Letter | Published:

An experiment to search for dark-matter interactions using sodium iodide detectors

Naturevolume 564pages8386 (2018) | Download Citation

Abstract

Observations of galaxies and primordial radiation suggest that the Universe is made mostly of non-luminous dark matter1,2. Several new types of fundamental particle have been proposed as candidates for dark matter3, such as weakly interacting massive particles (WIMPs)4,5. These particles would be expected to interact with nuclei in suitable detector materials on Earth, for example, causing them to recoil. However, no definitive signal from such dark-matter interactions has been detected despite concerted efforts by many collaborations6. One exception is the much-debated claim by the DAMA collaboration of a statistically significant (more than nine standard deviations) annual modulation in the rate of nuclear interaction events. Annual modulation is expected because of the variation in Earth’s velocity relative to the Galaxy’s dark-matter halo that arises from Earth’s orbital motion around the Sun. DAMA observed a modulation in the rate of interaction events in their detector7,8,9 with a period and phase consistent with that expected for WIMPs10,11,12. Several groups have been working to develop experiments with the aim of reproducing DAMA’s results using the same target medium (sodium iodide)13,14,15,16,17. To determine whether there is evidence for an excess of events above the expected background in sodium iodide and to look for evidence of an annual modulation, the COSINE-100 experiment uses sodium iodide as the target medium to carry out a model-independent test of DAMA’s claim. Here we report results from the initial operation of the COSINE-100 experiment related to the first task18,19. We observe no excess of signal-like events above the expected background in the first 59.5 days of data from COSINE-100. Assuming the so-called standard dark-matter halo model, this result rules out WIMP–nucleon interactions as the cause of the annual modulation observed by the DAMA collaboration20,21,22,23. The exclusion limit on the WIMP–sodium interaction cross-section is 1.14 × 10−40 cm2 for 10-GeV c−2 WIMPs at a 90% confidence level. The COSINE-100 experiment will continue to collect data for two more years, enabling a model-independent test of the annual modulation observed by the DAMA collaboration.

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Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request. Source Data for Figs. 14 are provided with the online version of the paper.

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Acknowledgements

We thank the Korea Hydro and Nuclear Power (KHNP) Company for providing underground laboratory space at Yangyang. This work is supported by: the Institute for Basic Science (IBS) under project code IBS-R016-A1 and NRF-2016R1A2B3008343, South Korea; UIUC campus research board, the Alfred P. Sloan Foundation Fellowship, NSF grant numbers PHY-1151795, PHY-1457995, DGE-1122492 and DGE-1256259, WIPAC, the Wisconsin Alumni Research Foundation, Yale University and DOE/NNSA grant number DE-FC52-08NA28752, USA; STFC grants ST/N000277/1 and ST/K001337/1, UK; and CNPq and grant number 2017/02952-0 FAPESP, Brazil.

Reviewer information

Nature thanks B. Sadoulet and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

Author notes

    • Antonia J. F. Hubbard

    Present address: Department of Physics and Astronomy, Northwestern University, Evanston, IL, USA

    • Jungsic Park

    Present address: High Energy Accelerator Research Organization (KEK), Tsukuba, Japan

    • Walter C. Pettus

    Present address: Center for Experimental Nuclear Physics and Astrophysics, Department of Physics, University of Washington, Seattle, WA, USA

    • Andrew Scarff

    Present address: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada

  1. A list of participants and their affiliations appears at the end of the paper.

Affiliations

  1. Department of Physics, Sejong University, Seoul, South Korea

    • Govinda Adhikari
    • , Pushparaj Adhikari
    •  & Yeongduk Kim
  2. Department of Physics, Yale University, New Haven, CT, USA

    • Estella Barbosa de Souza
    • , Antonia J. F. Hubbard
    • , Jay Hyun Jo
    • , Reina H. Maruyama
    • , Walter C. Pettus
    •  & William G. Thompson
  3. Physics Institute, University of São Paulo, São Paulo, Brazil

    • Nelson Carlin
  4. Department of Physics and Astronomy, Seoul National University, Seoul, South Korea

    • Seonho Choi
    • , Hanwool Joo
    •  & Sun Kee Kim
  5. Department of Physics, Bandung Institute of Technology, Bandung, Indonesia

    • Mitra Djamal
    •  & Hafizh Prihtiadi
  6. Department of Physics and Astronomy, University of Sheffield, Sheffield, UK

    • Anthony C. Ezeribe
    • , Vitaly A. Kudryavtsev
    • , Warren A. Lynch
    • , Frederic Mouton
    • , Andrew Scarff
    •  & Neil J. C. Spooner
  7. Center for Underground Physics, Institute for Basic Science (IBS), Daejeon, South Korea

    • Chang Hyon Ha
    • , Eunju Jeon
    • , Woon Gu Kang
    • , Bonghee Kim
    • , Hyounggyu Kim
    • , Kyungwon Kim
    • , Nam Young Kim
    • , Yeongduk Kim
    • , Yong-Hamb Kim
    • , Young Ju Ko
    • , Hyun Su Lee
    • , Jaison Lee
    • , Moo Hyun Lee
    • , Douglas S. Leonard
    • , Stephen L. Olsen
    • , Jungsic Park
    • , Kangsoon Park
    • , Sejin Ra
    • , Keon Ah Shin
    •  & Seok Hyun Yong
  8. Department of Science Education, Ewha Womans University, Seoul, South Korea

    • Insik Hahn
  9. Department of Physics, Sungkyunkwan University, Suwon, South Korea

    • Woosik Kang
    •  & Carsten Rott
  10. Department of Physics and Wisconsin IceCube Particle Astrophysics Center, University of Wisconsin-Madison, Madison, WI, USA

    • Matthew Kauer
  11. Department of Physics, Kyungpook National University, Daegu, South Korea

    • Hongjoo Kim
    •  & Jooyoung Lee
  12. Korea Research Institute of Standards and Science, Daejeon, South Korea

    • Yong-Hamb Kim
    •  & Hyeonseo Park
  13. IBS School, University of Science and Technology (UST), Daejeon, South Korea

    • Byungju Park
  14. Department of Accelerator Science, Korea University, Sejong, South Korea

    • Hyang Kyu Park
  15. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, USA

    • Liang Yang

Consortia

  1. The COSINE-100 Collaboration

Contributions

Y.K., H.S.L., R.H.M. and N.J.C.S. conceived the COSINE-100 experiment. Its design and installation were led by K.P. and C.H.H. and carried out by all members of the collaboration. Operation and maintenance were organized by C.H.H. with support from on-site crews, W.G.K., B.K. and S.H.Y. Jaison Lee, J.P., J.H.J., G.A., P.A., H. Prihtiadi, C.H.H., W.G.T., E.B.d.S., H.S.L. and K.K. contributed to data acquisition, production and verification. H.J., Hyeonseo Park and K.K. provided nuclear recoil data. P.A., G.A., J.P., K.K., H. Prihtiadi, N.Y.K. and C.H.H. performed the source calibrations. Hyounggyu Kim, N.Y.K., C.H.H. and H.S.L. developed the slow control framework. J.H.J. and W.G.T. developed the data monitoring package. N.Y.K., Jooyoung Lee and Y.J.K. provided the radiopurity of the detector materials. G.A., J.P. and N.Y.K. produced the liquid scintillator. Background simulations were performed by F.M., E.J., P.A., W.G.T. and E.B.d.S. C.H.H. and P.A. analysed the observational and simulated data. The manuscript and plots were produced by C.H.H. and H.S.L., and edited by R.H.M., S.L.O., N.J.C.S. and the other members of the collaboration. All authors participated in online data-monitoring shifts and approved the manuscript. Authors are listed alphabetically by their last names.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Chang Hyon Ha or Hyun Su Lee.

Extended data figures and tables

  1. Extended Data Fig. 1 The COSINE-100 detector.

    a, The detector is contained within a nested arrangement of shielding components, as indicated by different colours. The main purpose of the shield is to provide 4π coverage against external radiation from various background sources. The shielding components include plastic scintillator panels (blue), a lead brick enclosure (grey) and a copper box (reddish brown). b, c, The eight encapsulated sodium iodide crystal assemblies (c) are located inside the copper box and are immersed in scintillating liquid (b). All images are schematic.

  2. Extended Data Fig. 2 Typical waveforms from the COSINE-100 PMTs for 2–6-keV signals.

    a, The β and γ scintillation signals have a fast rise and then fall off with a decay time of about 250 ns. The waveform from WIMPs is expected to closely resemble the β and γ waveforms. b, c, Background waveforms from PMT noise (b) and external discharge (c).

  3. Extended Data Fig. 3 The BDT output (horizontal) versus the BDTA output (vertical).

    a, b, Events (colour scale) with energies below 10 keV are shown for two separate crystals, with (a) and without (b) PMT discharge. The events to the right and above the red dotted lines are scintillation events induced by real particle–crystal interactions. PMT noise events are to the left of the vertical dotted lines in both panels; PMT discharge events are below the horizontal dotted line in a.

  4. Extended Data Fig. 4 A comparison between data and simulation.

    ad, Four categories of data are shown: single-hit low-energy (2–70 keV; a); single-hit high-energy (70–3,000 keV; b); multiple-hit low-energy (2–70 keV; c); and multiple-hit high-energy (70–3,000 keV; d). The black points (with errors bars indicating the 68% confidence interval) are data. The green (yellow) band shows the ±1σ (±2σ) uncertainty range of the model. The peak near 3 keV in the multiple-hit, low-energy spectrum (c) is due to the tagged 40K events. The inset in a shows a zoomed-in view in the region of interest after efficiency corrections are applied. The major contributors to the radioactive background are labelled.

  5. Extended Data Fig. 5 Crystal-by-crystal fit results.

    af, The points (with errors bars indicating the 68% confidence interval) show the measured energy spectra for each of the six crystals. The fit results are shown as blue histograms, with the ±1σ (±2σ) error bands shown in green (yellow). To compare the signal strength of the DAMA sodium region with our data, a 10 GeV c−2 WIMP signal at 2.35 × 10−40 cm2 (the centre of the DAMA sodium region) is indicated for each crystal as a red histogram. The fit residuals, together with the expectations for the 10 GeV c−2 WIMP signal are also shown (bottom panels).

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https://doi.org/10.1038/s41586-018-0739-1

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