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Quarks

Quarks. By John Hennen. Outline. What Are Quarks? History of Quarks Properties Particles Confinement Recent Research Works Cited. What are they?. Subatomic Particles Classified as Fermions Make up all Hadrons (Mesons + Baryons) Substructure of Neutrons and Protons Come in 6 Flavors

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Quarks

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  1. Quarks By John Hennen

  2. Outline • What Are Quarks? • History of Quarks • Properties • Particles • Confinement • Recent Research • Works Cited

  3. What are they? • Subatomic Particles • Classified as Fermions • Make up all Hadrons (Mesons + Baryons) • Substructure of Neutrons and Protons • Come in 6 Flavors • Up, Down, Strange, Charm, Bottom, Top • Have Integer Spin • Non integer Charge

  4. History of Quarks • They’ve been around for a very long time

  5. History of the Discovery of Quarks • Murray Gell-mann and Kazuhiko Nishijima Proposed their existence in 1961 • A new classification of Hadrons • Based in Symmetry of Current Algebra • For its mathematical sense it was accepted in the Theoretical community, but not by the Experimental community.

  6. Origin of the Word • Gell-mann for whatever reason, came to enjoy saying “Kwork” • Came upon James Joyce’s “Finnigans Wake” • “Three Quarks for Muster Mark” • Intrigued by the use of three and the near pronunciation to Kwork, Gell-mann decided to refer to the theorized particles as Quarks.

  7. Original Theory on the Existence of Quarks • Analytical quark model was Fermionic. As such scientists believed they were stable and must exist in isolation. • Genoa Experiment • Stanford Experiment • No convincing evidence

  8. Monday 11/11/1974 Discovery of Charmed Quarks Opened all areas of HEP Research Initial Breaking of the Ice led to experimental discovery of all other Quark Types (except Top) within a few years This was called the November Revolution Burton Richter of SPEAR program at Stanford University and Samuel Ting of the Brookhaven Proton Synchrotron won the Nobel Prize in Physics in 1976 for their simultaneous discoveries of the J-Psi particle The November Revolution

  9. The J-Psi Particle • Also called “Charmonium” • Consists of a Charmed Quark and AntiQuark • Mass of 3.1 GeV • Half-life of 7.2*10^-21s, 1000 times longer than expected • Through inspection of the particle and its interactions, Quarks were finally found experimentally.

  10. Neutrons, as all Baryons, are made of three Quarks. 1 up 2 down (protons have 2 up 1 down) Each Down has a charge of –(1/3)e while each Up has a charge of +(2/3)e so total electric charge is 0 Properties of Quarks

  11. U: +2/3e 1.5-4.0 MeV D: -1/3e 4-8 MeV S:-1/3e 80-130 MeV C: +2/3e 1150-1350 MeV B: -1/3e 5GeV T:+2/3e 174.3 +/- 5.1 GeV (180 times the mass of a proton) Charge and Mass

  12. Confinement of Quarks • Quarks do typically exist freely in the universe and have not since the Big Bang. • A color force holds them together with Gluons • Even Quarks ripped from a Hadron cannot be observed as free. • “free” quarks quickly form quark anti-quark pairs • A common model is the Bag model

  13. When energy is placed into a Hadron to remove a Quark it is stretched and “explodes” into many quark and antiquark pairs. The energy required to sever a group of Quarks is greater than the energy for Pairing. The Bag Model

  14. Relatively recent research • The final quark to actually be discovered experimentally was the top quark discovered in 1995 in the Fermilab Tevatron. • The Top quark is extremely massive and decays into other particles before it can create a quark antiquark pair. Thus it was the first “free” quark ever experimentally observed.

  15. In 2003 discovered independently Osaka university Jefferson Accel. Facility Gamma radiation Lasted 10^-20s Analyzing the neutrons and k mesons implied a pentaquark. Pentaquark

  16. Works Cited • Physics News Update #216 March 3 1995 American Institute of Physics 11/14/07 www.aip.org/pnu/1995/physics.htm#1 • Quark Wikipedia 11/12/07 http://en.wikipedia.org/wiki/Quark • Pentaquark Wikipedia 11/12/07 http://en.wikipedia.org/wiki/Pentaquark • Pickering, Andrew. Constructing Quarks. Edinburgh, Edinburgh University Press, 1984 • Andrew Pickering. “The Hunting of the Quark.” Isis. Vol. 72 no. 2 1981: (216-236)

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