INTRODUCTION TO THE STANDARD MODEL OF PARTICLE

PHYSICS

Class MechanicsMy office (for now): Dantziger B Room 121

My Phone: x85200

Office hours: Call ahead, or better yet, email....

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.

Current Syllabus (wishful thinking)

1IntroductionReview of relativistic kinematicsIntro to scaering2Equations: Schroedinger, Klein-Gordon, and DiracIntro to Feynman DiagramsBasic QED Processes3More QEDQuarks. the Eightfold Way, and Isospin4Hadrons: Baryons, and MesonsQuark FamiliesThe Particle Zoo5Experimental Methods I: AcceleratorsTargetsParticle Detectors I

11Review of Modern Experiments I: Nucleon Structure and SpinEMC and Medium Modi"cationsLHC and Heavy Ion Experiments12Standard Model FailuresBeyond SM? Some possibilities13Beyond SM Modern Experiments:EDM, Extra Symmetries, Direct Searches14Intro to Quantum Field Theory:Why Relativistic QM is not enoughQFT FormalismSome Second Quantization

6Experimental Methods II:More Particle DetectorsExperiment DesignData Analysis7Nucleon Form Factors: Elastic and InelasticDIS and the Feynman's PartonsBjorken Scaling8QCD and Scaling ViolationIntro to Weak Interactions: Chirality, Maximal Parity Violation, and Beta Decay9Weak Interactions II:Charged and Neutral Weak CurrentsThe Conserved Vector Current HypothesisSome more Isospin10Spontaneous Symmetry Breaking and the Higgs Mechanism

Hierarchy of ParticlesStuff 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.

So what are “Elementary” ParticlesElementary 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, tauelectron neutrino, muon neutrino, tau neutrinoLeptons have no color.

AntiparticlesAll 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).

Particle Families

GenerationGenerationGeneration

1st 2nd 3rd

Quarks+2/3

Quarks-1/3

Leptons-1

Leptons0

u(up)

c(charm)

t(top)

d(down)

s(strange)

b(bottom)

e- µ- τ-

ve vµ vτ

Quarks and Leptons can be arranged in 3 ‘families’ or ‘generations’ (but we don’t know why!)

HadronsLeptons 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 u̅u̅d̅ -1

antineutron u̅d̅d̅ 0

π+ ud̅ +1

π- uu̅ or dd ̅ 0

π0 du̅ -1

No ‘exotics’ (like qqqqq̅) have been found yet

InteractionsThe 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.

Force Boson Range Boson Mass Boson Spin

Electromagnetism (QED) photon ∞ 0 1

Strong Interaction gluon 10-15 0 1

Weak Interaction W+, W-, Z0 10-18 ~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).

Standard Model

Range of the ForcesThe 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 = Mc2, 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/Mc2

Since the photon has zero mass, the range of the EM force is infinite.The W boson has a mass of ~80 GeV/c2 the range of the weak force is:

∆x = 0.197 (GeV fm)/80(GeV ) ∼ 2 · 10−3 fm ∼ 10−18 m

useful to remember

�c ∼ 0.197 GeV · fm

What works where?

Weak EM Strong

Quarks

Charged Leptons

Neutral Leptons

√ √ √

√ √ ×

√ × ×

UnitsIn this class we will try to use the so called ‘natural’ units, where we set

� = c = 1Using these units energy, mass, and momentum all have the same units (of energy).

Example: proton mass 938.272 MeV

1 eV ∼ 1.602 · 10−19J

�c ∼ 197 MeV fm

α =e2

�c∼ 1

1371 eV ∼ 1.78 · 10−36 Kg

1 eV −1 ∼ 6.58 · 10−16 sec

1 eV ∼ 1.14 · 104 ◦K

938.272 · 106eV = 1.5 · 10−10J

1.5 · 10−10/(3 · 108)2 = 1.67 · 10−27Kg

Example: ionization of H atoms at ~13.6 eV

13.6 · eV ∼ 155 · 103K