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Heavy Pentaquarks in the Diquark Model and the Large Nc Expansion


Wessling, Margaret Ellen (2005) Heavy Pentaquarks in the Diquark Model and the Large Nc Expansion. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6812-4G64.


Recent experimental evidence for the Θ⁺(1540) has given rise to much theoretical interest in exotic baryons. The Θ⁺ is a baryon that has strangeness S=+1, meaning that it contains an anti-strange quark. Thus it cannot be constructed from three quarks, unlike all other known baryons; it needs at least an extra quark-antiquark pair. It is usually modeled as a pentaquark state in the 10 bar representation of flavor SU(3), with flavor content s̅uudd.

This thesis considers possible heavy pentaquarks, in which the antiquark is charmed or bottom rather than strange. In the context of the diquark model of Jaffe and Wilczek, it is argued that negative-parity pentaquarks of this type may be lighter than their positive-parity counterparts, and hence are likely to be stable against strong decay. Estimates are made for their masses, and their weak decays are discussed. Isospin relations are found between the decay rates for different possible decay channels.

Negative-parity heavy pentaquarks are also considered in a less model-dependent way, in the context of a 1/Nc expansion, where Nc is the number of colors. Heavy quark effective theory is also employed. Mass relations are found between the mass splittings of heavy pentaquarks and those of nonexotic baryons, and SU(3)-breaking corrections to these relations are computed. The results could be helpful in interpreting experimental data if heavy pentaquarks are observed.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:exotic baryons; heavy quark effective theory; large number of colors
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Wise, Mark B.
Group:Caltech Theory
Thesis Committee:
  • Wise, Mark B. (chair)
  • Porter, Frank C.
  • Schwarz, John H.
  • Frautschi, Steven C.
Defense Date:16 May 2005
Record Number:CaltechETD:etd-05232005-174621
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1976
Deposited By: Imported from ETD-db
Deposited On:24 May 2005
Last Modified:22 May 2020 22:24

Thesis Files

PDF (wessling_thesis.pdf) - Final Version
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