First Results from KamLAND: Evidence for Reactor Antineutrino Disappearance

KamLAND has measured the flux of ${\overline{\ensuremath{\nu}}}_{e}$'s from distant nuclear reactors. We find fewer ${\overline{\ensuremath{\nu}}}_{e}$ events than expected from standard assumptions about ${\overline{\ensuremath{\nu}}}_{e}$ propagation at the 99.95% C.L. In a $162\text{ }\mathrm{\text{ton}}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{y}\mathrm{r}$ exposure the ratio of the observed inverse $\ensuremath{\beta}$-decay events to the expected number without ${\overline{\ensuremath{\nu}}}_{e}$ disappearance is…