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Dark photon dark matter constraints at the Taiwan axion search experiment with haloscope

Yuan-Hann Chang, Cheng-Wei Chiang, Hien Thi Doan, Nick Houston, Jinmian Li, Tianjun Li, Lina Wu, Xin Zhang

Abstract

The dark photon is a well motivated candidate for the dark matter which comprises most of the mass of our visible Universe, leading to worldwide experimental and observational efforts towards its discovery. A primary tool in this search is the cavity haloscope, which facilitates resonantly enhanced conversion to photons from both dark photons and axions. In this context, limits from axion search experiments are often directly converted into dark photon constraints, without re-analyzing the original data. However, this rescaling may not fully capture all of the relevant physics due to various reasons. By re-examining data taken by the Taiwan Axion Search Experiment with Haloscope (TASEH) experiment, we derive a world-leading constraint on the dark photon parameter space, excluding $|ε|\gtrsim2\times10^{-14}$ in the $19.46 - 19.84\,μ$eV mass range, which exceeds the na{ï}ve `rescaling limit' by roughly a factor of two. We emphasize that accounting for the scanning timing information is crucial for deriving limits for the polarized dark photon case. In the data, we also analyze a tentative signal excess with a local significance of 4.7$σ$ ($m_X \simeq 19.5\,μ$eV) that persists in the absence of a magnetic field. While this excess mimics the behavior of a dark photon signal, it has been excluded by recent results from the HAYSTAC and ORGAN-Q experiments. This case study, nevertheless, highlights the risk of discarding valid dark photon signals when relying on axion-specific magnetic field vetoes.

Dark photon dark matter constraints at the Taiwan axion search experiment with haloscope

Abstract

The dark photon is a well motivated candidate for the dark matter which comprises most of the mass of our visible Universe, leading to worldwide experimental and observational efforts towards its discovery. A primary tool in this search is the cavity haloscope, which facilitates resonantly enhanced conversion to photons from both dark photons and axions. In this context, limits from axion search experiments are often directly converted into dark photon constraints, without re-analyzing the original data. However, this rescaling may not fully capture all of the relevant physics due to various reasons. By re-examining data taken by the Taiwan Axion Search Experiment with Haloscope (TASEH) experiment, we derive a world-leading constraint on the dark photon parameter space, excluding in the eV mass range, which exceeds the na{ï}ve `rescaling limit' by roughly a factor of two. We emphasize that accounting for the scanning timing information is crucial for deriving limits for the polarized dark photon case. In the data, we also analyze a tentative signal excess with a local significance of 4.7 (eV) that persists in the absence of a magnetic field. While this excess mimics the behavior of a dark photon signal, it has been excluded by recent results from the HAYSTAC and ORGAN-Q experiments. This case study, nevertheless, highlights the risk of discarding valid dark photon signals when relying on axion-specific magnetic field vetoes.

Paper Structure

This paper contains 4 sections, 21 equations, 5 figures, 2 tables.

Table of Contents

  1. Appendix A: Polarised dark photon production in the early Universe
  2. Appendix B: Data analysis procedure
  3. Appendix C: Conversion factors for polarized dark photon DM
  4. Appendix D: Fitting procedure on the signal excess

Figures (5)

  • Figure 1: Constraints on the dark photon parameter space from TASEH. The green curve corresponds to the AxionLimits constraint AxionLimits, which follows the analysis strategy presented in Caputo:2021eaa. The blue bound corresponds to the random polarization case. The red, cyan, and orange curves respectively denote the bounds for polarized dark photon DM without bin merging and with merged bins using the average or minimal conversion factors; their overlap indicates the minimal effect of the merging procedure.
  • Figure 2: Rescaled RDP for the combined spectrum after rescans in the frequency range $[4.710120,4.710240]$ GHz. Red lines correspond to the RDP standard deviation, while the dark curve corresponds to the best-fit dark photon lineshape.
  • Figure 5: Left panel: The distribution of $\langle \cos^2 \theta(t) \rangle_T$ for the frequency $f=4.712705$ GHz with the TASEH scanning strategy. Right panel: The evolution of the conversion factor for $f=4.712705$ GHz with increasing numbers of scans.
  • Figure 6: The conversion factor for the full frequency range at the TASEH experiment. The blue, green, and red curves correspond respectively to the conversion factor prior to bin merging, and the conversion factors post bin merging by taking either the average or minimum conversion factor among five adjacent bins.
  • Figure 7: The signal-to-noise ratio for the merged spectrum before (left panel) and after (right panel) the addition of rescan data in the frequency range of $[4.710120,4.710240]$ GHz.