We present Chandra observations of EMSS 1358+6245, a relaxed cooling flow cluster of galaxies at z = 0.328. We employ a new deprojection technique to construct temperature, gas, and dark matter profiles. We confirm the presence of cool gas in the cluster core, and our deprojected temperature profile for the hot component is isothermal over 30 kpc < r < 0.8 Mpc. Fitting the mass profile to an NFW model yields r_s = 153 [+161,-83] kpc and c = 8.4 [+3.4,-2.3]. We find good agreement between our dark matter profile and weak gravitational lensing measurements. We place an upper limit of 42 kpc (90% confidence limit) on the size of any constant density core. We compare this result to recent simulations and place a conservative upper limit on the dark matter particle scattering cross section of 0.1 cm^2/g. This limit implies that the cross-section must be velocity dependent if the relatively shallow core mass profiles of dwarf galaxies are a direct result of dark matter self-interaction.
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