Axion dark matter detection by superconducting resonant frequency conversion

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Springer

Received: March 3, 2020 Accepted: June 24, 2020 Published: July 14, 2020

Asher Berlin,a Raffaele Tito D’Agnolo,b Sebastian A. R. Ellis,c Christopher Nantista,c Jeffrey Neilson,c Philip Schuster,c Sami Tantawi,c Natalia Toroc and Kevin Zhouc a

Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003, U.S.A. b Institut de Physique Th´eorique, Universit´e Paris Saclay, CEA, F-91191 Gif-sur-Yvette, France c SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, U.S.A.

E-mail: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Abstract: We propose an approach to search for axion dark matter with a specially designed superconducting radio frequency cavity, targeting axions with masses ma . 10−6 eV. Our approach exploits axion-induced transitions between nearly degenerate resonant modes of frequency ∼ GHz. A scan over axion mass is achieved by varying the frequency splitting between the two modes. Compared to traditional approaches, this allows for parametrically enhanced signal power for axions lighter than a GHz. The projected sensitivity covers unexplored parameter space for QCD axion dark matter for 10−8 eV . ma . 10−6 eV and axion-like particle dark matter as light as ma ∼ 10−14 eV. Keywords: Beyond Standard Model, Dark matter, Dark Matter and Double Beta Decay (experiments) ArXiv ePrint: 1912.11048

c The Authors. Open Access, Article funded by SCOAP3 .

https://doi.org/10.1007/JHEP07(2020)088

JHEP07(2020)088

Axion dark matter detection by superconducting resonant frequency conversion

Contents 1 Introduction

1

2 Conceptual overview

5

3 Signal power

7 11

5 Noise sources 5.1 Thermal and amplifier noise 5.2 Oscillator phase noise 5.3 Mechanical vibration noise 5.4 Field emission

13 15 16 17 21

6 Physics reach

23

7 Outlook

27

A Cavity geometry and overlap factor

28

B Geometric rejection

33

C Parametric optimization of coupling

34

1

Introduction

The axion is a hypothetical parity-odd real scalar, protected by a shift symmetry and derivatively coupled to Standard Model fields. It is predicted by the Peccei-Quinn solution to the strong CP problem [1–4] and expected to arise generically from string theory compactifications [5–7]. It was shown to be a viable dark matter (DM) candidate four decades ago [8, 9]. A generic prediction of axion models is the coupling to photons [10–14], L⊃−

gaγγ a F F˜ = −gaγγ a E · B . 4

(1.1)

This interaction can induce axion-photon conversion in the presence of a background electromagnetic field via the Primakoff process [15], which has been exploited in various axion searches [16–26]. These searches have started to cover parameter space motivated by the Peccei-Quinn solution to the strong CP problem [10–14], gaγγ ' 3×10−16 GeV−1 (ma /µeV), but for now without a positive detection.1 1

The value quoted is the