Scope of the Thesis

This thesis presents measurements of the masses and widths of the baryons. Mass measurements for all three states (, , and ) are given while width measurements are given for only the and . An observation of the decays $\sigcstar \to \lc \pion^\pm$ without a detailed analysis is also presented. Finally, a search for decays of doubly charmed baryons in the decay modes $\xicc \to \lc \kaon + n\pion$ is also discussed. These analyses are based on data from the FOCUS¹ experiment, a high statistics charm photoproduction experiment at Fermi National Accelerator Laboratory (Fermilab).

This introductory chapter is an overview of the of elementary particle physics, the theory which describes the nature of matter and its interactions. The theory governing weak interactions and properties of charmed particles, especially baryons is also covered. More detailed theoretical models, calculations, and predictions relating to the topics of this thesis are presented in the relevant chapters.

In beam the Fermilab Tevatron accelerator complex and the production of high energy photons for use by the FOCUS experiment is described in some detail.

spec describes the FOCUS experimental apparatus in detail. The individual detector elements are covered, with special emphasis on those most important to the analyses presented in this thesis. spec also contains information on the data acquisition system used to collect detector information.

In recon the reconstruction algorithms used by the experiment are explained. These algorithms transform raw detector information into tracking information, particle identification, and calorimetry information. The processing and reduction of data into summary sets suitable for individual analyses is also explained.

select covers the methods used to select $\pkpi$candidates² used in later analyses. In addition, the analysis techniques common to the other analyses are described and many cuts used later are defined.

sc_mass is concerned with measurements of the masses of baryons. We present $\sigc - \lc$ mass difference measurements for each of the three states. These mass differences are found to be $\mdsczlc = \ensuremath{167.54}\xspace\pm \ensuremath{0.19}\xspace\pm \ensuremath{0.34}\xspace~\mevcc$, $\mdscplc = \ensuremath{168.03}\xspace\pm \ensuremath{1.01}\xspace\pm \ensuremath{0.30}\xspace~\mevcc$, and $\mdscdlc = \ensuremath{167.59}\xspace\pm \ensuremath{0.20}\xspace\pm \ensuremath{0.27}\xspace~\mevcc$. (The first errors are statistical, the second are systematic.) We also determine mass differences between the states, which are especially sensitive probes of the various theoretical models. The measurements of the $\scz - \lc$, $\scd -\lc$, and $\scz -\scd$ mass differences represent improvements on the world's current best measurements.

sc_width details the measurement of the natural widths of the and baryons. In this analysis we determine that $\Gamma(\scz) = 2.58\xspace \pm 0.79\xspace\asserror{0.51}{0.55}$ and $\Gamma(\scd) = 2.53\xspace\pm 0.77\xspace \asserror{0.51}{0.56}$ . This analysis is challenging due to limited statistics and because the natural width is narrow compared to the experimental resolution.

sc_star presents an observation of two broad states decaying to $\lc \pion^\pm$ which are interpreted as states. The measured properties of these states are found to be $m_{\sczs} - m_{\lc} = 232.7 \pm 1.2~\mevcc$, $\Gamma(\sczs) = 9.4\pm3.7~\mevcc$, $m_{\scds}- m_{\lc} = 234.2 \pm 1.5~\mevcc$, and $\Gamma(\sczs) = 23.6\pm4.5~\mevcc$, but a detailed analysis is not performed. As a consequence, the statistical errors are not optimized and no systematic error is determined.

In doublec a search for the doubly charmed baryons and is described. No doubly charmed baryons have been observed to date, but they are needed to complete the spectrum of charmed baryons. We do not observe any evidence for doubly charmed baryon production in FOCUS.

Several appendices are also included. dpi0 presents a study of low momentum, or ``soft,'' reconstruction methods which bears on the mass difference analysis. syst describes the methods used to calculate systematic errors in all the analyses. glossary is a glossary of terms used throughout the thesis.