Scientists are continuously conducting experiments to identify the smallest unit of matter. The smallest units of matter that have been studied in detail are known as electrons, neutrons and protons. Physicists know smaller particles called leptons and quarks exist, but they have very little information about them. Researchers know that 6 different types of quarks exist and that these can change from one type to another on their own. The size of quarks cannot be measured accurately because when they appear, they only remain visible only for a fraction of a moment. Physicists do not know if particles smaller than quarks exist. Quarks were first discovered by physicists using a particle accelerator. Particle accelerators are machines that can force small particles to move at very high speeds. When these particles collide with other particles, scientists are able to study the pieces these break off into. The most powerful particle accelerator available today is known as the Large Hadron Collider and it is located in Switzerland.