INTRODUCTION TO THE STANDARD MODEL OF PARTICLE PHYSICS

Transcription

1 INTRODUCTION TO THE STANDARD MODEL OF PARTICLE PHYSICS

2 Class Mechanics My office (for now): Dantziger B Room 121 My Phone: x85200 Office hours: Call ahead, or better yet, ... Even better than office hours: Use the forum for the class on Moodle. I ll be reading it and answering questions so that everyone can have access to the questions/answers. Assignments: will be given posted on the website every week. Solutions will be posted after 2 weeks. There is no requirement to hand them in or even try to solve them, but... if you do not try to do them yourself you WILL fail. TA: There is none. Exams/quizzes: The final is on 24/5/2011, Moed B is on 18/7/2011. There will also be a midterm on 23/3/2011 which will be worth up to 25% of the final grade.

3 Current Syllabus (wishful thinking) 1 Introduction Review of relativistic kinematics Intro to sca ering 2 Equations: Schroedinger, Klein- Gordon, and Dirac Intro to Feynman Diagrams Basic QED Processes 3 More QED Quarks. the Eightfold Way, and Isospin 4 Hadrons: Baryons, and Mesons Quark Families The Particle Zoo 5 Experimental Methods I: Accelerators Targets Particle Detectors I 6 Experimental Methods II: More Particle Detectors Experiment Design Data Analysis 7 Nucleon Form Factors: Elastic and Inelastic DIS and the Feynman's Partons Bjorken Scaling 8 QCD and Scaling Violation Intro to Weak Interactions: Chirality, Maximal Parity Violation, and Beta Decay 9 Weak Interactions II: Charged and Neutral Weak Currents The Conserved Vector Current Hypothesis Some more Isospin 10 Spontaneous Symmetry Breaking and the Higgs Mechanism 11 Review of Modern Experiments I: Nucleon Structure and Spin EMC and Medium Modifications LHC and Heavy Ion Experiments 12 Standard Model Failures Beyond SM? Some possibilities 13 Beyond SM Modern Experiments: EDM, Extra Symmetries, Direct Searches 14 Intro to Quantum Field Theory: Why Relativistic QM is not enough QFT Formalism Some Second Quantization

4 Hierarchy of Particles Stuff you see around you is made up of molecules. Molecules are made up of Atoms. Atoms are made up of Nuclei and Electrons. Nuclei are made up of protons and neutrons (collectively nucleons). Nucleons are made from Quarks. Quarks and Electrons are (as far as we know) elementary particles.

5 So what are Elementary Particles Elementary Particles are point like (no internal structure) fermions (obey Fermi-Dirac) with spin 1/2. They have no size we can measure (nothing to do with the classical electron radius). We know of 2 types of elementary particles: Quarks and Leptons. (all) Quarks - have electric charge, either -1/3 or +2/3 the charge of an electron. Quarks come in 6 different flavors : up (u), down (d), strange (s), charmed (c), bottom (b), and top (t). They also come in three different colors (nothing to do with real color of course). Usually we label them Red, Green, Blue. Leptons - have charge 0 or -e. They also come in six flavor: electron, muon, tau electron neutrino, muon neutrino, tau neutrino Leptons have no color.

6 Antiparticles All particles have a corresponding antiparticle which has the exact opposite value for all quantum numbers (charge, color, magnetic moment,...) and the same mass. For notation we put either a + or - for the charges leptons (e - /e + ) etc., or we use a bar over the symbol for quarks and uncharged leptons. When a particle and an anti-particle meet they annihilate and to a state with zero quantum numbers (which can then recreate particles with quantum numbers, provided these some up to zero).

7 Particle Families Quarks and Leptons can be arranged in 3 families or generations (but we don t know why!) Generation 1 st 2 nd 3 rd Quarks +2/3-1/3 u (up) d (down) c (charm) s (strange) t (top) b (bottom) Leptons -1 0 e - µ - τ - ve vµ vτ

8 Hadrons Leptons show up as free particles (electrons mostly). Quarks are always bound into white (colorless) states called Hadrons. Red+Green+Blue=White, also Red+(anti)Red=Blue+(anti)Blue=Green+(anti) Green=White. Two type of Hadrons are found in nature: Baryons, which are states of three bound quarks or anti-quarks (for anti-baryons): Mesons (and anti-mesons) which are a bound state of a quark and anti quarks. A few examples are: particle composition charge proton uud 1 neutron udd 0 antiproton u u d -1 No exotics (like qqqqq ) have been found yet antineutron u d d 0 π + ud +1 π - uu or dd 0 π 0 du -1

9 Interactions The particles interact among themselves through 4 types of forces which we understand to happen through the exchange of field quanta, which are boson particles, also known as gauge bosons for technical reasons which you will understand later. Standard Model Force Boson Range Boson Mass Boson Spin Electromagnetism (QED) photon 0 1 Strong Interaction gluon Weak Interaction W +, W -, Z ~80 GeV 1 Gravity Graviton 0 2 The standard model also has at least one Higgs boson (but maybe more) which explains the masses of the other particles (without the Higgs mechanism they would be massless).

10 Range of the Forces The range of the interactions is related to the mass of the exchanges gauge boson (M). According to the uncertainty principle, it s possible to create a particle with energy Δ E = Mc 2, for a short time Δ t such that Δ E Δ t ~ h (these are called virtual particles ). Such a particle particle can move a maximum distance of: x = c t = c/ E = c/mc 2 Since the photon has zero mass, the range of the EM force is infinite. The W boson has a mass of ~80 GeV/c 2 the range of the weak force is: x =0.197 (GeV fm)/80(gev ) fm m useful to remember c GeV fm

11 What works where? Weak EM Strong Quarks Charged Leptons Neutral Leptons

12 Units In this class we will try to use the so called natural units, where we set = c =1 Using these units energy, mass, and momentum all have the same units (of energy). 1 ev J c 197 MeV fm α = e2 c ev Kg 1 ev sec 1 ev K Example: proton mass MeV ev = J /( ) 2 = Kg Example: ionization of H atoms at ~13.6 ev 13.6 ev K