Update (March 24, 2021): The Beauty Hadron Collider (LHCb) experiment still insists that there is a flaw in our best model of particle physics.
As explained below, previous results comparing the collision data with what we would expect from the Standard Model generated a curious discrepancy of about 3 standard deviations, but we needed more information to make sure it reflected with true something new in physics.
The recently released data has now pushed us closer to this confidence, placing the results at 3.1 sigma; there is another 1 in 1,000 possibility that what we see is the result of the fact that physics is simply disordered and not of a new law or particle. Read our original cover below to find out all the details.
Original (August 31, 2018): Previous experiments using CERN’s Large Hadron Collider (LHC) have suggested something unexpected. A particle called a beauty house decomposed in ways that simply did not align with predictions.
That means one of two things – our predictions are wrong or the numbers are out. And a new approach makes the observations less likely to be a mere coincidence, which makes it almost enough for scientists to start getting excited.
A small group of physicists took the data of the collision about the disintegration of the beauty parlor (or meson b in short) and investigated what might happen if they changed one hypothesis about its decay to another that assumed that interactions still occur after they have transformed.
The results were more than a little surprising. The alternative approach is doubled based on the fact that something really strange is happening.
In physics, anomalies are usually seen as good things. Fantastic things. Unexpected numbers could be the window to a whole new way of looking at physics, but physicists are also conservative – you have to be when the fundamental laws of the Universe are at stake.
So when the experimental results do not match the theory, it is first assumed to be a random blip into the statistical chaos of a complicated test. If a tracking experiment shows the same thing, it is supposed 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 a new interesting discovery. If an unexpected result differs from the predicted result by at least three standard deviations, it is called 3 sigma, and physicists are allowed to look at the results while enthusiastically nodding. It becomes an observation.
To really attract attention, the anomaly should persist when there is enough data to push this difference to five standard deviations: a 5-sigma event is the cause of the champagne outbreak.
Over the years, the LHC has been used to create particles called mesons, in order to track what happens in the moments after they are born.
Mesons are a type of hadron, somewhat like a proton. Just instead of being made up of three quarks in a stable formation under strong interactions, they are composed of only two – a quark and an antiquark.
Even the most stable house crumbles after a hundredth of a second. The framework we use to describe the construction and degradation of particles – the standard model – describes what we should see when different mesons separate.
The beauty inn is a down quark connected to a bottom anti-quark. When the properties of the particle are connected to the standard model, the degradation of meson b should produce electron and positron pairs or electron-like muons and their anti-muon opposites.
The result of this electron or muon should be 50-50. But that’s not what we see. The results show much more electron-positron products than muoni-anti-muoni.
This is worth paying attention to. But when the sum of the results is maintained along with the prediction of the standard model, they are outside two standard deviations. If we consider other effects, it could be even further – a real break from our models.
But how sure can we be that these results reflect reality and are not just part of the noise of experimentation? The significance is well below this 5 mark, which means that there is a risk that the gap from the standard model will not be, after all, anything interesting.
The standard model is an excellent work. Built over the decades on the basis of field theories first exposed by the brilliant Scottish theorist James Clerk Maxwell, it served as a map for the unseen realms of many new particles.
But it’s not perfect. There are things we have seen in nature – from dark matter to neutrino masses – that now seem out of the reach of the standard model.
In such moments, physicists change the basic assumptions about the model and see if they do a better job of explaining what we see.
“In previous calculations, it was assumed that when the meson disintegrates, there are no more interactions between its products,” said in 2018 physicist Danny van Dyk from the University of Zurich.
“In our latest calculations we have included the additional effect: long-distance effects called charm loop.”
The details of this effect are not for amateurs and are not even standard materials.
In short, they involve complicated interactions of virtual particles – particles that do not persist long enough to go anywhere, but appear in principle in fluctuations in quantum uncertainty – and an interaction between decomposition products after they have separated.
What is interesting is that, explaining the breakdown of the house through this loop of speculative charm, the significance of the anomaly jumps to a convincing sigma of 6.1.
Despite the leap, it is not yet a champagne business. More work is needed, which includes gathering observations in light of this new process.
“We will probably have a sufficient amount within two or three years to confirm the existence of an anomaly with a credibility that gives us the right to talk about a discovery,” said Marcin Chrzaszcz of the University of Zurich in 2018. (As you know , it’s 2021 and we’re not right there yet, we’re getting closer.)
If confirmed, it would show enough flexibility in the standard model to stretch its limits, potentially revealing pathways to new areas of physics.
It’s a tiny crack and yet it might not show anything. But no one said that solving the biggest mysteries in the universe would be easy.
The 2018 study was published in European Physical Journal C; the 2021 results await peer review, but are available to researchers to verify on arXiv.