Presentation on theme: "Quantum Phenomena II: Matter Matters Quantum Phenomena II: Matter Matters Chris Parkes April/May 2003 Hydrogen atom Quantum numbers Electron intrinsic."— Presentation transcript:
Quantum Phenomena II: Matter Matters Quantum Phenomena II: Matter Matters Chris Parkes April/May 2003 Hydrogen atom Quantum numbers Electron intrinsic spin Other atoms More electrons! Pauli Exclusion Principle Periodic Table Particle Physics The fundamental particles The fundamental forces Cosmology The big bang The evolution of the universe Fundamental Physics Atomic Structure 2 nd Handout Second Handout
The Structure of Matter Quarks have most of mass Electrons spatial extent and determine chemical properties
Fundamental ? 450BC Empedocles, Aristotle 4 basic elements Similar philosophies in China / India Democritus “Atoms & space” 1661 Boyle Elements …Medeleyev lots of them ! C19 Dalton, elements composed of atoms nucleus Protons, neutrons…. Lots more started turning up! Quarks Standard model "Young man, if I could remember the names of these particles, I would have been a botanist!”, Fermi
Looking at smaller scales Naked Eye10 -4 m Light Microscope10 -6 m Size of Atom m Size of Proton m Size of quark, electron, neutrino..0 (so far..) Fundamental particles No constituents Study using Particle Accelerators Labs: CERN, Fermilab… Acelerators: LEP/LHC, Tevatron Collide particles at high energies Look at what comes out !
Collisions are Fixed target or colliding beam colliding beam uses all available energy And accelerators: Linacs (straight) or synchotrons (circles) Particles are accelerated by electric fields Bent by magnetic fields Beams made to collide inside detectors Can keep particles travelling round and round in circle But lose energy, radiate photons, when travelling in a circle CERN’s big accelerators 27 km long tunnel,100m underground French/Swiss Border near Geneva 1989 – 2000 Large Electron Positron collider (LEP), colliding beam synchotron 2007 onwards Large Hadron Collider (LHC), proton collider Particle Physics Accelerators
Fermions & Bosons We introduced spin for electron…but general particle property Determines particle properties Half-integer spin particles – Fermions Fermi-Dirac Statistics Pauli Exclusion principle Whole-integer spin particles – Bosons Bose-Einstein statistics No Exclusion principle, as many as you want in same state Matter is made of the fundamental fermions Forces are carried by the fundamental bosons Standard Model is theory which contains these fundamental particles
Fermions: Building blocks of matter This is what everything around us is made of But there are more ! Proton: uudNeutron: uddelectron Neutrino given off in Beta decay rest masselectric chargeother charges in MeV/c 2 “up” quark u /3 e colour & weak “down” quark d /3 e colour & weak electron e e weak neutrino e v. small but >0 0 weak QUARKS LEPTONS The first generation fermions All spin ½ particles
Forces of nature Forces mediated by particle exchange e.g. electromagnetism : photon exchange between electrically charged particles Force acts on particles with that type of “charge” Feynman Diagram
Bosons: Force Carriers All particles feel gravity, graviton not discovered All particles have weak charge feel weak force Electric charged feel emag. Only quarks feel strong force, confined, colour neutral Forceboson massinteraction chargerelative strengthrange in GeV/c2 Gravity graviton?0?mass Weak W +,W -,Z 80/91weak charge m Electromagnetism Photon ( )0charge Strong gluon (g)0 colour charge m The four forces and their carriers Spin 1, except graviton spin 2
Forces : some basic consequences Strong glues quarks to make protons / neutrons Glues protons / neutrons to make nuclei Electromagnetism Bind electrons to nuclei Sticks atoms together to make molecules Gravity Holds large lumps of matter together: stars, planets, galaxies Weak Radioactive decay Cross-generational couplings….
Feynman Diagrams We already saw one for electron,positron annihilation Here is neutron decay By following sets of rules, we can see if this reaction will happen
Particle interactions Some basic standard model vertices:
Anti-matter Each particle has an anti-particle e.g. electron / positron Properties are opposite Opposite charge (and weak and colour) same mass and spin Bubble Chamber photo, A very old fashioned photographic form of particle detector Electron & positron bending in magnetic field Dirac 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 1931 Some particles are their own anti-particles: Photon, neutral pion Dirac: “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.”
A typical modern particle physics experiment DELPHI LEP collider
Particle and anti-particle annihilate to pure energy m is rest mass Add K.E. term Basis of most modern particle physics accelerator expts Smash highly energetic particle and anti-particle together E=mc 2 or rather E 2 =(pc) 2 +(mc 2 ) 2 Particles and their anti-particles 1 st generation fermionsBosons
Basic Kinematics Apply what you have learnt about relativity e.g. particle A decays into particles B & C Work in rest frame of particle AReactionmomentumEnergy So particles go off back-to-back and we must have enough energy to make them Energy,momentum conservation – but energy includes rest mass
II Rabi Three generations Muon discovered by Street & Stevenson 1937 using Wilson Cloud chamber …. b quark was found in 1977, Fermilab top quark MUCH heavier (40x) found in 1995, Fermilab W/Z found at CERN 20 years ago And ONLY 3 ! LEP from number of neutrinos Bosons: graviton, W+,W- Z0, gluon, photon + anti-particles. all fermions found Standard Model: one extra – the Higgs boson (H), responsible for mass No gravity Still to find… Higgs Boson ?Graviton ?
Conservation Laws Tell us which processes can happen Short-cut for Feynman diagrams Conserved quantities in a reaction Same before – initial state As after – final state 1.Momentum vector, p 2.Energy E, relativistic so due to momentum and rest mass 3.Baryon number B Number of quarks remains constant 4.Electric Charge Q Helpfully, most particles have charge as superscript on name e.g. + Lepton number, for each generation: L e,L ,L
Fundamental Particles Anti-particles have opposite properties e.g. Positron e + has Q=+1, L e =-1 Hence, particle- antiparticle combinations have zero everything! e.g. composite particle made of Baryon number is fractional, so that proton & neutron have B=1
Confinement Strong force very strong ! Quarks bound cannot break free No free quarks Lower energy to produce new particles than separate quarks All particles observed have no net colour Electric 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
Hadrons: where quarks hide Hadrons are the bound states of quarks we observe Controlled by strong force, remember leptons don’t feel this Only colourless states can be made 1. Coloured quark and anti- that same colour quark This is called a Meson (integer spin, hence a boson) Most common mesons are the pions 0, +, - 2. ‘Mix’ three colour charges together This is called a Baryon (½ integer spin, hence a fermion) Most common Baryons are proton & neutron These are the basic first generation composite states:
Other Hadrons These last states only contained up, down quarks Also have strange, charm, top, bottom Can make hadrons with these also ….hence very large number of combinations! We will consider only the strange quark Next lightest quark after up,down Like a heavy version of the d quark, mass 500 MeV, Q=-1/3 Strange quark has strangeness =-1 These states are unstable decay into proton, neutron, pions Kaon mesons are counterparts of pions with s rather than d quark Strange Baryons Sigma, Lamda, Xi (with spin ½) (with spin 0)
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 baryons Jet of mesons & Baryons Produced from one initial high Energy quark Or anti-quark Jet of particles seen in tracking System of detector
Some Key Points Forces are due to exchange of the fundamental force carrying bosons Photon,gluon,W +,W -,Z o (and presumably graviton) Know the fundamental particles Three generations of quarks and leptons Don’t observe free quarks Confined in colourless hadrons Added some more conservation laws Energy, momentum, electric charge Baryon number, lepton number Particle interactions can be written as Feynman diagrams Know the basic vertices, and conservation laws to see whether or not a reaction will occur.
Searching for a Grand Unified Theory Electroweak theory well established in SM Electromagnetic and weak forces are part of same theory Unify at high energy ?? Unifies with strong force also at high energy ?? ……then maybe eventually combine gravity also……
Particle Physics Glossary Fermion: ½ integer spin particle Quarks: fundamental fermions which come in six types up,down,strange,charm,top,bottom have fractional electrical charge and colour charge Leptons: 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 particles Strong Force: carried by gluon, interacts with colour charged particles – the quarks. Joins quarks into hadrons Weak Force: carried by Z0,W+,W-, responsible for nuclear Beta decay ElectroWeak Theory: Electromagnetic and Weak Forces are explained by one combined theory. Hadron: composite particle made of quarks Meson: 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 quarks Proton,neutron: the most common baryons Anti-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.
The Big Bang Evidence for the Big Bang It is dark at night! See Olbers Paradox Universe expanding Cosmic microwave background Relative abundance of elements in universe The evolution of the universe Stages in the formation of the universe Big Crunch ?
Looking at larger scales Man1 m Planet Earth10 7 m Solar System m1 light-day Star separation10 17 m10 light-years Galaxy size10 21 m100,000 light-years Galaxy separation 5 million light-years in a cluster of Galaxies 50 million light-years Large Scale Structure1 billion light-years Walls, voids etc.. in distribution of galaxies Solar system seen from the outside! Voyager … Picture, 1990
The expanding Universe Light from other galaxies is red-shifted Doppler shift Edwin Hubble (1929) Whole universe is uniformly expanding There is no centre to the universe Hubble’s law: v = Hx d, Velocity Hubble const. distance H ~ 20 km/s/million light yrs Expansion of space, not in space
Age of Universe Extrapolate back with Hubble’s law Hence universe came into existence with very high density, expanded out from there Particle and Nuclear physics determined the early stages of evolution of the universe
Olber’s “Paradox”: Why is the sky dark at night ? If the observable universe is 1. Static (eternal) 2. Infinite 3. Approximately uniformly filled with stars Then sky should be as bright as the surface of a star Then sky should be as bright as the surface of a star A faraway star looks dimmer, but there are more stars further away! Brightness falls off as 1/r 2 But area at distance r in some angular region, rises as r 2 Hence, 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)
Resolving Olbers “Paradox” The universe is not infinitely old Approx 15 billion years The speed of light is finite We can only see part of the universe Sky is dark at night because 1.Universe is young – distant light hasn’t reached us yet and also 2.Expansion causes doppler shift (red-shift) of light So,Big Bang solves Paradox
Stages in the evolution of the Universe 1. Planck Era 2. GUT Era 3. Electroweak Era 4. Particle Era 5. Era of Nucleosynthesis 6. Era of Nuclei 7. Era of Atoms 8. Era of Galaxies – Now! Book: “The first three minutes”, by Steven Weinberg
(1) Planck Era: up to seconds Mysterious ! Universe begins at very high temperature Maybe gravity unified with the other forces ? General Relativity and Quantum mechanics have never been successfully combined. We need a theory of Quantum Gravity Characteristic Planck Time and Planck Length Highly Speculative theories include M-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 string closed string
(2) The GUT Era: up to 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 particles Maybe the electroweak and strong forces (separate in Standard Model) become united ? (GUT) Particle physics experiments give some support for converging coupling constants Inflation: a short period of rapid expansion in the universe. Universe starts as a rapidly expanding quantum bubble Analysis of cosmic background radiation of universe gives some support for this model
( 3) The Electroweak Era: up to seconds Universe cooling, but still very hot, K Again, no composite particles yet. Three forces in the universe Gravity Strong Electroweak Electromagnetism and weak force are unified in Electroweak W +,W -,Z are massless, like the photons and gluons
(4) The Particle Era: up to seconds Temperature now dropped to ~10 12 K Contains almost equal amount of particles and anti-particles And 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 neutrons Antimatter disappears Matter/anti-matter cancel out. Small excess of matter ? Why ? Particle physics experiments are investigating
(5) Era of Nucleosythensis: 0.001seconds to 3 minutes Temperature to 10 9 K The first composite particles, the protons and neutrons combine to form light nuclei: At the End: 75% (by mass) Hydrogen nuclei p,pn,pnn 25% (by mass) Helium nuclei ppn,ppnn ~0% Lithium Nuclei only, energy too high to bind electrons into atoms The other nuclei come from Stars much later 75/25 % as measured, good evidence for big bang No stable nuclei with 5 particles, so very few nuclei above He formed
(6) The Era of Nuclei: 3 minutes to 300,000 years Universe is as hot as centre of sun (10 7 K) Plasma of light nuclei and electrons and photons
(7) Era of Atoms: 300,000 to 1 billion years Universe cools so atoms can be formed (3000K) Electrons captured by nuclei Universe is transparent – photons can fly around freely ! No longer electrons that interact with them This is how the microwave background was created Most impressive evidence for big bang Universe was once very hot!
Cosmic Microwave Background Photons from when atoms formed Universe continued to expand and cool Expect remnant radiation with 2.7K blackbody spectrum with isotropic spectrum Discovered Penzias,Wilson 1965 COBE satellite, 1990 BUT not completely uniform at K scale COBE was first to see anisotropy, small fluctuations in temperature. Latest results WMAP Feb Compatible with inflation model
(8) Era of Galaxies: 1 billion to 15 billion years (NOW) Gravity plays its role Neutral H and He gas attracted Small density variations are amplified Form gas clouds ….And eventually stars Thermonuclear reactions in stars form heavier atoms Helium nuclei fusion e.g. 12 C is lower energy state than 3 x 4 He Get nuclei up to Iron Iron is most stable nuclei (binding energy per nuclei) Higher nuclei require additional energy input Provided in supernova explosions So, earth is supernova debris (but measurements on galaxy rotation show particle physics does not give enough matter! Dark matter ?)
The Future of the Universe ? Gravity fights the acceleration of the universe Expansion of universe could slow,stop, and then contract. Big Crunch? Amount of visible matter is not enough But strong evidence for additional dark matter But 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 pressure Expansion of universe may be accelerating!
“ I’d like to thank the Swedish Academy”: five ways you can win a Nobel prize! 1. Why is there more matter than anti-matter in the universe ? 2. Find the Higgs Boson. 3. Is there a Cosmological constant ? 4. What is dark matter ? 5. Develop a Theory Of Everything !