A high sensitivity search for electron anti-neutrinos from the sun and other sources at Kamland

Data corresponding to a KamLAND detector exposure of 0.28 kton-year has been used to search for {bar {nu}}{sub e}'s in the energy range 8.3 MeV < E{sup {bar {nu}}{sub e}} < 14.8 MeV. No candidates were found for an expected background of 1.1 {+-} 0.4 events. This result can be used to obtain a limit on {bar {nu}}{sub e} fluxes of any origin. Assuming that all {bar {nu}}{sub e} flux has its origin in the Sun and has the characteristic {sup 8}B solar {nu}{sub e} energy spectrum, we obtain an upper limit of 3.7 x 10{sup 2} cm{sup -2} s{sup -1} (90 percent C.L.) on the {bar {nu}}{sub e} flux. We interpret this limit, corresponding to 2.8 x 10{sup -4} of the Standard Solar Model {sup 8}B {nu}{sub e} flux, in the framework of spin-flavor precession and neutrino decay models.