Leptonic B Decays at BaBar

The authors present results on searches for the rare B decays B{sup 0} {yields} {ell}{sup +}{ell}{sup -} ({ell} = e or {mu}) and B{sup +} {yields} K{sup +} {nu}{bar {nu}} in {Upsilon}(4S) decays. The data used in these analyses were collected with the BABAR detector at the PEP-II e{sup +}e{sup -} storage ring during the years 2000 and 2001. The B{sup 0} {yields} {ell}{sup +}{ell}{sup -} search was performed using an integrated luminosity of 54.4 fb{sup -1} accumulated at the {Upsilon}(4S) resonance (about 60 million B{bar B} pairs) while the B{sup +} {yields} K{sup +} {nu}{bar {nu}} search was performed with 50.7 fb{sup -1} (about 56 million B{bar B} pairs). Both analyses use an additional 6.4 fb{sup -1} of data accumulated about 40 MeV below resonance. They see no evidence for a signal in either the B {yields} {ell}{sup +}{ell}{sup -} or B {yields} K{sup +}{nu}{bar {nu}} decay modes and set the following upper limits at the 90% CL: {Beta}(B{sup 0} {yields} e{sup +}e{sup -}) < 3.3 x 10{sup -7}, {Beta}(B{sup 0} {yields} {mu}{sup +}{mu}{sup -}) < 2.0 x 10{sup -7}, {Beta}(B{sup 0} {yields} e{sup {+-}}{mu}{sup {-+}}) < 2.1 x 10{sup 7}, and {Beta}(B{sup +} {yields} K{sup +} {nu}{bar {nu}}) < 9.4 x 10{sup -5}.