So let us start this with a fact. All particles that makeup matter around us have antimatter versions of them which are almost identical but have mirrored properties. Examples include electrons, protons which have their antimatter counterparts such as antielectrons, antiprotons. These could just be the opposite charge or vary in a few other properties. When a matter and an antimatter particle meet, they annihilate in a flash of energy.
If at all this antimatter and matter are truly identical and are actually mirrored copies of each other, then they should’ve been produced in equal amounts in the Big Bang. So now it raises a question. Won’t it have made all annihilate? To our surprise, there’s nearly no antimatter left in the universe. As of now, we see it only in some radioactive decays and in a small part of cosmic rays.
So where did the antimatter vanish? A fresh way has been discovered using the LHCb experiment at CERN, and this could have the answer to it.
Antimatter’s existence was predicted by physicist Paul Dirac’s equation, which described the motion of electrons in 1928. Initially, it wasn’t clear if this was just a mathematical quirk or a description of a real particle.
In 1932, Carl Anderson discovered an antimatter partner to the electron–the positron–while studying cosmic rays that rain down on Earth from space, thus clearing the doubt. As research continued on, these physicists have found that all matter particles have antimatter counterparts.
Scientists believe that there must be a process that gave preference to matter over antimatter in the hot and dense state shortly after the Big Bang, which created a small surplus amount of matter. All the antimatter would have been annihilated by an equal amount of matter, leaving a tiny surplus of matter.
It is this tiny amount of matter that makes up everything that we see today. The process that caused this is unclear, and we are still on a search for it.
We know that quarks are the fundamental building blocks of matter, along with leptons. Study on their behaviour could shed us some information on the difference between matter and antimatter. There are six kinds of quarks – up, down, charm, strange, bottom and top. And they have corresponding six anti-quarks.
Up and Down quarks are what makeup protons and neutrons in the nuclei of ordinary matter. We can produce the other quarks via high-energy processes–for instance by colliding particles in accelerators such as the Large Hadron Collider at CERN.
Mesons are particles that comprise quarks and antiquarks. There are four neutral mesons (B0S, B0, D0 and K0) that exhibit a fascinating behaviour. These mesons can spontaneously turn into their antiparticle partner and back again. This was first observed in 1960.
Their instability causes them to decay (fall apart) into more stable particles at some point during their oscillation. This kind of decay is slightly different for mesons when compared to anti-mesons, which combined with oscillation means that the rate of the decay varies over time.
The Cabibbo-Kobayashi-Maskawa (CKM) mechanism is a theoretical framework which has the rules for the oscillations and decays. Even though it predicts that there is a difference in the behaviour of matter and antimatter, we still need to know what caused the surplus of matter in the early universe required to explain the abundance we see today.
This is a clear sign that there are a few things that we still don’t understand, and study of such things could challenge our fundamental theory in physics.
New physics?
The latest result from the LHCb experiment is based on a study on neutral B0S mesons. This was focused on their decays into pairs of charged K mesons. B0S mesons were created by the collision of protons with other protons in Large Hadron Collider, where they were oscillated into their anti-meson and back at a rate of three trillion times per second. These collisions also created anti-B0S mesons that oscillate in the same way, giving us a good amount of samples of mesons and anti-mesons that could be compared.
To see how this difference varied, there was a count on the number of decays from the two samples and a comparison was done. The slight difference found was that there were more decays happening for one of the B0S mesons. This is the first time that for B0S mesons we observed the difference in decay, or asymmetry, varied according to the oscillation between the B0S meson and the anti-meson.
Measuring the size of asymmetries was an additional bonus in the study of matter and antimatter differences. These can be translated into measurements of several parameters of the underlying theory.
A comparison of these results with other measurements can give us a consistency check. Since the small preference of matter over antimatter that we observe on the microscopic scale cannot explain the overwhelming abundance of matter that we observe in the Universe, it is likely that our current understanding is an approximation of a more fundamental theory.
Studying the world on the smallest scale is our best chance to be able to understand what we see on the largest scale.
