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6 Accelerators and Detectors: The Tools of Elementary-Particle Physics
Pages 78-100

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From page 78...
... Elementary-particle physics (EPP) is distinguished from other acceleratorbased sciences by its reliance on accelerators operating at the highest energies attainable with present technology the "energy frontier." To sustain continued progress in elementary-particle physics it is necessary to create conditions under which elementary particles protons, electrons, muons, neutrinos (and their antiparticles)
From page 79...
... However, over the past 30 years, energy performance has been greatly enhanced by the development of the "particle collider" an accelerator configuration in which particles and/or antiparticles collide head-on. As described in Chapter 2, the collider configuration provides the most efficient mechanism for translating beam energy into collision energy and thus provides the most direct access to the energy frontier.
From page 80...
... Although the total mass contained in these beams is minuscule, less than one ten-billionth of a gram, the energy is contained within an incredibly small volume. Beam sizes range from the size of a human hair, in the Fermilab Tevatron, to a hundred times smaller in the Stanford Linear Collider (SLC)
From page 81...
... per beam and is based on superconducting magnet technology. The Tevatron supports operations in both collider and stationary target mode and will remain the highest-energy facility in the world until the initiation of operations at the Large Hadron Collider (LHC)
From page 84...
... By interacting electrons with lead it is possible to produce approximately one positron for every electron, whereas it takes approximately 60,000 protons interacting in a nickel target to produce a single usable antiproton. Performance of Existing Accelerators Modern accelerators used in support of elementary-particle physics research come in two basic types: linear accelerators (linacs for short)
From page 85...
... In principle, the energy could be increased indefinitely in a synchrotron by continued application of the accelerating voltage over many revolutions, but the product of the confining magnetic field and accelerator radius must be high enough to keep the particle beam circulating at the highest energy. The maximum energy attainable in proton synchrotrons has been increased most recently through the application of superconducting magnet technology.
From page 86...
... The Main Injector project at Fermilab involves construction of a new rapidcycling 150-GeV proton accelerator that will support an increase in the intensity of the proton and antiproton beams in the Tevatron. The goal is to boost Tevatron collider luminosity by a factor of five beyond current operations.
From page 87...
... ACCELERATORS AND DETECTORS TABLE 6.2a Major Upgrades and New Facilities Under or Approved for Construction Facilities Upgrades 87 Start of Laboratory, Project Operational Goal Operations Location Fermi National Accelerator Laboratory, Main Injector Proton-antiproton collisions at 1999 Batavia, 2,000 GeV and 2 x 1032 cm-2 s-l Illinois 120-GeV protons for stationary target operations Stanford Linear Asymmetric electron-positron 1999 Palo Alto, Accelerator Center, collisions at 10 GeV and California PEP-II 3 x 1033 cm-2 s-l Cornell University, CESR Symmetric electron-positron collisions at 10 GeV and 2 x 1033 cm-2 s-l CERN, LEP-II Electron-positron collisions at 1998 192 GeV and 1 x 1032 cm-2 s-l 1 998 Ithaca, New York Geneva, Switzerland KKK, B Factory Asymmetric electron-positron 1999 Tsukuba, collisions at 10 GeV and Japan 3 x 1033 cm-2 s-l TABLE 6.2b Major Upgrades and New Facilities Under or Approved for Construction New Facilities Start of Laboratory, Project Operational Goal Operations Location Brookhaven National Polarized proton-proton collisions 2000 Upton, Laboratory, RHIC at 500 GeV and 2 x 1032 cm-2 s-l New York Frascati, DAPHNE Symmetric electron-positron 1998 Frascati, collisions at 1 GeV and Italy 5 x 1032 cm-2 s-l CERN, LHC Proton-proton collisions at 14,000 2005 Geneva, GeV and 1 x 1034 cm-2 s-l Switzerland
From page 88...
... The LHC will be constructed within the existing 26 km LEP tunnel and is based on the superconducting magnet technology first developed at the Fermilab Tevatron and improved on at Brookhaven, HERA, and the SSC. Options for Future Facilities A variety of projects that could extend the energy frontier up to or beyond the LHC are in various stages of development in the United States and abroad.
From page 89...
... Highintensity particle beams and targeting Superconducting magnets. Costefficient manufacturing and tunneling Research and development programs aimed at new electron colliders are by far the most advanced of the areas listed above.
From page 90...
... For example, proton targeting for muon production shares many issues in common with antiproton or neutron production, whereas the muon-accelerating structures required are very similar to those being developed for the linear collider effort at DESY. With sufficient support, development of a complete conceptual design for such a facility, if one can be built, could probably be forthcoming in the period 2005 to 2010.
From page 91...
... Significant support will be required in the areas of superconducting materials, superconducting magnet design, superconducting accelerating structures, development of very high intensity proton beams, and ionization cooling if hadron or muon collider concepts are to be developed to a degree that will offer the United States viable choices for continued leadership in elementary-particle physics into the extended future. DETECTORS IN ELEMENTARY-PARTICLE PHYSICS The role of the accelerators described earlier is to bring high-energy particles into collision at a well-defined point in space the interaction point.
From page 92...
... For example, when Henri Becquerel discovered in 1896 that uranium was radioactive, he saw light traces in photographic paper. The light was produced by the ionization and subsequent de-excitation of some atoms by the passage of charged particles produced in the radioactive decay of uranium.
From page 93...
... Particle Detector Topologies The goal of physicists assembling a variety of individual detection elements into an integrated detector is to obtain an accurate snapshot of an event. This usually means measuring the momentum and ascertaining the identity of as many of the particles produced in the event as possible.
From page 94...
... Figure 6.4 shows a typical topology for a detector utilized in a colliding beam experiment. The integration of a variety of individual detection elements into a large detector represents a particular strategy for creating the event snapshot.
From page 95...
... Outside the silicon detectors, the remainder of the tracking volume is filled with detectors of moderately high precision immersed in a magnetic field. The goal here is to measure the momentum of individual charged particles by measuring the trajectories as they traverse the magnetic field.
From page 96...
... Thus, their calorimetric signature is the same as that of electrons. However, being electrically neutral, photons can be distinguished from electrons photons leave no track in the charged particle tracking volume whereas electrons will.
From page 97...
... Sometimes, this material is iron, which may be magnetized in an attempt to enhance identification. In other cases, large magnetic field volumes may be employed, with little interleaved material, in an attempt to improve the momentum measurement of muons in a region free of confusion by other trajectories.
From page 98...
... With a properly designed trigger, the interesting events, which represent new phenomena, survive through the highest trigger level whereas uninteresting events do not. Challenges for the Next 10 to 20 Years The needs for detector research and development for the next 10 years or more are dominated by issues involved in experimentation at the LHC and, to a lesser extent, in a possible future lepton collider.
From page 99...
... The occupancy in a detector element can be reduced by reducing the size of the element. This is happening with silicon detectors.
From page 100...
... In terms of neutron damage, gallium arsenide held promise. However, measurements were then made with charged particles, pions, and protons, and gallium arsenide was found to be less resistant than silicon.


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