New Constraints on Dark Photon Dark Matter with Superconducting Nanowire Detectors in an Optical Haloscope (2110.01582v2)

Abstract: Uncovering the nature of dark matter is one of the most important goals of particle physics. Light bosonic particles, such as the dark photon, are well-motivated candidates: they are generally long-lived, weakly-interacting, and naturally produced in the early universe. In this work, we report on LAMPOST (Light $A'$ Multilayer Periodic Optical SNSPD Target), a proof-of-concept experiment searching for dark photon dark matter in the eV mass range, via coherent absorption in a multi-layer dielectric haloscope. Using a superconducting nanowire single-photon detector (SNSPD), we achieve efficient photon detection with a dark count rate (DCR) of $\sim 6\times10^{-6}$ counts/s. We find no evidence for dark photon dark matter in the mass range of $\sim 0.7$-$0.8$ eV with kinetic mixing $\epsilon \gtrsim 10^{-12}$, improving existing limits in $\epsilon$ by up to a factor of two. With future improvements to SNSPDs, our architecture could probe significant new parameter space for dark photon and axion dark matter in the meV to 10 eV mass range.

• The paper demonstrates that using SNSPDs with a dielectric haloscope achieves ultra-low dark count rates (≈6×10⁻⁶ counts/s) for sensitive dark photon detection.
• The study employs a multilayer dielectric structure for coherent absorption and momentum matching, improving kinetic mixing constraints (ε ≳ 10⁻¹²) by up to a factor of two in the 0.7–0.8 eV range.
• The research paves the way for future explorations by proposing advancements in detector design and material choices to extend the search for light dark matter.

Overview of "New Constraints on Dark Photon Dark Matter with Superconducting Nanowire Detectors in an Optical Haloscope"

The manuscript under review explores exploring the constraints on dark photon dark matter using the LAMPOST (Light $A'$ Multilayer Periodic Optical SNSPD Target) experimental setup, a proof-of-concept project. This research focuses on leveraging Optical Haloscopes with Superconducting Nanowire Single-Photon Detectors (SNSPDs) to probe potential dark photon dark matter within the electronvolt mass range. The emphasis is on utilizing coherent absorption in multilayer dielectric structures to detect signals indicative of dark photons.

Experimental Setup and Methodology

The experimental apparatus used in LAMPOST involves a stack structure known as a dielectric haloscope. This structure consists of alternating layers of amorphous silicon and silica, forming a resonant optical cavity that allows manipulation of photon frequencies to match those predicted for dark photon conversion. The superconducting nanowires involved in detection are tuned to have an ultra-low dark count rate—approximately $6 \times 10^{-6}$ counts per second—thereby facilitating the detection of rare signal events. The detectors are sensitive to photons ranging from 0.1 eV to 10 eV, making them appropriately suited for this dark matter detection effort.

The dielectric stack facilitates momentum matching required for the conversion of non-relativistic dark photon dark matter into detectable photons of the same energy but with differing momenta. The multilayer dielectric setup functions similarly to a photonic crystal, enhancing conversion rates due to coherent photon emission from the stacked layers. The experiment's focal range was meticulously aligned using optical fiber calibration, ensuring light from dark photons would sufficiently overlap the SNSPD area to be captured.

Results

The findings of 180 hours of data collection reveal no significant evidence for dark photon dark matter within the 0.7-0.8 eV mass range with a kinetic mixing $\epsilon \gtrsim 10^{-12}$. Importantly, this result improves existing constraints on dark photon mixing parameters by up to a factor of two. Calculations indicate enhanced dark photon conversion rates were achieved compared to isotropic mirror targets, further verifying the efficacy of dielectric haloscopes for probing new parameter spaces in dark photon and axion dark matter searches.

Implications and Future Directions

This work positions itself as a critical step toward deeper explorations of lightweight dark matter particles, such as dark photons and axions, at energies previously challenging to probe experimentally. The outcomes encourage the advancement of detector technologies and methodologies, promoting research into broader mass ranges by refining the dielectric layer compositions and investigating other potential materials like ZnSe or TiO$_2$.

In future applications, integrating large-volume targets, extending detector sensitivity, or accelerating data acquisition using parallel operation could significantly enhance search capabilities. These expansions could further propel axion detection efforts in the meV mass spectrum using similar SSE-based systems. The paper thereby presents a call to speculate and innovate upon the current methodology, likely offering insight into inferred cosmological parameters if such bosonic dark matter candidates are detected.

Overall, this research contributes to the evolving landscape of dark matter exploration, suggesting potential methodologies to refine and extend our search strategies. As technological improvements unfold, such frameworks exhibit pronounced capacity to probe unexplored stretches of dark photon parametric space, consistently offering paths toward untangling the intricacies of dark matter's contribution to cosmological constructs.