The Quantum Frontier www.com The Quantum Frontier The Large Hadron Collider Don Lincoln Foreword by Leon Lederman The Johns Hopkins University Press Baltimore www.com © 2009 The Johns Hopkins University Press All rights reserved. Published 2009 Printed in the United States of America on acid-free paper 987654321 The Johns Hopkins University Press 2715 North Charles Street Baltimore, Maryland 21218-4363 www.edu Library of Congress Cataloging-in-Publication Data Lincoln, Don. The quantum frontier : the large hadron collider / Don Lincoln ; foreword by Leon Lederman. Includes bibliographical references and index.
ISBN-13: 978-0-8018-9144-1 (hardcover : alk. paper) ISBN-10: 0-8018-9144-2 (hardcover : alk. Large Hadron Collider (France and Switzerland).7'376—dc22 2008022647 A catalog record for this book is available from the British Library. Special discounts are available for bulk purchases of this book.
For more information, please contact Special Sales at 410-516-6936 or specialsales@press. The Johns Hopkins University Press uses environmentally friendly book materials, including recycled text paper that is composed of at least 30 percent post-consumer waste, whenever possible. All of our book papers are acid-free, and our jackets and covers are printed on paper with recycled content.com To those giants on whose shoulders I have stood www.com This page intentionally left blank www.com Contents Foreword, by Leon Lederman ix Acknowledgments xiii Prologue 1 1 What We Know: The Standard Model 4 2 What We Guess: Theories We Want to Test 23 3 How We Do It: The Large Hadron Collider 67 4 How We See It: The Enormous Detectors 96 5 Where We’re Going: The Big Picture, the Universe, and the Future 136 Epilogue 163 Suggested Reading 165 Index 169 www.com This page intentionally left blank www.com Foreword The Large Hadron Collider, or LHC, is a new scientific tool. The invention of tools, instruments to aid in observation and measurement, has been crucial to the advancement of science.
Even though there is a robust debate as to the relative virtues of pure versus applied research, instruments are vital to both branches and serve as a harmonious bridge. In the late nineteenth and early twentieth centuries, progress in both basic research and applied re- search has been utilized to create ever more powerful tools. Many of these were designed for comfort and entertainment but their use to advance the under- standing of nature led the way. It’s really cozy: research creates new knowledge, which enables the creation of new instruments, which make possible the dis- covery of new knowledge.
An example: Galileo constructed many telescopes after hearing about their invention in Holland. In one stunning weekend, he turned a telescope to the sky and discovered four of the moons of Jupiter! This convinced him that indeed the Earth was in motion as surmised by Copernicus. The evolution of telescopes ultimately gave humans a measure of the vastness of our universe with its bil- lions of galaxies, each hosting billions of suns. And in the more sophisticated science, more powerful telescopes were developed.
A further example relevant to our book about the LHC: the structure and properties of electrons are about as basic as one can get in the grand quest for understanding how the world works. But many of these properties make elec- trons a powerful component in countless instruments. Electrons make x-rays for medical use and for determining the structure of biological molecules. Electron beams make oscilloscopes, televisions, and hundreds of devices found in labo- ratories, hospitals, and the home.
An impressive technology enabled the control of energetic electron beams in particle accelerators. These were invented in the 1930s and provided precise data on the size, shape, and structure of atoms. To probe the nucleus of atoms, higher energies were required, and the acceleration of protons was added to the toolkit of physicists.com x Foreword An approximate timetable of progress in accelerators may be useful and is shown below. Note that eV equals one electron volt, so keV is 103 elec- tron volts, MeV is 106 electron volts, GeV is 109 electron volts, and TeV is 1012 electron volts.
You can see in the table that the higher the energy of the ac- celerated particle, the smaller the distance probed. However, to probe the very small, the accelerators also grew in size, complexity, and cost. Accelerators are then in essence powerful microscopes, taking over when light is no longer sufficient. Date Energy Distance Probed 1930 ~100 keV 10–11 meters 1950 ~100 MeV 10–14 meters 1970 100 GeV 10–17 meters 1990 1 TeV 10–18 meters 2010 10 TeV 1–19 meters 2020 ? ? Over the past 80 years, hundreds of accelerators have been constructed world- wide, predominantly to address the unknowns in the field of particle physics.
Other applications of accelerators are these: in medical treatment, as powerful x-ray sources, in industry, and in oil explorations. The complexity and cost of the newer machines have forced large international collaborations. For the first time, construction costs of an accelerator, the LHC, will be shared by Europe, Russia, Japan, China, and the United States. There is a matching set of requirements for the construction of the detectors (see chapter 4) that must observe the new domain exposed by the accelerators— essentially supermicroscopes.
Here, intimate collaborations of over a thousand scientists and students are involved. The official language of these collabora- tions is, of necessity, “broken English.” It should be noted that, though high energy physics came out of a marriage of nuclear and cosmic ray physics in the late 1940s, we now recognize a new merger of high energy particle physics, which is accelerator based, with astro- physics, which is telescope based. The long-recognized connections of the in- ner space of particles with the outer space of the cosmos has been reinforced by baffling data on gravitation (dark matter and dark energy) and the continuing mystery of particle symmetry-breaking. However, the “inner space-outer space” connection teaches us that the newly born universe consisted of the elemen- tary particles out of which the stars, galaxies, planets, and people eventually emerged.
So, in the first decade of the twenty-first century, the venerable Tevatron ac- celerator at Fermilab, born in the scientific dreams of 1985, is operating at full capacity in the hopes of adding to its distinguished list of discoveries before the www.com Foreword xi advent of its CERN (in Geneva, Switzerland—the lab we love to hate) successor, the LHC, scheduled to begin operations in 2008. At the entrance to the accelerator, the atmosphere is heavy with the prom- ise of discovery. The list of burning open questions today is longer and more profound than that with which we struggled in 1985 (see chapter 5 for a few of today’s questions). Our list of questions will not all be solved by the LHC, and new ones will surely be added.
For now, a new generation of accelerators grows in the minds and in the R & D of a new generation of accelerator physicists and their students. This is a glorious time for them. But in the meantime, this book by Don Lincoln tells of the excitement ex- perienced by physicists as the LHC commences operations and lets the reader appreciate why the LHC is of such great interest to all physicists. We live in very interesting times.
Leon Lederman A few quotes as salsa for the repast that awaits you in the journey ahead with Don Lincoln. One of man’s enduring hopes has been to find a few simple general laws that would explain why nature, with all its seeming complexity and variety, is the way it is. We will still need the LHC to pin down the details of the symmetry-breaking mech- anism that gives mass to elementary particles. Steve Weinberg, Nobel laureate, Physics 1979 The supreme test of the physicist is to arrive at those universal elementary laws from which the cosmos can be built up by pure deduction.
Albert Einstein When Anton von Leeuwenhoek first saw his “animacules” in a drop of pond water in the seventeenth century, he was in fact extending the ability of humans to see the world in modes not accessible to eyes alone. The number of dimensions is the number of quantities you need to know to com- pletely pin down a point in space.com xii Foreword Supersymmetry is an extension of known particle physics concepts and has a good chance of being tested in forthcoming experiments. String theory is different. Lisa Randall, professor of physics, Harvard University The expanding cloud of billions of galaxies that we call the Big Bang may be just a fragment of a much larger universe in which Big Bangs go all the time, each with different values for the fundamental constants.
Andrei Linde, professor of physics, Stanford University Every day in a handful of particle accelerators throughout the world, scientists ac- celerate protons or electrons to tremendous energies and collide them. In these collisions it is possible to create, for a brief instant, the conditions that have not existed in the universe for fourteen billion years. Edward “Rocky” Kolb, professor of astrophysics, University of Chicago The scientist does not study nature because it is useful to do so. He studies it be- cause he takes pleasure in it and he takes pleasure in it because it is beautiful.
If nature were not beautiful, it would not be worth knowing and life would not be worth living. It is because simplicity and vastness are both beautiful that we seek simple facts and vast facts. Henri Poincaré, mathematician and physicist www.com Acknowledgments First and foremost I’d like to thank the physicists, engineers, computing professionals, technicians, and other support staff who had the vi- sion and determination to make the Large Hadron Collider and its associated detectors a reality. The LHC is one of the most complex scientific endeavors ever attempted, and I have the greatest respect for a group of people who can make it all work.
As the scientific results start coming in, and certain people become known as the “voice of the LHC,” we should never forget the teams that de- signed and built this equipment. Without them, those voices would be forever mute. I would like to thank Dan Claes for contributing several hand-drawn figures for the text. He has helped me out in the past and I am very grateful, as if I had included my versions of these figures, well, it wouldn’t have been pretty.
I’d also like to thank Barry Panas and Jeffery Mitchell for various computer-generated figures. I’d like to thank Leon Lederman for his gracious contribution of the fore- word. Leon is one of the greatest living particle physicists, with more than one discovery that would have nominated him to the Nobel club. He is also a tireless cheerleader for basic research and spends more time in retirement crisscrossing the country, speaking with the public and policy makers alike than most people do at the height of their careers.
The Energizer Bunny’s got nothing on Leon. I am deeply indebted to my test readers, without whom the text would have been vastly less readable. Linda Allewalt, Drew Alton, Lee Blakley, Rebecca Messer, Frank Norton, Chuck Osborne, Mandy Rominsky, and Michael Walsh all made invaluable suggestions as to language, scope, depth and breadth. I also asked several colleagues to check that I had not typed in a wrong num- ber when describing all the equipment.
This is very easy to do, as the as-built numbers of a complex technical project such as the LHC and its associated de- tectors are often somewhat different than the formal design documents. Marzio Nessi checked the ATLAS section, while David Barney checked the CMS descrip- tion. Yves Schutz and Roger Forty looked over the ALICE and LHCb sections re- xiii www.com xiv Acknowledgments spectively, while Michael Koratzinos vetted the accelerator section. In addition, I’d like to thank James Gilles for helping to identify these experts, each with a talent for public communication and a willingness to help out.