Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.|Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.|Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.|Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.|Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.