A quirky type of subatomic particle known as the charm meson has the seemingly magical ability to switch states between matter and antimatter (and back again), according to the team of over 1,000 physicists who were involved in documenting the phenomenon for the first time.
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Oxford researchers, using data from the second run of the Large Hadron Collider (LHC)—a particle accelerator at the Switzerland-based European Organization for Nuclear Research (known internationally as CERN)—made the determination by taking extremely precise measurements of the masses of two particles: the charm meson in both its particle and antiparticle states.
Yes, this breakthrough in quantum physics is as heady as it sounds. A charm meson particle, after all, can exist in a state where it is both itself and its evil twin (the antiparticle version) at once. This state is known as "quantum superposition," and it's at the heart of the famous Schrödinger's Cat thought experiment.
As a result of this situation, the charm meson exists as two distinct particles with two distinct masses. But the difference between the two is infinitesimally small—0.00000000000000000000000000000000000001 grams to be exact, according to the scientists' research, described in a new paper published last month on the arXiv preprint server (that means the work hasn't been peer-reviewed yet). They've recently submitted the work for publication in the journal Physical Review Letters.
While the findings are basically the definition of minuscule, the ramifications are anything but; the physicists say the charm meson particle's ability to exist as both itself and its alter-ego could shake up our assumptions about the very nature of reality.
What Is a Charm Meson Particle?
To understand what's going on here, we first have to unpack the meson particle. These are extremely short-lived subatomic particles with a balanced number of quarks and antiquarks. In case you skipped that lecture in quantum physics, quarks are particles that combine together to form "hadrons," some of which are protons and neutrons—the basic components of atomic nuclei.
The Standard Model of particle physics includes the matter particles (quarks and leptons), the force carrying particles (bosons), and the Higgs boson. VIA SYMMETRY MAGAZINE: A JOINT FERMILAB/SLAC PUBLICATION. ARTWORK BY SANDBOX STUDIO, CHICAGO.
There are six "flavors" of quark: up, down, charm, strange, top, and bottom. Each also has an antiparticle, called an antiquark. Quarks and antiquarks vary because they have different properties—like electrical charge of equal magnitude, but opposite sign.
Back to mesons: They're almost the size of neutrons or protons, but are extremely unstable. So, they're uncommon in nature itself, but physicists are interested in studying them in artificial environments (like in the LHC) because they want to better understand quarks. That's because, along with leptons, quarks make up all known matter.
Charm mesons can travel as a mixture of both its particle and antiparticle states (a phenomenon appropriately called "mixing"). Physicists have known that for over a decade, but the new research shows for the first time that charm mesons can actually oscillate back and forth between the two states.
What Is Antimatter?
Antiquarks are the opposite of quarks and are considered a type of antimatter. These particles can cancel out normal matter—which is kind of a problem if you want the universe to, well, exist. The various kinds of antimatter are almost all named using the anti- prefix, like quark versus antiquark. More specifically, a charm meson typically has a charm quark and an up antiquark, and its anti- partner has a charm antiquark and an up quark.
It's important to note the charm meson is not the only particle that can oscillate between matter and antimatter states. Physicists have previously observed three other particles in the Standard Model—the theory that explains particle physics—doing so. That includes strange mesons, beauty mesons, and strange-beauty mesons.
Why was the charm meson a holdout for so long? The charm meson oscillates incredibly slowly, meaning physicists had to take measurements at an extremely fine degree of detail. In fact, most charm mesons will fully decay before a complete oscillation can even take place, like an aging person with a very slow-growing tumor.
How Did Scientists Catch the Charm Meson in Quantum Superposition?
Illustration of the mass difference between the D1 and D2 mesons. CERN
The large-scale undertaking that produced the charm meson data is called the Large Hadron Collider beauty experiment. It seeks to examine why we live in a world full of matter, but seemingly no antimatter, according to CERN.
Using a vast amount of data from the charm mesons generated at the LHC, the scientists measured particles to a difference of 1 x 10^-38 grams. With that unbelievably fine-toothed comb, they were able to observe the superposition oscillation of the charm mesons.
How did scientists measure this incredibly tiny difference in mass? In short, the LHC regularly produces mesons of all kinds as part of its scientists' work.
"Charm mesons are produced at the LHC in proton-proton collisions, and normally they only travel a few millimeters before they decay into other particles," according to a University of Oxford press release. "By comparing the charm mesons that tend to travel further versus those that decay sooner, the team identified differences in mass as the main factor that drives whether a charm meson turns into an anti-charm meson or not."
Charm Meson Oscillations Could Have Saved the Universe
Now that scientists have finally observed charm meson oscillation, they're ready to open up a whole new can of worms in their experimentation, hoping to unearth the mysteries of the oscillation process itself.
That path of study could lead to a new understanding about how our world began in the first place. Per the Standard Model of particle physics, the Big Bang should have produced matter and antimatter in equal parts. Thankfully, that didn't happen—because if it had, all of the antimatter particles would have collided with the matter particles, destroying everything.
Clearly, physicists say, there is an imbalance in matter and antimatter collisions in our world, and the answer to that mystery could lie in the incomprehensibly small oscillations of particles like the charm meson. Now, scientists want to understand if the rate of transition from particle to antiparticle is the same as the rate of transition from antiparticle to particle.
Depending on what they find, our very conceptions of how we exist—why we live in a world full of matter rather than antimatter, and how we got here—could change forever.
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