What happened at the beginning of the universe, in the very first moments? We don’t really know since it takes such huge amounts of energy and precision to recreate and understand the cosmos on such short timescales in the lab. But scientists at the Large Hadron Collider at CERN in Switzerland aren’t giving up:
The Standard Model of particle physics describes the fundamental particles which make up the universe, and the forces that act between them. The elementary particles include quarks, of which there are six: up, down, strange, charm, top, and bottom. Similarly, there are six leptons which include the electron, a heavier version called the muon, and the still heavier tau, each of which has an associated neutrino. There are also antimatter pairs of all quarks and leptons which are identical particles apart from an opposite charge.
The Standard Model is experimentally verified to an incredible degree of accuracy but has some significant shortcomings.
The model suggests this event should have produced equal amounts of matter and antimatter. Yet today, the universe is almost entirely made up of matter. And that’s lucky for us, because antimatter and matter annihilate in an enormous flash of energy when they touch.
One of the biggest open questions in physics today is: why is there more matter than antimatter. Were there processes at play in the early universe that favored matter over antimatter? To get to the answer, researchers are studying a process where matter transforms into antimatter and back.
Quarks are bound together to form particles called baryons or mesons, which consist of quark-antiquark pairs. Mesons with zero electric charge continually undergo a phenomenon called mixing by which they spontaneously change into their antimatter particle, and vice versa.
Our latest discovery, announced at the Charm conference, measured a parameter that corresponds to a mass difference of 6.410-6 electron Volts or 10-38 grams, one of the smallest mass differences between two particles ever measured.
The key is precision. We know from theory that the particle oscillations follow the path of a a familiar type of wave. Measuring the start of the wave very precisely, we can infer its full period as we know its shape. The measurement therefore had to reach record precision on several fronts. This is made possible by the unprecedented amount of charm particles produced at the LHC.
But why is this important? To understand why the universe produced less antimatter than matter we need to learn more about the asymmetry in the production of the two, a process known as CP-violation. It has already been shown that some unstable particles decay in a different way to their corresponding antimatter particle. This may have contributed to the abundance of matter in the universe, with previous discoveries of it leading to Nobel Prizes
We also want to find CP-violation in the process of mixing. If we start with millions of D0 particles and millions of D0 antiparticles, will we end up with more D0 normal matter particles after some time? Knowing the oscillation rate is a key step towards this goal.
While we cannot yet completely solve the mysteries of the universe, our latest discovery has put the next piece in the puzzle. The new upgraded LHCb detector will open the door to an era of precision measurements that have the potential to uncover yet unknown phenomena, and perhaps even physics beyond the Standard Model.