Schlüsselexperimente der Elementarteilchenphysik: Overview

 The of SM and their properties

 Interaction forces between particles

 Feynman diagrams

 Interactions: more

 Challanges ahead

 Open questions The :

What elementary particles are there?

The beginning…  : 1897, Thomson  have nuclei: 1911, Rutherford  : 1928, Dirac  : 1932, Chadwick; , Anderson  …lots of more particles…

Elementary particles

Ordinary :

Gauge : Mediators

Antiparticles: Same mass, and all other properties reversed! Energy & momentum

 Total relativistic energy: E2 = p2c2 + m2c4  Energy of a massless : E = pc  Rest energy: E = mc2

An interaction is possible only if the initial total energy exceeds the rest energy of the reaction products.

All interactions conserve total relativistic momentum! Conservation rules Conserved quantities in all particle interactions:

 Charge conservation

number (electron, , )

number

 Flavour (EM & ) conservation rules

Examples:

1. Electromagnetic:

2. Strong:

3. Weak: The Standard model:

Quantum Electrodynamics

Quantum Chromodynamics

Quantum Flavourdynamics Feynman diagrams

 Visualization & mathematics (not the paths of the particles!)

 Time upwards (convention)

 Particle as arrow in time-direction

as arrow in opposite direction

 Mediators as waves, lines or spirals

 EXAMPLES  Feynman diagrams EM: Best known of fundamental forces!

Many Feynman diagrams of same constituents.

Energy and momentum not conserved by one vertex alone.

Possible ”violation” in 1 vertex because of virtual particles. Cross sections & coupling

There are infinitely many Feynman diagrams for a particular process.

Feynmans golden rules: each vertex contributes to the scattering amplitude…

The strength of the coupling in a vertex is given by:

..an infinite contribution to scattering amplitude..?

Solution:

 Search for patterns; Eightfold way

 1964: theory (Gell-Mann,Zweig): Up, Down, Strange

 The and J/Ψ

 Tau, Bottom and Top J/Ψ: First particle with c quark. Computer reconstruction of its decay. Slac, Slide747

Finding a : - collision creates top which decay to W and b. Nature, June 2004

…but what about Ω- & the Pauli principle? Quantum Chromodynamics

 Quarks in nuclei held together by their colour

 Antiquarks have anticolour.

 A quark can ”be” either red, green or blue.

mediates the strong force. They have a colour and an anticolour. Self-interaction!

Only bound states of 2 or 3 quarks are observed; forming ”colourless states”. Cross-section & Coupling

 Srong coupling constant: running!

 Decreasing αs with increasing number of vertices  Asymptotic freedom: Coupling less at short distances; ”free” quarks inside the nucleus.  Quark confinement: Coupling increases at distances > nuclei  Reason that quarks only detected in colorless combinations 3-jet event from decaying Z0 into quark-antiquark + .  Large separation energy: Jets LEP, CERN Cross-section & Colour

Experimental evidence for the 3 colours (e-e+-colliders):

(e e ) 4 2 R (e e ) 2

(e e ) 3ECM

(e e hadrons) qi 2 2 1 2 1 2 2 , uds 3 3 3 3 10 11 , udsc , udscb 9 9 Quantum Flavourdynamics

6 flavours of quarks, 6 flavours of . All can interact weekly.

Flavour is conserved in strong and electromagnetic interaction. Flavour in weak interaction

Flavour is not conserved in weak interactions!

Neutron (β) decay Muon decay Observation

Problem: strong interaction screen the weak; easier to observe leptonic decay!

Problem: Neutral interaction is rarely observed, competing with much stronger EM interaction.

Weak interaction is more easily observed in flavour- changing processes…

Flavour change; for quarks also between generations Electroweak theory

 Why so heavy?  Glashow, Weinberg, Salam: EM and weak forces are unified at high energies!

Prediction: e 4 Weak coupling g = e MW,Z ~ ~ ~ 90 GeV G ~ 10-5 GeV-2 G G

M = 81GeV, M = 94 GeV Measured: W Z

Theory: responsible for their masses is the Higgs field, causing spontaneous symmetry breaking. Higgs ? (Peter Higgs, 1964) Higgs field &

 4-component field  3 components  massive W, Z  1 component  Higgs boson  Field VEV: 246 GeV   Symmetry breaking   Mass to all particles

Higgs boson is the only SM particle not yet observed. Above: Simulated Higgs boson decay, ATLAS.

Four possible processes involving a Higgs boson Three important examples

1) In the sun: Transmutation pn gives deuterium, which fusionates 2) Build-up of heavy nuclei ( + capture) 3) Stability of elementary particles A very special one…

Weak force not only breaks the flavour conserving…

Also: Non-conservation of parity! Parity = symmetry under inversion of space. Example: left-handed..

CP-invariance?...

…CPT-invariance? Standard Model

 Elementary particles: 6 leptons, 6 quarks, 12 bosons. Each have spin, charge and mass

 Fundamental forces: Conservation rules obeyed in all interactions EM: ; Strong: colour charge; gluons Weak: charged and neutral currents; W´s and Z

 Cross-sections and transition rates can be calculated and the range of forces estimated  better understanding of the forces

 Electromagnetic and weak interactions as one unified Limitations of SM

The Standard Model is confirmed by many different experiments. But fundamental questions are left open:

 Free parameters. What gives mass to the elementary particles? Intensive research of the Higgs particle at CERN (LHC).

 Why observed tiny between matter and antimatter? Reason that universe still exists…?  Are known elementary particles really elementary? So far…

 New elementary particles? Possible example: super-symmetric particles...

 More complete theory, including e.g. gravitational interaction?

Simulated Higgs event, ATLAS Beyond the Standard Model

 GUT: Electroweak QCD at 1016 GeV?  TOE?  SUSY?

Higher energies in experiments ↓ Heavier particles may be found ↓ Possible extension of Standard Model!

Final conclusion: Still a lot to be done! At last…