Early results from the MIT millimeter and sub‐millimeter balloon‐borne anisotropy measurement

The MIT balloon‐borne bolometric search for Cosmic Microwave Background Radiation (CMBR) anisotropies places the most stringent constraints to date on the fluctuations in the CMBR. Four maps of half of the Northern Hemisphere at 1.8, 1.1, 0.63 and 0.44 mm wavelength, have a beam size of 3.8° with a 1 sigma sensitivity of less than 0.1 mK (thermodynamic) per FOV in each of the first two channels. Analysis of the sky map at 1.8 mm wavelength using a likelihood ratio test for galactic latitudes ‖ b ‖≥15° yields a 95% confidence level (CL) upper limit on fluctuations of the CMBR at ΔT/T≤1.6×10−5 with a statistical power of 92% for Gaussian fluctuations at a correlation angle of 13°. Between 3° and 22°, the upper limit of fluctuations is ΔT/T≤4.0×10−5 (95% CL). An anisotropy is detected in the map but it cannot yet be attributed to primordial sources. The ultimate sensitivity for this experiment is ΔT/T∼7×10−6 (95% CL) over this angular range for Gaussian fluctuations.