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Topic: Large Electron Positron

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Van Morrison

	LEP; Photo Pack
		LEP brings beams of matter (electrons) and antimatter (positrons) to meet head-on in collisions that echo the energies of the early Universe.
		Electrons and positrons radiate energy when their paths bend, so to have high-energy beams in LEP requires a very gently curving path.
		The LEP ring is depicted beneath the surface (but not at scale depth!), together with the ring of the Super Proton Synchrotron which acts as a pre-accelerator, bringing the electron and positron beams to a suitable energy for injection to LEP.
	outreach.web.cern.ch /outreach/public/cern/PicturePacks/LEP/captions.html (4109 words)

	Large Electron-Positron Collider - Wikipedia, the free encyclopedia
		LEP is a giant evacuated ring with a circumference of 27 kilometers built in an tunnel under the border of Switzerland and France.
		The Super Proton Synchrotron (an older ring collider) is used to accelerate electrons and positrons to nearly the speed of light.
		When an electron and a positron collide, they annihilate to a virtual particle, either a photon or a Z boson.
	en.wikipedia.org /wiki/Large_Electron-Positron_Collider (672 words)

	Positron Summary
		The positron is the antiparticle or the antimatter counterpart of the electron.
		When a low-energy positron collides with a low-energy electron, undergoing an annihilation event, their mass is converted into the kinetic energy of two gamma ray photons (see electron-positron annihilation).
		Anderson also unsuccessfully suggested renaming electrons "negatrons." The positron was the first evidence of antimatter and was discovered by passing cosmic rays through a gas chamber and a lead plate surrounded by a magnet to distinguish the particles by bending differently charged particles in different directions.
	www.bookrags.com /Positron (1041 words)

	Encyclopedia: Large Electron-Positron Collider (Site not responding. Last check: 2007-11-05)
		The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron.
		When the particles are accelerated to maximum energy (and focused to so-called bunches), an electron and a positron bunch is made to collide with each other at one of the collision points of the detector.
		At the end of 2000, LEP was shut down and then dismantled in order to make room in the tunnel for the construction of the Large Hadron Collider (LHC).
	www.nationmaster.com /encyclopedia/Large-Electron_Positron-Collider (1687 words)

	Large Electron-Positron Collider (Site not responding. Last check: 2007-11-05)
		LEP is a giant evacuated ring with a circumference of 27 kilometers built in an underground tunnel under the border of Switzerland and France.
		The Super Proton Synchrotron (an older ring collider) is used to accelerate electrons and positrons to nearly the speed of light which are then injected into the ring.
		The results of the LEP exeriments allowed to gat precise values of many quantities of the Standard Model --most importantly the mass of the Z boson and the W boson (which were discovered in 1983 at an earlier CERN collider)-- and so confirm it and put it on a solid fundament of empirical data.
	www.sciencedaily.com /encyclopedia/large_electron_positron_collider (635 words)

	Introduction to the LEP e+e- Collider at CERN (Site not responding. Last check: 2007-11-05)
		The Large Electron Positron (LEP) e+e- collider is an electron positron synchroton operated by the European Organisation for Nuclear Research (CERN) in Geneva, Switzerland.
		Beams of electrons and positrons are circulated in opposite directions in an evacuated tube at almost the speed of light (the electron/positron energy is approximately 45GeV).
		The electrons and positrons are collided together at four equidistant points around the ring, such that they annihilate to form a Z boson which subsequently decays into a fermion-antifermion pair.
	l3www.cern.ch /lepintro.html (128 words)

	What's a Neutrino?
		Hence, the "electron neutrino" is associated with the electron, and two other neutrinos are associated with heavier versions of the electron called the muon and the tau (elementary particles are frequently labelled with Greek letters, to confuse the layman).
		This is the origin of the long-standing "solar neutrino problem." The possibility that the missing electron neutrinos may have transformed into another type (undetectable to this experiment) is soon suggested, but unreliability of the solar model on which the expected neutrino rates are based is initially considered a more likely explanation.
		It is soon recognized to be a heavier version of the electron and muon, and its decay exhibits the same apparent imbalance of energy and momentum that led Pauli to predict the existence of the neutrino in 1931.
	www.ps.uci.edu /~superk/neutrino.html (946 words)

	Accelerators and Nobel Laureates
		In the first phase, collisions between positrons and electrons at a collision energy of 91.2 GeV, corresponding to the rest mass of the Z boson, were studied.
		The average velocity of the electrons was adjusted to be the same as the average velocity of the protons and the electron beam current was significantly larger than the proton beam current.
		The large energy loss increasing with the fourth power of the energy of the electrons is the main reason why it is difficult and impractical to use synchrotrons for the acceleration of electrons to the same high energies as protons.
	nobelprize.org /nobel_prizes/physics/articles/kullander (11518 words)

	Introduction to the LEP e+e- Collider at CERN (Site not responding. Last check: 2007-11-05)
		The Large Electron Positron (LEP) e+e- collider is an electron positron synchroton operated by the European Organisation for Nuclear Research (CERN) in Geneva, Switzerland.
		Beams of electrons and positrons are circulated in opposite directions in an evacuated tube at almost the speed of light (the electron/positron energy is approximately 45GeV).
		The electrons and positrons are collided together at four equidistant points around the ring, such that they annihilate to form a Z boson which subsequently decays into a fermion-antifermion pair.
	l3.web.cern.ch /l3/lepintro.html (128 words)

	High Field Science: Publications
		The goal is to build cheap table-top accelerators that are able to shoot electrons or protons (or their antimatter counterparts) at the energies achieved by huge and expensive conventional accelerators.
		Electrons, which carry negative charges, tend to repel each other, and as a beam of them spreads out, fewer electrons are available for collision experiments.
		High-energy electron beams fired at targets made of heavy metals like tungsten generate X-rays, and X-ray pulses produced by electrons from one of the new laser accelerators would be short enough and powerful enough to probe lightning-fast chemical processes like photosynthesis, which sustains green plants.
	www.unl.edu /dumstadter/times.html (1458 words)

	CERN Courier - The final curtain falls on L - IOP Publishing - article
		LEP was thus given a six-week "stay of Higgs execution" (seeNovember 2000 News).
		The electrons and positrons for LEP came via a chain of more mature machines, including the 28 GeV PS synchrotron, which, when it first came into operation in 1959, was briefly the world's highest-energy accelerator, and the 450 GeV SPS synchrotron, commissioned in 1976.
		LEP was the initial reason for the 27 km tunnel excavated under the Swiss-French frontier, but it was understood almost from the outset of LEP preparations in the mid-1970s that the tunnel would be a valuable piece of physics research real estate that would one day house a more powerful machine - LHC.
	cerncourier.com /main/article/41/1/2/1 (744 words)

	Patricia Gonçalves
		LEP was the largest electron-positron circular accelerator ever built, operating at the at the highest energies achieved in e+e- colliding beams.
		The Large Electron Positron collider (LEP) was built after the discovery of the Z0 and W bosons at the SPS at CERN in 1983.
		LEP enabled as well to perform many different types of searches, such as searches for new particles, as new quarks and leptons, and to search for anomalies with respect to the predictions of the Standard Model of Electroweak Interactions.
	www.lip.pt /~patricia/tese/tese.html (2051 words)

	CERN Courier - The W and Z at LEP - IOP Publishing - article
		The Large Electron Positron collider made significant contributions to the process of establishing the Standard Model as the basis for matter and forces, and also built a platform for physics scenarios beyond the model.
		The properties of the Z boson and the underlying electroweak theory were studied at LEP by measuring the overall formation cross-section, the forward-backward asymmetries of the leptons and quarks, and the polarization of tau leptons.
		One of the central tasks of the LEP experiments at energies beyond the W-pair threshold was the analysis of the electroweak three-gauge-boson couplings, predicted in form and magnitude by the gauge symmetry.
	www.cerncourier.com /main/article/44/4/15 (2374 words)

	The LLNL Electron-Positron Beams Facility
		The positron facility provides a wide range of capabilities, including high-current beams for investigation of bulk materials properties, low-emittance beams for studies of one-component plasmas, and a positron microprobe.
		Experiments underway at the positron facility are probing the mechanisms by which defects arise in materials, of vital importance for science-based stockpile stewardship in this era of a comprehensive ban on nuclear weapons testing.
		Two-photon annihilation is the dominant decay mode for positrons in a material; unless a positron collides with an electron, it is stable.
	www-phys.llnl.gov /Research/Positrons (275 words)

	The Large Electron Positron Collider
		LEP collides together bunches of electrons with bunches of positrons, as they travel in opposite directions round a ring 27km in circumference, at velocities close to the speed of light.
		LEP is a circular machine, as big as the Circle Line on London's Underground, and a direct descendant of the first accelerators that Lawrence and Livingston built at Berkeley almost 60 years ago.
		Electrons and positrons radiate energy as their paths bend, the amount of energy lost in this way increasing both with the energy of the particles themselves and with the curvature of the path.
	hepwww.rl.ac.uk /pub/bigbang/file9.html (719 words)

	Materials Science at the LLNL Positron Facility
		Positrons in materials have lifetimes that are governed by the electron density in the material; the higher the electron density, the shorter the lifetime.
		A graph of the number of positron decays as a function of time after entry into the material (Figure 2) reveals two distinct decay constants, corresponding to two lifetimes: a short lifetime for positrons that annihilate in the bulk material, and a longer lifetime for positrons trapped in defects.
		To perform micro-analysis and thin-film analysis of defects, we are currently developing an intense, pulsed, sub-micron size positron beam (a positron microprobe) capable of 3-dimensional maps of buried defects and defect profiling in thin films and at interfaces.
	www-phys.llnl.gov /Research/Positrons/PositronMaterials.html (938 words)

	CERN Courier - The W and Z at LEP - IOP Publishing - article
		The Large Electron Positron collider made significant contributions to the process of establishing the Standard Model as the basis for matter and forces, and also built a platform for physics scenarios beyond the model.
		The properties of the Z boson and the underlying electroweak theory were studied at LEP by measuring the overall formation cross-section, the forward-backward asymmetries of the leptons and quarks, and the polarization of tau leptons.
		One of the central tasks of the LEP experiments at energies beyond the W-pair threshold was the analysis of the electroweak three-gauge-boson couplings, predicted in form and magnitude by the gauge symmetry.
	cerncourier.com /main/article/44/4/15/1 (2374 words)

	James Hansen
		Thus, as the massless electron propagates through the quagmire of the Higgs field, it is forced to drag along its massive brethren, and thus appears “massive” to the observing physicist.
		Because the electrons and positrons (anti-electrons) are totally annihilated in the reaction, all of the energy of the reaction goes into the newly formed particles.
		The LEP collider in Geneva, Switzerland is housed in an underground circular tunnel, 27-kilometers in diameter.
	www.its.caltech.edu /~sciwrite/journal03/A-L/hansen.html (2988 words)

	LEP - Light Emitting Polymer
		The Large Electron Positron collider, the world's largest particleaccelerator, which is 26.7 km in circumference and some 100 metres underground,situated at CERN.
		LEP collides electrons and positrons atenergies sufficent to produce the Z and (soon) W particles, carriers of theweak force.
		LEP collides electrons and positrons at energies sufficient to produce the Z and (soon) W particles, carriers of the weak force.
	www.auditmypc.com /acronym/LEP.asp (512 words)

	Experimental High-Energy Physics
		LEP is one of the largest facilities in the world developed for experimental high energy physics.
		The L3 experiment at LEP is based on a large magnetic detector optimized for the precision measurement of photons, electrons, muons, and hadron jets.
		Due to the large fiducial volume and high sensitivity to minute energy depositions which generate sequences of single photoelectrons in the phototubes, flux limits for Grand Unified Theory magnetic monopoles and for new particles predicted by superstring and supersymmetric theories are expected to greatly exceed any similar search to date.
	buphy.bu.edu /bu/ExHepPhy.html (1375 words)

	Large Hadron Collider - Wikipedia, the free encyclopedia
		The Large Hadron Collider (short LHC) is a particle accelerator and collider located at CERN.
		In contrast to the previous it will collide protons (one type of hadron particle) instead of electrons and positrons.
		Two of them, ATLAS and CMS are large, "general purpose" particle detectors.
	www.wikipedia.org /wiki/LHC (354 words)

	Experimental High-Energy Physics and Astrophysics
		The L3 experiment at LEP is based on a large magnetic detector optimized for the precision measurement of photons, electrons, muons, and hadron jets.
		Large volume water detectors were invented to discover proton decay, but so far have only set limits (well in excess of the first predictions of the SU(5) Grand Unified Theory).
		The ATLAS Experiment is a large detector system being developed by a collaboration of physicists from all around the world to study very-high-energy proton-proton interactions at the Large Hadron Collider at CERN.
	physics.bu.edu /bu/exh.html (2640 words)

	Physics News Update Number 502 - Story AN INTRIGUING HINT OF THE HIGGS BOSON (Site not responding. Last check: 2007-11-05)
		CERN decided today that the high energy electron-positron collisions at LEP will continue, the better to supplement the meager, but potentially crucial, evidence for the Higgs boson, the particle widely thought to be responsible for endowing other known particles with mass.
		Theorists have said that in some collisions a Higgs boson (h) might be produced back to back with a Z boson, one of the carriers of the weak force and itself the object of a dramatic particle hunt at CERN 20 years ago.
		The enhancement is not statistically significant enough for CERN to claim a discovery yet, even when all four detector groups combine their data, but sufficient to cause excitement since the Higgs is perhaps the most sought after particle in all of high energy physics.
	www.aip.org /enews/physnews/2000/split/pnu502-1.htm (259 words)

	The LEP Accelerator
		As the name suggests, LEP was designed to bring extremely high energy electrons and positrons into collision with one another.
		The complete LEP collider does not consist of just the very large LEP ring, although this is easily the greatest engineering feat of the project.
		Some of the electrons are collided with a tungsten target to produce the positrons, the remaining electrons, along with the positrons, are then passed into the Electron Positron Accumulator ring (EPA), where they are stored and accumulated before injection.
	www.hep.ucl.ac.uk /~jpc/all/ulthesis/node15.html (714 words)

	James Hansen
		Because the electrons and positrons (anti-electrons) are totally annihilated in the reaction, all of the energy of the reaction goes into the newly formed particles.
		The LEP collider in Geneva, Switzerland is housed in an underground circular tunnel, 27-kilometers in diameter.
		The large circle indicates the path of the Large Electron Positron (LEP) Collider.
	www.cco.caltech.edu /~sciwrite/journal03/A-L/hansen.html (2988 words)

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