Cosmic rays

Cosmic rays are raining down on us continuously, many having high energies comparable with those of particles from our accelerators.

Occasionally, cosmic rays entered bubble chambers while they were still active, leaving trails of bubbles, reminding us of what we might call the `cosmic connection’: we live in a quantum universe, and to understand the early times when the particles were very energetic we must study the properties of elementary particles.

The thick line running from top to bottom in this picture is caused by a positive cosmic ray muon. We know it is going from top to bottom (against the flow of the electromagnetic shower) because of the little curly knock-on electron track near the top of the picture. We can tell that the cosmic ray is positive because it curves in the opposite way to the electron.

A possible reason for the track being thick is that it did not arrive at the bubble chamber in time with the incoming beam from the accelerator.

The cosmic connection is beautifully illustrated in the following picture (click here), where a rich particle interaction is cradled within two thick cosmic ray tracks.