Knowledge of the electric and magnetic elastic form factors of the nucleon is essential for an understanding of nucleon structure. Of the form factors, the electric form factor of the neutron has been measured over the smallest range in Q{sup 2} and with the lowest precision. Jefferson Lab experiment 02-013 used a novel new polarized {sup 3}He target to nearly double the range of momentum transfer in which the neutron form factor has been studied and to measure it with much higher precision. Polarized electrons were scattered off this target, and both the scattered electron and neutron were detected. G{sup n}{sub E} was measured to be 0.0242 ± 0.0020(stat) ± 0.0061(sys) and 0.0247 ± 0.0029(stat) ± 0.0031(sys) at Q{sup 2} = 1.7 and 2.5 GeV{sup 2}, respectively.

The inclusive production of b-jets with a Z boson is an important background to searches for the Higgs boson in associated ZH {yields} llb{bar b} production at the Fermilab Tevatron collider. This thesis describes the most precise measurement to date of the ratio of inclusive cross sections {sigma}(p{bar p} {yields} Z + b-jet)/{sigma}(p{bar p} {yields} Z + jet) when a Z boson decays into two electrons or muons. The measurement uses a data sample from p{bar p} collisions at the center of mass energy {radical}s = 1.96 TeV corresponding to an integrated luminosity of 4.2 fb{sup -1} collected by the D0 detector. The measured ratio {sigma}(Z + b-jet)/{sigma}(Z + jet) is 0.0187 {+-} 0.0021(stat) {+-} 0.0015(syst) for jets with transverse momentum p{sub T} > 20 GeV and pseudorapidity |{eta}| {le} 2.5. The measurement is compared with the next-to-leading order theoretical predictions from MCFM and is found to be consistent within uncertainties.

This dissertation describes a measurement of the mass of the top quark using a method developed by G. Goldstein and R.H. Dalitz. It is based on 2.0 fb{sup -1} of data collected by the Collider Detector Facility at Fermi National Accelerator Laboratories. Di-lepton events were observed from colliding protons with anti-protons with {radical}s = 1.96 TeV in the Tevatron Collider. A total of 145 candidate events were observed with 49 expected to be from background. These events include two neutrinos which elude detection. The method begins by assuming an initial top quark mass and solves for the neutrino momenta using a geometrical construction. The method samples over a range of likely top quark masses choosing the most consistent mass via a likelihood function. An important distinguishing feature of this method from others is its lack of dependence on the missing transverse energy, a quantity that is poorly measured by the experiment. This analysis determines the top quark mass to be M{sub top} = 172.3 {+-} 3.4(stat.) {+-} 2.0(syst.) GeV/c{sup 2} (M{sub top} = 170.5 {+-} 3.7(stat.) {+-} 1.8(syst.) GeV/c{sup 2} with b-tagging).

In the Standard Model of particle physics, the Higgs boson generates elementary particle masses. Current theoretical and experimental constraints lead to a Higgs boson mass between 114.4 and 158 GeV with 95% confidence level. Moreover, Tevatron has recently excluded the mass ranges between 100 and 109 GeV, 158 and 175 GeV with 95% confidence level. These results gives a clear indication to search for a Higgs boson at low mass. The D0 detector is located near Chicago, at the Tevatron, a proton-antiproton collider with an energy in the center of mass of 1.96 TeV. The topic of this thesis is the search for a Higgs boson in association with a Z boson. This channel is sensitive to low mass Higgs boson (<135 GeV) which has a branching ratio H {yields} bb varies between 50% and 90% in this mass range. The decay channel ZH {yields} {nu}{bar {nu}}b{bar b} studied has in the final state 2 heavy-flavor jets and some missing transverse energy due to escaping neutrinos. The heavy-flavor jets identification ('b-tagging') is done with a new algorithm (SLTNN) developped specifically for semi-leptonic decay of b quarks. The Higgs boson search analysis was performed with 3 fb{sup -1} of data. The …

The Standard Model of particle physics provides an excellent description of particle interactions at energies up to {approx}1 TeV, but it is expected to fail above that scale. Multiple models developed to describe phenomena above the TeV scale predict the existence of very massive, vector-like quarks. A search for single electroweak production of such particles in p{anti p} collisions at a center-of-mass energy of 1.96 TeV is performed in the W+jets and Z+jets channels. The data were collected by the D0 detector at the Fermilab Tevatron Collider and correspond to an integrated luminosity of 5.4 fb{sup -1}. Events consistent with a heavy object decaying to a vector boson and a jet are selected. We observe no significant excess in comparison to the background prediction and set 95% confidence level upper limits on production cross sections for vector-like quarks decaying to W+jet and Z+jet. Assuming a vector-like quark -- standard model quark coupling parameter {tilde {kappa}}{sub qQ} of unity, we exclude vector-like quarks with mass below 693 GeV for decays to W+jet and mass below 449 GeV for decays to Z+jet. These represent the most sensitive limits to date.