Matter-Antimatter Asymmetry: After Mesons, Hints Of Charge-Parity Violation Detected In Baryons

Where is all the antimatter?

That is the question that physicists have, for the longest time, tried to find the answer to. So far, though, they have failed to find one.

The problem, as we understand it, is that if the Big Bang created equal quantities of matter and antimatter 13.8 billion years ago, why does the universe we currently reside in exist? Why didn’t matter and antimatter particles annihilate each other, as they are wont to do whenever they come in contact with each other?

The answer, for now, at least, is that we don’t know. What is obvious is that there is a fundamental difference between matter and antimatter — one that gave the former an edge over the latter in the race for survival. Either significantly more matter was created by the Big Bang, or there is an as-of-yet-undiscovered asymmetry between matter particles and their antimatter counterparts.

That is why scientists have been hunting for violations of what is known as charge-parity (CP) symmetry — a central tenet of the Standard Model of particle physics, which states that the laws of physics remain unchanged even if a particle is replaced with its antiparticle, which has the opposite charge, and if its spatial coordinates are inverted.

Here’s where we hit a dead end. So far, the extent of CP violation detected among elementary particles is not significant enough to explain the observed matter-antimatter asymmetry. And, until now, even these tiny hints of CP violations had not been detected in baryons — a class of particles that includes protons and neutrons.

As described in a new study submitted for publication in the journal Nature Physics, researchers associated with the LHCb collaboration at CERN’s Large Hadron Collider describe the first-ever measurement of CP violation in the decays of a particle known as lambda-b baryon.

“Differences in the behaviour of matter and antimatter have been observed in K and B meson decays, but not yet in any baryon decay,” the authors said in the study. “These four-body hadronic decays are a promising place to search for sources of CP violation both within and beyond the Standard Model of particle physics.”

It is important to note that the extent of CP violation detected in these three-quark bodies is not yet enough to explain the current imbalance between matter and antimatter. However, scientists hope that further measurements of baryons may just reveal deviations from the Standard Model and provide the answer to the million-dollar question — why is there something rather than nothing?