ACTPol: The Atacama Cosmology Telescope with Polarization

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The Atacama Cosmology Telescope (ACT) is a project to investigate the Cosmic Microwave Background (CMB) at high angular resolution that was constructed and operated under NSF support over 2005-2010. The ACT facility - a 6m off-axis Gregorian telescope, detectors, and infrastructure - has had two successful seasons of science observations during 2008 and 2009. The awarded project is a follow-on program, called ACTPol, to greatly increase the number and sensitivity of the detectors, and to add linear polarization capability. ACTPol will upgrade and extend instrumentation on the existing telescope, which is located on Cerro Toco (17,030') above the ALMA site on the Chajnator Plateau in Northern Chile. It will address important questions in both basic physics and astrophysics, and if successful will perform transformative research. The program will run for five years. A new bolometer camera with polarization sensitivity will be constructed and used with the ACT for the following science goals: 1) Constrain the initial conditions of universe and measure "running" of scalar spectral index with k; 2) Measure spatial curvature of the universe and dark energy; 3) Discover or constrain the sum of the neutrino masses; 4) Measure the amount of primordial helium; 5) Determine the growth rate of structure; 6) Complement the Planck satellite on smaller angular scales; and 7) Enable future large-scale B-mode polarization measurements.ACTPol will continue to pursue the types of broader impacts already successfully undertaken by the ACT project. These include a commitment to training students and postdoctoral researchers, continuing strong international partnerships, exchange of technology and personnel with NIST, and outreach to teachers and middle school students, among other activities.