Deep Inelastic Scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons. It provided the first convincing evidence of the reality of quarks, which up until that point had been considered by many to be a purely mathematical phenomenon. It is a relatively new process, first attempted in the 1960s and 1970s. It is conceptually similar to Rutherford Scattering, but with important differences. In particle physics, a hadron is a subatomic particle which experiences the strong nuclear force. ... In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called Greek barys, meaning heavy, as they are heavier than the other main groups of particles. ... For alternative meanings see proton (disambiguation). ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 940 MeV/c² (1. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... Rutherford scattering is a phenomenon that was observed by Ernest Rutherford in 1911 that led to the development of the orbital theory of the atom. ...

Quarks

The Standard Model of physics, particularly given the work of Murray Gell-Mann in the 1960s, had been successful in uniting much of the previously disparate concepts in particle physics into one, relatively straightforward, scheme. In essence, there were three types of particles. The Standard Model of Fundamental Particles and Interactions The Standard Model of particle physics is a theory which describes the strong, weak, and electromagnetic fundamental forces, as well as the fundamental particles that make up all matter. ... Murray Gell-Mann at Harvard University Murray Gell-Mann (born September 15, 1929) is an American physicist who received the 1969 Nobel Prize in physics for his work on the theory of elementary particles. ... Particles erupt from the collision point of two relativistic (100 GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...

• The Leptons, which were light (as in not particularly massive) particles such as electrons, neutrinos and their anti-particles. They have integer (or no) charge
• The Bosons, which were particles that exchange forces. These ranged from the massless, easy-to-detect photon (the carrier of the electro-magnetic force) to the relatively massive and exotic gluons that carry the strong nuclear force
• The Quarks, which were massive particles that carried fractional charges. They are the "building blocks" of the hadrons. They are also the only particles to be affected by the strong interaction

The leptons had been detected since 1897, when J. J. Thomson had shown that electric current is a flow of electrons. Some of bosons were being routinely detected, although the W⁺, W^- and Z⁰ particles of the electroweak force were only categorically seen in the early 1980s, and gluons were only firmly pinned down in Hamburg at about the same time. Quarks, however, were still elusive. A lepton is also a unit of currency. ... Boson (game) Bosons, named after Satyendra Nath Bose, are particles which form totally-symmetric composite quantum states. ... For the Science Fiction weapon, as seen in Star Trek, see Photon torpedo. ... In physics, gluons are the bosonic particles which are responsible for the strong nuclear force. ... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics. ... 1897 was a common year starting on Friday (see link for calendar). ... Sir Joseph John Thomson Sir Joseph John Thomson (18 December 1856 – 30 August 1940), often known as J. J. Thomson, was an English physicist, the discoverer of the electron. ... In physics, the electroweak theory presents a unified description of two of the four fundamental forces of nature: electromagnetism and the weak nuclear force. ... Hamburg is Germanys second largest city (after Berlin) and, with the Hamburg Harbour, its principal port. ...

The Experiments

Drawing on Rutherford's groundbreaking experiments in the early years of the Twentieth Century, ideas for detecting quarks were formulated. Rutherford had proven that atoms had a small, massive, charged nucleus at their centre by firing alpha particles at atoms in gold. Most had gone through with little or no deviation; however a few were deflected through large angles or came right back. This suggested that atoms had internal structure, and a lot of empty space. Ernest Rutherford, 1st Baron Rutherford of Nelson, known as the father of nuclear physics. ... (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s The 20th century lasted from 1901 to 2000 in the Gregorian calendar (often from (1900 to 1999 in common usage). ... An alpha particle is deflected by a magnetic field Alpha particles or alpha rays are a form of particle radiation which are highly ionizing and have low penetration. ...

In order to enter baryons (where quarks were theoretically to be found), a small, penetrating (ie easily accelerated; in reality this meant charged) and easily produced particle needed to be found. Electrons were considered ideal for the role, and in a series of remarkable technological and engineering leaps, electrons were fired as tiny bullets at protons and neutrons in nuclei. As an added bonus, the electrostatic attraction of the positively charged nucleus and the negatively charged electron increased the speed. Later experiments were conducted with mesons, but the same principles apply. In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ...

The collision absorbed some kinetic energy, and as such it is inelastic (this compares to Rutherford Scattering which is elastic, with no loss of kinetic energy, taking into account recoils of the nuclei). The electrons emerges from the nucleus, and its trajectory and velocity can be detected.

Analysis of the results led to the following conclusions:

• The hadrons do have internal structure
• In baryons, there are three points of deflection (ie baryons consist of three quarks)
• In mesons, there are two points of deflection (ie mesons consist of a quark and an anti-quark. The reason they do not consist of two quarks is to do with their colour; see the quark article for more explanation)
• Quarks appear to be point charges, as electrons appear to be, with the fractional charges suggested by the Standard Model

The experiments were important because, not only did they confirm the physical reality of quarks but also proved again that the Standard Model was the correct avenue of research for particle physicists to pursue. Quarks are one of the two basic constituents of matter in the Standard Model of particle physics. ...