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  • Open Access

Axion emission from nuclear magnetic dipole transitions

R. Massarczyk, P.-H. Chu, and S. R. Elliott
Phys. Rev. D 105, 015031 – Published 26 January 2022
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  • INTRODUCTION
  • AXIONIC DEEXCITATION OF NUCLEAR STATES
  • CALCULATION OF THE AXION FLUX
  • AXION LIFETIME
  • SOLAR AXIONS REVISITED
  • AXIONS FROM NUCLEAR REACTORS
  • DETECTION OF AXIONS
  • SUMMARY
  • ACKNOWLEDGMENTS
    • References

    Abstract

    Nuclear transitions are one possible source of axions but past searches were restricted to specific transitions. In this manuscript, we propose to extend the search for axions and axionlike particles to a more complex environment that would result in a number of correlated observables. By including creation mechanisms that have their origin in the Carbon-Nitrogen-Oxygen (CNO) cycle, we show that the search for solar axions should not only be restricted to the keV-mass region. We discuss limitations, such as the lifetime and the mass, that create a challenge for an Earth-bound experiments. We show that it is possible to use the same creation mechanisms as used in solar axions to search with a comparable rate at nuclear power reactors.

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    • Received 13 December 2021
    • Accepted 10 January 2022

    DOI:https://doi.org/10.1103/PhysRevD.105.015031

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    AxionsBeta decayNuclear reactionsParticle dark matterResonance reactionsSolar neutrinosWeakly interacting massive particles
    Particles & FieldsNuclear Physics

    Authors & Affiliations

    R. Massarczyk*, P.-H. Chu, and S. R. Elliott

    • Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

    • *massarczyk@lanl.gov

    Article Text

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    Vol. 105, Iss. 1 — 1 January 2022

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    • Figure 1
      Figure 1

      Current limits on axion-photon and axion-electron coupling [10]. The expectation values for the KSVZ model [4], the DFSZ model [6], the PQWW model [1], and HW model [8] are shown in black and gray.

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    • Figure 2
      Figure 2

      Axion-to-photon branching for a 1.115-MeV magnetic dipole transition in Cu65 [41] as a function of axion mass calculated using Eq. (8). For illustration, the nuclear parameters are randomized in each mass bin. The probability functions are normalized for each individual axion-mass bin. The cross marks the branching calculated in Ref. [41].

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    • Figure 3
      Figure 3

      Photon-axion branching as function of β and η for a 150-keV axion in Cu65. The shaded area marks the parameter range covered in this work, the stars mark existing calculations, see Table 1. Values of β∼−0.52 minimizes the branching (gray-white area), while values along η∼0.38β+4.71 maximize it (dark red).

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    • Figure 4
      Figure 4

      Distribution of the M1/E2 mixing ratios for the magnetic dipole transitions available in the ENSDF entries of the RADWARE package. The red curve shows a fit with a Lorentzian curve. Random values using this fit were applied to transitions with unmeasured values.

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    • Figure 5
      Figure 5

      Schematic illustration of Eq. (9) for the case of an isotope that could undergo a β-decay or a β, n-decay. The different factors are highlighted in red. For each of the five steps, the red highlighted part depicts the factor above.

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    • Figure 6
      Figure 6

      Lifetime for a 5.5-MeV axion as created in the solar burning process. The lifetime of the standard QCD axion (black, different values of x) decreases at 1.022 MeV where the electron-positron pair production channel opens up. The flight time to Earth (red) prevents the observation of high-mass axions at the Earth, even when relativistic effects are included. In addition, the flight times for a reactor based experiment using a 10-m long flight path is shown as well (blue).

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    • Figure 7
      Figure 7

      Expected axion flux from the Sun by an axionic component within magnetic dipole transitions. The dashed lines show which spectrum would be visible by the individual contributors in the solar environment without decay-in-flight. The red solid line represents the sum and takes into account that axions decay on the way to the Earth.

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    • Figure 8
      Figure 8

      Total flux of the solar axions for different axion masses. For an axion mass of ∼45  keV the flux, shown in Fig. 7, reaches its maximum for a detector situated at the Earth radius distance.

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    • Figure 9
      Figure 9

      Expected axion flux from HFIR (85  MWth) at a 10-meter distance due to a possible mixing of an axionic component into the deexcitation of magnetic dipole transitions. The red solid line represents the sum of the individual contributions (colored). The dashed lines enclose the area between the worst and best case of all Monte-Carlo realizations. The short half-lives of heavy axions limit the observable masses to less than 1.022 MeV.

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    • Figure 10
      Figure 10

      Total energy spectrum of the reactor axions for different axion masses. The same experimental condition as in Fig. 9 are used for this spectrum. For an axion mass of the ∼450  keV the flux reaches its maximum.

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    • Figure 11
      Figure 11

      Total axion flux from different sources. For reactor based searches, we choose conditions as possible at HFIR, or a power reactor [44]. The expected axion flux from Ref. [41] is calculated using the branching from Fig. 2, a 10.9 kCi-strong Cu65 source, and a detector at 20 inches distance.

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    • Figure 12
      Figure 12

      Cross section for Primakoff- (red), and Compton-conversion (black) as a function for axion mass for a 1.115-MeV transition as in Fig. 2. For both cross sections the coupling constants gaγγ and gaee are set to 10−6. The cross marks the prediction from Ref. [9].

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    • Figure 13
      Figure 13

      Expected integral count rate for the axion spectra shown in Figs. 8 and 10 for one kilogram of germanium or carbon-based scintillation detector. The flux value means are given for solar axions on the Earth (top figure) and a HFIR-reactor based experiment (bottom), cf. Figs. 7 and 9. Count rates were calculated with the gaγγ and gaeee=10−6 as input.

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    • Figure 14
      Figure 14

      Count rate over 50-keV bins as calculated from the spectrum in Fig. 10 for an axion mass around 450 keV. The two detection processes, Primakoff (green) and Compton (red), result in different detection count rates using the current limits. The dashed line shows the achieved background from Ref. [10].

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