Particle tracks in a bubble chamber. Coloured photograph of a neutrino interaction event in a bubble chamber at the Brookhaven National Laboratory on Long Island, New York. The neutrino enters the bubble chamber at the bottom of the picture, but does not leave a track itself because it is electrically neutral. It interacts with a proton in the liquid filling the bubble chamber, producing a spray of other particles that travel up the picture. Most of the tracks visible are the characteristic spiral curlicues of electrons & positrons.