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Where the Hunt for Missing Antimatter and New Physics Are One and the Same

Physics says we shouldn't exist, basically. So why do we?
LHCb experiment. Image: CERN

One of the cosmos' most elusive mysteries may be a bit closer to an explanation with new analysis of a highly odd particle produced at the Large Hadron Collider. The mystery: What happened to the universe's vanished share of antimatter? The particle: the Bs meson, an extremely short-lived pairing of two quarks capable of changing identities between matter and antimatter some three million million times per second.

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It's reasonably obvious that we live in a universe of "proper" matter. Basically, that just means that we live in a universe dominated by only one of matter's two types/mirror images. (Whether we live in a matter or antimatter universe is really a feature only of what we choose to call it.) If the situation were otherwise, we would observe a whole lot more meetings between antimatter and matter—explosive events involving the most perfect release of energy from matter allowed by nature, e.g. 100 percent.

This seeming imbalance is a problem. Antimatter is the natural product of any matter creation process and, clearly, we live in a world populated by matter (as opposed to one made of just pure energy/radiation), which should not be the case if equal amounts of antimatter were produced in concert with all of the matter we see and experience. The antimatter/matter scales appear to be unbalanced.

When a pair of photons (which can be viewed as energy, not matter) bop into each other, they might join together into an electron and a positron (matter) pair. The positron is the antimatter version of the electron, a particle with all of the same properties as the electron, but with an opposite charge (positive).

Usually, when a positron is produced, it only exists for a very short period of time before meeting some regular matter particle and annihilating in precisely the same process as matter creation but in reverse: an electron meets a positron and the result is the release of two photons as gamma rays. The whole relationship is very elegant.

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The perplexing thing is that, given the above, the universe exists at all. When all of this matter came into being, it should have produced just as much antimatter. If that were the case, the material universe would have annihilated just as quickly as it was formed. That it didn't suggests a deep imbalance, enough of a preference toward one variety of matter to have enough left over to form and fill the cosmos we observe.

This imbalance is explained by physicists usually in terms of CP violation, which is a general term for how the universe (or how physics) may treat matter and antimatter differently. That is, if CP symmetry is maintained, the physical laws relating to particle charge and spin should be precisely the same for matter and antimatter. If they were in fact different, as in the case of CP violation, that might explain the imbalance.

The Bs meson is made up of two quarks, one "regular" quark and one antiquark. These quarks can swap places spontaneously, with the result being an "anti" mirror image of the original quark. What a team of physicists at Syracuse University (and many more around the world) are investigating is the meson's apparent preference for regular matter over antimatter in its oscillations. Currently, this hunt is taking place at the Large Hadron Collider-beauty experiment, so named for the "beauty" quark.

This meson would seem to prefer an existence as regular matter, something first hinted at by results collected at the since-defunct Tevatron collider at Fermilab. "Results from [Tevatron detection experiments] D0 and CDF showed that the matter-antimatter oscillations of the Bs meson deviated from the Standard Model of Physics, but the uncertainties of their results were too high to make any solid conclusions," said Sheldon Stone, the Syracuse team's lead investigator, in a statement.

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The Syracuse researchers refined their technique for collisions at the Large Hadron Collider, making it more sensitive and, as such, more certain.

Their results are about what should be expected given physics' Standard Model, a periodic table of sorts for particles and their interactions. A post at the LHCb's project page explains, "The value of φs [CP violation] is precisely predicted in the Standard Model and sets the scale for the difference between properties of matter and antimatter for Bs mesons, known to physicists as CP violation. The predicted value is small and therefore the effects of New Physics could change its value significantly."

The Syracuse physicists, whose results are slated to be formally published next month, according to Stone, found Bs mesons to behave as expected from the Standard Model. It's a rare case of conformity being the most exciting possible result.

"In the CP violation that drives φs, the role of Bs oscillations is very important," the LHCb news posting notes. "Here the Standard Model predicts very small effects, thereby allowing New Physics to manifest itself." That is, the Standard Model predictions, if true, aren't enough to account for the observed matter-antimatter imbalance. Beyond the Standard Model, there is something unknown out there guiding the universe toward matter and life rather than radiation and noise.