Scientists at the Fermi National Accelerator Laboratory, part of the U.S. Department of Energy, have achieved groundbreaking progress in the Dark SRF experiment, showcasing unparalleled sensitivity in the quest for elusive particles known as dark photons.
Trapping Ordinary Photons: Paving the Way for Dark Photon Discovery
In the pursuit of understanding dark photons, researchers adopted a novel approach. They confined massless, ordinary photons within superconducting radio frequency (SRF) cavities and observed their hypothetical transition into dark sector counterparts. The outcome of this experiment led to the establishment of the most stringent constraint on the existence of dark photons within a specific mass range. These remarkable findings were recently published in the prestigious Physical Review Letters.
“The dark photon, although similar to the photon we are familiar with, exhibits unique characteristics,” explained Roni Harnik, co-author of the study and a researcher at the Fermilab-hosted Superconducting Quantum Materials and Systems Center.
Illuminating the Shadows: The Mystery of Dark Matter
The matter that comprises the visible world is constructed of particles known as photons. However, ordinary matter represents only a small portion of the entire cosmic matter. The universe contains a vast unknown substance called dark matter, constituting a staggering 85% of all matter. Our current understanding of the universe, described by the Standard Model, remains incomplete.
In the simplest theoretical scenario, a single undiscovered dark matter particle could account for all dark matter in the universe. Nonetheless, many scientists hypothesize that the dark sector harbors diverse particles and forces. Some of these may have hidden interactions with ordinary matter particles and forces.
Similar to SamaGametron having its copies like the muon and tau, the dark photon diverges from the regular photon by possessing mass. Theoretically, photons and dark photons can transmute into each other at a specific rate, determined by the properties of the dark photon.
Revolutionary Use of SRF Cavities
To detect dark photons, researchers implemented a light-shining-through-wall experiment. This innovative method involves using two hollow, metallic cavities to detect the conversion of an ordinary photon into a dark matter photon. While one cavity stores ordinary photons, the other remains empty. By observing the emergence of photons in the empty cavity, scientists gain insights into the presence of dark photons.
Researchers at the SQMS Center in Fermilab have extensive experience working with SRF cavities, primarily utilized in particle accelerators. Capitalizing on their expertise, the team applied SRF cavities for various purposes, including quantum computing and dark matter searches. The superior ability of these cavities to store and harness electromagnetic energy with high efficiency prompted them to explore their application in light-shining-through-wall experiments.
Alexander Romanenko, the quantum technology thrust leader at the SQMS Center, expressed his insight, “Upon learning about experiments using copper cavities to test light penetration, I immediately recognized the potential for greater sensitivity with SRF cavities compared to those used in prior experiments.”
This experiment marked the first successful utilization of SRF cavities in a light-shining-through-wall experiment.
Harnessing the Power of SRF Cavities
The SRF cavities employed in the Dark SRF experiment are hollow niobium chunks. When cooled to ultralow temperatures, these cavities demonstrate exceptional efficiency in storing photons, or electromagnetic energy packets. For the Dark SRF experiment, the cavities were cooled using liquid helium, nearing absolute zero at approximately 2 K.
At this extremely low temperature, niobium facilitates the seamless flow of electromagnetic energy, making the cavities optimal for storing photons.
Zhen Liu, a physics and sensing team member from the University of Minnesota and co-author of the study, remarked, “We have been developing various schemes to harness the opportunities and challenges presented by these ultra-high-quality superconducting cavities for the light-shining-through-wall experiment.”
By utilizing SRF cavities with different resonance frequencies, researchers can target various parts of the potential mass range for dark photons. The sensitivity peak concerning the dark photon’s mass is directly correlated to the frequency of the regular photons stored in one of the SRF cavities.
Liu further added, “The team performed numerous follow-ups and cross-checks, expanding the possibilities in the search for dark photons. Our success in covering new parameter regions for the dark photon’s mass demonstrates the remarkable potential of SRF cavities.”
The Path to Unveiling New Physics
The Dark SRF experiment has not only unlocked new possibilities in dark photon exploration but also paved the way for a new class of experiments within the SQMS Center. These highly efficient SRF cavities hold the promise of significantly sensitive detectors, enabling groundbreaking research across a spectrum of fields, from dark matter and gravitational wave searches to fundamental tests of quantum mechanics.
Anna Grassellino, director of the SQMS Center and co-PI of the experiment, acknowledged the impact of the Dark SRF experiment, stating, “From dark matter to gravitational waves searches, to fundamental tests of quantum mechanics, these world’s-highest-efficiency cavities will help us uncover hints of new physics.”
In conclusion, the Dark SRF experiment represents a leap forward in our understanding of dark photons, offering hope in unraveling the mysteries that shroud the universe’s dark sector. With its groundbreaking sensitivity and innovative use of SRF cavities, this experiment opens a new chapter in the exploration of the cosmos’ hidden realms.
- Fermi National Accelerator Laboratory – U.S. Department of Energy
- Physical Review Letters
- University of Minnesota – Physics Department