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35-860: LPI comprised the LEP Injector Linac (LIL) and the Electron Positron Accumulator (EPA) . After groundbreaking for the LEP Collider had taken place in September 1983, the design for its injection scheme, the LEP Pre-Injector (LPI), was finalized in 1984. The construction was planned and implemented in close collaboration with Laboratoire de l'accélérateur linéaire (LAL) in Orsay, France. Since there had been no electron/positron accelerators at CERN before, LAL

70-520: A tungsten target, where the positrons were produced. In LIL W, both the electrons and positrons could then be accelerated to 500 MeV at lower currents than in LIL V. In the initial reports, LIL was designed to reach beam energies of 600 MeV. However, during the first months of operation, it became clear that an output energy of 500 MeV allowed for a more reliable running of the machine. LIL consisted of so-called S band Linacs . These linear accelerators used

105-410: A 35 MW pulsed klystron that drove microwave cavities at a frequency of 3 GHz, which accelerated the electrons and positrons. After passing through LIL, the particles were injected into EPA, electrons rotating clockwise and positrons counterclockwise. There, both particle types were accumulated to achieve sufficient beam intensities and to match the high frequency output of LIL (100 Hz) to

140-422: A positron collide, they annihilate to a virtual particle , either a photon or a Z boson . The virtual particle almost immediately decays into other elementary particles, which are then detected by huge particle detectors . The Large Electron–Positron Collider had four detectors, built around the four collision points within underground halls. Each was the size of a small house and was capable of registering

175-504: A roughly circular shape in opposite directions and therefore can be collided over and over. This enables a high rate of collisions and facilitates collection of a large amount of data, which is important for precision measurements or for observing very rare decays. However, the energy of the bunches is limited due to losses from synchrotron radiation . In linear colliders, particles move in a straight line and therefore do not suffer from synchrotron radiation, but bunches cannot be re-used and it

210-419: A total length of approximately 100 meters. First, at the starting point of LIL V, electrons with an energy of 80 keV were created by a thermionic gun. LIL V then accelerated electrons at high currents to an energy of around 200 MeV. These were either accelerated further or used to create positrons, their antiparticles . At the beginning of LIL W, which followed directly behind LIL V, the electrons were shot onto

245-433: Is not straightforward to determine the energy of the collisions), and therefore more challenging to analyze and less amenable to precision measurements. The shape of the collider is also important. High energy physics colliders collect particles into bunches, and then collide the bunches together. However, only a very tiny fraction of particles in each bunch actually collide. In circular colliders, these bunches travel around

280-585: Is therefore more challenging to collect large amounts of data. As a circular lepton collider, LEP was well suited for precision measurements of the electroweak interaction at energies that were not previously achievable. Construction of the LEP was a significant undertaking. Between 1983–1988, it was the largest civil engineering project in Europe. When the LEP collider started operation in August 1989 it accelerated

315-470: The Higgs particle of a mass around 115 GeV might have been observed, a sort of Holy Grail of current high-energy physics . The run-time was extended for a few months, to no avail. The strength of the signal remained at 1.7 standard deviations which translates to the 91% confidence level , much less than the confidence expected by particle physicists to claim a discovery, and was at the extreme upper edge of

350-654: The Tevatron had not been sensitive enough to confirm or refute these hints. Beginning in July 2012, however, the ATLAS and CMS experiments at LHC presented evidence of a Higgs particle around 125 GeV, and strongly excluded the 115 GeV region. L3 experiment The L3 experiment was one of the four large detectors on the Large Electron–Positron Collider (LEP). The detector was designed to look for

385-731: The synchrotron radiation emitted by the electrons that were circling EPA. Until the beginning of 2001, the effects of synchrotron radiation on LHC's vacuum chambers were studied at SLF 92 with the COLDEX experiment. SLF 42 was used for research on getter strips, which were getting prepared to be used in LHC's vacuum chambers. LPI's final success was the PARRNe experiment: The electrons provided by LPI-generated gamma rays , which were used to create neutron-rich radioactive krypton and xenon atoms. LEP The Large Electron–Positron Collider ( LEP )

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420-620: The LEP experiments allowed 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, the Proton-Antiproton Collider ) to be obtained—and so confirm the Model and put it on a solid basis of empirical data. Near the end of the scheduled run time, data suggested tantalizing but inconclusive hints that

455-611: The accelerating system was further commissioned, threading the electron and positron beams through LIL, EPA, the Proton Synchrotron (PS), the Super Proton Synchrotron (SPS), until finally reaching LEP. The first injection into LEP's ring was achieved on July 14, 1989, one day earlier than originally scheduled. The first collisions were performed on August 13 and the first physics run, allowing LEP's experiments to take data, took place on September 20. LPI

490-543: The collisions cannot reach the same energy that can be achieved with heavier particles. Hadrons are composite particles (composed of quarks) and are relatively heavy; protons, for example, have a mass 2000 times greater than electrons. Because of their higher mass, they can be accelerated to much higher energies, which is the key to directly observing new particles or interactions that are not predicted by currently accepted theories. However, hadron collisions are very messy (there are often many unrelated tracks, for example, and it

525-449: The detection range of the experiments with the collected LEP data. There was a proposal to extend the LEP operation by another year in order to seek confirmation, which would have delayed the start of the LHC . However, the decision was made to shut down LEP and progress with the LHC as planned. For years, this observation was the only hint of a Higgs Boson; subsequent experiments until 2010 at

560-476: The electro-magnetic and hadronic calorimeters: one of their functions was to help in recognising and rejecting signals coming from cosmic ray muons, very highly energetic particles which come from the space and can disturb the measurement. The outermost layer contained the magnet that generated, inside the detector, a magnetic field about 10,000 times the average field on the surface of the Earth. This field deflected

595-438: The electrons and positrons to a total energy of 45  GeV each to enable production of the Z boson , which has a mass of 91 GeV. The accelerator was upgraded later to enable production of a pair of W bosons, each having a mass of 80 GeV. LEP collider energy eventually topped at 209 GeV at the end in 2000. At a Lorentz factor ( = particle energy/rest mass = [104.5 GeV/0.511 MeV]) of over 200,000, LEP still holds

630-622: The experiment was a play on words, as some of the founding members of the scientific collaboration which first proposed the design had previously worked on the JADE detector at DESY in Hamburg . OPAL was a general-purpose detector designed to collect a broad range of data. Its data were used to make high precision measurements of the Z boson lineshape, perform detailed tests of the Standard Model, and place limits on new physics. The detector

665-541: The first stage (so-called preliminary phase) starting accelerator commissioning in September 2001. At the end of 2016, CTF3 stopped its operation. From 2017 on, it was transformed into the CERN Linear Electron Accelerator for Research (CLEAR). LPI comprised the LEP Injector Linac (LIL) , which had two parts ( LIL V and LIL W ), as well as the Electron Positron Accumulator (EPA) . LIL consisted of two linear accelerators in tandem, having

700-535: The frequency at which the PS operated (approximately 0.8 Hz). After passing EPA, the particles were delivered to the PS and SPS for further acceleration, before they reached their final destination, LEP. EPA had a circumference of 125.7 m, which corresponded to exactly one fifth of PS' circumference. LPI didn't just provide electrons and positrons to LEP, but also fed different experiments and test installations located directly at LPI's infrastructure. The first of these

735-665: The mass of the W-boson and Z-boson to within one part in a thousand. The number of families of particles with light neutrinos was determined to be 2.982 ± 0.013 , which is consistent with the Standard Model value of 3. The running of the quantum chromodynamics (QCD) coupling constant was measured at various energies and found to run in accordance with perturbative calculations in QCD. DELPHI stands for DE tector with L epton, P hoton and H adron I dentification . OPAL stands for O mni- P urpose A pparatus for L EP . The name of

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770-557: The middle of the EPA ring, the LIL Experimental Area (LEA) was set up. The electrons coming there were used for many different applications throughout LIL's operation, testing and preparing LEP's and later LHC 's detectors. Most famously, the optical fibres for one of CMS 's calorimeters were tested here in 2001 during the preparation time of the LHC. Additionally, the two Synchrotron Light Facilities SLF 92 and SLF 42 used

805-581: The particle accelerator speed record, extremely close to the limiting speed of light. 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). LEP was fed with electrons and positrons delivered by CERN's accelerator complex. The particles were generated and initially accelerated by the LEP Pre-Injector , and further accelerated to nearly

840-422: The particle beam (i.e. keep the particles together). The function of the accelerators was to increase the particles' energies so that heavy particles can be created when the particles collide. When the particles were accelerated to maximum energy (and focused to so-called bunches), an electron and a positron bunch were made to collide with each other at one of the collision points of the detector. When an electron and

875-411: The particles by measuring their deflection in the magnetic field present in the detector. The three main outer layers were the electro-magnetic calorimeter (also called BGO because it is made of bismuth germanium oxide ), the hadronic calorimeter (HCAL) and the muon detector. Calorimeters are dense and stop most particles, measuring their energy. A set of scintillation counters was placed between

910-502: The particles by their energy , momentum and charge, thus allowing physicists to infer the particle reaction that had happened and the elementary particles involved. By performing statistical analysis of this data, knowledge about elementary particle physics is gained. The four detectors of LEP were called Aleph, Delphi, Opal, and L3. They were built differently to allow for complementary experiments . ALEPH stands for A pparatus for LEP pH ysics at CERN . The detector determined

945-537: The physics of the Standard Model and beyond. It started up in 1989 and stopped taking data in November 2000 to make room for construction of the Large Hadron Collider (LHC). Now, the ALICE detector sits in the cavern that L3 used to occupy, reusing L3's characteristic red octagonal magnet. The L3-detector was a multi-layered cylindrical set of different devices, each of them measuring physical quantities relevant to

980-558: The reconstruction of the collision under study. Starting from the centre, close to the pipe where electrons and positrons circulate and collide, there were first the Silicon strip Microvertex Detector (SMD) and the Time Expansion Chamber (TEC). These two sub-detectors traced the paths of charged particles produced in the collision. One also gathered information about the momentum (a quantity related to mass and energy) of

1015-422: The speed of light by the Proton Synchrotron and the Super Proton Synchrotron . From there, they were injected into the LEP ring. As in all ring colliders , the LEP's ring consisted of many magnets which forced the charged particles into a circular trajectory (so that they stay inside the ring), RF accelerators which accelerated the particles with radio frequency waves , and quadrupoles that focussed

1050-514: Was a valuable source of expertise and experience in this regard. The first electron beam with an energy of 80 keV was produced on May 23, 1985. LIL injected electrons with an energy of 500 MeV into EPA from July 1986 on, and soon after EPA reached its design intensity. The same was achieved for positrons in April 1987, so the LPI-complex was fully operational in 1987. For the following two years,

1085-512: Was dismantled in 2000 to make way for LHC equipment. The lead glass blocks from the OPAL barrel electromagnetic calorimeter are currently being re-used in the large-angle photon veto detectors at the NA62 experiment at CERN. L3 was another LEP experiment. Its enormous octagonal magnet return yoke remained in place in the cavern and became part of the ALICE detector for the LHC. The results of

LEP Pre-Injector - Misplaced Pages Continue

1120-448: Was one of the largest particle accelerators ever constructed. It was built at CERN , a multi-national centre for research in nuclear and particle physics near Geneva , Switzerland . LEP collided electrons with positrons at energies that reached 209 GeV. It was a circular collider with a circumference of 27 kilometres built in a tunnel roughly 100 m (300 ft) underground and passing through Switzerland and France . LEP

1155-550: Was serving as a source of electrons and positrons for LEP from 1989 until November 7, 2000, when the last beams were delivered to LEP. Nevertheless, the source continued to operate for other experiments until April 2001 (see section below). After this, work begun to convert LPI facility to be used for the CLIC Test Facility 3 (CTF3), which conducted preliminary research and development for the future Compact Linear Collider (CLIC). The conversion happened in stages, with

1190-596: Was the Hippodrome Single Electron (HSE) experiment. The unusual request for single electrons was made in March 1988 by the L3 collaboration. By the end of 1988, the setup was running, allowing for a precise calibration of the L3 detector, which was to be installed at LEP soon after. Those particles that were not deflected into EPA when coming from LIL, were directed straight into a "dump line". There, in

1225-651: Was used from 1989 until 2000. Around 2001 it was dismantled to make way for the Large Hadron Collider , which re-used the LEP tunnel. To date, LEP is the most powerful accelerator of leptons ever built. LEP was a circular lepton collider – the most powerful such ever built. For context, modern colliders can be generally categorized based on their shape (circular or linear) and on what types of particles they accelerate and collide (leptons or hadrons). Leptons are point particles and are relatively light. Because they are point particles, their collisions are clean and amenable to precise measurements; however, because they are light,

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