EXPERIMENTAL LIMITS ON THE DARK MATTER HALO OF THE GALAXY FROM GRAVITATIONAL MICROLENSING.

We have monitored 8.6 million stars in the Large Magellanic Cloud for 1.1 years and have found 3 events consistent with gravitational microlensing. We place strong constraints on the Galactic halo content in the form of compact lensing objects in the mass range ${10}^{-4}\text{msun}$ to ${10}^{-1}\text{msun}$. Three events is fewer than expected for a standard spherical halo of objects in this mass range, but appears to exceed the number expected from known Galactic populations. Fitting a naive spherical halo model to our data yields a MACHO fraction $f=0.20_{-0.14}^{+0.33}$, which implies a total MACHO mass (inside 50 kpc) of $8.0_{-6}^{+14}\text{ten}10\text{msun}$, and a microlensing optical depth $9_{-7}^{+15}\text{ten}-8$ ($\sim 68$% CL).