After the Big Bang, it’s predicted that our universe had equal and large quantities of matter and anti-matter, but today we observe only matter around us, no anti-matter. So why this imbalance of matter and anti-matter occurred at the beginning of our universe? What exactly caused matter to dominate over anti-matter?
Well, such a question might be answered by baryonic asymmetry or CP-violation. The CP-symmetry is the combination of two different symmetries; C-symmetry and P-symmetry, where ‘C’ means charge conjugation and ‘P’ mean parity transformation.
The C-symmetry has a tendency to convert matter to anti-matter, for eg. Neutrino to anti-neutrino. The P-symmetry has a tendency to form a mirror image of particles called as mirror particles i.e. by simply flipping the spatial coordinates, for eg. Left-handed neutrino to right-handed neutrino.
Therefore, if we join these two symmetries we get CP-symmetry which will convert left-handed neutrino to right-handed anti-neutrino.
CP–symmetry holds well in electromagnetism, gravity, and strong interaction, but it is observed experimentally that CP is violated in weak interactions; i.e. not all particles were converted into their mirror image in weak decays. Also, it not even conserved the laws of P – symmetry.
However, in Quantum Chromodynamics (QCD), there is no violation seen experimentally. As there is no known reason for it to be conserved in QCD specifically, this is a “fine-tuning” problem known as the strong CP problem.
So after the Big Bang when there were equal amounts of matter and anti-matter, they should have created a sea of radiations in space due to the annihilation of matter and anti-matter. If CP-symmetry was preserved, then, there would have been the cancellation of both matter and anti-matter, but today we know that this is not the case.
At one instant of time, physical laws must have acted differently for matter and antimatter, i.e. violating CP–symmetry. There might be a matter which did not annihilate with its anti-partner causing him to survive till today; or there might be a matter which didn’t get converted to its anti-matter, leading to making 5% of our universe.
LHCb is a detector of the large hadron collider (L.H.C.) which is investigating, what happened to the missing antimatter. I talked about the working of the L.H.C. and explained the detectors functions in my, ‘the working of large hadron collider‘ blog post, so do have a look 🙂