*Drawing Source: Fermi National Accelerator Laboratory

By: Joel Tenenbaum

What are Quarks?

Quarks are one of three types of fundamental particles that make up all matter and forces

*Drawing Source: Fermi National Accelerator Laboratory

Matter and energy are interchangeableMatter can be converted to energy by E=mc2, where m is the mass of the matter being converted (in kg), c is the speed of light (3 x 108m/s), and E is the amount of energy (in J). For example a 1kg block, if converted entirely into energy would be 9x1012kJ (about 21 megatons of TNT or 1600 Hiroshima nuclear bombs!)Mass no longer needs to be conserved because it can become energyEnergy does not need to be conserved because it can become massInstead, the sum of mass and energy (mass energy) is conservedThere are four different forces governing all interactions and each force is transmitted through its force particle

Gravity (graviton)

Electromagnetism (photon)

Weak Force (Weak Nuclear Force) (weak gauge bosons)

Strong Force (Strong Nuclear Force) (gluon)

Three Groups of Elementary Particlesi

Bosons – particles that transmit forces (Gluon is responsible for Strong interactions)

Leptons – particles that do not participate in Strong interactions

Quarks – particles that individually participate in Strong interactions, cannot be individually isolated

i. Stanford Linear Accelerator Center

Quark Rest Mass* (in MeV/c2)1

Charge1 Date Discovered2

Up 5 2/3 1968

Down 9 -1/3 1968

Strange 170 -1/3 1964

Charm 1400 2/3 19743

Bottom 4400 -1/3 1977

Top 174000 2/3 1995

*Apparent masses are approximate numbers only, your quark masses may vary 1Source: NOVA, The Elegant Universe 2Fermi National Accelerator Laboratory

3Source: HyperPhysics, ©2000 CR Nave, Georgia State University

Mass?How do you find the mass of a particle you can’t isolate?

Physicists find the apparent mass of a quark based on its tendency to be acceleratedi.

i Stanford Linear Accelerator Center

Accelerators

*Drawing Source: Fermi National Accelerator Laboratory

Electric fields accelerate the proton and anti-protons in opposite directions

Magnetic fields keep the particles in a circular path

Electric fields accelerate the proton and anti-protons in opposite directions

•In the case of the up and down quarks, the most salient evidence was in the inelastic scattering of electrons aimed at neutrons or protons, suggesting a substructure of each.i

•The existence of the strange quark was postulated when research was being conducting with proton-nucleus collisions. The “lambda” particle (discovered in 1947) produced from these collisions could not have been made up of only up and down quarks based on color neutrality, mass, and chargeii.

•The psi/J particle discovered in 1974 could not have been made from the existing 3 quarks for similar reasons.

•Even more energetic proton collisions yielded the upsilon particle, which was concluded to be made of bottom quarks for similar reasons.

i Deutcsches Elektronen-Synchotron ii HyperPhysics, ©2000 CR Nave, Georgia State University

•The top quark was discovered by analyzing the particles it very quickly decays into

Illustrations: Fermi National Accelerator Laboratory

A Proton/Anti-Proton Collision

• Negatively charged electron circles around in circular orbits

• Much more massive nucleus contains electrically neutral neutrons and positively charged protons

Simplified View of Atom

Drawing source: ©Encyclopaedia Britannica 1998

Extended View Electron is still fundamental particle (lepton) Proton and neutron now thought of as being

collection of quarks and the gluons hold them together

Kind of….The quark model is the best explanation for the observed phenomena, but no quark has ever been directly observed because of…

Quarks are bound very tightly inside larger particles meaning it takes a lot of energy to separate them

If you put energy into the system, it produces quark-antiquark pairs long before there is enough energy to separate a quark

A Proton Energy is put into the proton to separate a quark

Before there is enough energy to separate the quark, the energy goes into producing quark-antiquark mesons

Drawing source: HyperPhysics, ©2000 CR Nave, Georgia State University

"Truth decays into beauty, while beauty soon becomes merely charm. Charmends up as strangeness, and even that doesn't last, but up and down are forever." - The Laws of Physics (James Walden)1•Top and bottom were allegedly called “truth” and “beauty” at one

point, which made the above quote a valid description of quark behavior

•Apparently, the names “truth” and “beauty” were too quaint even for the physicists who study them – the ‘t’ and ‘b’ came to stand for “top” and “bottom” instead

The name is said to have been taken by Murray Gell-Mann from the novel Finnegan's Wake by James Joyce2. The line in which the word “quark” appears is, “Three quarks for Muster Mark…”. Gell-Mann received the 1969 Nobel prize for his work in quantum physics.

1 Source: Raycomm.com, Peter Bancel

2 Source: HyperPhysics, ©2000 CR Nave, Georgia State University

SourceSourcess

• Deutches Electronen-Synchotron, ©2003, Deutches Electronen-Synchotron, ©2003, http://www.desy.de/f/hera/engl/chap1.htmlhttp://www.desy.de/f/hera/engl/chap1.html

• Raycomm.com, Peter Bancel, ©2003, Raycomm.com, Peter Bancel, ©2003, http://www.raycomm.com/techwhirl/archives/9512/techhttp://www.raycomm.com/techwhirl/archives/9512/techwhirl-9512-00470.htmlwhirl-9512-00470.html

• ““The Elegant Universe”, NOVA Public Broadcasting Service The Elegant Universe”, NOVA Public Broadcasting Service (PBS), ©2003, http://www.pbs.org/wgbh/nova/elegant/(PBS), ©2003, http://www.pbs.org/wgbh/nova/elegant/

• Stanford Linear Accelerator Center, ©2003, Stanford Linear Accelerator Center, ©2003, http://www2.slac.stanford.edu/vvc/Default.htmhttp://www2.slac.stanford.edu/vvc/Default.htm

• Fermi National Accelerator Laboratory, ©2001, Fermi National Accelerator Laboratory, ©2001, http://www.fnal.gov/http://www.fnal.gov/

• HyperPhysics, ©2000 CR Nave, Georgia State University, HyperPhysics, ©2000 CR Nave, Georgia State University, http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

• ““Rutherford Atomic Model”, Encyclopedia Britannica online, Rutherford Atomic Model”, Encyclopedia Britannica online, ©1997 http://www.britannica.com/nobel/micro/514_59.html©1997 http://www.britannica.com/nobel/micro/514_59.html