New ALPS Results on Hidden-Sector Lightweights

TL;DR

This work reports ALPS laboratory limits on WISPs in the sub-eV mass range using an upgraded light-shining-through-a-wall experiment with resonant SHG, a high-power production resonator, refractive-index tuning, and a high-quantum-efficiency CCD. The analysis translates absence of signal into 95% CL bounds on ALP couplings $g_\pm$ versus mass $m_\phi$, hidden-photon mixing $\chi$ versus $m_{\gamma'}$, and mini-charged particles, with vacuum runs providing the strongest constraints and gas runs filling coherence gaps. The results constitute the most stringent purely laboratory constraints to date in this mass region and carry implications for cosmological models invoking extra radiation density, while outlining a feasible path for future experiments to explore deeper into hidden-sector parameter space and potentially test QCD axions. The paper argues that advancing magnets, laser power, detectors, and resonant-regeneration techniques will be crucial for reaching these ambitious sensitivity goals.

Abstract

The ALPS collaboration runs a "Light Shining through a Wall" (LSW) experiment to search for photon oscillations into "Weakly Interacting Sub-eV Particles" (WISPs) often predicted by extensions of the Standard Model. The experiment is set up around a superconducting HERA dipole magnet at the site of DESY. Due to several upgrades of the experiment we are able to place limits on the probability of photon-WISP-photon conversions of a few 10^{-25}. These limits result in today's most stringent laboratory constraints on the existence of low mass axion-like particles, hidden photons and minicharged particles.

Figures (6)

• Figure 1: Schematic view of the ALPS LSW experiment. See the text for a description.
• Figure 2: An example of the distribution of baseline ADUred values in the signal and background sets. The lines show Gaussians fitted to the data.
• Figure 3: The difference of the mean ADUred values in signal and background frames in the low-intensity test of our experiment. The signal pixel excess of $23\pm 3$ ADUs is evident in the central bin.
• Figure 4: Exclusion limits ($95\%$ C.L.) for pseudoscalar (left) and scalar (right) axion-like-particles as described in this paper from the vacuum and gas runs. Shown for comparison are results from the BMV Fouche:2008jkRobilliard:2007bq, BFRT Cameron:1993mr, GammeV Chou:2007zzc, LIPSS Afanasev:2008jt and OSQAR Pugnat:2007nu LSW experiments. Dashed and dotted lines show the bounds on ALP-induced dichroism and birefringence from the PVLAS experiment Zavattini:2007ee.
• Figure 5: $95\%$ C.L. exclusion limits for hidden photons. For comparison we show the exclusion limits from the BMV Fouche:2008jk, GammeV Ahlers:2007qf and LIPSS Afanasev:2008jt experiments. Also shown are limits from searches of modifications of Coulomb's law Bartlett:1988yy, distortions of the CMB spectrum Jaeckel:2008fi and the solar axion search by CAST Redondo:2008aa. Hidden photons in the horizontal redish band could account for the apparent excess in the relic neutrino density recently reported by WMAP-7 Komatsu:2010fb.