Quarks, Leptons and the Big Bang Second Edition Quarks, Leptons and the Big Bang Second Edition Jonathan Allday The King’s School, Canterbury Institute of Physics Publishing Bristol and Philadelphia (cid:1)c IOPPublishingLtd2002 All rights reserved. No part of this publication may be reproduced, storedinaretrievalsystemortransmittedinanyformorbyanymeans, electronic, mechanical, photocopying, recording or otherwise, without the priorpermission of the publisher. Multiple copyingis permitted in accordancewiththetermsoflicencesissuedbytheCopyrightLicensing Agency under the terms of its agreementwith the Committee of Vice- ChancellorsandPrincipals. BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary. ISBN0750308060 LibraryofCongressCataloging-in-PublicationDataareavailable Firsteditionprinted1998 Firsteditionreprintedwithminorcorrections1999 CommissioningEditor:JamesRevill ProductionEditor:SimonLaurenson ProductionControl:SarahPlenty CoverDesign:Fre´de´riqueSwist MarketingExecutive:LauraSerratrice Published by Institute of Physics Publishing, wholly owned by The InstituteofPhysics,London InstituteofPhysicsPublishing,DiracHouse,TempleBack,BristolBS1 6BE,UK USOffice: InstituteofPhysicsPublishing,ThePublicLedgerBuilding, Suite1035,150SouthIndependenceMallWest,Philadelphia,PA19106, USA TypesetinLATEX2ε byText2Text,Torquay,Devon PrintedintheUKbyMPGBooksLtd,Bodmin,Cornwall Contents Prefacetothesecondedition ix Prefacetothefirstedition xiii Prelude:Settingthescene 1 1 Thestandardmodel 5 1.1 Thefundamentalparticlesofmatter 5 1.2 Thefourfundamentalforces 10 1.3 Thebigbang 14 1.4 Summaryofchapter1 18 2 Aspectsofthetheoryofrelativity 21 2.1 Momentum 21 2.2 Kineticenergy 28 2.3 Energy 31 2.4 Energyandmass 32 2.5 Reactionsanddecays 37 2.6 Summaryofchapter2 40 3 Quantumtheory 42 3.1 Thedoubleslotexperimentforelectrons 44 3.2 Whatdoesitallmean? 49 3.3 Feynman’spicture 50 3.4 Asecondexperiment 53 3.5 Howtocalculatewithamplitudes 56 3.6 Followingamplitudesalongpaths 59 3.7 Amplitudes,statesanduncertainties 72 3.8 Summaryofchapter3 82 vi Contents 4 Theleptons 85 4.1 Aspotter’sguidetotheleptons 85 4.2 Thephysicalpropertiesoftheleptons 87 4.3 Neutrinoreactionswithmatter 89 4.4 Somemorereactionsinvolvingneutrinos 93 4.5 ‘Whoorderedthat?’ 95 4.6 Solarneutrinosagain 98 4.7 Summaryofchapter4 99 5 Antimatter 101 5.1 Internalproperties 101 5.2 Positronsandmysteryneutrinos 107 5.3 Antiquarks 110 5.4 Thegeneralnatureofantimatter 112 5.5 Annihilationreactions 114 5.6 Summaryofchapter5 116 6 Hadrons 118 6.1 Thepropertiesofthequarks 118 6.2 Areviewofthestrongforce 122 6.3 Baryonsandmesons 123 6.4 Baryonfamilies 124 6.5 Mesonfamilies 129 6.6 Internalpropertiesofparticles 131 6.7 Summaryofchapter6 132 7 Hadronreactions 134 7.1 Basicideas 134 7.2 Basicprocesses 135 7.3 Usingconservationlaws 140 7.4 Thephysicsofhadronreactions 142 7.5 Summaryofchapter7 147 8 Particledecays 148 8.1 Theemissionoflightbyatoms 148 8.2 Baryondecay 149 8.3 Mesondecays 162 8.4 Strangeness 164 8.5 Leptondecays 165 8.6 Summaryofchapter8 166 9 Theevidenceforquarks 167 9.1 Thetheoreticalidea 167 Contents vii 9.2 Deepinelasticscattering 167 9.3 Jets 173 9.4 TheNovemberrevolution 178 9.5 Summaryofchapter9 179 10 Experimentaltechniques 181 10.1 Basicideas 181 10.2 Accelerators 182 10.3 Targets 188 10.4 Detectors 190 10.5 Acasestudy—DELPHI 197 10.6 Summaryofchapter10 201 Interlude1: CERN 203 11 Exchangeforces 210 11.1 Themodernapproachtoforces 210 11.2 Extendingtheidea 217 11.3 Quantumfieldtheories 222 11.4 Grandunification 234 11.5 Exotictheories 236 11.6 Finalthoughts 237 11.7 Summaryofchapter11 238 Interlude2: Antihydrogen 241 12 Thebigbang 244 12.1 Evidence 244 12.2 Explainingtheevidence 251 12.3 Summaryofchapter12 265 13 Thegeometryofspace 267 13.1 Generalrelativityandgravity 267 13.2 Geometry 269 13.3 Thegeometryoftheuniverse 272 13.4 Thenatureofgravity 276 13.5 Thefutureoftheuniverse? 279 13.6 Summary 281 14 Darkmatter 284 14.1 Thebaryonicmatterintheuniverse 284 14.2 Theevidencefordarkmatter 286 14.3 Whatisthedarkmatter? 298 14.4 Summaryofchapter14 315 viii Contents Interlude3: Abriefhistoryofcosmology 319 15 Inflation—acureforallills 326 15.1 Problemswiththebigbangtheory 326 15.2 Inflation 334 15.3 Thereturnof(cid:2) 357 15.4 Thelastwordongalaxyformation 366 15.5 Quantumcosmology 368 15.6 Thelastword 370 15.7 Summaryofchapter15 370 Postlude: Philosophicalthoughts 374 Appendix1: NobelPrizesinphysics 378 Appendix2: Glossary 386 Appendix3: Particledatatables 403 Appendix4: Furtherreading 408 Index 413 Preface to the second edition Itissurelyatruismthatifyouwroteabooktwice,youwouldnotdoit thesamewaythesecondtime. Inmycase,Quarks,LeptonsandtheBig Bangwashauledroundseveralpublishersundertheguiseofatextbook for schools in England. All the time I knew that I really wanted it to beapopularexpositionofparticlephysicsandthebigbang,butdidnot thinkthatpublisherswouldtakeariskonsuchabookfromanunknown author. Well, they were not too keen on taking a risk with a textbook either. IntheendIdecidedtosendittoIOPPasalasttry. Fortunately Jim Revill contacted me to say that he liked the book, but thought it shouldbemoreofapopularexpositionthanatextbook... Thisgoessomewaytoexplainingwhatsomehaveseenasslightlyodd omissionsfromthematerialinthisbook—somementionofsuperstrings asoneexample.Suchmaterialwasnotneededinschoolsandsodidnot make it into the book. However, now that we are producing a second editionthereis a chanceto correctthatandmake ita little morelike it wasoriginallyintendedtobe. I am very pleased to say that the first edition has been well received. Reviewers have been kind, sales have been satisfying and there have beenmanyemailsfrompeoplesayinghowmuchtheyenjoyedthebook. Sixth formstudentshavewritten to say theylike it, a Universityof the ThirdAge adoptedit as a coursebookand severalpeoplehave written toaskmefurtherquestions(whichItriedtoanswerasbestIcould). It has been fun to have my students come up to me from time to time to saythattheyhavefoundoneofmybooksontheAmazonwebsiteand (slightlysurprisedtoneofvoice)thereviewersseemtolikeit. ix