Quarks are one type of matter particle. Most of the matters we see around us are made from protons and neutrons, which are composed of quarks. A Quark is a fundamental particle which possesses both electric charge and strong charge. They combine in groups of 2 or 3 to form composite objects (called mesons and baryons, respectively), held together by the strong force. Protons and neutrons are familiar examples of such composite objects-both are made up of 3 quarks. In other words, a quark is a tiny theoretical particle that makes up protons and neutrons in the atomic nucleus. Along with gluons, quarks also make up more exotic hadrons such as mesons, which are unstable. The quark is known as theoretical because while assuming its existence makes for a better physics theory. Physicists are on the watch for theorized quark matter, a hypothetical lattice made of continuous quark connected by gluons. It is not yet known whether this type of matter is possible physically. If so, it would probably be found in the core of extremely compact stars that not yet collapsed into a black hole.
The quark model was independently proposed by physicists Murray Gell-Mann and George Zweig in 1964. The proposal came shortly after Gell-Mann’s 1961 formulation of a particle classification system known as the ‘Eightfoldway’. Eightfold way is the theory organizing subatomic particles baryons and mesons into octets. Physicist Yuval Ne’eman had independently developed a scheme similar to the Eightfold way in the same year. The name ‘Quark’ was originally chosen by Gell-Mann.
The currently accepted theory of elementary particles predicts that there should be 6 different kinds of quarks, designated by the following letters. These names are purely arbitrary and do not suggest anything about each quarks properties.
The normal matter that makes up the majority of the universe is made up of ‘up’ quarks and ‘down’ quarks. The lightest quarks are the ‘up’ and ‘down’ quarks, which compose the more common, ordinary particles like protons and neutrons. The ‘up’ and ‘down’ quarks are assigned an electric charge or +2/3 of the electronic charge and -1/3 of the electronic charge, respectively. Since no free particles have ever been observed with a charge equal to fraction of an electric charge, the quarks must combine in groups of 3. For instance, a proton is made up of 2 ‘up’ quarks and 1 ‘down’ quark, giving it a total charge of +1 electronic charge, while neutron is made up of 2 ‘down’ quarks and 1 ‘up’ quark.
Quarks have varying masses, which are measured in GeV (giga electron-volts) over the speed of light squared. Subatomic particles are measured in terms of the energy they produce rather than mass in grams. The ‘down’ quark is about twice as massive as the ‘up’ quark. The ‘strange’ quark is a bout 20 times as massive as the ‘down’ quark. The ‘charm’ quark is about 10 times as massive as that, followed by the ‘bottom’ quark which is about 3 times as massive as the last. The ‘top’ quark is the most massive of all. Increasing mass tends to correspond to scarcity of the quark and demands more exotic physical conditions for its demonstration.