enough data can be collected to compare the chances of errors with the probability of an interesting new discovery. If an unexpected result differs from the predicted result by at least three standard deviations, it is called 3 sigma, and physicists can look at the results while enthusiastically nodding with raised eyebrows. It becomes an observation.
To really attract attention, the anomaly should persist when there is enough data to bring that difference to five standard deviations – a 5 sigma event is the cause for breaking the champagne.
Over the years, the LHC has been used to create particles called mesons, in order to observe what happens in the moments after they are born.
Mesons are a type of hadron, somewhat similar to the proton. Only instead of consisting of three quarks in a stable formation under strong interactions, they are made of just two: a quark and an antiquark.
Even the most stable mesons fall apart after hundredths of a second. The framework we use to describe the construction and disintegration of particles, the Standard Model, describes what we should see when different mesons divide.
The beauty meson is a descending quark connected to a lower anti-quark. When the properties of the particle are connected to the standard model, the decay of the b-meson should produce pairs of electrons and positrons, or electron-like muons and their opposites, anti-muons.
This result for electrons or muons should be 50-50. But that is not what we are seeing. The results show many more electron and positron products than muon anti-muons.
This is worth paying attention to. But when the sum of the results is kept together with the prediction of the standard model, they are left out by a couple of standard deviations. If we take into account other effects, it could be even further, a real break with our models.
But how sure can we be that these results reflect reality and are not just part of the noise of experimentation? The importance is well below that 5 sigma, which means there is a risk that the gap to the standard model is not at all interesting after all.
The standard model is a good job. Built over decades on the foundations of field theories first laid down by the brilliant Scottish theorist James Clerk Maxwell, it has served as a map of the invisible realms of many new particles.
But it is not perfect. There are things that we have seen in nature, from dark matter to neutrino masses, that currently seem to be outside the scope of the Standard Model.
At times like this, physicists tweak the basic assumptions of the model and see if they do a better job of explaining what we are seeing.
“In previous calculations, it was assumed that when the meson disintegrates, there are no more interactions between its products,” said physicist Danny van Dyk of the University of Zurich in 2018.
“In our last calculations we have included the additional effect: long distance effects called the charm loop.”
The details of this effect are not for hobbyists and are not standard model material.
In short, they involve complicated interactions of virtual particles (particles that do not persist long enough to go anywhere, but arise in principle in fluctuations in quantum uncertainty) and an interaction between the decay products after they have divided.
What is interesting is that when explaining the breakdown of the meson through this speculative charm loop, the meaning of the anomaly jumps to a convincing 6.1 sigma.
Despite the jump, it’s still not a champagne affair. More work needs to be done, including accumulating observations in light of this new process.
“We will probably have a sufficient quantity within two or three years to confirm the existence of an anomaly with a credibility that gives us the right to speak about a discovery,” said Marcin Chrzaszcz of the University of Zurich in 2018 (as you know, it is 2021) . and we’re not quite there yet, but we’re getting closer.)
If confirmed, it would show enough flexibility in the Standard Model to expand its limits, potentially revealing pathways into new areas of physics.
It’s a small crack, and still nothing may appear. But no one said that solving the greatest mysteries of the Universe would be easy.
The 2018 study was published in European Physical Journal C; The 2021 results are awaiting peer review, but are available for researchers to review on arXiv.