What is ALPHA-g?

ALPHA-g is an experiment at CERN that seeks to answer a fundamental question: does antimatter fall under gravity the same way as matter?

To investigate this ALPHA-g traps antihydrogen, a neutral antimatter atom made of an antiproton and a positron, in a magnetic trap. The atom is then released and allowed to fall. When it annihilates on contact with matter, it produces several detectable particles.

Our job is to figure out where that annihilation happened. This position, the vertex, is key to determine how the antihydrogen moved and whether gravity influenced it.

The detector records a series of 3D points left by charged particles resulting from the annihilation. Reconstructing the vertex from these points is what this tutorial is all about.

If you'd like a visual overview of the ALPHA-g experiment, this short animation by CERN provides an excellent introduction.