This thesis focuses on tau identification efficiencies in Monte Carlo simulations of various processes by implementing optimization techniques to determine optimal values for selection cuts on discriminant variables. Two sets of discriminants were studied: the first set consisted of only the Fisher discriminant, and the second set comprised the jet width and profile. Results obtained for the two sets are comparable for the central region (|eta| < 1.1) of the DO detector. For the forward region (|eta| ≥ 1.1), the optimization procedure did not yield optimal values for the set of variables used, suggesting that the signatures of the tau decay products in the forward regions is different from that in the central region, so that it appears that a different approach is required to identify the tau in the forward region. Given that the tau is to be identified through a reconstruction of its decay products, the complex interplay of the multitude of variables that need to be taken into account make the task of tau identification an ideal candidate for a multivariate analysis.

This thesis details the measurement of the pp¯ → W gamma + X → munugamma + X cross section at s = 1.96 TeV using the DO detector at Fermilab, in 134.5 pb -1 of integrated luminosity. From the photon E T spectrum limits on anomalous couplings of the photon to the W are obtained. At 95% confidence level, limits of -1.05 < Deltakappa < 1.04 for lambda = 0 and -0.28 <lambda < 0.27 for Deltakappa = 0 are obtained on the anomalous coupling parameters. The charge signed rapidity difference from the data is displayed, and its significance discussed.

The BNL-AGS Experiment 896 intended to measure neutral strange particles, including the Λ hyperon and Ks meson, by recognizing and reconstructing their charged decay daughters. As designed, E896 had no means of directly identifying the species of these daughters, which is a powerful tool for the rejection of certain background processes that can mimic the signatures of such decays. A Time-Of-Flight (TOF) detector system was thus added to this experiment to provide a means for direct particle identification of the charged decay products. The detectors were constructed and installed in the E896 apparatus, and experimental data was collected with these new detectors during several runs of the experiment both with single hadron beams and central collisions of gold nuclei at a beam momentum of 11.6 GeV/c/N. Software was written to calibrate the raw TOF detector information, to make the crucial association of tracks in the experiment to hits in the TOF system, and to optimize the timing performance and particle identification capabilities. This software was then used to form samples of reconstructed neutral strange particles under the more stringent criteria possible with the addition of the TOF information to the E896 data. The transverse mass distributions of Λ hyperons and Ks mesons from central 11.6 GeV/c/N Au+Au collisions, obtained from the analyses including direct daughter particle identification, will be presented and compared with other experiments and a theoretical model.

We have designed and implemented various components of the STAR Level 3 trigger, including a Sector Level 3, a Global Level 3 and a Sector Broker. In addition, we have implemented and studied a small prototype of the STAR tracking farm, using Intel dual Pentiums connected via an ethernet ring.

Experiments E799 Phase-II (E79911) and E832 of the Kaons at the TeVatron (KTeV) project at the Fermi National Accelerator Laboratory (Fermilab) were designed to study rare and CP-violating kaon decays. The experiments ran first during 1996 and 1997, and then again during 1999. This study focused on the E799II search for the lepton-flavor-violating decay mode KL → pi 0mu+/-e∓, and on its accompanying background decays, in the full set of 1996--7 and 1999 KTeV data. For the combined data sets, we calculated a new 90% confidence level branching ratio limit BR(KL → pi 0mu+/-e∓) < 3.37 x 10-10.

A study has been made of 400 GeV proton-nucleus collisions using a large acceptance calorimeter. The targets used were LH$\sb2$, He, Be, C, Al, Cu, Sn and Pb. A geometrically unbiased trigger efficient at selecting hadronic jet events was utilized. The A-dependence of the production of jet-like events is like that seen in high transverse momentum single- and di-hadron production. The dependence upon A of high E$\sb{\rm T}$ production is found to weaken with increasing planarity and when the observed event p$\sb{\rm T}$ balance improves. The flow of energy in the events is found to have a number of features in common with soft high-energy proton-nucleus collisions.

The Central Track Trigger (CTT), a subsystem of the DO collider detector at Fermilab, plays a key role in selecting which of the 1.7 million proton-antiproton beam crossing events are written to permanent storage. In order to provide constant monitoring of this triggering process, a software package, the CTT Examine, was created. This monitoring program provides useful immediate feedback about the output of the CTT and allows control room operators to diagnose many problems that might otherwise compromise data quality. The performance of the CTT is also directly tested by examining Z → ee events. The global efficiency of the CTT for finding high transverse momentum (pT) tracks in the run range [151831, 178310), taken between April 20th, 2002 and June 24th, 2003, is found to be 85.1 +/- 1.0%. The efficiency of the CTT with respect to offiine reconstructed tracks is 91.3 +/- 1.0%.

This thesis compares the performance of Probability Density Estimation and Neural Networks as applied to the identification of tau leptons and electrons at the DO detector for Run II. The theory behind each method of multivariate analysis is briefly described. The efficiencies of each of the methods are compared from analysis of Monte Carlo data samples, and optimal choices for the discrimination between signal and background are made.

We find evidence for an infrared fixed point in perturbative QCD using two complementary approximations: The Banks-Zaks expansion and the large-b resummations. Analyzing the $e\sp+e\sp-$ annihilation ratio and the polarized Bjorken-sum-rule of deep-inelastic-scattering, we use the recent calculation of the renormalization-group $\beta$-function to four-loops in QCD to confirm that the Banks-Zaks expansion is relevant when extrapolated from sixteen down to two light quark flavors. We also search for indications of infrared 'freezing' in the Borel-renormalon-inspired 'large-b' resummations. We find the 'large-b' approximation also indicates perturbative 'freezing' of the $e\sp+e\sp-$ annihilation ratio and the polarized Bjorken-sum-rule at leading order. Finally, we study the region, $n\sb{f}$ = 2, where the 'large-$n\sb{f}$' resummation and Banks-Zaks expansion complement one another. We conclude that there is strong evidence for the existence of a perturbative infrared fixed point in the Standard Model QCD.

Experiments E799 Phase-II (E799II) and E832 of the Kaons at the TeVatron (KTeV) project at the Fermi National Accelerator Laboratory (Fermilab), are in the process of studying rare and CP-violating kaon decays. The experiment ran during 1996 and 1997, and the resulting data are being analyzed. This study focuses on the E7991I search for the decay mode KL→p0m+/- e∓ , and its accompanying background decays, in approximately 60% of the 1996--7 KTeV data.