Cracking the Particle Code of the Universe
Cracking the Particle Code of the Universe
The Hunt for the Higgs Boson
JOHN W. MOFFAT
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© John W. Moffat 2014
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Library of Congress Cataloging-in-Publication Data
Moffat, John W.
Cracking the particle code of the universe : the hunt for the Higgs boson / John W. Moffat.
pages cm
Includes bibliographical references.
ISBN 978–0–19–991552–1 (alk. paper)
1. Higgs bosons. 2. Particles (Nuclear physics) I. Title. II. Title: Hunt for the Higgs boson.
QC793.5.B62M64 2014
539.7’21—dc23
2013029713
9 8 7 6 5 4 3 2 1
Printed in the United States of America
on acid-free paper
To Patricia, with love
CONTENTS
Prelude: CERN, April 2008
1. What Is Everything Made Of?
2. Detecting Subatomic Particles
3. Group Theory and Gauge Invariance
4. Looking for Something New at the LHC
5. The Higgs Particle/Field and Weak Interactions
6. Data That Go Bump in the Night
7. Trying to Identify the 125-GeV Bump
8. Electroweak Gauge Theories
9. The Discovery of a New Boson: Is It the Higgs or Not?
10. Do We Live in a Naturally Tuned Universe?
11. The Last Word until 2015
Acknowledgments
Glossary
Further Reading
Index
PRELUDE: CERN, APRIL 2008
In April 2008, I traveled to Geneva for a week to visit the new facilities at the European Organization for Nuclear Research, known as CERN—the large hadron collider (LHC), the biggest and most expensive scientific experiment ever built. My wife Patricia and I stayed in Ferney-Voltaire, just across the border from Switzerland. From our hotel window, we could see the jagged white caps of the Jura Mountains rising over the charming little French town. Driving each day to CERN on a narrow country road, we crossed the French–Swiss border twice, and enjoyed the views of meadows, farms, and villages.
This was a pilgrimage that I had intended to make for years. I wanted to see with my own eyes the enormous particle accelerator whose experiments promised to answer important questions and settle long-standing disputes in particle physics. The $9 billion machine would be hunting for several discoveries. One is the so-called supersymmetric particles, necessary components of the Holy Grail of physics, the yet-to-be-discovered unified theory of all the forces of nature. Another possible discovery is extra space dimensions, beyond the three we inhabit, which are required by string theory. Thirdly, the LHC experimentalists hope to find the elusive “dark matter” particles that the majority of physicists believe make up more than 80 percent of the matter in the universe. The LHC might even succeed in producing mini black holes during its proton–proton collisions, a possibility that, stoked by media reports, initially flared up into worldwide hysteria, with certain individuals attempting to close down the LHC by litigation.
But most important, the LHC was built for the main purpose of finding the final puzzle piece required to confirm the standard model of particle physics, the so-called Higgs boson. Within the almost half-century-old, widely accepted theory describing the subatomic elementary particles and the three subatomic forces (excluding gravity), the mother of all particles was the Higgs. In this standard theory, on which thousands of physicists had worked and contributed to since the mid 1960s, the Higgs particle, or boson, or field, gave all the other elementary particles their masses back near the very beginning of the universe.1
Most physicists believe that elementary particle masses come about because of the special relationship the Higgs boson and its field enjoy with the vacuum. This is the physical state of lowest energy existing at all times, including at the beginning of the universe. The modern concept of the vacuum, quantum mechanics tells us, is not simply a void containing nothing; it is a teeming cauldron of particles and antiparticles flashing into existence and immediately annihilating one another. According to the standard model of particle physics, without the Higgs boson, the basic constituents of matter—the quarks and leptons—would have no mass.2 Physicists sometimes liken the Higgs field to a river of flowing molasses or a viscous kind of ether permeating space. When the original, massless elementary particles moved through it at the beginning of the universe, they picked up sticky mass. The idea that we require a Higgs field originated with the physics of low-temperature superconductors—mainly with Russian physicists Lev Landau and Vitaly Lazarevich Ginzburg, and later with the American Nobel laureate Philip Anderson. The Higgs is so important to the standard theory of particle physics that it has been nicknamed the God particle.
To date, all the other predictions of the standard model have been validated by experiments. During the 1970s, experiments at the Stanford Linear Accelerator (SLAC) verified Murray Gell-Mann’s and George Zweig’s 1960s-era predictions of quarks. And, in 1983, the so-called W and Z bosons, the predicted carriers of the weak nuclear force of radioactive decay, were discovered at CERN. Over time, three basic families of quarks and leptons have been detected by colliders, and the carrier of the strong nuclear force, the gluon, was also verified to exist. Today, only the Higgs boson remains to be found. Its detection had to wait until a much larger accelerator could be built to create the incredibly high energies that would be necessary to detect this massive particle, energies equivalent to the temperature at the beginning of the universe, a fraction of a second after the Big Bang.
On July, 4, 2012, two groups associated with the compact muon solenoid (or CMS) and a toroidal LHC apparatus (ATLAS) detectors at the LHC announced the discovery of a new boson at about 125 GeV, that is, at a mass of 125 billion electron volts.3 This boson appeared to have the properties of the standard-model Higgs boson, but the experimental groups were cautious about identifying it as the Higgs boson. Although the majority of physicists now believe that the new boson is the Higgs boson, we are currently waiting for LHC experimentalists to complete th
e analysis of the 2012 data and for the accelerator to start up again in 2015 to collect even more data to confirm definitively the identity of the new boson.
The standard theory of particle physics is one of the most successful physics theories of all time. It is on par with James Clerk Maxwell’s electromagnetism, Isaac Newton’s gravitation, Albert Einstein’s general theory of relativity, and the theory of quantum mechanics, which was a cooperative venture by about a dozen physicists during the early 20th century. Even though the final mechanism that keeps the whole edifice together, the Higgs boson, had not yet been detected in 2008 when I visited CERN, the majority of physicists accepted the theory almost without question, and assumed that the discovery of the Higgs would be inevitable, almost a formality. The Nobel committee, too, had already given out five Nobel Prize(s) in Physics to theorists and experimentalists working on the standard model of particle physics, even though the Higgs had not yet been detected and, therefore, the theory had not been fully proved. Finding the Higgs boson was considered such a certainty in 2008 that a dispute had arisen about who would get the Nobel Prize for predicting it. In 1964, during a three-month period, a total of six physicists published short papers in Physical Review Letters promoting a way of giving elementary particles their masses. These physicists were François Englert, Robert Brout, Peter Higgs, Carl Hagen, Gerald Guralnik, and Tom Kibble. Because the Stockholm committee can award one prize to no more than three people, if the Higgs was discovered, they would have quite a dilemma deciding among these six physicists. All were eagerly awaiting their Nobel Prizes, and trying to stay alive until the Higgs was found, because the Nobel committee is also constrained by the rule that no prizes can be given posthumously.4 To complicate matters further, there is a seventh physicist, Philip Anderson at Princeton University, who published a seminal paper in 1963 proposing what is now called the Higgs mechanism to give masses to particles. It is worth noting, however, that only the English physicist Peter Higgs had predicted explicitly the existence of an actual particle in his paper.
But what if the standard theory of particle physics was not correct and the particles derived their masses in some other way? Or had their masses right from the beginning, with no intervention necessary by a God particle? What if the Nobel committee had been premature with its awards for the standard model of particle physics? What if the enticing hints of the Higgs boson at 125 GeV either evaporated or turned out to be another new particle entirely? What if the enormous LHC never found the Higgs boson after all?
This was the second reason for my pilgrimage to Geneva in 2008. Along with my research in gravitation and cosmology, I had been working on an alternative theory of particle physics since 1991, and there was no Higgs boson in my theory. In the mathematics of my alternative electroweak theory, all the elementary particles were massless at the beginning; but, except for the massless photon, their masses were then generated not by a single particle with its associated special vacuum features, but by the usual dynamical processes of quantum field theory.5 That is, the primary observed elementary particles such as the quarks and leptons, and the W and Z bosons conspired—through the quantum field dynamics of self-energies—to produce their own masses. Moreover, my theory did not require the discovery of any new particles beyond the already observed ones in the standard model. For example, it did not require any hypothesized particles of supersymmetry, which had, over the years, become a large research industry. My theory seemed to me an economical description of the elementary particles, fields, and forces. I was not the first or only physicist to try to construct an alternative electroweak theory. Attempts to avoid introducing scalar fields and the Higgs mechanism into the standard model had been proposed during the early 1970s by, among others, Roman Jackiw and Kenneth Johnson at the Massachusetts Institute of Technology (MIT).6
I called the talk that I gave to the theory division at CERN during that week in April 2008 “Electroweak Model without a Higgs Particle,” a provocative title to the theorists and experimentalists who had been working for years, in some cases decades, on the standard model of particle physics, on the Higgs mechanism, and on figuring out exactly how the enormous new machine might detect it. Two weeks before my talk, the LHC had had its official opening. Present at the launch was Peter Higgs, retired professor of physics at the University of Edinburgh. During an interview at the LHC opening, a journalist asked Higgs how he felt about having $9 billion spent on finding a particle named after him, and did he think they would find it? Peter replied, “I’m 96 percent certain that they will discover the particle.”
**********************
On the day of my talk, Patricia and I parked our rental car outside the visitors’ entrance to CERN and made our way across the sprawling research compound to the theory building. I remembered the building well from my days visiting CERN when I was on sabbatical leave at Cambridge University in 1972 and also when I was a visiting fellow at CERN in 1960/1961. As we mounted the scuffed stairs to the second-floor administrative office, it struck me that the building had changed little in nearly half a century. The halls were dark and dingy, exuding an air of weariness and neglect. I soon discovered that the toilet roll holder in the men’s room was broken, just as it had been those many years ago during my last visit. Apparently the $9 billion price tag for the LHC had not included renovations to the theoretical physicists’ working quarters.
My talk was scheduled for two o’clock in the large seminar room on the second floor. At five minutes to two, I stood waiting at the front of the hall with the CERN theoretician who had organized the seminar, staring out at the large amphitheater with its rising rows of desks that was completely empty except for my wife sitting in the fourth row. I thought, My goodness! Maybe no one is going to turn up because of my audacious title. Then, at three minutes to two, about 50 theorists and experimentalists swarmed into the room and sat down. Five minutes into my talk, I noticed a professor from New York University (NYU), with whom I had had encounters before, walk in and sit at the back. Sure enough, he soon erupted into loud technical protestations about my theory. A verbal duel ensued and, thanks to many years of experience at such seminars, I was able to subdue him sufficiently to continue. There were other interruptions, and I could feel the audience growing increasingly hostile to the idea of a particle physics theory without a Higgs particle. Near the end of my talk, the NYU professor again got excited and explained, as he understood it, that the Higgs particle existed in my theory, but in an altered way. Alvaro de Rújula, a senior theorist at CERN, who was sitting next to him in the back row, could be overheard saying quite loudly, “Moffat does not have a Higgs particle in his theory!” This seemed to flummox our friend and from then on, he kept quiet.
After my talk, Guido Altarelli, a senior physicist in the theory division who is an expert on the electroweak theory and the standard model of particle physics, declared dramatically, “If Moffat is correct, and no new particles are discovered, then that’s the end of particle physics! What are we going to do?”
“You can all retire!” I quipped, trying to break the tension in the room with a joke—but no one laughed.
So I pursued Altarelli’s point. “What do you mean, Guido, that this will be the end of particle physics?”
Guido, a strongly built, tall Italian, turned to the audience and said, “What I mean is that governments will no longer give us money to build new accelerators and continue our experiments. In that sense, it’s the end of particle physics.”
“But this is not the way physics works,” I said, genuinely astonished. “Not finding the Higgs and, in fact, not needing to find any other exotic particles would open up many new questions about the nature of matter. New mysteries would unfold. This kind of situation often leads to a revolution in physics.”
I reminded the audience of the famous Michelson–Morley experiment in the United States during the late 19th century that failed to detect the “ether,” which virtually every scientist of the day accepted as real.
To those scientists, it had seemed obvious that a medium was necessary for electromagnetic waves to propagate. The waves had to be moving through something. But Michelson and Morley’s ingenious experiment turned up nothing where the ether should have been. Although the physics community of the time was shocked, it was certainly not the end of physics. It heralded a new beginning, with Einstein’s subsequent discovery of special relativity, and Max Planck’s discovery of the quantization of energy, which led to quantum physics. A similar boost to the whole enterprise of physics, especially particle physics, would occur if the LHC did not detect the Higgs boson, I concluded.
But neither Altarelli nor the rest of the audience seemed convinced. The questions and comments at the end of my talk continued to be skeptical in tone, even hostile.
**********************
I was disappointed by the reception of my alternative electroweak theory at the CERN theory group, but I was not surprised. I knew that even expressing doubts about a prevailing paradigm causes conflict. Physicists are like most other human beings; they become emotionally invested in the truth and beauty of the theoretical structures they have helped to build. To contemplate that those structures might be faulty or incomplete simply pulls the rug out from under their feet. On the other hand, the standard model with the Higgs boson has very attractive features, such as the elegant prediction during the 1960s of the W and Z bosons by Sheldon Glashow, Steven Weinberg, and, independently, by Abdus Salam. The discovery of the W and Z bosons at CERN in 1983 confirmed this remarkable prediction. Moreover, the inclusion of the Higgs boson into the unified electroweak theory guaranteed that one could perform finite calculations of physical quantities in the standard model.
Soon, in a matter of years rather than decades, the answers to the Higgs boson puzzle would be known. The LHC’s beams of protons would smash together, spraying subatomic debris into the largest and most sophisticated detectors ever built. Physicists would analyze the statistical patterns of those collisions, an immense amount of data. Eventually, after a great many such experiments, CERN would make its announcement. Either the LHC would have finally discovered the Higgs boson, and therefore proved that the standard model of particle physics was correct in all respects, or the LHC would not have found a Higgs boson, and therefore the standard model would have to be reexamined and changed. If the latter happened, I’d told the skeptical crowd of CERN physicists at the end of my talk, I would be standing at the head of the queue called “Other Ideas,” offering my alternative electroweak theory without a Higgs boson for serious consideration.
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