This thesis describes a search for the decay B{sup -} {yields} {tau}{sup -}{bar {nu}}{sub {tau}} in 231.8 x 10{sup 6} {Upsilon}(4S) decays recorded with the BABAR detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed exclusive semi-leptonic B decay (B{sup +} {yields} {bar D}*{sup 0} {ell}{sup +}{nu}{sub {ell}}) is selected, and in the recoil a search for B{sup -} {yields} {tau}{sup -} {bar {nu}}{sub {tau}} signal is performed in the following {tau} decay modes: {tau}{sup -} {yields} e{sup -}{bar {nu}}{sub e}{nu}{sub {tau}}, {tau}{sup -} {yields} {mu}{sup -}{bar {nu}}{sub {mu}}{nu}{sub {tau}}, {tau}{sup -} {yields} {pi}{sup -}{nu}{sub {tau}}, {tau}{sup -} {yields} {pi}{sup -}{pi}{sup 0}{nu}{sub {tau}}, and {tau}{sup -} {yields} {pi}{sup -}{pi}{sup +}{pi}{sup -}{nu}{sub {tau}}. They find no evidence of signal, and they set a preliminary upper limit on the branching fraction of {beta}(B{sup -} {yields} {tau}{sup -}{bar {nu}}{sub {tau}})

We present a search for the decay B− →?− {bar {nu}}{sub?} in a sample of 88.9 x 106 B{bar B}pairs recorded with the BABAR detector at the SLAC B-Factory. One of the two B mesons from the?(4S) is reconstructed in a hadronic or a semileptonic final state and the decay products of the other B in the event are analyzed for consistency with a B− →?− {bar {nu}}{sub {tau}} decay. We find no evidence of a signal and set an upper limit on the branching fraction of?(B− → {tau}− {bar {nu}}{sub {tau}})

We present a search for the decay B{sup +} {yields} {tau}{sup +}{nu}{sub {tau}} in 88.9 x 10{sup 6} {Upsilon}(4S) decays recorded with the BABAR detector at the SLAC B-Factory. A sample of semi-exclusive, semi-leptonic B decays (B{sup -} {yields} D{sup 0}{ell}{sup -}{bar {nu}}{sub {ell}}X), where X is either a photon, {pi}{sup 0}, or nothing, is used to identify the daughter particles that are associated with the other B meson in each event. These particles are searched for evidence of a one-prong leptonic B{sup +} {yields} {tau}{sup +}{nu}{sub {tau}} decay. For this data sample we set a preliminary upper limit on the branching fraction of {Beta}(B{sup +} {yields} {tau}{sup +}{nu}{sub {tau}})

We present a search for the decay B[sup+][yields][tau][sup+][nu][sub[tau]] in 88.9 x 10[sup 6][Upsilon](4S) decays recorded with the BABAR detector at the SLAC B-Factory. A sample of semi-exclusive, semi-leptonic B decays (B[sup -][yields] D[sup 0][ell][sup -][bar[nu]][sub[ell]]X), where X is either a photon, [pi][sup 0], or nothing, is used to identify the daughter particles that are associated with the other B meson in each event. These particles are searched for evidence of a one-prong leptonic B[sup+][yields][tau][sup+][nu][sub[tau]] decay. For this data sample we set a preliminary upper limit on the branching fraction of[Beta](B[sup+][yields][tau][sup+][nu][sub[tau]])

The authors present a search for the decay B[sup +] --> [tau][sup +][nu][sub [tau]] in 124.1 x 10[sup 6] [Upsilon](4S) decays recorded with the BABAR detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed exclusive semi-leptonic B decay (B[sup -] --> D*[sup 0][ell][sup -][bar [nu]][sub [ell]]) is selected, and in the recoil a search for B[sup +] --> [tau][sup +][nu][sub [tau]] signal is performed. The [tau] is identified in the following channels: [tau][sup +] --> e[sup +][nu][sub e][bar [nu]][sub [tau]] --> [mu][sup +][nu][sub [mu]][bar [nu]][sub [tau]], [tau][sup +] --> [pi][sup +][bar [nu]][sub [tau]], [tau][sup +] --> [pi][sup +][pi][sup 0][bar [nu]][sub [tau]], [tau][sup +] --> [pi][sup +][pi][sup -][pi][sup +][bar [nu]][sub [tau]]. The authors find no evidence of signal, and they set a preliminary upper limit on the branching fraction of B(B[sup +] --> [tau][sup +][nu][sub [tau]]) 4.3 x 10[sup -4] at the 90% confidence level (CL). This result is then combined with a statistically independent BABAR search for B[sup +] -- [tau][sup +][nu][sub [tau]] to give a combined preliminary limit of B(B[sup +] --> [tau][sup +][nu][sub [tau]])

The authors present a search for the decay B -->?+?{sub?} in 124.1 x 106?(4S) decays recorded with the BABAR detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed exclusive semi-leptonic B decay (B− --> D*°l−{bar?}{sub {ell}}) is selected, and in the recoil a search for B+ -->?+?{sub?} signal is performed. The? is identified in the following channels:?+ --> e+?{sub e}{bar?}{sub?} -->?+?{sub {mu}}{bar?}{sub?},?+ -->?+{bar {nu}}{sub?}, {tau}+ -->?+?°{bar {nu}}{sub {tau}}, {tau}+ -->?+?−?+{bar {nu}}{sub {tau}}. The authors find no evidence of signal, and they set a preliminary upper limit on the branching fraction of B(B+ --> {tau}+{nu}{sub {tau}}) 4.3 x 10−4 at the 90% confidence level (CL). This result is then combined with a statistically independent BABAR search for B+ -- {tau}+{nu}{sub {tau}} to give a combined preliminary limit of B(B+ --> {tau}+{nu}{sub {tau}})