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Particle Dark Matter and Solar Axion Searches with a small germanium detector at the Canfranc Underground Laboratory

A. Morales, F. T. Avignone, R. L. Brodzinski, S. Cebrian, E. Garcia, D. Gonzalez, I. G. Irastorza, H. S. Miley, J. Morales, A. Ortiz de Solorzano, J. Puimedon, J. H. Reeves, M. L. Sarsa, S. Scopel, J. A. Villar

TL;DR

This work uses a compact, natural germanium detector (COSME) operated deep underground at Canfranc to search for WIMPs and solar axions. With a $72.7$ kg d exposure and improved shielding, COSME achieves a $2.5$ keV threshold and significantly reduced background, enabling new WIMP exclusion limits that improve the low-mass region (notably $m_{ m WIMP} ext{ in the } ext{12–30 GeV}$ range) and a competitive axion limit from solar Primakoff conversion with Bragg diffraction. The axion analysis yields $g_{a extgamma extgamma} < 2.78 imes 10^{-9} ext{ GeV}^{-1}$ at 95% C.L. (with $oldsymbol{ ext{λ}}<0.006$), highlighting the sensitivity of crystal detectors to axion-photon couplings. Overall, the results are competitive with other contemporary Ge-based experiments and demonstrate the viability of small, well-shielded detectors for probing WIMPs and solar axions, contributing valuable constraints to the dark matter parameter space.

Abstract

A small, natural abundance, germanium detector (COSME) has been operating recently at the Canfranc Underground Laboratory (Spanish Pyrenees) in improved conditions of shielding and overburden with respect to a previous operation of the same detector. An exposure of 72.7 kg day in these conditions has at present a background improvement of about one order of magnitude compared to the former operation of the detector. These new data have been applied to a direct search for WIMPs and solar axions. New WIMP exclusion plots improving the current bounds for low masses are reported. The paper also presents a limit on the axion-photon coupling obtained from the analysis of the data looking for a Primakoff axion-to-photon conversion and Bragg scattering inside the crystal.

Particle Dark Matter and Solar Axion Searches with a small germanium detector at the Canfranc Underground Laboratory

TL;DR

This work uses a compact, natural germanium detector (COSME) operated deep underground at Canfranc to search for WIMPs and solar axions. With a kg d exposure and improved shielding, COSME achieves a keV threshold and significantly reduced background, enabling new WIMP exclusion limits that improve the low-mass region (notably range) and a competitive axion limit from solar Primakoff conversion with Bragg diffraction. The axion analysis yields at 95% C.L. (with ), highlighting the sensitivity of crystal detectors to axion-photon couplings. Overall, the results are competitive with other contemporary Ge-based experiments and demonstrate the viability of small, well-shielded detectors for probing WIMPs and solar axions, contributing valuable constraints to the dark matter parameter space.

Abstract

A small, natural abundance, germanium detector (COSME) has been operating recently at the Canfranc Underground Laboratory (Spanish Pyrenees) in improved conditions of shielding and overburden with respect to a previous operation of the same detector. An exposure of 72.7 kg day in these conditions has at present a background improvement of about one order of magnitude compared to the former operation of the detector. These new data have been applied to a direct search for WIMPs and solar axions. New WIMP exclusion plots improving the current bounds for low masses are reported. The paper also presents a limit on the axion-photon coupling obtained from the analysis of the data looking for a Primakoff axion-to-photon conversion and Bragg scattering inside the crystal.

Paper Structure

This paper contains 7 sections, 7 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Experimental setup
  3. Experimental Results
  4. Spectrum
  5. WIMP exclusion plot
  6. Limit on axion-photon coupling
  7. Conclusion

Figures (4)

  • Figure 1: The thick line shows the data reported in this paper, obtained with 72.7 kg days of exposure with COSME detector. The thin line shows the previous running of the same detector COSME1 for comparison.
  • Figure 2: Exclusion plot for spin-independent interaction where bounds coming from different experiments are drawn. The thick line shows the exclusion obtained with the data reported in this paper, obtained with 72.7 kg-days of exposure with COSME detector. The thick dashed line shows the one from the previous running of the same detector COSME1 for comparison. Limits from a recent result of IGEX-DM experimentIGEXDM (thin-dashed), from the Heidelberg-Moscow experimentBau (dot-dashed) and from a combination of previous germanium experimentsCOSME1GotthardTWIN (dots) are also shown. The closed region corresponds to the (3$\sigma$) annual modulation effect reported by the DAMA collaboration (including NaI-1,2,3,4 runnings)Ber99.
  • Figure 3: Expected axion signals for coherent Primakoff conversion in a germanium crystal as a function of time for $\lambda=1$, for two different energy windows: a) 2 keV$\leq E_{ee}\leq$2.5 keV; b) 4 keV$\leq E_{ee}\leq$4.5 keV.
  • Figure 4: Values of $\lambda$ obtained for different assumed rotations around the fixed vertical axis.