## Physics 357/457 Spring 2011

(Chapter 1: getting started)

   

## Elementary particle:

   

### spin, charge & mass(energy)

Intrinsic property  “ constituents ” do not exist We don’t know how to account for the property by classical, quantum mechanical or relativistic (field theoretic) models

### what is charge?

Charge (Q) is a quantity we have defined in order to describe how certain particles (with this charge) interact. If the particles don’t interact in the prescribed way, they don’t have charge.

The force,

F

, between two charges (and the classical mathematical model, Coulomb’s Law, kQ 1Q2 /r 2 ), was derived experimentally.

Subsequent to this we developed the ideas of electric fields, electrostatic potentials, Ф, magnetic fields, model in physics.

B E= Q

1

F

, (produced by moving charges) and ultimately, Maxwell’s equations, the most rigorous These equations do not tell us what charge is.

In fact, as is usually the case, the model led us to a startling new model ( Quantum Electrodynamics ) which “explains” why two charges interact: they exchange photons (a new kind of particle with no charge and travelling with the speed of light).

Still, we do not know what charge is.

### charge

We do know that charge is “quantized”: it comes only in multiples of the electronic charge, e = 1.6 x 10 -19 Coulombs. Furthermore, the electron itself, although having both

mass and charge,

e , has a “size” so small that we are able only to say it is smaller than what we can detect!

This is indeed a phenomenon!

## the elementary particles

 

n

e

m n m t n t

### )

all have spin = ½  they are fermions that’s it!

### size

Like the electron, these elementary particles have “sizes” smaller than we can detect. Another phenomenon!

### -Q m

an antiparticle is like a particle going backwards in time

### Building composite particles – with sizes we can detect:

Quarks (q) can be bound together to form composite particles, like protons, neutrons and pions. But, we only find in the laboratory composite particles corresponding to quark-antiquark or qqq combinations.

These composite particles of quarks are held together by the strong force mediated by the exchange of gluons.

Like the electric charge producing Coulomb forces, the color “charge” is carried by the quarks.

# the forces

   

+

-

0

not yet observed

### )

all have spin = 1 (or 2 for graviton)  they are bosons

## some particle physics puzzles

th

### century, there are still many things which are not known.

Dark Energy: http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy /

## Dark Energy

http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy /

What Is Dark Energy?

More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe's expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 70% of the Universe is dark energy. Dark matter makes up about 25%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the Universe. Come to think of it, maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the Universe.

## Dark Matter

According to observations of structures larger than galaxies, as well as Big Bang cosmology dark matter accounts for 23% of the mass-energy density of the observable universe. In comparison, ordinary matter accounts for only 4.6% of the mass-energy density of the observable universe, with the remainder being attributable to dark energy. From these figures, dark matter constitutes 80% of the matter in the universe, while ordinary matter makes up only 20%.

http://chandra.harvard.edu/xray_astro/dark_matter/index.html

## Higgs Mechanism

The Higgs mechanism is a “model ” in which vector bosons ( W + , W and Z) can take on mass. Originally, they are massless. At a point in time, when kT ~ 100 GeV, they undergo a (symmetry breaking) transformation in which energy from the vacuum becomes particle mass. We will talk about it later.

It was proposed in 1964 independently and almost simultaneously by three groups of physicists: François Englert and Robert Brout;, [5] by Peter Higgs, Gerald Guralnik, C. R. Hagen, and Tom Kibble,.

[7] [6] (who was inspired by the ideas of Philip Anderson); and by

## How can we understand all this?

### Feynman: we have to “imagine” what is going on – that is the difficult part.

We “imagine” particle physics in terms of models, and one of these is the Standard Model (SM). Gluons and color charge and ideas of mass and the Higgs particle also require models – extensions of the SM.

Since we need to use E = mc mathematically.

2 (creation and annihilation of particles), we need to learn a bit about special relativity and how to express the important assumptions

## Where to find things

Particle chart source : http://www.cpepweb.org/cpep_sm_large.html

Particle chart p357/457: http://web.mst.edu/~hale/courses/Physics_357_457/particle_chart.2002.jpg

Quarks info: http://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html

Physics 357/457

Instructor: Barbara Hale, 205 Physics [email protected]

Text: Gordon Kane, Modern Elementary Particle Physics, Addison-Wesley, New York, Updated Edition, 1993.

It is not necessary to purchase a text.

Copies of the lecture notes will available.

Note below References which will be useful for extra reading on the topics A good reference for background material: David Griffiths, Introduction to Elementary Particle Physics, Wiley, New York.

Course Outline:

1. The elementary particles: Quarks and leptons 2. Field Theories, Quantum Electrodynamics (QED) and Feynman diagrams 3. Unification of the Weak and Electromagnetic Interactions 4. The Standard Model, gauge invariance and gauge bosons 5. The Gluons and the Strong Force 6. Grand unified theories and Beyond 7. Particle Physics and Cosmology

Course Structure

There will be two exams (100 points each) plus a comprehensive final (150 points). Homework sets will count as one exam (100 points). Total points = 200 + 100 + 150 = 450 points. 85% = A, 70% = B.

References for Elementary Particle Physics Topics

1. Donald Perkins, Introduction to High Energy Physics, Addison-Wesley, New York (1987) 3rd Ed. [description of experiments & results; uses little field theory] 2. R. Hagedorn, Relativistic Kinematics, Benjamin, New York (1964) 3. I.J.R. Aitchison, An Informal Introduction to Gauge Field Theories, Cambridge University Press, London (1982) 4. Chris Quigg, Gauge Theories of the Strong, Weak and Electromagnetic Interactions, Frontiers in Physics Lecture Notes Series 56, Benjamin/Cummings, Reading Massachusetts (1983) [advanced] 5. P. Becher, M. Bohm and H. Joos, Gauge Theories of Strong and Electroweak Interactions, Wiley, New York (1984) [advanced]

6. Elliot Leader and Enrico Predazzi, An Introduction to Gauge Theories and the 'New Physics', Cambridge University Press, Cambridge (1983) [advanced] 7. Kurt Gottfried and Victor F. Weisskopf, Concepts of Particle Physics, Oxford Press, New York (1984) [written for nonspecialists] 8. Particles and Fields, Readings from Scientific American, W. H. Freeman and Co. (1980) [ a good introduction; written for nonspecialists; see also other recent articles appearing in Scientific American] 9. F. Halzen and Alan D. Martin, Quarks and Leptons, John Wiley & Sons (1984) 10. New Particles Edited by J. L. Rosner, American Association of Physics Teachers (AAPT) Reprint Books, (1981) [good review of the history of particle discoveries up to 1981; also has some 'famous' reprints]

11. Steven Weinberg, The Discovery of Subatomic Particles, (a Scientific American Book) W. H. Freeman (1983) [historical approach; for nonspecialist] 12. L. B. Okun, Leptons and Quarks, North Holland, New York (1982) [ advanced ] 13. P. Collins, A. Martin and E. Squires, Particle Physics and Cosmology, John Wiley and Sons, New York (1991) 14. Stephen W. Hawking, A Brief History of Time, Bantam, New York (1988) 15. Sheldon Glashow, Interactions, Warner, New York (1988) 16. Steven Weinberg, The First Three Minutes, Bantam, New York (1977)

17. Quarks, Quasars and Quandries, Ed. G. Aubrecht, Published by American Assoc. Physics Teachers 5112 Berwyn Rd., College Park, MD 20740 (1987) (You can also purchase a poster from the publisher.) 18. Gordon Kane, Modern Elementary Particle Physics, Addison-Wesley, New York (1987), updated 1993.

19. David Griffiths, Introduction to Elementary Particle Physics, Wiley, New York (1987) 20. W. S. C. Williams, Nuclear and Particle Physics, Clarendon Press, Oxford (1991) 21. P. E. Hodgson, Nuclear Reactions and Nuclear Structure, Clarendon Press, Oxford (1971) 22. J. M. Blatt and V. F. Weisskopf, Theoretical Nuclear Physics, John Wiley & Sons, New York (1952)

23. John C. McGervey, Introduction to Modern Physics, Academic Press, New York Second Edition (1983) Chapters 10, 13-15 24. Arthur Beiser, Perspectives of Modern Physics, McGraw-Hill, New York (1969) Chapters 21-24 Old book, simple explanations.

25. Robert Eisberg and Robert Resnick, Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles, John Wiley and Sons (1985) Chapters 15 and 16 26. Robert Mann, An Introduction to Particle Physics and the Standard Model, CRC Press, 2010, good reference.

27. B. R. Martin and G. Shaw, Particle Physics, Wiley, NY 2008

MORE: Dark Matter, Dark Energy (NOVA): http://www.youtube.com/watch?v=NyZ-TH1OnLA&feature=related Dark Energy:

Feynman: Numbers 2