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The MACHO collaboration reports on the analysis of our first year LMC data,9.5 million light curves with an average of 235 observations each. Automatedselection procedures give 3 events consistent with microlensing. We evaluateour experimental detection efficiency using a range of Monte- Carlosimulations. Using a `standard' halo density profile we find that a halocomprised entirely of Machos in the mass range 3 \ten{-4} to 0.06 \msun wouldpredict > 15 detected events in this dataset; thus a standard spherical halocannot be dominated by objects in this mass range. Assuming all three eventsare microlensing of halo objects and fitting a naive spherical halo model toour data yields a Macho halo fraction f =0.19+0.16-0.10, a total mass in Machos(inside 50 kpc) of 7.6+6-4 \ten{10} \msun, and a microlensing optical depth8.8+7-5 \ten{-8} (68\% CL). Exploring a wide range of halo models we find thatour constraints on the Macho fraction are quite model-dependent, butconstraints on the total mass in Machos within 50 kpc are quite secure.Comment: 34 pages, uuencoded compressed tarred postscript, 14 figures  included; Entire package including large image and important lightcurve  figures (not included in above package) available via anonymous ftp at  ftp://igpp.llnl.gov/pub/macho/LMC1/LMC1_all.uu, submitted to Astrophys.

The MACHO Project First-Year Large Magellanic Cloud Results: The Microlensing Rate and the Nature of the Galactic Dark Halo