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Theorist’s questions spur search for sub-atomic particles

Charles A. Nelson spends his time looking for quirks in quarks. At the end of the day, if he ends up with more questions than answers, it’s  a job well done.

Nelson, a theoretical physicist who explores the world of quarks and leptons—the basic particle building blocks of the universe—was awarded the 2000 University Award for Excellence in Research.

Not content to rest on his reputation, Nelson thinks his latest research question could be the most important of his 33year career. The question is rooted in some curious results obtained while working with data regarding top quarks, a mercurial variety of one of the two elementary building blocks of matter, quarks and leptons.

While “tuning” a calculation re­garding the polarity of the top quark, Nelson realized that three resulting numbers, in which he originally had no particular interest, were agreeing to a tenth of a percent.

“This is the thing I am most curious about in my career,” he said. “This three-number puzzle is potentially very important. It is an inconsistency not explained by anything heretofore known.”

Nelson suspects that the numbers could mean that top quarks, which are produced only in particle accelerators and decay almost instantly (10 to the power of -24 second—which would be expressed as a decimal point and 24 zeroes followed by a 1), have a property analogous to each electron having a built-in “may net” that arises because of their charge and spin.

If Nelson is correct, his work could spur a change in the standard model of particle physics, the name given to the theoretical framework that de­scribes the current level of human un­derstanding about the interactions between the elementary building block of matter and energy.

Discovered experimentally in 1995 top quarks are the sixth and, according to the standard model, possibly the last, of the quarks. They are as small compared to the atom, as the atom in to the human body. Other members of the quark family bear the names “up, “down,” “charm,” “strange” and “bottom.” Up and down quarks make u; protons and neutrons. Electrons are variety of leptons which, along with up and down quarks, make up the entire periodic table.

Looking for quirks in quarks isn’t the only thing Nelson does. As a theoretical physicist, he is always looking for new holes in the standard model, hoping, like all physicists, that a gap might prove to be a doorway to a deeper understanding of the basic interactions of matter and energy.

“I’m sure there is much more that we don’t know,” Nelson said. “I don’t think we’ll ever find a theory of everything. I’m excited, however, to be involved in the process. I guess that it really is a lot better to be on the journey than to have arrived.”

If Nelson’s major challenge was simply to find holes in the standard model, his work would be easy. Physicists universally agree that the model is inconsistent and incomplete. Gravity, for instance, the most familiar force on earth, is still not accounted for. Even the particle that carries it, while already named graviton by theorists, has yet to be discovered experimentally.

“The standard model has about 20 parameters that you just stick in hand —the mass of the electron, the by mass of all these quarks,” Nelson noted “The standard model doesn’t explain why these things exist, and it doesn’t explain the value of the numbers that you stick in to make things work. Ideally, you’d like to have a theory that explained these numbers.”

For theorists like Nelson, then, the real work is not in coming up with questions, the challenge is proposing possible answers. The answers take the form of questions that are plausible enough to pique the interest of experimental physicists, who ultimately must validate or invalidate the work of theorists. Theorists attract the attention of experimentalists by publishing their work in refereed journals. Nelson has seen close to 100 of his articles published.

Experimentalists who have taken up Nelson’s theories look to prove or dis­prove his work by colliding atoms at high speeds and then analyzing the results. These collisions are staged in the world’s largest   laboratories—superconducting particle accelerators and colliders like those at Fermi National Accelerator Laboratory in Chi­cago and CERN in Geneva, Switzerland. Particles are raced around circu­lar underground tracks that range from about four to 10 miles in circumference until they reach velocities near the speed of light. They are then slammed together so that the particles split into their component parts—and in some instances end up forming new par­ticles. These violent collisions are re­corded by particle detectors the size of apartment buildings that gather a record of the collision and its particle by products .

“If you were to collide two Lamborghinis at high speed,” Nelson said, “you’d get everything flying out —the steering wheels, the trunk lids, everything. In this particular case, because you’re colliding them with so much energy, it’s as if you can make a whole different car by doing this.”

While the experiments to validate Nelson’s work typically involve large international collaborations and teams of more than 300 people, Nelson and other theorists generally work alone or in small groups, often with paper and pencil or a personal computer. Federal funding for theoretical particle research is competitive. Over the past seven years, Nelson has secured more than $400,000 in federal grants.

In Nelson’s parlance, even the simple question “What’s the matter?” be­comes a double entendre. His work, populated as it is by quarks, leptons, fermions and bosons, sounds to many like some alien landscape. His calcula­tions look, to untrained eyes, like a troubled marriage between hieroglyph­ics and algebra.

Nelson’s feet, nevertheless, are securely planted and his curiosity is keenly focused on the nature of matter and energy in this universe. In fact, it’s his appreciation for the balance in the world that awakens in him such ques­tions as, “Why are there not particles other than fermions and bosons?”

Fermions are particles, such as elec­trons, protons or neutrons, that obey statistical rules requiring that no more than one occupy a particular quantum state. Bosons, such as the photon, pion, or alpha particle, obey statistical rules permitting any number of identical particles to occupy the same quantum state. Nelson wonders why it is that there are no particles in a middle camp, where two or three could pile into the same “telephone booth,” he said. He is currently working on that algebraically complex question with associates in the People’s Republic of China.

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