The White Mountain polarimeter telescope and an upper limit on cosmic microwave background polarization

The White Mountain Polarimeter (WMPol) is a dedicated ground-based microwave telescope and receiver system for observing polarization of the cosmic microwave background. WMPol is located at an altitude of 3880 m on a plateau in the White Mountains of Eastern California, at the Barcroft Facility of the University of California White Mountain Research Station. Presented here is a description of the instrument and the data collected during 2004 April through October. We set an upper limit on E-mode polarization of 14 μK (95% confidence limit) in the multipole range 170 < l < 240. This result was obtained with 422 hr of observations of a 3 deg2 sky area about the North Celestial Pole, using a 42 GHz polarimeter. This upper limit is consistent with EE polarization predicted from a standard ΛCDM concordance model.