Abstract
Kaluza-Klein (KK) axions appear in theories with extra dimensions as higher mass, significantly shorter lifetime, excitations of the Peccei-Quinn axion. When produced in the Sun, they would remain gravitationally trapped in the solar system, and their decay to a pair of photons could provide an explanation of the solar corona heating problem. A low-density detector would discriminate such a signal from the background, by identifying the separation of the interaction point of the two photons. The NEWS-G collaboration uses large volume Spherical Proportional Counters, gas-filled metallic spheres with a spherical anode in their centre. After observation of a single axionlike event in a 42 day long run with the SEDINE detector, a $90\%$ C.L. upper limit of $g_{a\gamma\gamma}<8.99\cdot10^{-13}\,GeV^{-1}$ is set on the axion-photon coupling for a KK axion density on Earth of $n_{a}=4.07\cdot10^{13}\,m^{-3}$ and two extra dimensions of size $R = 1\,eV^{-1}$.
Highlights
The Peccei-Quinn (PQ), or quantum chromodynamics, axion was first proposed to solve the Strong CP problem [1]
After observation of a single axionlike event in a 42 day long run with the SEDINE detector, a 90% C.L. upper limit of gaγγ < 8.99 × 10−13 GeV−1 is set on the axion-photon coupling for the benchmark of a Kaluza-Klein axion density on Earth of na 1⁄4 4.07 × 1013 m−3 and two extra dimensions of size R 1⁄4 1 eV−1
The signal from a single primary electron is the current induced by the ions generated in the avalanche as they drift away from the central sensor. This is given by the Shockley-Ramo theorem [44], which states that a particle induces a portion of its charge on any given electrode given by the electric potential that would exist at the particle’s instantaneous position if the selected electrode was at unit potential, all other electrodes at zero potential, and all charges removed [45]
Summary
The Peccei-Quinn (PQ), or quantum chromodynamics, axion was first proposed to solve the Strong CP problem [1]. Reference [18] used the standard solar model to predict production of KK axions through the first two processes, with ABC reactions being negligible for axion models without tree-level coupling to electrons, such as KSVZ They demonstrate that a proportion of such heavy axions, mainly created through photon coalescence, will leave the surface of the Sun with speeds under escape velocity, and will remain trapped in closed orbits in the Solar System, accumulating throughout the Sun’s lifetime. For these values, the local density of axions on Earth is na 1⁄4 4.07 × 1013 m−3, and the integrated decay rate is approximately 0.08 event=m3=day, mainly in the 5–15 keV range.
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