The past several years have seen the emergence of a standard cosmological model, in which small temperature differences in the cosmic microwave background (CMB) radiation on angular scales of the order of a degree are understood to arise from acoustic oscillations in the hot plasma of the early Universe, arising from primordial density fluctuations. Within the context of this model, recent measurements of the temperature fluctuations have led to profound conclusions about the origin, evolution and composition of the Universe. Using the measured temperature fluctuations, the theoretical framework predicts the level of polarization of the CMB with essentially no free parameters. Therefore, a measurement of the polarization is a critical test of the theory and thus of the validity of the cosmological parameters derived from the CMB measurements. Here we report the detection of polarization of the CMB with the Degree Angular Scale Interferometer (DASI). The polarization is deteced with high confidence, and its level and spatial distribution are in excellent agreement with the predictions of the standard theory.
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Acknowledgements We are grateful for the efforts of B. Reddall and E. Sandberg, who wintered over at the National Science Foundation (NSF) Amundsen–Scott South Pole research station to keep DASI running smoothly. We are indebted to M. Dragovan for his role in making DASI a reality, and to the Caltech CBI team led by T. Readhead, in particular, to S. Padin, J. Cartwright, M. Shepherd and J. Yamasaki for the development of key hardware and software. We are indebted to the Center for Astrophysical Research in Antarctica (CARA), in particular to the CARA polar operations staff. We are grateful for contributions from K. Coble, A. Day, G. Drag, J. Kooi, E. LaRue, M. Loh, R. Lowenstein, S. Meyer, N. Odalen, R. Pernic, D. Pernic and E. Pernic, R. Spotz and M. Whitehead. We thank Raytheon Polar Services and the US Antarctic Program for their support of the DASI project. We have benefitted from many interactions with the Center for Cosmological Physics members and visitors. In particular, we gratefully acknowledge many conversations with W. Hu on CMB polarization and suggestions from S. Meyer, L. Page, M. Turner and B. Winstein on the presentation of these results. We thank L. Knox and A. Kosowsky for bringing the Markov technique to our attention. We thank the observatory staff of the Australia Telescope Compact Array, in particular B. Sault and R. Subrahmanyan, for providing point source observations of the DASI fields. This research was initially supported by the NSF under a cooperative agreement with CARA, a NSF Science and Technology Center. It is currently supported by an NSF-OPP grant. J.E.C. gratefully acknowledges support from the James S. McDonnell Foundation and the David and Lucile Packard Foundation. J.E.C. and C.P. gratefully acknowledge support from the Center for Cosmological Physics.
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