B-mesons to turn into their antimatter counterparts and back again, a process known as mixing.
The CDF team think they have found a bit more of it, in particles known as D0-mesons.
Mesons measured by LHCb have already hinted at an answer, and Prof Parkes says that is the next target.
According to the Standard Model, the matter and antimatter versions of these mesons should give birth to such daughters in the same proportions.
B0-mesons do indeed break up more easily than their matter counterparts.
That is because B-mesons are sometimes born as quantum-mechanically conjoined twins.
The new paper represents the last of the four mesons that had never been seen flipping from matter to antimatter and back in a single measurement.
Other experiments, notably at the Fermi National Accelerator facility in the US, have not definitively found a notable difference between the two kinds of decay of D-mesons.
K-mesons, implied that matter and antimatter are not truly symmetrical.
Since the predicted decay patterns of the two mesons were a result of the ways that matter and antimatter blended in them, that suggested that those substances are not quite equal and opposite after all.
The old linear accelerator at Stanford was repurposed, turning it from the machine that co-discovered a particle known as the charm quark (thus winning its operators a Nobel prize) into a factory for making particles called B mesons.
Our best understanding of physics so far, called the Standard Model, suggests that the complicated cascades of decay of D-mesons into other particles should be very nearly the same - within less than 0.1% - as a similar chain of antimatter decays.
"The last thing people want is long lists of particle names - one's got to relate it to the bigger picture, and I think today is sort of a milestone in that picture - it's the first time that we've seen anything in Bs mesons, " Prof Parkes told BBC News.
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