Quarks

1
Quarks

• By John Hennen

2
Outline

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

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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

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History of Quarks

• Theyve been around for a very long time

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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.

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Origin of the Word

• Gell-mann for whatever reason, came to enjoy
  saying Kwork
• Came upon James Joyces 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.

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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

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The November Revolution

• 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

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The J-Psi Particle

• Also called Charmonium
• Consists of a Charmed Quark and AntiQuark
• Mass of 3.1 GeV
• Half-life of 7.210-21s, 1000 times longer than
  expected
• Through inspection of the particle and its
  interactions, Quarks were finally found
  experimentally.

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Properties of Quarks

• 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

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Charge and Mass

• 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
• T2/3e 174.3 /- 5.1 GeV (180 times the mass of
  a proton)

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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

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The Bag Model

• 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.

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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
Pentaquark

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

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Works Cited

• Physics News Update 216 March 3 1995 American
  Institute of Physics 11/14/07 www.aip.org/pnu/1995
  /physics.htm1
• 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)