Why does matter exist? We wouldn’t be around to ask the question if it didn’t, but our best theory of material reality implies that the existence of stable matter is an anomaly. So how did everything around us come to be?
We don’t have an answer. But in our efforts to make sense of this, the anomaly to begin all anomalies, we are uncovering other hints that our understanding of the stuff contained in the universe is far from complete.
That understanding is rooted in the standard model of particle physics, the quantum-theory-based melange that bundles up our knowledge of all the forces of nature besides gravity (see diagram). One of its revelations is that every fundamental matter particle has an antimatter twin – a particle identical in every way apart from having the opposite electric charge. For the familiar negatively charged electron there is a positively charged “positron”, and so on.
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The big bang should have made equal amounts of matter and antimatter. But here’s the thing: when matter and antimatter meet, they annihilate in a puff of energy. So neither should have survived the early days of the universe.
Yet one of them did. Various experiments have tried to find some mismatch between processes involving matter and antimatter to explain this. The latest is LHCb at the CERN particle physics lab, which is looking for an imbalance in decays of particles known as mesons, made up of a quark and an antiquark.
In 2011, one result looked promising: a type of D meson decayed at a different rate from its mirror version with quark and antiquark reversed. This anomaly disappeared when more data came in. Meanwhile, others arose.
For instance, heavier B mesons were found to be decaying into tau particles more often than the standard model predicts. Tau particles, along with muons, are just heavier versions of the electron. According to the standard model, once you adjust for their different masses, B mesons should decay into all three at the same rate.
Such decays are known as “penguin” processes, supposedly because the standard diagrams physicists use to sketch them out end up looking rather like penguins. Unbalanced penguins have now popped up in three different experiments, including LHCb. The energies and trajectories of muons produced in B meson decays are also persistently aberrant in LHCb data. “This anomaly stands,” says of the University of Oxford, who works on LHCb.
Statistically speaking, none of the anomalies is significant enough to definitively say that something fishy is going on. But they do point to at least a shared misunderstanding, or false assumption, about the standard model. “This could be an indication of new physics,” says of the University of Cambridge and LHCb.
Perhaps B mesons decay momentarily into as-yet-undetected particles before decaying further into muons, skewing their final distributions. One favoured culprit is a leptoquark – a kind of hybrid of lepton- and quark-type particles. Another is a new kind of Higgs boson. But these are still little more than speculations. “We will have to wait for a couple of years to know more,” says Wilkinson.
Solving the original riddle of the matter-antimatter anomaly might take considerably longer, judging by the lack of any hint of an imbalance big enough to explain it. But it is the original proof that small anomalies can have big consequences.
That’s odd: unreliable Uranus
Small anomalies between the actual orbit of Uranus and that predicted by Newton’s gravity led French mathematician Urbain Le Verrier to predict the existence of an eighth planet in 1846. Following Le Verrier’s lead, Johann Galle of the Berlin Observatory discovered Neptune barely a month later.
Read more: “The 6 biggest glitches in physics”
This article appeared in print under the headline “That’s odd… Unruly penguins”
