Bubble chamber photograph of the tracks of charged subatomic particles created when a proton acceler- ated to an energy of 300 GeV collided with a proton at rest in the 75cm (30-inch) bubble chamber at the Fermi National Accelerator Laboratory (Fermilab) near Chicago. The accelerat- ed proton enters from left. The energy of the collision goes into creating the spray of 26 new particles, mostly pions. The tightly spiralling tracks are produced by electrons, which because of their lightness are bent more easily than heavier particles in the bubble chamber's magnetic field.