Biggest cosmic mystery ‘step closer’ to solution
BBC:  Stars, galaxies, planets, pretty much everything that makes up our everyday lives owes its existence to a cosmic quirk.  The nature of this quirk, which allowed matter to dominate the Universe at the expense of antimatter, remains a mystery.  Now, results from an experiment in Japan could help researchers solve the puzzle – one of the biggest in science.  It hinges on a difference in the way matter and antimatter particles behave.  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.
 But matter has a shadowy counterpart called antimatter. Each sub-atomic particle of ordinary matter has a corresponding “antiparticle”.
 Today, there is far more matter than antimatter in the Universe. But it wasn’t always this way.  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.