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  Particle Physics: A Very Short Introduction

  VERY SHORT INTRODUCTIONS are for anyone wanting a stimulating and accessible way in to a new subject. They are written by experts, and have been published in more than 25 languages worldwide.

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  PARTICLE PHYSICS

  A Very Short Introduction

  Frank Close

  Great Clarendon Street, Oxford OX2 6DP

  Oxford University Press is a department of the University of Oxford.

  It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide in Oxford New York

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  Published in the United States by Oxford University Press Inc., New York

  © Frank Close, 2004

  The moral rights of the author have been asserted Database right Oxford University Press (maker)

  First published as a Very Short Introduction 2004

  All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, or under terms agreed with the appropriate reprographics rights organizations. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above

  You must not circulate this book in any other binding or cover and you must impose this same condition on any acquirer

  British Library Cataloguing in Publication Data

  Data available

  Library of Congress Cataloging in Publication Data

  Particle physics: a very short introduction / Frank Close. (Very short introductions)

  Includes bibliographical references and index.

  ISBN 0–19–280434–0

  1. Particles (Nuclear physics)—Popular works. I. Title. II Series.

  QC778.C56 2004

  539.7′2—dc22 2004049295

  ISBN 0–19–280434–0

  1 3 5 7 9 10 8 6 4 2

  Typeset by RefineCatch Ltd, Bungay, Suffolk

  Printed in Great Britain by

  TJ International Ltd., Padstow, Cornwall

  Contents

  Foreword

  List of illustrations and tables

  1 Journey to the centre of the universe

  2 How big and small are big and small?

  3 How we learn what things are made of, and what we found

  4 The heart of the matter

  5 Accelerators: cosmic and manmade

  6 Detectors: cameras and time machines

  7 The forces of Nature

  8 Exotic matter (and antimatter)

  9 Where has matter come from?

  10 Questions for the 21st century

  Further reading

  Glossary

  Index

  Foreword

  We are made of atoms. With each breath you inhale a million billion billion atoms of oxygen, which gives some idea of how small each one is. All of them, together with the carbon atoms in your skin, and indeed everything else on Earth, were cooked in a star some 5 billion years ago. So you are made of stuff that is as old as the planet, one-third as old as the universe, though this is the first time that those atoms have been gathered together such that they think that they are you.

  Particle physics is the subject that has shown how matter is built and which is beginning to explain where it all came from. In huge accelerators, often several miles in length, we can speed pieces of atoms, particles such as electrons and protons, or even exotic pieces of antimatter, and smash them into one another. In so doing we are creating for a brief moment in a small region of space an intense concentration of energy, which replicates the nature of the universe as it was within a split second of the original Big Bang. Thus we are learning about our origins.

  Discovering the nature of the atom 100 years ago was relatively simple: atoms are ubiquitous in matter all around, and teasing out their secrets could be done with apparatus on a table top. Investigating how matter emerged from Creation is another challenge entirely. There is no Big Bang apparatus for purchase in the scientific catalogues. The basic pieces that create the beams of particles, speed them to within an iota of the speed of light, smash them together, and then record the results for analysis all have to be made by teams of specialists. That we can do so is the culmination of a century of discovery and technological progress. It is a big and expensive endeavour but it is the only way that we know to answer such profound questions. In the course of doing so, unexpected tools and inventions have been made. Antimatter and sophisticated particle detectors are now used in medical imaging; data acquisition systems designed at CERN (the European Organization for Nuclear Research) led to the invention of the World Wide Web – these are but some of the spin-off from high-energy particle physics.

  The applications of the technology and discoveries made in high-energy physics are legion, but it is not with this technological aim that the subject is pursued. The drive is curiosity; the desire to know what we are made of, where it came from, and why the laws of the universe are so finely balanced that we have evolved.

  In this Very Short Introduction I hope to give you a sense of what we have found and some of the major questions that confront us at the start of the 21st century.

  List of illustrations and tables

  1 Inside the atom

  2 The forces of Nature

  3 Comparisons with the human scale and beyond normal vision

  4 Correspondence between scales of temperature and energy in electronvolts

  5 Energy and wavelength

  6 Result of heavy and light objects hitting light and heavy targets, respectively

  7 Properties of up and down quarks

  8 Quark spins and how they combine

  9 Beta decay of a neutron

  10 Fundamental particles of matter and their antiparticles

  11 First successful cyclotron, built in 1930

  Photo: Lawrence Berkeley National Laboratory. Illustration: © Gary Hincks