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Experimental Searches for Oscillating and Transient effects from the Dark Sector

Periodic Reporting for period 4 - Dark-OsT (Experimental Searches for Oscillating and Transient effects from the Dark Sector)

Reporting period: 2021-02-01 to 2021-07-31

The Dark-OST project aims to search for ultralight cosmic particles that are hypothesized to be the constituent of Dark Matter, the dominant yet elusive part of the matter in our Universe. Discovering such particles will also help answer other important questions in modern science, including: What is the reason of the observed predominance of matter over antimatter in the Universe? What is the mechanism of the CP violation? Why are all observed elementary particles so light compared to the fundamental energy scales (the grand-unification scale and the Planck scale)?

Understanding of the most fundamental laws of nature is a high intellectual pursuit that has led to revolutionary technological advances along the way. In Dark-OST, we are developing novel magnetic-resonance technologies that will be useful in applications to chemistry and biology, apart from advancing fundamental science. See image001.png - Caption: conceptual illustration of the GNOME concept. Shielded atomic magnetometers spread around the globe detect the passage of a domain wall of a pseudoscalar field (the dark matter candidate), forming a signal pattern that depends on the direction and speed of the wall.

In addition to these major scientific goals, we also seek to address the following questions:

What are the ultimate limits of sensitivity of quantum sensors? How do these limits depend on the type of the signal, for example, those due to actual magnetic perturbations as opposed to the “pseudomagnetic” ones, such as those due to exotic fields (e.g. dark matter), or in a more practical context, due to platform rotation.
What is the intrinsic relation between possible dark matter signals of different types, for instance, due to the simultaneous presence of pseudoscalar couplings (affecting particles’ spins) and scalar couplings (manifesting as an apparent variation of fundamental ``constants’’). What are the benefits of hybrid networks, for example, those incorporating magnetometers, atomic clocks, interferometers, etc.?
What are the optimal configurations of sensor networks? How can one extract maximal possible information from a network of sensors in the presence of various kinds of noise sources? This question is equally important for fundamental physics and practical applications, for instance, measuring feeble magnetic fields from the brain with a network of sensors around the patient’s head.
As part of the Dark-OST project, we have developed and implemented new hardware and data analysis techniques for the CASPEr and GNOME experiments, have collected experimental data, and are currently in the process of writing several papers reporting on the results. Several paper on the development of the apparatus and the associated techniques have been published during the reporting period.

Two recent manuscripts highlight the achievements of the Dark-OST program. One of these, recently accepted to Nature Physics, describes the results of the GNOME searches for topological dark matter during the experimental run #2, exploring a previously inaccessible parts of the dark-matter parameter space and charting the course towards significant further improvement in the scope and sensitivity in the planned “Advanced GNOME” version of the experiment.

The second manuscript published earlier this year in Physical Review Letters presents the results of the initial experimental run of the full-featured CASPEr experiment developed in the course of Dark-OST, validating our original concept of a novel type of dark matter searches based on nuclear magnetic resonance (NMR), and, once again, extended the search for dark matter into a region of parameter space previously inaccessible to laboratory searches.

Our searches have not as yet yielded statistically significant signal from dark matter. However, they have allowed us to limit the option for what the ubiquitous yet illusive dark matter could be. We have also developed powerful novel technologies for further, more sensitive, searches, which can also be applied beyond just the fundamental physics research.

One example of the latter is development of novel techniques in NMR. The results of our work are included as an integral part of an ERC Proof-of-Concept proposal recently submitted by our collaborator Prof. Dr. Magdalena Kowalska (CERN) and will form the basis of the planned international cooperation.
Until the end of the project, we anticipate to complete and publish the results from three experimental runs of the GNOME experiment, the first stage of the CASPEr-E experiment (with magnetic fields up to 7 T), as well as complete and publish the experiments with the CASPEr-ZULF (zero-and ultralow-field) setup using parahydrogen-hyperpolarized nuclei, significantly cutting into the currently unexplored parameter space for axions and axion-like particles (ALPs).

It should be noted that Dark-OST has additionally led to the development of other “spin-off” techniques for fundamental-physics searches. Specifically, as part of the collaboration with our former group member, Dr. Jiang Min, and other colleagues at the University of Science and Technology (USTC) in Hefei, China, we have introduced novel devices: a so-called “Floquet maser” and a “spin amplifier” that were used for moth direct dark-matter searches (significantly improving on our CASPEr-ZULF results obtained in an earlier phase of Dark-OST) as well as to conduct an indirect search based on the measurement of the so-called “fifth force.” A paper on the latter results will be submitted shortly. The results of all of these experiments are all beyond the hitherto state of the art.
Caption: conceptual illustration of the GNOME concept.