Polarization observations in a low synchrotron emission field at 1.4 GHz

We present the first observation of the diffuse polarized synchrotron radiation of a patch (similar to3degrees x 3degrees) in the BOOMERanG field, one of the areas with the lowest cosmic microwave background foreground emission. The work has been carried out with the Australia Telescope Compact Array at 1.4 GHz with 3.'4 resolution and sensitivity of similar to0.18 mJy beam(-1). The mean polarized signal has been found to be P-rms = (Q(rms)(2) + U-rms(2))(1/2) = 11.6 +/- mK, nearly 1 order of magnitude below that in the Galactic plane. Extrapolations to frequencies of interest for cosmological investigations suggest that polarized synchrotron foreground noise should allow the detection of the CMB polarization E-mode already at 32 GHz and make us confident that, at 90 GHz, it is accessible with no relevant foreground contamination. Last but not least, even the B-mode detection for T/S > is not ruled out in such a low-emission patch.