European Muon Collaboration
Encyclopedia
The European Muon Collaboration (EMC) conducted high energy particle physics
experiments at CERN
. In 1983, it discovered that nucleons inside a nucleus
have a different distribution of momentum among their component quarks. This is the original so-called "EMC Effect".
In 1987, the group discovered that only a small part of the proton
spin
is carried by quarks, and that the strange quark
sea
is probably polarized. The former is sometimes
referred to as the "proton spin crisis
".
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
experiments at CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...
. In 1983, it discovered that nucleons inside a nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
have a different distribution of momentum among their component quarks. This is the original so-called "EMC Effect".
In 1987, the group discovered that only a small part of the proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
is carried by quarks, and that the strange quark
Strange quark
The strange quark or s quark is the third-lightest of all quarks, a type of elementary particle. Strange quarks are found in hadrons, which are subatomic particles. Example of hadrons containing strange quarks include kaons , strange D mesons , Sigma baryons , and other strange particles...
sea
Dirac sea
The Dirac sea is a theoretical model of the vacuum as an infinite sea of particles with negative energy. It was first postulated by the British physicist Paul Dirac in 1930 to explain the anomalous negative-energy quantum states predicted by the Dirac equation for relativistic electrons...
is probably polarized. The former is sometimes
referred to as the "proton spin crisis
Nucleon spin structure
Nucleon spin structure describes the partonic structure of nucleon intrinsic angular momentum . The key question is how nucleon spin 1/2 is carried by its constituents, say partons . It was originally expected before the 1980s that quarks carry all of the nucleon spin, but later experiments...
".