1. Standard Model of Particle Physics

2. History Work of 20th century physics “Finished” in 1973ish
Combination of relativity, quantum mechanics
List of all the fundamental particles and forces
How many can you name?

3. Original Particles Matter  Atoms Late 19th century/Early 20th century
Discovered with periodic table and trends
Late 19th century/Early 20th century
 Atoms made up of nucleus with electrons
1920s  Nucleus made up of protons and neutrons
1950s-1970s  Protons and neutrons made up of quarks
What about the forces??

4. Forces There are 4 fundamental forces Gravity Electromagnetism
Weak nuclear force
Strong nuclear force

5. Gravity
Weakest force
Attractive force between ALL objects with mass (energy)
Acts over long ranges (1/r2)
Responsible for motion of large scale objects like stars and planets

6. Electromagnetism Stronger than gravity (by a lot)
Attractive or repulsive force between objects with electric charge
Long range force (1/r2)
Responsible for forces of electric charges and magnetism

7. Weak nuclear force Slightly weaker than electromagnetism
Much more complicated interaction
Not attractive or repulsive but allows particles to change their type
Short range force – typically nuclear sized
Responsible for certain types of radioactive decay

8. Strong nuclear force Strongest force Always attractive
Acts over very short distances – within nuclei
Responsible for nuclear binding

9. Force particles Each force acts over a distance
Can explain using the idea that one particle sends out a messenger particle to another to communicate the force
Gravity – graviton
Electromagnetism – photon
Weak force – W & Z particles
Strong force - gluons

10. Classifying Particles
Need to classify based off various inherent properties of each particle
If we do this, can we see a pattern?
Can we make a thing like a periodic table for these particles?
Important properties:
Mass, electric charge, spin

11. Classifications of particles
Fermions
Definition: have half-integer spin (1/2,3/2,5/2,…)
Examples: most particles that you are familiar with
Bosons
Definition: have integer spin (0,1,2,3,…)
Examples: The force carrying particles

12. Fermions Leptons Quarks Charged: Electron, muon, tauon
Muon and tauon are heavier copies of electron
Neutral: 3 types of neutrinos
Feel the weak force
Quarks
All charged and feel the strong force
Up, down, charm, strange, top, bottom

13. Particles

14. Particles
EVERYTHING (so far) in the universe is made up of these particles in the chart
Almost everything made up of
Proton: 2 up quarks and 1 down quark
Neutron: 1 up quark and 2 down quarks
Electrons

15. Antimatter All particles have an opposite Called antimatter
Same mass, spin, ….
Opposite charge
Called antimatter
Electron  Positron
All others  anti – “name”
When matter and antimatter collide, they annhilate
Produce lots of energy  light

16. One more particle Standard model requires one more particle
Higgs boson:
Interacts with all the other particles to give them their effective mass
Like a dense fluid that slows them all down
Predicted in 1964 by 6 physicists (including Dr. Higgs)
Discovered on July 4th, 2012 in CERN
Won Nobel prize in 2013 (very fast)

17. Standard Model of Particle Physics
List of all the fundamental particles
A description of all the forces/interactions
Can write as an equation and make calculations and predictions to test
Most successful theory in the history of the mankind
Theory: (±86).
Experiment: (±28),
“Like measuring the distance from the Earth to the Moon to within a width of a human hair”

18. Standard Model Allows us to write down how all the forces behave
From this equation, I can calculate anything we have done all year
Including relativity and quantum mechanics

19. Theory of Everything? 2 main issues
Requires inputs – theory doesn’t predict certain things (like masses and interaction strengths)
At least 19 undetermined constants
Doesn’t include gravity
All known tricks of the standard model that make it work have failed to incorporate gravity in a similar way
Simpler terms: gravity and relativity work fine  gravity with relativity and quantum mechanics don’t get along

20. The ledge People have spent a lifetime trying to make a new theory
Want to incorporate gravity
Want to predict the masses/other constants from first principles
Most widely known/accepted version  string theory

21. String theory is “crazy”?
Basic idea: all particles are made up of tiny vibrating strings
How they vibrate gives them their identity
Incorporates gravity quite well
Craziness:
Requires 11 dimensions of spacetime to get it to work
Requires every particle to have a heavier secret particle with all the same properties except spin (supersymmetry)
Has different possible configurations, so can make it fit any data

22. Particle Physics What do people do?
Theorists: work on the calculations to test against known data or new calculations for future experiments
Experiments: smash things together and see what happens

23. Particle smashers
Basic idea: Take a particle and slam it REALLY fast into a target (or another particle) and see what comes out
3 major particle accelerators still operating
LHC at CERN
RHIC at Brookhaven National Lab
SLAC at Stanford

24. Particle Zoo
Have discovered hundreds of heavier particles over the last 30 years
Including the Higgs 3 years ago
Higher energy beams (more speed) means that you can create heavier particles

25. LHC/CERN LHC: Large Hadron Collider
Collides proton/anti-proton beams or Gold or Lead beams with each other
CERN: Center for European Nuclear Research (in French)

26. LHC

27. LHC
Tube Detector Data