Elementary-Particle Physics (1986) / Chapter Skim
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6 Instruments and Detectors for Elementary-Particle Physics
6 Instruments and Detectors for Elementary-Particle Physics
Pages 132-156
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From page 132... ...
A wide range of detectors exists including the small but often sophisticated instruments designed for fixed-target work, the large detectors used tor recording rare events such as the interactions of neutrinos or the decays of nucleons, and the large collider detectors that provide almost complete angular coverage and characterization of the interactions occurring in these machines. This latter class of collider detectors 1` among the most costly and demanding.
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From page 133... ...
Fixed-target detectors usually are more selective than the large collider detectors. The neutrino detectors are vast instrumented targets, usually incorporating magnetic analysis of produced muons and calorimetric measurement of produced hadrons.
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From page 134... ...
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From page 135... ...
parent accelerators. Unlike the early pioneering experiments of particle physics, a modern experiment may well require the simultaneous collaboration of several hundred physicists from 20 or more institutions.
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From page 137... ...
In general this technique differentiates velocities only for relatively small particle energies. · In the presence of a magnetic field, charged particles are deflected into curved orbits.
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From page 138... ...
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From page 139... ...
The detectors for collider experiments are based on a series of concentric shells or layers, one behind the other, each of which is devoted to some particular aspect or aspects of the detection process. The initial detector layers are used to characterize the charged-particle component and are designed to be nondestructive, i.e., to contain little material so that charged particles will not interact or degrade in energy and thus will maintain their identity while traversing the layers.
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From page 140... ...
The first generation of such vertex detectors was h~cer1 on ~nn~rentional track-detection methods for charged particles, using multiwire drift chambers or time-projection chambers (TPC)
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From page 141... ...
Charged-Particle Tracking Chambers In a typical collider detector, beyond the vertex detector are charged-particle tracking chambers. These chambers serve to measure the directions and curvatures of the paths of the individual particles.
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From page 142... ...
The larger the field, the more the tracks curve, and the easier it is to measure the track momentum. To provide the highest possible magnetic fields, it is desirable to use superconducting coils to carry the required large currents.
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From page 143... ...
The final layers of a collider detector therefore comprise thick, highly instrumented blocks of material calorimeters in which electromagnetic and hadronic particles cascade and convert their energy into ionization. These final instrumented blocks are placed at large radii, away from the point at which the beams interact, to leave sufficient space in which to insert the nondestructive low-density systems.
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From page 144... ...
This is often the case when the physicist is studying a simple reaction of elementary particles or studying one particular property of a particle. Two examples are given
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From page 145... ...
Figure 6.8 shows a neutrino detector used at the AGS proton accelerator at Brookhaven to test the stability of muon neutrinos.
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From page 147... ...
This sequence of analysis steps is the same as that used in most collider detectors, but the target is not surrounded by all the components of the detector as it is in a collider detector. Figure 6.10 shows a rather complex detector that combines modern detector elements with the old nuclear emulsion technique.
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From page 149... ...
n 11111111 J hhL] DC II ._ ~ _ ~ Time of Flight Hodoscopes 100" Muon Steel Color'me er>, ~ 11 ~ I Leod Gloss v, to m d5D 149 : 1 ~Muon' Hodoscopes _`lII FIGURE 6.10 This fixed-target particle detector combines the old technique of the nuclear emulsion with new techniques of chambers.
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From page 150... ...
For example, a Z" decay into hadrons has an average of about 20 charged particles and " neutral particles, and the off-line analysis time for such events in the detectors proposed for the SLC or LEP is of the order of 100 seconds of central processor unit (CPU) time for moderate-size computers.
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From page 151... ...
' the overall costs of computing increase. Thus computers of both large and medium size are now necessary parts of almost all elementary-particle physics experiments.
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From page 152... ...
Experiments Using Radioactive Material or Reactors There are experiments using radioactive material or reactors that are important in both elementary-particle physics and nuclear physics. An outstanding example is the study of the radioactive beta decay of tntium.
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From page 153... ...
It is the third area that concerns us here. Earlier in this century, cosmic rays were the only source of veryhigh-energy particles; hence substantial discoveries in particle physics were often made with cosmic rays.
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From page 154... ...
Turning to another example, current unified theories predict that there should be massive magnetic monopoles with a rest mass of about 10'6 times the proton mass and further that these should have been produced in the early universe and still be present among cosmic rays. An experiment in early 1982 reported evidence for the passage of one such monopole through a superconducting coil of a few cm' area.
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From page 155... ...
The Solar Neutrino Experiment A major nonaccelerator facility with ramifications in particle physics, nuclear physics, and astronomy is ~ Brookhaven National Laboratory detector for solar neutrinos. This detector is seeking evidence for inverse beta decay produced by neutrinos from the Sun.
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From page 156... ...
SUMMARY AND FUTURE PROSPECTS In the preceding discussion a number of trends in instrumentation and detection systems for high-energy physics have been identified. Jets signatures produced by quark interactions at high momentum transfers have led to great emphasis on finely segmented detection systems and to calorimetric detectors for the measurement of energy flow.
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