BBC: [2] Stars, galaxies, planets, pretty much everything that makes up our everyday lives owes its existence to a cosmic quirk. [3] The nature of this quirk, which allowed matter to dominate the Universe at the expense of antimatter, remains a mystery. [4] Now, results from an experiment in Japan could help researchers solve the puzzle – one of the biggest in science. [5] It hinges on a difference in the way matter and antimatter particles behave. [6] The world that’s familiar to us – including all the everyday objects we can touch – is made up of matter. The fundamental building blocks of matter are sub-atomic particles, such as electrons, protons and neutrinos.
[7] But matter has a shadowy counterpart called antimatter. Each sub-atomic particle of ordinary matter has a corresponding “antiparticle”.
[8] Today, there is far more matter than antimatter in the Universe. But it wasn’t always this way. [9] The Big Bang should have created matter and antimatter in equal amounts.
“When particle physicists make new particles in accelerators, they always find that they produce particle-antiparticle pairs: for every negative electron, a positively charged positron (the electron’s antimatter counterpart),” said Prof Lee Thompson from the University of Sheffield, a member of the 350-strong T2K collaboration, which includes a relatively large number of scientists from UK universities.

“So why isn’t the universe 50% antimatter? This is a long-standing problem in cosmology – what happened to the antimatter?”

However, when a matter particle meets its antiparticle, they “annihilate” – disappear in a flash of energy.

During the first fractions of a second of the Big Bang, the hot, dense Universe was fizzing with particle-antiparticle pairs popping in and out of existence. Without some other, unknown mechanism at play, the Universe should contain nothing but leftover energy.