Photon Regeneration Plans

TL;DR

The paper argues that precision, low-energy photon experiments can complement high-energy colliders by probing very light, weakly interacting particles predicted by extensions of the Standard Model. It surveys polarization-based tests and the regeneration (light-shining-through-walls) approach as means to test ALP and millicharged particle hypotheses, highlighting the PVLAS results and their interpretation. It outlines the experimental programs and sensitivities, notably ALPS at DESY, and discusses how coherence and buffer-gas tuning influence sensitivity to ALPs. The work emphasizes that decisive laboratory tests in the near term can confirm or exclude ALP and MCP explanations for PVLAS, underscoring the continued relevance of small-scale experiments in fundamental physics.

Abstract

Precision experiments exploiting low-energy photons may yield information on particle physics complementary to experiments at high-energy colliders, in particular on new very light and very weakly interacting particles, predicted in many extensions of the standard model. Such particles may be produced by laser photons send along a transverse magnetic field. The laser polarization experiment PVLAS may have seen the first indirect signal of such particles by observing an anomalously large rotation of the polarization plane of photons after the passage through a magnetic field. This can be interpreted as evidence for photon disappearance due to particle production. There are a number of experimental proposals to test independently the particle interpretation of PVLAS. Many of them are based on the search for photon reappearance or regeneration, i.e. for ``light shining through a wall''. At DESY, the Axion-Like Particle Search (ALPS) collaboration is currently setting up such an experiment.

Figures (7)

• Figure 1: Possible changes of the polarization state of initially linearly polarized photons after the passage through a magnetic field (adapted from Ref. Brandi:2000ty).
• Figure 2: ALP interpretation of BFRT and PVLAS data: two photon coupling $g$ versus mass $m_\phi$. The 95 % confidence level upper limits from BFRT data Cameron:1993mr on polarization (rotation and ellipticity data) and photon regeneration are displayed as dotted lines. The preferred values corresponding to the anomalous rotation signal observed by PVLAS Zavattini:2005tm are shown as a thick solid line.
• Figure 3: MCP interpretation of BFRT and PVLAS data: fractional electric charge $\epsilon = Q_\epsilon/e$ versus mass $m_\epsilon$. The preferred values corresponding to the anomalous rotation signal observed by PVLAS Zavattini:2005tm are shown as a thick solid line.
• Figure 4: Schematic view of ALP production through photon conversion in a magnetic field (left), subsequent travel through a wall, and final detection through photon regeneration (right).
• Figure 5: Schematic view of the experimental setup of the ALPS experiment ALPS.