We present observations of the HD 15115 debris disk from the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm that capture this intriguing system with the highest resolution (0.″6 or 29 au) at millimeter wavelengths to date. This new ALMA image shows evidence for two rings in the disk separated by a cleared gap. By fitting models directly to the observed visibilities within a Markov Chain Monte Carlo framework, we are able to characterize the millimeter continuum emission and place robust constraints on the disk structure and geometry. In the best-fit model of a power-law disk with a Gaussian gap, the disk inner and outer edges are at 43.9 ± 5.8 au (0.″89 ± 0.″12) and 92.2 ± 2.4 au (1.″88 ± 0.″49), respectively, with a gap located at 58.9 ± 4.5 au (1.″2 ± 0.″10) with a fractional depth of 0.88 ± 0.10 and a width of 13.8 ± 5.6 au (0.″28 ± 0.″11). Because we do not see any evidence at millimeter wavelengths for the dramatic east–west asymmetry seen in scattered light, we conclude that this feature most likely results from a mechanism that only affects small grains. Using dynamical modeling and our constraints on the gap properties, we are able to estimate a mass for the possible planet sculpting the gap to be 0.16 ± 0.06 M Jup.
