Measurements of cosmic background radiation anisotropy at intermediate angular scale

Results from an Antarctic ground-based experiment devoted to the search for fluctuations in the cosmic background radiation (CBR) are presented. We have developed an off-axis telescope with a Gaussian beam response of 50′ FWHM and with a beam-throw adjustable from 0° to 2°. The detector was a 3He bolometer working at 0.35 K and operating at 2.2 mm wavelength. The data collected show evidence of fluctuations at a level of ΔTrms/T = 4.5 × 10-5 at an angular scale of 40′. The expected fluctuations obtained by extrapolating the COBE result down to this angular scale, in a cold dark matter scenario, are a factor 2.5 lower (1.8 × 10-5). If residual systematic effects or cold galactic dust emission are responsible for the signal detected, our result should be considered as an upper limit to CBR anisotropy.