This thesis presents two measurements of the top quark pair production cross section at {radical}s = 1:96 TeV using data from the D0 experiment. Both measurements are performed in the dilepton final state and make use of secondary vertex b-tagging.

The author presents the measurement of p{bar p} {yields} Z/{gamma}* {yields} e{sup +}e{sup -} + X inclusive differential cross section as a function of boson rapidity. The data, which correspond to an integrated luminosity of 0.4 fb{sup -1}, were collected with D0 detector at Tevatron p{bar p} collider. At the Run II energy of {radical}s = 1.96 TeV, Z bosons are produced with rapidity out to {+-} 3. The cross section is measured in a mass range between 71 to 111 GeV for the allowed kinematic range.

Quantum Chromodynamics (QCD) is the gauge theory that governs the strong interactions between quarks and gluons inside hadrons like, for example, protons and neutrons. It shows two well established characteristics, related to the non-Abelian nature of the theory, that dominate its phenomenology: asymptotic freedom and color confinement. The dependence of the strong coupling, {alpha}{sub s}(Q{sup 2}), with the hard scale is such that it decreases with decreasing the distance between partons. This allows to perform precise theoretical calculations at large energy transfer (short distances) using perturbative QCD (pQCD). On the other hand, the strength of the interaction increases with the distance between partons and thus colored quarks and gluons are forced to be confined inside colorless hadrons.

In this thesis they report the measurement of ratios of branching fractions: {Beta}(B{sub s}{sup 0} {yields} D{sub s}{sup -}{pi}{sup +}{pi}{sup +}{pi}{sup -})/{Beta}(B{sup 0} {yields} D{sup -}{pi}{sup +}{pi}{sup +}{pi}{sup -}), and {Beta}(B{sup 0} {yields} D{sup -}D{sub s}{sup +})/{Beta}(B{sup 0} {yields} D{sup -}{pi}{sup +}{pi}{sup +}{pi}{sup -}), using 355 pb{sup -1} of data collected by CDF detector at the Tevatron p{bar p} collider at {radical}s = 1.96 TeV.