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.

The triggered photon structure function at center-of-mass energy 21 GeV is measured from the interaction $\gamma$p $\to$ jets. Descriptions of the experimental apparatuses are given and the physics goals of the experiment are discussed. The methods used to calculate the photon structure function $x\sb{\gamma}$ are discussed in detail, with particular attention given to Monte Carlo simulation. The energy of the photon beam is carefully analyzed and methods of understanding and compensating for multiple bremsstrahlung photons, among other beam effects, are determined. Results from experimental data are compared with theoretical predictions from both leading-order and next-to-leading-order calculations and with the results of another experiment. Some examination of other targets and other beam energies is made. We observe substantial disagreement between data and lowest order Monte Carlo. Experimental results are more consistent with NLO calculations. No experimental separation of direct and resolved photons is observed or predicted by calculation.

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