Roper resonance

The Roper resonance, also known as P₁₁(1440), is an unstable baryon state/particle with a mass of about 1,440 MeV/c² and with a relatively wide full Breit-Wigner width Γ≈300 MeV/c². It contains three quarks (up (u) or down (d)) with total spin J=1/2 and total isospin I=1/2. In the quark model it is considered to be a radially excited three-quark state with radial quantum number N=2 and positive parity. The Roper Resonance has been a subject of many studies because its mass is actually lower than three-quark states with radial quantum number N=1.

Discovery

The Roper resonance was discovered in 1963 by a computer fit of particle-scattering theory to large amounts of pion-nucleon scattering data. The analysis was done on computers at Lawrence Livermore National Laboratory for Ph.D. thesis work of [http://arts.bev.net/roperldavid/ L. David Roper] at Massachusetts Institute of Technology under the direction of [http://www-tech.mit.edu/V113/N8/feld.08n.html Prof. Bernard Taub Feld] at MIT and [http://www.garfield.library.upenn.edu/essays/v13p009y1990.pdf Dr. Michael J. Moravcsik] at LLNL. The computer code was developed by [http://www.gwu.edu/~physics/fcda2.htm Richard Allen Arndt] and Robert M. Wright.

Decay

Because of the relatively large full width, which according to uncertainty principle means a shorter lifetime, the Roper resonance decays into a system consisting of other hadrons with sum of the masses less than the mass of the original state. The Roper resonance decays most of the time via the strong force into an ordinary nucleon plus a pion, nucleon plus two pions, or Δ plus a pion.

References

"Evidence for a P₁₁ Pion-Nucleon Resonance at 556 MeV", L. D. Roper, Phys. Rev. Letters 12, 340 (1964)

[http://arts.bev.net/roperldavid/roperres.htm "The Development of Pion‑Nucleon Scattering Analysis: A Personal History of Discovery" by R. Gordon Moorhouse and L. David Roper]

[http://www.dogpile.com/info.dogpl/search/redir.htm?r_fcid=415&r_fcp=top&advanced=1&top=1&nde=1&qcat=web&q_all=&q_phrase=Roper+Resonance&q_any=&q_not=&topadvancedsubmit=Go+Fetch%21&lang=&tviewby=1&qk=20&qafterm=01&qafterd=01&qaftery=1990&qbeforem=12&qbefored=05&qbeforey=2006&domaint=&adultfilter=moderate Search for web articles about the Roper Resonance]

Composition

See also

* List of baryons
* particle physics
* quark model