A Cavity Experiment to Search for Hidden Sector Photons

Abstract

We propose a cavity experiment to search for low mass extra U(1) gauge bosons with gauge-kinetic mixing with the ordinary photon, so-called paraphotons. The setup consists of two microwave cavities shielded from each other. In one cavity, paraphotons are produced via photon-paraphoton oscillations. The second, resonant, cavity is then driven by the paraphotons that permeate the shielding and reconvert into photons. This setup resembles the classic ``light shining through a wall'' setup. However, the high quality factors achievable for microwave cavities and the good sensitivity of microwave detectors allow for a projected sensitivity for photon-paraphoton mixing of the order of χ~10^{-12} to 10^{-8}, for paraphotons with masses in the μeV to meV range -- exceeding the current laboratory- and astrophysics-based limits by several orders of magnitude. Therefore, this experiment bears significant discovery potential for hidden sector physics.

Figures (5)

• Figure 1: Schematic picture of a "light shining through a wall" experiment. The crosses denote the non-diagonal mass terms that convert photons into paraphotons. The photon $\gamma$ oscillates into the paraphoton $\gamma'$ and, after the wall, back into the photon $\gamma$ which can then be detected.
• Figure 2: Existing bounds on the existence of massive paraphotons with kinetic mixing and projected sensitivity for the proposed experiment. Upper limit on the mixing parameter $\chi$ versus the mass $m_{\gamma^\prime}$, obtained from the non-observation of deviations from Coulomb's law Williams:1971msBartlett:1988yy (blue, labelled "Coulomb"), from the non-observation of laser "light shining through a wall" (black, labeled "Laser"; thick: published limit from BFRT Cameron:1993mr; thin: projected sensitivity of ongoing experiments Ahlers:2007rd), and from solar energy balance considerations Popov:1991Popov:1999 (red, labelled "Sun"). Also shown is the projected sensitivity of our proposed "microwaves permeating through a shielding" setup (darkred, labelled "Cavities"). The dashed dotted line corresponds to the optimistic scenario ($Q=Q^\prime =10^{11}$, $\mathcal{P}_{\rm em}\sim 1$ W, $\mathcal{P}_{\rm detectable}=10^{-26}$ W, $\nu_0=1.3\,{\rm{GHz}}$, i.e. $\omega_0\approx 5.4\, \mu {\rm{eV}}$) and the dashed fat line to the more modest one ($Q=10^{10}$, $Q^\prime =10^{4}$, $\mathcal{P}_{\rm em}\sim 1$ W, $\mathcal{P}_{\rm detectable}=10^{-20}$ W, $\nu_0=1.3\ {\rm GHz}$) in the text. In both cases we have used $|G|=1$ for $m_{\gamma^{\prime}}\leq\omega_{0}$ and $|G|=0$ for $m_{\gamma^{\prime}}>\omega_{0}$, for simplicity, for the "geometry factor" \ref{['geofac']}. The thin dashed dotted line corresponds to the sensitivity which one might get from the optimistic scenario, if one scans the frequency between $250\ {\rm MHz}\lesssim \nu_0\lesssim 250\ {\rm GHz}$, corresponding to $1\,\mu {\rm eV} \lesssim \omega_0\lesssim 1\,{\rm meV}$ (for frequencies $\nu_{0}>3\,{\rm{GHz}}$, the losses in the cavities grow due to an increased surface resistance Aune:2000gb; accordingly, we have assumed a drop in the $Q$ value for frequencies higher than $3 \,{\rm{GHz}}$.)
• Figure 3: Schematic illustration of a "microwaves permeating through a shielding" experiment for the search for massive hidden sector photons mixing with the photon (a high-frequency (HF) generator drives the emitter cavity).
• Figure 4: Geometry factor $|G|$ for a setup with two identical cubic cavities with side length $L=\sqrt{2}\pi/\omega_{0}$ in the $n=1,m=1,p=0$ mode of Eq. \ref{['cubic']}. The cavities are placed parallel and are separated by a distance $d=0$ (red), $d=L$ (blue) and $d=5\,L$ (green) along the z-axis. As expected $|G|$ scales roughly with $1/d$.
• Figure 5: Schematic illustration of a "microwaves permeating through a shielding" experiment for the search for an axion-like particle $\phi$ mixing with the photon in the presence of a magnetic field.