The Cosmology Large Angular Scale Surveyor

Abstract

The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array\ndesigned to characterize relic primordial gravitational waves from inflation\nand the optical depth to reionization through a measurement of the polarized\ncosmic microwave background (CMB) on the largest angular scales. The\nfrequencies of the four CLASS telescopes, one at 38 GHz, two at 93 GHz, and one\ndichroic system at 145/217 GHz, are chosen to avoid spectral regions of high\natmospheric emission and span the minimum of the polarized Galactic\nforegrounds: synchrotron emission at lower frequencies and dust emission at\nhigher frequencies. Low-noise transition edge sensor detectors and a rapid\nfront-end polarization modulator provide a unique combination of high\nsensitivity, stability, and control of systematics. The CLASS site, at 5200 m\nin the Chilean Atacama desert, allows for daily mapping of up to 70\\% of the\nsky and enables the characterization of CMB polarization at the largest angular\nscales. Using this combination of a broad frequency range, large sky coverage,\ncontrol over systematics, and high sensitivity, CLASS will observe the\nreionization and recombination peaks of the CMB E- and B-mode power spectra.\nCLASS will make a cosmic variance limited measurement of the optical depth to\nreionization and will measure or place upper limits on the tensor-to-scalar\nratio, $r$, down to a level of 0.01 (95\\% C.L.).\n