Hands-on Particle Astrophysics

Introduction to Particle PhysicsPart II

Make up hadrons baryons: mesons:

Fermions (spin ½) Bosons (spin 1)

electromagnetic

strong

weak

Smallest Building Blocks (Fermion Interactions)

• Quarks:

• Neutrinos (neutral leptons):

• Charged leptons:

Smallest Building Blocks (Fermion Interactions)

• Quarks:

• Neutrinos (neutral leptons):

• Charged leptons:

Symmetries andconservation laws determine what is allowed

Smallest Building Blocks (Force Carrier Interactions)

g

g g gg

gg

Gluon self-interactions

W

W

WW

W

WW W

W W

Electroweak interactions

ZZ

Z

ZW

W W

W

Smallest Building Blocks (Force Carrier Interactions)

g

g g gg

gg

Gluon self-interactions

W

W

WW

W

WW W

W W

Electroweak interactions

ZZ

Z

ZW

W W

W

Symmetries andconservation laws determine what is allowed

Symmetries of Standard Model

• Excellent description of all interactions• Masses are not allowed!• Works well for photons/gluons• BUT W, Z massive• Fermions have mass!

• Way out?

Symmetries of Standard Model

• Excellent description of all interactions• Masses are not allowed!• Works well for photons/gluons• BUT W, Z massive• Fermions have mass!

• Way out? “Hide” the symmetry• Interactions with new particle obey symmetries• the “ground state” is not symmetric• Familiar example:

gravitational interactions: spherical symmetry(force: inverse square law)

and yet solar system not spherically symmetric

Simplest model – the standard model Higgs mechanism

• specific allowed interactions• allows massive W’s, Z’s• allows fermion masses

• specific relations among - masses of W’s, Z - interaction rates of various processes

+ verified by data over last 40 years!

• one spin 0 Higgs boson• specific

- production modes/rates - decay modes/rates

• unknown mass• discovered this year!• m = 125 GeV

Higgs self-interactions

H

H

H

H H H

H

HHH

H

H H H

W

f

ZW W WZ Z Z

f

Smallest Building Blocks (Higgs Interactions)

H

Higgs – fermion interactions

Higgs- force carrier interactions

ATLAS

CMS

LHC detectors