application for a CERN antimatter project
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CERN Antimatter project for


Does antimatter fall down or up?

Help the AEgIS experiment at CERN to work out how antimatter is affected by gravity. Just join the dots!


The observable universe is composed almost entirely of matter but we can produce stuff called antimatter in the lab. Antimatter is material composed of antiparticles.

Antiparticles have the same mass as normal matter particles but the opposite charge. When an antiparticle collides with an ordinary matter particle they both annihilate - producing a burst of other particles and radiation.

Antiparticles should interact gravitationally just like particles of ordinary matter because Einstein's weak equivalence principle states that gravity doesn't depend on composition. But if they don't then gravity is much more complicated than our current understanding indicates.

The experiment

The AEgIS experiment at CERN shoots antihydrogen atoms horizontally - whereupon they fly and fall - at a wall made of matter. On hitting the wall the antihydrogen annihilates with a matter nucleus in the wall to produce a burst of mostly pions and some heavier particles. These particles travel through a special gel called an emulsion which makes their tracks visible. Pions leave thin tracks while heavier particles leave much fatter tracks.

Tracing these tracks to their point of origin tells the AEgIS team exactly where the annihilation occurred, which in turn allows them to calculate how far each particle travels. They can then work out - from the distance each particle flew and fell - how antimatter interacts with gravity.

AEgIS will start annihilating antihydrogen atoms in 2015. In the meantime the team needs to better understand the process of annihilation by shooting antiprotons at different target materials which will result in different kinds of particle bursts. AEgIS scientists need to fine-tune their understanding of annihilation by mapping the particle tracks and counting the number of thin and fat tracks for many particle bursts.

Check out the first prototype

If you want to help us finding antimatter tracks go to this link and start reporting tracks!

If you want to help us with the code, just clone the repository and send us pull request!

You can check also some more info about the project in this Mozilla Webmaker Movie.