Physics 3: Particle Physics Lecture 1: Introduction to the Standard Model of Particle Physics February 11th 2008 Particle Physics (PP) a.k.a. High-Energy Physics (HEP) 1 Particle Physics and Me CDF Dr Victoria Martin JCMB room 4405 [email protected] p p My research deals with Particle 1.96 TeV Physics at Colliders. Two projects: • CDF at the Fermilab Tevatron, near Chicago: colliding protons and anti-protons at ~2TeV. Currently the world’s highest energy collider. • The international linear collider (ILC). World’s next electron ! position collider. Currently under design. 2 Today’s Particle Physics • High-energy colliders: trying to produce new, heavy, particles • Study of difference between matter and anti-matter • Studying neutrinos from the atmosphere, the sun, and man-made neutrinos. • Precise measurements of muon decay properties • Developing new detector technologies and computing strategies for TBs of data • Developing theories for the shortcomings of our models • Massive numerical calculations of quantum chromodynamics 3 !"#$#%&'(&%)*+,-"&.-//,"&01-*2$"')%34 N%,"$@<&/#.,&-%3&3,%7#/@&7*-+,7 Particle physics looks at physics at: GCH 5%#6,"7,&$',7&/8"')$8& U@9#*-+&,%,"$@&7*-+,&#%& EF 7 7)9,"(-7/&#%(+-/#'% %)*+,#&0X,Y4&#7&.)*8& • very high energy densities 8#$8,"&/8-%&#%&-/'.#*&*-7,& EFGHI7 EFIK&'L :'7/&#%(+-/#'%&; 7')9&'(& 0,Y4B&Z#(,/#.,7&'(&,R*#/,3& • very short distances ,+,*/"'%7<&=)-"27&-%3& 7/-/,7&-",&/@9#*-++@&'(& '/8,"&9-"/#*+,7 '"3,"&EFGEI 7&*'.9-",3& • very early times O#/8&EFGM&7&('"&-/'.#*& } EFGJ7 EFEH&'L >)-"27&*+).9&#%/'&9"'/'%7 98@7#*7& -%3&%,)/"'%7 At high energies, neutrons, EFI 7 EFM&'L ?)9,"8'/&('$&09"'/'%7& [)*+,#&-",&3,%7,&'AT,*/7\ -%3&,+,*/"'%7&%'/&@,/&A')%3& E*.H&8-7&.-77&]&IBHREFEE& protons (and other hadrons) #%/'&-/'.74B&:"#.'"3#-+& 2$&0,=)#6-+,%/&/'&JHF& break into their constituent %)*+,'7@7%/8,7#7&0)9&/'&CD,4 ,.9#",&7/-/,&A)#+3#%$7^^4 V quarks. HREF @" EFV&'L N+,*/"'%7&*'.A#%,&O#/8& 9"'/'%7&-%3&%,)/"'%7&/' U8,&*'++#7#'%7&'(&%)*+,'%7&#%&/8,&%)*+,)7&-",&"-",+@&'(& ('".&-/'.7&0D<&D,4 7)((#*#,%/&,%,"$@&/'&,R*#/,&/8,&9"'/'%7P%,)/"'%7 ∴ /8,@&-",&-&6,"@&,((,*/#6,&3,$",,&'(&(",,3'.&/'& Particle physics always uses EREFW @" GIFF&'L ?/-"PQ-+-R@&('".-/#'%& 3,7*"#A,&%)*+,# 7@%/8,7#7&'(&8,-6#,"&%)*+,# relativity (high energy) and _8#/,&`O-"( [,)/"'%&7/-" 1+-*2&8'+, quantum mechanics (very EVREFW @" GIKF&'L S#"7/&7/-"7&3#,&-%3&,T,*/& ?'+#3&7/-/, 8,-6@&%)*+,#&#%/'&79-*,&; small). ()"/8,"&7/-"&('".-/#'%&0-%3& 9+-%,/74 H EFF EFV EFEF EFEV $P*. Scale set by !c = 197.3 MeV fm 3,%7#/@ U#., O-/," [)*+,-"&.-//," 4 Course Outline Lecture 1 - Introduction The fundamental particles and forces Lecture 2 - Practical Particle Physics Lecture 6 - Strong Interactions Natural units, kinematics Gluons, hadronisation Collisions, scattering and decay Confinement, running coupling Lecture 3 - Electromagnetic force and constant Feynman Diagrams Lecture 7 - Weak Interactions Anti-particles and virtual particles Muon and tau decay Quantum electromagnetic force (QED) Lepton universality Feynman diagrams Weak quark decays Lecture 4 - Experimental Methods Lecture 8 - Neutrinos Particle accelerators, detectors and Neutrino mass and oscillations experiments. Lecture 9 - Electroweak Theory and Lecture 5 - Quarks and Leptons, Mesons beyond and Baryons W and Z bosons, LEP Quantum numbers Higgs Boson Evidence for quarks and colour ... e+e!! hadrons 5 Books! • In conjunction with attending the lectures you will need to read around the subject to fully understand the material. Particle Physics, second edition, by B.R. Martin & G. Shaw. 2nd edition (Wiley 1997) 7 copies in JCMB Library. Introduction to High Energy Physics - D.H. Perkins, 4th edition (CUP 2000) Introduction to Elementary Particles - D. Griffiths (Wiley 1987) Quarks and Leptons –F. Halzen & A.D. Martin (Wiley 1984) For more information that you could ever need on every particle ever: http://durpdg.dur.ac.uk/lbl/ 6 The Standard Model The current understanding of the fundamental particles and the interactions between them is called the “Standard Model of Particle Physics”. Boson-mediated FORCES Gravity ? Electro- # magnetism photon W± Weak Z0 Strong gluons 7 Basic Particles (1st Generation) ! The particles that you know already, e.g. from beta decay: n ! p e "e! Leptons Basic Constituents of Matter Electron and neutrino Four spin-"ℏ fermions Electric Quarks Particle Symbol Type Nucleons are bounds Charge states of up-quarks electron e! -1 lepton and down-quarks neutrino "e 0 lepton up-quark u +2/3 quark down-quark d !1/3 quark ! • Particle physics description of beta decay: d ! u e "e! 8 Higher Generations Nature replicates itself: there are three generations of quarks and leptons 1st Generation 2nd Generation 3rd Generation charge,e electron e! muon $! tau %! -1 electron muon tau neutrino 0 neutrino "e neutrino "$ "% strange bottom down quark !" d quark s quark b up quark u charm quark c top quark t +# Ordinary Matter: built from the 1st generation Higher Generations: Why 3 generations? • copies of ("e, e!, u, d) • undergo identical interactions symmetry/structure not • only difference is mass of particles understood! • generations are successively heavier 9 Antiparticles Relativistic QM ⇒ every particle has a corresponding antiparticle Antiparticles of the SM particles are antimatter Positron “track” Compared to its matter partner, an antiparticle has: • equal mass • opposite electric charge • opposite “additive” quantum numbers Example: positron (e+) antiparticle of the electron (“anti-electron”) Discovered in 1931 by Carl Anderson Notation: bar over symbol or minus ↔ plus + e.g. for first generation: u u¯ d d¯ e− e ν ν¯ ↔ ↔ ↔ e ↔ e 10 The forces of particle physics Strong Electromagnetic • Strongest force • 2nd strongest force • Acts on quarks only • Acts on charged particles • propagated by (8) gluons, g • propagated by photon, $ Weak Gravity 23 Higher Orders • 3rd strongest force • weakest force - negligible at • Acts on all particles So far onlyPPconsidered scale lowest order term in the ± 0 • propagated by W and Z bosonsperturbation• Actsseries. on allHigher particlesorder terms also contribute • Quantum mechanical description uses + + “messenger particles” to propagateLowest Order: e µ the force between particles. γ • Messenger particles are spin-1ℏ bosons - - e µ 6 + ! + ! • e.g. e e #µ µ scattering propagated Summary of Standartimed Model Vertices by photon ! At this point have discussed all fundamental fermions Second Order:and their interactions with the force carrying bosons. + + + + 11 e ! µInteractionse characterizµed by SM vertices 23 ELECTROMAGNETIC (QED) 6 - +.... e Higher Orderq s e- Summar- e- y of Standar- d ModelCouplesV toe CHARGErtices µ- e Qµ e e Does NOT change So far! onlAt thisy consideredpoint haveqdiscussedlowestall fundamentalorder termfermionsin the FLAVOUR and theire2 interactions with the force carrying bosons. perturbationα = series.γ Higher order terms also 4 γ Third Order:! Interactionsπ characterized by SM vertices What do the particlescontribSTRuteONG (QCD) do? ELECTROMAGNETIC+ (QED)q + Dynamics and relativity lectures 2, Lo14,west 15 Order: - e Couplesµ to COLOUR e g +....q Couples to CHARGE s γ Does NOT change - e q Q e Particles interact via one of the forces: strong,e FLAVOURDoes NOT change 2 q gs - - α = 2 g FLAVOUR electromagnetic or weak. s 4eπ e µ α = γ γ WEAK4πCharged Current STRONG (QCD)ν d’u Second order suppressede by relativeChangesto FLAVOURfirst Two main interactions: g g V q Couples to COLOUR Second- Order:w d w ckm order. Providede is smallu, i.eg. perturbationFor" e!QUARKS:is coupling Particle scattering + + + s + Does NOT change • e µ eq µBETWEEN generations 2 - small, lowest ordergw dominates.W W + FLAVOUR can be elastic or inelastic αw =g 2 W • α = 4sπ g +.... s 4π • we’ll mainly consider inelastic scattering-WEAK Neutral- Current- - e! e WEAK Charg- ed Currente Dr M.A. Thomson µ µ Lent 2004 e , νe q • e.g. scattering of electron and positron,- ν "d’µ e , ν e Changes FLAVOUR producing a pair of muons e+e!#µ+µ! eg ! g V - w µ q w ckm Does NOT change e u For" e!QUARKS: coupling 0 FLAVOUR Third Order: - 0 BETWEEN generations g 2 ZW + α = w W ZW • Particle decay w 4π Dr M.A. Thomson +.... Lent 2004 ! WEAK Neutral Current ! • e.g. Beta decay: d ! u e "e! - e e , ν q ! ! - e e.g. Muon decay: µ #e "e! "µ • e , νe q timeDoes NOT change 0 FLAVOUR12 Z Z0 Second order suppressed by relative to first Dr M.A. Thomson Lent 2004 order. Provided is small, i.e. perturbation is small, lowest order dominates. Dr M.A. Thomson Lent 2004 Fermi’s Golden Rule Nuclear physics lecture 4 The rate at which a decay or a scattering proceeds is given by Fermi’s Golden Rule: 2π 2 Ti f = ρ Where: → ! |M| • ! is the matrix element - we will see how these are calculated for different processes in future lectures. • % is the density of states - we will consider this only for some key processes. • T is related to the cross section of scattering, &. + ! + ! + ! + ! 2 e.g. &(e e #µ µ ) ∝ |! (e e #µ µ )| . • T is related to the inverse lifetime of a decay, '. ! ! ! ! 2 e.g. '(µ #e "e! "µ) ∝ 1/|! (µ #e "e! "µ)| . 13 Quantum Numbers Every particle carries a set of quantum numbers, e.g. • electric charge, Q • strangeness, S: number of (anti-strange ! strange) quarks Each force conserves some or all of the quantum numbers, e.g.: • all forces conserve electric charge Qinitial = Qfinal e.g. e+e!#µ+µ! • Qinitial = 0 =! Qfinal ! ! ! • strong and electromagnetic forces conserve strangeness • weak force does not conserve strangeness We can use conservation of quantum numbers to work out if a process (decay, scattering) is allowed or forbidden. • In addition, four-momentum and energy are conserved: p = p , Einitial = Efinal initial final ! ! ! ! 14 Hadrons: Mesons & Baryons • Free quarks have never been observed - quarks are locked inside hadrons • Hadrons are bound states of quarks: either (qqq) or (qq$) • Charge of hadron is always integer multiple of electric charge, e • Colour charge of hadron is always neutral • Two types of hadrons – mesons and baryons (also anti-baryons! qq" q" ) Baryons = qqq Mesons = qq$ Three quark bound states Bound states of quark anti-quark pair Fermions: spin 1/2ℏ, 3/2ℏ ..