On this day, 31 years ago, on April 26, 1994 (March 16, 1994 in the lunar calendar), physicists at the Fermi Laboratory in the United States discovered the term quark. Quarks are elementary particles of matter that are smaller than protons and neutrons. Before the 1960s, the physics community believed that protons and neutrons were the smallest constituent particles of matter. Through experimental observations and theoretical calculations, scientists believe that there should be six types of quarks. (u up quark, d down quark, c charm quark, s odd quark, t top quark, b bottom quark) After 1963, scientists successively discovered the fourth and fifth types of quarks, of which the "charm quark" was discovered by a research group led by Chinese scientist Ding Zhaozhong. Three years later, the research group led by Liederman confirmed the existence of "bottom quarks". Finding the last type of quark has been the direction of particle physicists 'efforts for 19 years. Only by confirming the existence of the top quark can the theory of particle physics be verified. The mass of the top quark exceeds scientists 'speculation. The mass of the top quark is about 200 times that of the proton. According to the relativistic mass-energy conversion formula, to produce the top quark by proton collision, the proton must be made to move at an extremely high speed. The faster the speed, the higher the energy, the top quark can be generated only at the moment of collision. Fermilab's accelerator has a circumference of 6.3 kilometers. It uses 1000 superconducting magnets to accelerate protons and antiprotons to an energy of 900 billion electron volts each before colliding. It takes an average of 1 trillion collisions to observe the top quark once. After the top quark appears, it disappears "immediately". Experiments have shown that after the top quark appears, it decays into other particles within 1×10-24s (before the observer can blink). In 1964, Gellman proposed the quark model, believing that mesons are composed of quarks and antiquarks, and baryons are composed of three quarks. He won the 1969 Physics Prize for this.