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European Muon Collaboration
The European Muon Collaboration (EMC) was a consortium of particle physicists formed in 1973 to study the interactions of high energy muons at CERN. These experiments were motivated by the interest in determining the quark structure of the nucleon following the discovery of high levels of deep inelastic scattering at SLAC. In 1972 two muon beams were proposed for the then new Super Proton Synchrotron (SPS) machine. One by Roger Clifft and Erwin Gabathuler and one by Friedhelm Brasse and Joerg Gayler. The two teams came together to design a high intensity muon beam of energy up to 280 GeV to do the experiments. The collaboration, which became known as the European Muon Collaboration (EMC), was formed around these people to carry out the experiments. A proposal for the beam and an apparatus to do the experiments was submitted to CERN in 1974 (the White Book). The experiments were approved and the apparatus was built between the years 1974–78. The collaboration grew in size to abo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Particle Physicists
Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the study of combinations of protons and neutrons is called nuclear physics. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of up and down quarks which form protons and neutrons, and electrons and electron neutrinos. The three fundamental interactions known to be mediated by bosons are electromagnetism, the weak interaction, and the strong interaction. Quarks cannot exist on their own but form hadrons. Hadrons that contain an odd number of quarks are called baryons and those that contain an even number ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PYTHIA
Pythia (; ) was the title of the high priestess of the Temple of Apollo (Delphi), Temple of Apollo at Delphi. She specifically served as its oracle and was known as the Oracle of Delphi. Her title was also historically glossed in English as the Pythoness. The Pythia was established at the latest in the 8th century BC (though some estimates date the shrine to as early as 1400 BC), and was widely credited for her prophecy, prophecies uttered under divine possession (enthusiasmos) by Apollo. The Pythian priestess emerged pre-eminent by the end of the 7th century BC and continued to be consulted until the late 4th century AD. During this period, the Delphic Oracle was the most prestigious and authoritative oracle among the Greeks, and she was among the most powerful women of the classical world. The oracle is one of the best-documented religious institutions of the classical Greeks. Authors who mention the oracle include Aeschylus, Aristotle, Clement of Alexandria, Diodorus, Diogen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
INSPIRE-HEP
INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1970s. History SPIRES was (in addition to the CERN Document Server (CDS), arXiv and parts of Astrophysics Data System) one of the main Particle Information Resources. A survey conducted in 2007 found that SPIRES database users wanted the portal to provide more services than the, at that time, already 30-year-old system could provide. On the second annual Summit of Information Specialists in Particle Physics and Astrophysics in May 2008, the physics laboratories CERN, DESY, SLAC and Fermilab therefore announced that they would work together to create a new Scientific Information System for high energy physics called INSPIRE. It interacts with other HEP service providers like arXiv.org, Particle Data Group, NASA The National A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleon Spin Structure
In particle physics, nucleon spin structure describes the partonic structure of nucleon (proton and neutron) intrinsic angular momentum (spin). The key question is how the nucleon's spin, whose magnitude is 1/2 ħ, is carried by its constituent partons (quarks and gluons). It was originally expected before the 1980s that quarks carry all of the nucleon spin, but later experiments contradict this expectation. In the late 1980s, the European Muon Collaboration (EMC) conducted experiments that suggested the spin carried by quarks is not sufficient to account for the total spin of the nucleons. This finding astonished particle physicists at that time, and the problem of where the missing spin lies is sometimes referred to as the proton spin crisis. Experimental research on these topics has been continued by the Spin Muon Collaboration (SMC) and the COMPASS experiment at CERN, experiments E142, E143, E154 and E155 at SLAC, HERMES at DESY, experiments at JLab and RHIC, and others. G ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neutron Detection
Neutron detection is the effective detection of neutrons entering a well-positioned detector. There are two key aspects to effective neutron detection: hardware and software. Detection hardware refers to the kind of neutron detector used (the most common today is the scintillation detector) and to the electronics used in the detection setup. Further, the hardware setup also defines key experimental parameters, such as source-detector distance, solid angle and detector shielding. Detection software consists of analysis tools that perform tasks such as graphical analysis to measure the number and energies of neutrons striking the detector. Basic physics Signatures by which a neutron may be detected Atomic and subatomic particles are detected by the signature they produce through interaction with their surroundings. The interactions result from the particles' fundamental characteristics. * Charge: Neutrons are neutral particles and do not ionize directly; hence they are harde ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton Spin Crisis
The proton spin crisis (or proton spin puzzle) is a theoretical crisis precipitated by a 1987 experiment by the European Muon Collaboration (EMC), which tried to determine the distribution of spin within the proton. Physicists expected that the quarks carry all a proton's spin. However, not only was the total proton spin carried by quarks far smaller than 100%, these results were consistent with almost zero (4–24%) proton spin being carried by quarks. This surprising and puzzling result was termed the "proton spin crisis". The problem is considered one of the important unsolved problems in physics. Background A key question is how the nucleons' spins are distributed amongst their constituent parts ( "partons": quarks and gluons). The components of the proton's spin are the expectation values of the individual sources of angular momentum. These values depend on the renormalization scale, because their operators are not separately conserved. Physicists originally expected that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dirac Sea
The Dirac sea is a theoretical model of the electron vacuum as an infinite sea of electrons with negative energy, now called '' positrons''. It was first postulated by the British physicist Paul Dirac in 1930 to explain the anomalous negative-energy quantum states predicted by the relativistically-correct Dirac equation for electrons. The positron, the antimatter counterpart of the electron, was originally conceived of as a hole in the Dirac sea, before its experimental discovery in 1932.This was not the original intent of Dirac though, as the title of his 1930 paper (''A Theory of Electrons and Protons'') indicates. But it soon afterwards became clear that the mass of holes must be that of the electron. In hole theory, the solutions with negative time evolution factors are reinterpreted as representing the positron, discovered by Carl Anderson. The interpretation of this result requires a Dirac sea, showing that the Dirac equation is not merely a combination of special relativ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strange Quark
The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons (), strange D mesons (), Sigma baryons (), and other strange particles. According to the IUPAP, the symbol s is the official name, while "strange" is to be considered only as a mnemonic. The name sideways has also been used because the s quark (but also the other three remaining quarks) has an isospin, I value of 0 while the u ("up") and d ("down") quarks have values of + and − respectively. Along with the charm quark, it is part of the generation (physics), second generation of matter. It has an electric charge of elementary charge, ''e'' and a bare mass of . Like all quarks, the strange quark is an elementary particle, elementary fermion with Spin (physics), spin spin-1/2, , and experiences all four fundamental interactions: gravit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin (physics)
Spin is an Intrinsic and extrinsic properties, intrinsic form of angular momentum carried by elementary particles, and thus by List of particles#Composite particles, composite particles such as hadrons, atomic nucleus, atomic nuclei, and atoms. Spin is quantized, and accurate models for the interaction with spin require relativistic quantum mechanics or quantum field theory. The existence of electron spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which silver atoms were observed to possess two possible discrete angular momenta despite having no orbital angular momentum. The relativistic spin–statistics theorem connects electron spin quantization to the Pauli exclusion principle: observations of exclusion imply half-integer spin, and observations of half-integer spin imply exclusion. Spin is described mathematically as a vector for some particles such as photons, and as a spinor or bispinor for other particles such as electrons. Sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the proton-to-electron mass ratio). Protons and neutrons, each with a mass of approximately one Dalton (unit), dalton, are jointly referred to as ''nucleons'' (particles present in atomic nuclei). One or more protons are present in the Atomic nucleus, nucleus of every atom. They provide the attractive electrostatic central force which binds the atomic electrons. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol ''Z''). Since each chemical element, element is identified by the number of protons in its nucleus, each element has its own atomic number, which determines the number of atomic electrons and consequently the chemical characteristi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
EMC Effect
The EMC effect is the surprising observation that the cross section for deep inelastic scattering from an atomic nucleus is different from that of the same number of free protons and neutrons (collectively referred to as nucleons). From this observation, it can be inferred that the quark momentum distributions in nucleons bound inside nuclei are different from those of free nucleons. This effect was first observed in 1983 at CERN by the European Muon Collaboration, hence the name "EMC effect". It was unexpected, since the average binding energy of protons and neutrons inside nuclei is insignificant when compared to the energy transferred in deep inelastic scattering reactions that probe quark distributions. While over 1000 scientific papers have been written on the topic and numerous hypotheses have been proposed, no definitive explanation for the cause of the effect has been confirmed. Determining the origin of the EMC effect is one of the major unsolved problems in the field of n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Muon
A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of ''ħ'', but with a much greater mass. It is classified as a lepton. As with other leptons, the muon is not thought to be composed of any simpler particles. The muon is an unstable subatomic particle with a mean lifetime of , much longer than many other subatomic particles. As with the decay of the free neutron (with a lifetime around 15 minutes), muon decay is slow (by subatomic standards) because the decay is mediated only by the weak interaction (rather than the more powerful strong interaction or electromagnetic interaction), and because the mass difference between the muon and the set of its decay products is small, providing few kinetic degrees of freedom for decay. Muon decay almost always produces at least three particles, which must include an electron of the same charge as the muon and t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
