New exclusion limits on scalar and pseudoscalar axionlike particles from light shining through a wall

Physics beyond the Standard Model predicts the possible existence of new particles that can be searched at the low-energy frontier in the sub-eV range. The OSQAR photon regeneration experiment looks for “light shining through a wall” from the quantum oscillation of optical photons into “weakly interacting sub-eV particles,” such as axion or axionlike particles (ALPs) in a 9 T transverse magnetic field over a length of $2\times 14.3\mathrm{m}$. In 2014, this experiment was run with an outstanding sensitivity, using an 18.5 W continuous wave laser emitting in the green at the single wavelength of 532 nm. No regenerated photons have been detected after the wall, pushing the limits for the existence of axions and ALPs down to an unprecedented level for such type of laboratory experiment. The diphoton couplings of possible pseudoscalar and scalar ALPs can be constrained in the nearly massless limit to be less than $3.5\times {10}^{-8}{\mathrm{GeV}}^{-1}$ and $3.2\times {10}^{-8}{\mathrm{GeV}}^{-1}$, respectively, at 95% confidence level.

Figure 1

Principle of the OSQAR LSW experiment.

Figure 2

Initial and final positions of the attenuated laser beam on the CCD for run-90 devoted to the search of S-ALPs (${\overrightarrow{E}}_{\gamma }\perp \overrightarrow{B}$). The signal region covers seven pixels.

Figure 3

Distribution of the cumulated counts $n_{90j}$ of background clusters $j$ of size and shape identical to the signal region shown Fig. 2 for run-90, after applying all background corrections (see text). Gaussian fit gives mean ${\mu }_{90}^{\mathrm{bkg}}=125.24\pm 0.05$ and standard deviation ${\sigma }_{90}^{\mathrm{bkg}}=14.77\pm 0.04$ with reduced chi-squared ${\chi }^2/\mathrm{n}.\mathrm{d}.\mathrm{f}.=1.04$. The red line represents the cumulated count $N_{90}=119$ of the signal region. It crosses the Gaussian distribution at about 2000, which corresponds to the number of background clusters with the same cumulated count as the signal region.

Figure 4

Posterior probability distribution function $p(dN/dt|\text{data})$ of reconverted photon rate $dN/dt$ for incoming photon polarization parallel (${\overrightarrow{E}}_{\gamma }\parallel \overrightarrow{B}$) (left) and perpendicular (${\overrightarrow{E}}_{\gamma }\perp \overrightarrow{B}$) (right) to the magnetic field $\overrightarrow{B}$.

Figure 5

Posterior probability distribution function $p(dN/dt|\text{data})$ of reconverted photon rate $dN/dt$ for incoming photon polarization parallel (${\overrightarrow{E}}_{\gamma }\parallel \overrightarrow{B}$) (top) and perpendicular (${\overrightarrow{E}}_{\gamma }\perp \overrightarrow{B}$) (bottom) to the magnetic field $\overrightarrow{B}$, with an artificially imposed fake signal of $1\times {10}^{-3}\mathrm{ADU}{\mathrm{s}}^{-1}$.

Figure 6

Exclusion limits for the searches of PS-ALPs and S-ALPs at 95% C.L. obtained in vacuum by the present OSQAR LSW experiment. Also reported for comparison is the latest result of ALPS LSW experiment in vacuum.