Why Antihydrogen Research?
That the particles in the Universe are dominated by those comprised of matter is seemingly well established - as is the assertion that at the Big Bang, matter and antimatter were present in equal amounts. Just why this imbalance has evolved is not understood, and is one of the central questions of physics beyond the Standard Model.
ALPHA has chosen to bring the powerful toolbox of atom trapping and atomic spectroscopy to bear on this problem. In short, we create and capture antihydrogen, which provides us with an unprecedented ability to pin down its properties and behaviour. Any difference between matter and antimatter, however small, will have profound consequences for our understanding of nature.
Our recent projects:
We are developing a new instrument, ALPHA 3, and in one set of experiments we will investigate the transition between the ground state of the anti-atom and its first excited state using two-photon Doppler-free spectroscopy. We hope to determine its frequency with a precision similar to that currently achieved for the hydrogen atom, for which it is known to almost 15 decimal places. We have already measured the same transition in antihydrogen to almost 12 decimal places, and now have the hydrogen precision firmly in our sights.
In our second major avenue, ALPHA-g, we will analyse the trajectories of antihydrogen atoms as they leave a purpose-built atom trap to investigate the gravitational behaviour of the anti-atom. We expect to make the first determination of g for antimatter, and hope to improve on this to achieve an accuracy of 1% or better.
Interest in the behaviour of gravity on (anti-)atomic systems stems in part from another puzzle of modern physics, namely that Einstein's General Relativity is incompatible with currently accepted quantum field theories. Whilst the Equivalence Principle dictates that all objects, irrespective of their content, should fall with the same acceleration towards the Earth, testing the (classical) theory of gravity on quantum objects is of fundamental interest.
Members of the ALPHA Collaboration from Canada were recently awarded the NSERC John C. Polanyi Award for their contributions to ALPHA's sucesses in trapping and measuring antihydrogen atoms.
Physicists have long wondered if the gravitational interaction between antimatter and matter might be different than that between matter and itself. Do atoms made of antimatter, like antihydrogen, fall at a different rate to those made of matter, or might they even fall up – antigravity?