In a new groundbreaking study, researchers at CERN may be one step closer to explaining where the universe's missing antimatter went. By smashing protons together at high speed and studying the leftovers of the collision, they have made some fascinating discoveries about the nature of the universe as we know it.
Where has all the antimatter gone?
You are likely all familiar with "matter", after all, you and everything around you is made from it, but have you heard of antimatter? Of all the electrons, protons, neutrons, and other subatomic particles around us there are also anti- versions of them which are nearly identical but have mirrored properties to them -- like an opposing electrical charge.
Discovered in 1932 by physicist Carl Anderson, when matter and antimatter collide they are both annihilated in a flash of energy. Anderson discovered antimatter when studying cosmic rays that rain down on Earth from space.
Over the next few decades, many other physicists found that all matter particles do indeed have antimatter equivalents.
Since matter and antimatter are mirrored copies of one another they should, physicists believe, have been created in equal quantities during the "Big Bang".
However, if true, we should expect all matter and antimatter to have been annihilated shortly after being created. Interestingly something appears to have happened in these early days of the universe to leave barely any antimatter and a relatively small, but significant, "surplus" of matter.
It is this "surplus" that makes up everything we see in the universe today.
Most antimatter so far discovered, and there is a pitifully small amount of it, can be observed in radioactive decays in a small fraction of cosmic rays.
The absence of antimatter in the universe has puzzled physicists for many years now, but a team at CERN may have uncovered a potential reason for it.
Explaining the "asymmetry" of matter and antimatter
To help answer this apparent asymmetry of matter and antimatter in the universe, scientists have turned to study quarks which are the fundamental building blocks to matter, as well as leptons. Quarks come in a variety of forms, or flavors, known colloquially as "up", "down", "charm", "strange", "bottom", and "top" depending on how they spin.
Each of these matter quarks also has six corresponding anti-quarks too.
"Up" and "down" quarks make up protons and neutrons in the nuclei of atoms, and the others can be created by high-energy processes like smashing things at high speed in the Large Hadron Collider at CERN.
Some particles, called mesons, can also be created by combining quarks and anti-quarks, and four of them, called neutral mesons (B0S, B0, D0, and K0) exhibit a fascinating behavior. For example, these strange particles can turn into their antimatter partners spontaneously and back again many times a second.
This behavior was first seen all the way back in 1960.
Since these particles consist of matter and antimatter they are inherently unstable and will decay into more stable particles fairly rapidly at some point during this matter-antimatter oscillation cycle.
Meson decay also happens slightly differently for mesons when compared with anti-mesons which results in different decay rates over time.
This behavior is well described in a theoretical framework called the Cabibbo-Kobayashi-Maskawa (CKM) mechanism.
The CKM mechanism predicts that while there is a difference between how matter and antimatter behave, it is too small to generate the surplus of matter in the early Universe.
Clearly, physicists are missing something else critical to explaining the "missing" antimatter.
The big unknown unknowns of physics
This is one of the major, as yet, unknown unknowns of physics that need further investigation to find an explanation. To this end, researchers at CERN are attempting to discover why through their LHCb experiment to study neutral B0S mesons looking at their decays into pairs of charged K mesons.
Mesons were created by colliding protons in the LHC which resulted in them oscillating between their meson and anti-meson forms about three trillion times per second. The collisions also created anti-B0S mesons that oscillate in the same way, giving us samples of mesons and anti-mesons that could be compared.
By counting the number of decays from both samples, the researchers found that there was a slight difference, with more decays seen for one of the B0S mesons. They also found and managed to quantify, that the difference in decay, aka asymmetry, varied according to the oscillation between the B0S meson and the anti-meson.
This could, in theory, be used to measure several parameters of the underlying CKM theory. By making more and more measurements, this kind of experiment could be used to provide a "reality check" of the currently accepted theory.
Because the difference is too small to explain the apparent preference of matter over antimatter in the universe, the CERN team believes that the current CKM theory is likely an approximation of a more fundamental, but as yet unknown, theory.
"Investigating this mechanism that we know can generate matter-antimatter asymmetries, probing it from different angles, may tell us where the problem lies. Studying the world on the smallest scale is our best chance to be able to understand what we see on the largest scale," said Lars Eklund Professor of Particle Physics, the University of Glasgow in an article on The Conversation.
The study was first published at CERN in October of this year.