Doctor of Philosophy (Ph.D.)
Christopher D Carone
An extensive study of the production, decay and spectroscopy of pentaquarks has been done in this dissertation. at the time of this writing, the existence of the pentaquark has not been conclusively established. New experimental results for the pentaquark will come in the months ahead. A brief review of the current experimental status of the pentaquark is given in the Introduction. The pentaquark states are analyzed using the constituent quark model with the lowest-lying pentaquark multiplet shown to be an antidecuplet. The mass splittings within the antidecuplet emerge from spin-color and spin-flavor interactions between constituents and from hidden strangeness in the antidecuplet, rendering the nucleon-like states heavier than the S=1 theta+ state. In order to calculate such interactions, decompositions of the quark model color-flavor-spin-orbital wave functions must be obtained. A spin-1/2 state is assumed in this work. Assigning all quarks to the orbital ground state yields an odd parity state, while giving one quark a unit of orbital angular momentum leads to a state with even parity. Dominant spin-flavor interactions render certain parity-even pentaquark states lighter than states with all quarks in the spatial ground state. In this even-parity scenario, it is possible to explain the unusually narrow width of the theta+ by computing the overlap of this state with the kinematically allowed final states. The results are numerically small. Decays of other states within the antidecuplet are related to the theta+ by SU(3) symmetry and phase space. The photo-production of the theta+(1540) resonance on the nucleon, through K and K* Regge exchanges is also studied in this thesis. The size of the cross sections for the gamma n → K-theta+ and gammap → K?Â»0theta + reactions are compared and their sensitivity to the spin-parity assignments JP = 1/2+/-, 32 +/- for the theta+ resonance is investigated. This model allows us to estimate the cross sections corresponding to a given upper bound on the theta+ width. The cross sections on the neutron are found to be around a factor 5 larger than the ones on the proton, due to the presence of charged Kaon exchange. Furthermore, the photon asymmetry is found to display a pronounced sensitivity to the parity of the theta +, making it a promising observable for determining the spin and parity of the theta+ resonance.
© The Author
Kwee, Herry, "Spectroscopy, production and decays of pentaquarks" (2006). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539623492.