A Positron Named Priscilla Scientific Discovery at the Frontier (1994) / Chapter Skim
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8 A Family Affair: The Top Quark and the Higgs Particle
8 A Family Affair: The Top Quark and the Higgs Particle
Pages 236-257
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From page 236... ...
Werner Heisenberg, Erwin Schroedinger, Max Born, and Niels Bohr had taken the lead in inventing quantum mechanics, offering insights so powerful that graduate students were solving problems that had bedeviled savants for decades. Studies of atoms held the focus of concern, and here too there was fundamental advance.
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From page 237... ...
It began just after the war, as the federal government allocated funds for construction of an increasingly powerful series of particle accelerators. In studies of the atom's nucleus, they quickly replaced the older technique of relying on observations of cosmic rays.
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From page 238... ...
This had proven to be more than an exercise in taxonomy; it had pointed toward an underlying order, for the periodicity in this table demanded an explanation based on fundamental principles. Similarly, in 1960, physicists faced the issue of building a counterpart to the periodic table, able to describe their particles in terms of their own underlying principles.
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From page 239... ...
The quark concept offered a compelling theory, but to win widespread acceptance it would have to pass the test of observation and experiment. The work that would provide this confirmation got under way during 1967 at the Stanford Linear Accelerator Center (SLAC)
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From page 240... ...
Hence, by 1972, particle physics had turned around. A decade earlier it had been experiment rich and theory poor, beset by a plethora of newly discovered particles that resisted understanding.
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From page 241... ...
In Glashow's words, "You can't even pull one out with a quarkscrew." But the theory predicted that charmed quarks should join with others to form new types of particles, having observable characteristics. At Brookhaven and SLAC, groups headed by Samuel Ting and Burton Richter, respectively, went on to find them.
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From page 242... ...
Glashow quickly declared that it was indeed a type of charmed particle, which he called "charmonium." Here was a decisive confirmation of the quark theory, showing that this theory was sufficiently powerful to predict the existence of a new particle. Indeed, it could predict a whole new class of particles, containing one or more charmed quarks and assembled along the lines of the strange particles in Gell-Mann's SW(3)
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From page 243... ...
It helped that this colliding beam approach fitted in neatly with the engineering design of accelerators. The big ones, as at Fermilab, featured long strings of powerful magnets set end to end like a train of railroad cars, with the magnets curving gently to form a ring.
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From page 244... ...
Rather than shooting a 200-GeV beam at a fixed target, the new system would produce beams with energies of 1000 GeV, a trillion electron volts, or TeV. Two such beams, countercirculating, would collide head on to produce a total energy of 2 TeV.
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From page 245... ...
That meant it would be even heavier than the W or Z particles, the heaviest yet found. There still remained the question of how many such quark families existed in nature.
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From page 246... ...
Yet the Z particle, featured in electroweak theory, proved to offer the key to the problem of quark families. The reason lay in the uncertainty principle of quantum mechanics.
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From page 247... ...
The SLAC machine, an upgrade of the existing system, raised the collisional energy to 100 GeNl, working with colliding beams of electrons and positrons (see Figure 8.4~. However, the LEP was the workhorse of the effort, producing Zs at a rate ELECTRONS FIGURE 8.2 Graphic presentation of events allows physicists to visualize the trajectories and energies of particles within the structure of the detector (in this case, the Aleph experimentJ.
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From page 248... ...
During the main experimental run, which lasted 4 months, LEP produced some 100,000 Zs. Late in 1989 the directors of the five experimental groups pooled their data and announced the result: The number of quark families was 3.09 + 0.09.
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From page 249... ...
This origin, which would account for the masses of elementary particles, stands as a very deep issue. The Standard Model has little to say on the subject.
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From page 250... ...
A key attribute of that theory is its ability to make precise calculations based on only a few parameters, calculating experimentally observable quantities to any desired accuracy. As Gerard 't Hooft first showed in 1971, it is the Higgs particle that gives electroweak theory this power.
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From page 251... ...
Gravity should couple with the Higgs particles that pervade free space, and this would cause the entire universe to curl up into something the size of a football. Needless to say, this is contrary to observation.
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From page 252... ...
If one wishes to achieve an honest 1 or 2 TeV in a particle collision, the actual energy of the colliding proton and antiproton must be vastly higher, because each quark or gluon holds only a small fraction of the whole. Indeed, the total energy, within the colliding beams, would be as great as 40 TeV, 20 in each.
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From page 253... ...
As was true when Carlo Rubbia was searching for the W and Z particles in the early 1980s, it will help greatly if physicists can begin with a reasonably clear idea of the specific energy that will create the Higgs. Fortunately, such a prediction is achievable-if experimenters first succeed in discovering the top quark.
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From page 254... ...
The answer lay in electronic detectors, massive arrays of circuitry that could cope with almost any number of particle collisions. The first of them went into operation at CERN and proved essential to Carlo Rubbia's discovery of the W and Z in 1983.
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From page 255... ...
CDF generates over 10,000 bits of Formation regarding each such particle. A typical collision produces 30 or more of them, and the Fermilab accelerator can generate over 100,000 collisions per second, with CDF faithfully keeping pace.
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From page 256... ...
None of this is guaranteed, to be sure. Diligent search might fail to find the top quark, and this would be a disaster for the Standard Model.
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From page 257... ...
Our researchers may divert themselves with the pretty shells of the top quark and even the Higgs, but Newton's ocean still conceals many of the truly deep issues: The origin of mass; the origin of the universe; the character of a truly ultimate theory of nature, if indeed a theory exists. For all our hope and all our work to date, we still must stand with Paul: "We know in part, and we prophesy in part....
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