We present an analysis of electron recoils in cryogenic germanium detectors operated during the SuperCDMS Soudan experiment. The data are used to set new constraints on the axioelectric coupling of axionlike particles and the kinetic mixing parameter of dark photons, assuming the respective species constitutes all of the galactic dark matter. This study covers the mass range from 40 eV/c2 to 500 keV/c2 for both candidates, excluding previously untested parameter space for masses below ∼1 keV/c2. For the kinetic mixing of dark photons, values below 10-15 are reached for particle masses around 100 eV/c2; for the axioelectric coupling of axionlike particles, values below 10-12 are reached for particles with masses in the range of a few-hundred eV/c2.
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The SuperCDMS collaboration gratefully acknowledges technical assistance from the staff of the Soudan Underground Laboratory and the Minnesota Department of Natural Resources. The iZIP detectors were fabricated in the Stanford Nanofabrication Facility, which is a member of the National Nanofabrication Infrastructure Network, sponsored and supported by the NSF. Funding and support were received from the National Science Foundation, the U.S. Department of Energy, Fermilab URA Visiting Scholar Grant No. 15-S-33, NSERC Canada, the Canada Excellence Research Chair Fund, the McDonald Institute (Canada), MultiDark (Spanish MINECO), and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project No. 420484612. The SuperCDMS collaboration prepared this document using the resources of the Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science, HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute under Contract No. DE-AC05-76RL01830 for the U.S. Department of Energy. SLAC is operated under Contract No. DEAC02-76SF00515 with the U.S. Department of Energy.
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