arXiv subjects

Simon Capstick

Publications and source records attributed to Simon Capstick.

21 records · Page 2Linked to original sources

arXiv1996

Baryon Magnetic Moments in a Relativistic Quark Model

Magnetic moments of baryons in the ground-state octet and decuplet are calculated in a light-front framework. We investigate the effects of quark mass variation both in the current operator and in the wavefunctions. A simple fit uses single oscillator wavefunctions for the baryons and allows the three flavors of quark to have nonzero anomalous magnetic moments. We find a good fit to the data without allowing for strange quark contributions to the nucleon moments. A slightly better fit is obtained by allowing for explicit SU(3)_f breaking in the wavefunctions through a simple mechanism. The predictions for magnetic moments in our relativistic model are also much less sensitive to the values chosen for the constituent quark masses than those of nonrelativistic models. Relativistic effects can be of order 20% in general, and can alter familiar relationships between the moments based on SU(3)_f and a nonrelativistic treatment of spin.

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arXiv1994

Baryon Current Matrix Elements in a Light-Front Framework

Current matrix elements and observables for electro- and photo-excitation of baryons from the nucleon are studied in a light-front framework. Relativistic effects are estimated by comparison to a nonrelativistic model, where we use simple basis states to represent the baryon wavefunctions. Sizeable relativistic effects are found for certain transitions, for example, to radial excitations such as that conventionally used to describe to the Roper resonance. A systematic study shows that the violation of rotational covariance of the baryon transition matrix elements stemming from the use of one-body currents is generally small.

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arXiv1993

Quasi-Two-Body Decays of Nonstrange Baryons

We examine the decays of nonstrange baryons to the final states $Δπ$, $Nρ$, $Nη$, $Nη^\prime$, $Nω$, $N1/2^+(1440)π$, and $\Delta3/2^+(1600)π$, in a relativized pair-creation($^3P_0$) model which has been developed in a previous study of the $Nπ$ decays of the same baryon states. As it is our goal to provide a guide for the possible discovery of new baryon states at CEBAF and elsewhere, we examine the decays of resonances which have already been seen in the partial-wave analyses, along with those of states which are predicted by the quark model but which remain undiscovered. The level of agreement between our calculation and the available widths from the partial-wave analyses is encouraging.

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