A Measurement of the CMB {\ltEE\gt Spectrum from the 2003 Flight of BOOMERANG}

We report measurements of the CMB polarization power spectra from the 2003 January Antarctic flight of BOOMERANG. The primary results come from 6 days of observation of a patch covering 0.22\% of the sky centered near R.A.=82.5d, decl.=-45$^{deg$. The observations were made using four pairs of polarization-sensitive bolometers operating in bands centered at 145 GHz. Using two independent analysis pipelines, we measure a nonzero \ltEE\gt signal in the range 201\ltl\lt1000 with a significance of 4.8 $\sigma$, a 2 $\sigma$ upper limit of 8.6 $\mu$K$^2$ for any \ltBB\gt contribution, and a 2 $\sigma$ upper limit of 7.0 $\mu$K$^2$ for the \ltEB\gt spectrum. Estimates of foreground intensity fluctuations and the nondetection of \ltBB\gt and \ltEB\gt signals rule out any significant contribution from Galactic foregrounds. The results are consistent with a $\Lambda$CDM cosmology seeded by adiabatic perturbations. We note that this is the first detection of CMB polarization with bolometric detectors.