Presentation on theme: "Quantum Phenomena II: Matter Matters"— Presentation transcript:
1 Quantum Phenomena II: Matter Matters 2nd HandoutSecond HandoutAtomic StructureFundamental PhysicsHydrogen atomQuantum numbersElectron intrinsic spinOther atomsMore electrons!Pauli Exclusion PrinciplePeriodic TableParticle PhysicsThe fundamental particlesThe fundamental forcesCosmologyThe big bangThe evolution of the universeChris ParkesApril/May 2003
2 The Structure of Matter Quarks have most of massElectrons spatial extent and determine chemical properties
3 Fundamental ? 450BC Empedocles, Aristotle Democritus “Atoms & space” 4 basic elementsSimilar philosophies in China / IndiaDemocritus “Atoms & space”1661 Boyle Elements…Medeleyev lots of them !C19 Dalton, elements composed of atomsnucleusProtons, neutrons….Lots more started turning up!QuarksStandard model"Young man, if I could remember the names of these particles, I would have been a botanist!”, Fermi
4 Looking at smaller scales Naked Eye mLight Microscope mSize of Atom mSize of Proton mSize of quark, electron, neutrino.. 0 (so far..)Fundamental particlesNo constituentsStudy using Particle AcceleratorsLabs: CERN, Fermilab…Acelerators: LEP/LHC, TevatronCollide particles at high energiesLook at what comes out !
5 Particle Physics Accelerators Collisions are Fixed target or colliding beamcolliding beam uses all available energyAnd accelerators:Linacs (straight) or synchotrons (circles)Particles are accelerated by electric fieldsBent by magnetic fieldsBeams made to collide inside detectorsCan keep particles travelling round and round in circleBut lose energy, radiate photons, when travelling in a circleCERN’s big accelerators27 km long tunnel,100m undergroundFrench/Swiss Border near Geneva1989 – 2000 Large Electron Positron collider (LEP), colliding beam synchotron2007 onwards Large Hadron Collider (LHC), proton collider
6 Fermions & BosonsWe introduced spin for electron…but general particle propertyDetermines particle propertiesHalf-integer spin particles – FermionsFermi-Dirac StatisticsPauli Exclusion principleWhole-integer spin particles – BosonsBose-Einstein statisticsNo Exclusion principle, as many as you want in same stateMatter is made of the fundamental fermionsForces are carried by the fundamental bosonsStandard Model is theory which contains these fundamental particles
7 Fermions: Building blocks of matter rest mass electric charge other chargesin MeV/c2“up” quark u /3 e colour & weak“down” quark d /3 e colour & weakelectron e e weakneutrino e v. small but > weakQUARKSLEPTONSThe first generation fermionsThis is what everything around us is made ofBut there are more !Proton: uud Neutron: udd electronNeutrino given off in Beta decayAll spin ½ particles
8 Forces of nature Forces mediated by particle exchange Force acts on particles with that type of “charge”e.g. electromagnetism :photon exchange between electrically charged particlesFeynman Diagram
9 Bosons: Force Carriers Force boson mass interaction charge relative strength rangein GeV/c2Gravity graviton ?0? mass Weak W+,W-,Z /91 weak charge mElectromagnetism Photon () 0 charge Strong gluon (g) 0 colour charge mThe four forces and their carriersAll particles feel gravity, graviton not discoveredAll particles have weak charge feel weak forceElectric charged feel emag.Only quarks feel strong force, confined, colour neutralSpin 1, except graviton spin 2
10 Forces : some basic consequences Strongglues quarks to make protons / neutronsGlues protons / neutrons to make nucleiElectromagnetismBind electrons to nucleiSticks atoms together to make moleculesGravityHolds large lumps of matter together: stars, planets, galaxiesWeakRadioactive decayCross-generational couplings….
11 Feynman Diagrams We already saw one for electron,positron annihilation We already saw one for electron,positron annihilationHere is neutron decayBy following sets of rules, we can see if this reaction will happen
12 Particle interactions Some basic standard model vertices:
13 Anti-matter Each particle has an anti-particle Properties are opposite e.g. electron / positronProperties are oppositeOpposite charge(and weak and colour)same mass and spinElectron & positron bending in magnetic fieldDirac Equation, 1930, relativistic version of Schrödinger for electrons,but it seemed to have -ve energy electrons !No, positive energy but anti-matter!Anderson discovered in 1931Some particles are their own anti-particles:Photon, neutral pionDirac: “This result is too beautiful to be false; it is more important to have beauty in one's equations than to have them fit experiment.”Bubble Chamber photo,A very old fashioned photographic form of particle detector
14 A typical modern particle physics experiment DELPHI LEP collider
15 E=mc2 or rather E2=(pc)2+(mc2)2 Particle and anti-particle annihilate to pure energym is rest massAdd K.E. termBasis of most modern particle physics accelerator exptsSmash highly energetic particle and anti-particle together1st generation fermionsBosonsParticles and their anti-particles
16 Basic Kinematics Apply what you have learnt about relativity e.g. particle A decays into particles B & CWork in rest frame of particle AReactionmomentumEnergyEnergy,momentum conservation – but energy includes rest massSo particles go off back-to-backand we must have enough energy to make them
17 Three generations And ONLY 3 ! LEP from number of neutrinos Bosons: graviton, W+,W- Z0, gluon, photonII RabiMuon discovered by Street & Stevenson 1937 using Wilson Cloud chamber….b quark was found in 1977, Fermilabtop quark MUCH heavier (40x) found in 1995, FermilabW/Z found at CERN 20 years agoStill to find…Higgs Boson?Graviton ?Standard Model: one extra –the Higgs boson (H), responsible for massNo gravity+ anti-particles. all fermions found
18 Conservation Laws Tell us which processes can happen Short-cut for Feynman diagramsConserved quantities in a reactionSame before – initial stateAs after – final stateMomentum vector, pEnergy E, relativistic so due to momentum and rest massBaryon number BNumber of quarks remains constantElectric Charge QHelpfully, most particles have charge as superscript on namee.g. +Lepton number, for each generation: Le,L,L
19 Fundamental Particles Anti-particles have opposite propertiese.g. Positron e+ hasQ=+1, Le=-1Hence, particle-antiparticle combinations have zero everything!e.g. composite particlemade ofBaryon number is fractional, so that proton & neutron have B=1
20 Confinement Strong force very strong ! Quarks bound cannot break free No free quarksLower energy to produce new particles than separate quarksAll particles observed have no net colourElectric charge has one type +, and its opposite -Colour charge comes in three types: red, green, blue and their opposites: anti-red,anti-green anti-blue
21 Hadrons: where quarks hide Hadrons are the bound states of quarks we observeControlled by strong force, remember leptons don’t feel thisOnly colourless states can be madeColoured quark and anti- that same colour quarkThis is called a Meson (integer spin, hence a boson)Most common mesons are the pions 0 ,+ ,-‘Mix’ three colour charges togetherThis is called a Baryon (½ integer spin, hence a fermion)Most common Baryons are proton & neutronThese are the basic first generation composite states:
22 Other Hadrons These last states only contained up, down quarks Also have strange, charm, top, bottomCan make hadrons with these also….hence very large number of combinations!We will consider only the strange quarkNext lightest quark after up,downLike a heavy version of the d quark, mass 500 MeV, Q=-1/3Strange quark has strangeness =-1These states are unstable decay into proton, neutron, pions(with spin ½)Kaon mesons are counterparts of pions with s rather than d quarkStrange Baryons Sigma , Lamda, Xi(with spin 0)
23 Quark Jets Don’t observe free quarks Quarks form into composite states of two quarks (mesons) or three quarks (baryons)in particle detectors often see showers of these particles – jets of mesons and baryonsJet of particles seen in trackingSystem of detectorJet of mesons &BaryonsProduced fromone initial highEnergy quarkOr anti-quark
25 Some Key PointsForces are due to exchange of the fundamental force carrying bosonsPhoton,gluon,W+,W-,Zo (and presumably graviton)Know the fundamental particlesThree generations of quarks and leptonsDon’t observe free quarksConfined in colourless hadronsAdded some more conservation lawsEnergy, momentum, electric chargeBaryon number, lepton numberParticle interactions can be written as Feynman diagramsKnow the basic vertices, and conservation laws to see whether or not a reaction will occur.
26 Searching for a Grand Unified Theory Electroweak theory well established in SMElectromagnetic and weak forces are part of same theoryUnify at high energy?? Unifies with strong force also at high energy ??……then maybe eventually combine gravity also……
27 Particle Physics Glossary Fermion: ½ integer spin particleQuarks: fundamental fermions which come in six types up,down,strange,charm,top,bottomhave fractional electrical charge and colour chargeLeptons: fundamental fermions which come in six types electron, muon,tau (all with electric charge) and electron neutrino, muon neutrino, tau neutrino (all neutral)Generations: quarks and leptons come in three generations. Each generation looks like the previous but heavier.Boson: integer spin particle. The fundamental bosons are the force carrier particles.Electromagnetic force: carried by photon, interacts with electrically charged particlesStrong Force: carried by gluon, interacts with colour charged particles – the quarks. Joins quarks into hadronsWeak Force: carried by Z0,W+,W-, responsible for nuclear Beta decayElectroWeak Theory: Electromagnetic and Weak Forces are explained by one combined theory.Hadron: composite particle made of quarksMeson: type of hadron containing 2 quarks (or more precisely one quark, one anti-quark)Pions: the most common mesons (Kaons are most common meson with s quark)Baryon: type of hadron containing 3 quarksProton,neutron: the most common baryonsAnti-matter: particles have anti-matter equivalents with same mass,opposite charge these behave identically.Standard Model: very precisely tested theory of particle physics, containing electroweak and strong forces and fundamental particles.
28 The Big Bang Evidence for the Big Bang The evolution of the universe It is dark at night! See Olbers ParadoxUniverse expandingCosmic microwave backgroundRelative abundance of elements in universeThe evolution of the universeStages in the formation of the universeBig Crunch ?
29 Looking at larger scales Man 1 mPlanet Earth 107 mSolar System m 1 light-dayStar separation 1017 m 10 light-yearsGalaxy size m 100,000 light-yearsGalaxy separation 5 million light-yearsin a cluster of Galaxies 50 million light-yearsLarge Scale Structure 1 billion light-yearsWalls, voids etc.. in distribution of galaxiesSolar system seen from the outside!Voyager 11977…Picture, 1990
30 The expanding Universe Expansion of space, not in spaceLight from other galaxies is red-shiftedDoppler shiftEdwin Hubble (1929)Whole universe is uniformly expandingThere is no centre to the universeHubble’s law:H ~ 20 km/s/million light yrsv = H x d,Velocity Hubble const distance
31 Age of Universe Extrapolate back with Hubble’s law Hence universe came into existence with very high density, expanded out from thereParticle and Nuclear physics determined the early stages of evolution of the universe
32 Olber’s “Paradox”: Why is the sky dark at night ? If the observable universe isStatic (eternal)InfiniteApproximately uniformly filled with starsThen sky should be as bright as the surface of a starA faraway star looks dimmer, but there are more stars further away!Brightness falls off as 1/r2But area at distance r in some angular region, rises as r2Hence, these cancel and sky should be equally bright as sun.(e.g. Snowy mountains on a sunny day, equally bright in all directions irrespective of distance)
33 Resolving Olbers “Paradox” The universe is not infinitely oldApprox 15 billion yearsThe speed of light is finiteWe can only see part of the universeSky is dark at night becauseUniverse is young – distant light hasn’t reached us yetand alsoExpansion causes doppler shift (red-shift) of lightSo,Big Bang solves Paradox
34 Stages in the evolution of the Universe Planck EraGUT EraElectroweak EraParticle EraEra of NucleosynthesisEra of NucleiEra of AtomsEra of Galaxies – Now!Book:“The first three minutes”, by Steven Weinberg
35 (1) Planck Era: up to 10-43 seconds Mysterious !Universe begins at very high temperatureMaybe gravity unified with the other forces ?General Relativity and Quantum mechanics have never been successfully combined.We need a theory of Quantum GravityCharacteristic Planck Time and Planck LengthHighly Speculative theories includeM-theory particles are excitations on high dimensional membranes. This has taken over from(and includes) String Theory, where particles are different vibrations of one type of string.open stringclosed string
36 (2) The GUT Era: up to 10-35 seconds We still don’t know a great deal but have some better ideas !Universe full of fundamental particles, antiparticles, photons, gluons…everything!No composite particlesMaybe the electroweak and strong forces (separate in Standard Model) become united ? (GUT)Particle physics experiments give some support for converging coupling constantsInflation: a short period of rapid expansion in the universe.Universe starts as a rapidly expanding quantum bubbleAnalysis of cosmic background radiation of universe gives some support for this model
37 (3) The Electroweak Era: up to 10-10 seconds Universe cooling, but still very hot, 1028KAgain, no composite particles yet.Three forces in the universeGravityStrongElectroweakElectromagnetism and weak force are unified in ElectroweakW+,W-,Z are massless, like the photons and gluons
38 (4) The Particle Era: up to 10-3 seconds Temperature now dropped to ~1012KContains almost equal amount of particles and anti-particlesAnd photons, gluons…Electroweak Force splits into Electromagnetism and Weak Interaction.W+,W-,Z become heavy, get the Higgs boson (not found yet)As we cool further…Confinement starts:Quarks, anti-quarks,gluons combine to form protons and neutronsAntimatter disappearsMatter/anti-matter cancel out.Small excess of matter ? Why ?Particle physics experiments are investigating
39 (5) Era of Nucleosythensis: 0.001seconds to 3 minutes Temperature 1012 to 109 KThe first composite particles, the protons and neutrons combine to form light nuclei:At the End:75% (by mass) Hydrogen nuclei p,pn,pnn25% (by mass) Helium nuclei ppn,ppnn~0% LithiumNuclei only, energy too high to bind electrons into atomsThe other nuclei come from Stars much later75/25 % as measured, good evidence for big bangNo stable nuclei with 5 particles, so very few nuclei above He formed
40 (6) The Era of Nuclei: 3 minutes to 300,000 years Universe is as hot as centre of sun (107K)Plasma of light nuclei and electrons and photons
41 (7) Era of Atoms: 300,000 to 1 billion years Universe cools so atoms can be formed (3000K)Electrons captured by nucleiUniverse is transparent – photons can fly around freely !No longer electrons that interact with themThis is how the microwave background was createdMost impressive evidence for big bangUniverse was once very hot!
42 Cosmic Microwave Background Photons from when atoms formedUniverse continued to expand and coolExpect remnant radiation with 2.7K blackbody spectrum with isotropic spectrumDiscovered Penzias,Wilson 1965BUT not completely uniform at 10-5 K scaleCOBE was first to see anisotropy, small fluctuations in temperature.Latest results WMAP Feb. 2003COBE satellite, 1990Compatible with inflation model
43 (8) Era of Galaxies: 1 billion to 15 billion years (NOW) Gravity plays its roleNeutral H and He gas attractedSmall density variations are amplifiedForm gas clouds….And eventually starsThermonuclear reactions in stars form heavier atomsHelium nuclei fusione.g. 12C is lower energy state than 3 x 4HeGet nuclei up to IronIron is most stable nuclei (binding energy per nuclei)Higher nuclei require additional energy inputProvided in supernova explosionsSo, earth is supernova debris(but measurements on galaxy rotation show particle physics does not give enough matter! Dark matter ?)
44 The Future of the Universe ? Gravity fights the acceleration of the universeExpansion of universe could slow,stop, and then contract.Big Crunch?Amount of visible matter is not enoughBut strong evidence for additional dark matterBut still not enough!Could expand forever, but expansion slower and slower…And if there is a cosmological constant…An extra term that can give dark energy with negative pressureExpansion of universe may be accelerating!
45 “I’d like to thank the Swedish Academy”: five ways you can win a Nobel prize! Why is there more matter than anti-matter in the universe ?Find the Higgs Boson.Is there a Cosmological constant ?What is dark matter ?Develop a Theory Of Everything !
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