First attempt at measuring the CMB cross-polarization

We compute upper limits on cosmic microwave background cross-polarization by cross-correlating the PIQUE and Saskatoon experiments. We also discuss theoretical and practical issues relevant to measuring cross-polarization and illustrate them with simulations of the upcoming BOOMERANG 2002 experiment. We present a method that separates all six polarization power spectra (TT, EE, BB, TE, TB, EB) without any other “leakage” than the familiar EE-BB mixing caused by incomplete sky coverage. Since E and B get mixed, one might expect leakage between TE and TB, between EE and EB and between BB and EB—our method eliminates this by preserving the parity symmetry under which TB and EB are odd and the other four power spectra are even.