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European Muon Collaboration
The European Muon Collaboration (EMC) was 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 about 100 physicists. This was among the ... [...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 , 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; that is, it is a fundamental particle. 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 non-elementary 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 o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ratio). Protons and neutrons, each with masses of approximately one atomic mass unit, 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 has a unique number of protons, each element has its own unique atomic number, which determines the number of atomic electrons and consequently the chemical characteristics of the element. The word ''proton'' is Greek language, G ... [...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's Astrophysics Data System. and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleon Spin Structure
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 1/2ħ, 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. Global analysis o ... [...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 harder than c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton Spin Crisis
The proton spin crisis (sometimes called the "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 the protons' 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). Components of proton's spin are expectation values of individual sources of angular momentum. These values depend on the renormalization scale, because their operators are not separately conserved. Physicists originally expected t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 (electrons traveling near the speed of light). 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 relativit ... [...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 has an 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 second generation of matter. It has an electric charge of − ''e'' and a bare mass of . Like all quarks, the strange quark is an elementary fermion with spin , and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. The antiparticle of the strange quark is the strange antiq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spin (physics)
Spin is a conserved quantity carried by elementary particles, and thus by composite particles ( hadrons) and atomic nuclei. Spin is one of two types of angular momentum in quantum mechanics, the other being ''orbital angular momentum''. The orbital angular momentum operator is the quantum-mechanical counterpart to the classical angular momentum of orbital revolution and appears when there is periodic structure to its wavefunction as the angle varies. For photons, spin is the quantum-mechanical counterpart of the polarization of light; for electrons, the spin has no classical counterpart. 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 existence of the electron spin can also be inferred theoretically from the spin–statistics theorem and from the Pauli exclusion principle— ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PYTHIA
Pythia (; grc, Πυθία ) was the name of the high priestess of the 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 name ''Pythia'' is derived from ''Pytho'', which in myth was the original name of Delphi. Etymologically, the Greeks derived this place name from the verb () "to rot", which refers to the sickly sweet smell from the decomposing body of the monstrous Python after it was slain by Apollo. 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 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 or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CERN
The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Geneva, on the France–Switzerland border. It comprises 23 member states, and Israel (admitted in 2013) is currently the only non-European country holding full membership. CERN is an official United Nations General Assembly observer. The acronym CERN is also used to refer to the laboratory; in 2019, it had 2,660 scientific, technical, and administrative staff members, and hosted about 12,400 users from institutions in more than 70 countries. In 2016, CERN generated 49 petabytes of data. CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research — consequently, numerous experiments have been constructed at CERN through international collaborations. CERN is the site o ... [...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 o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
