Production and Detection of Axion-Like Particles in a HERA Dipole Magnet - Letter-of-Intent for the ALPS experiment -

TL;DR

The paper proposes ALPS, a photon-regeneration ('light shining through walls') experiment using a DESY HERA dipole magnet to test the PVLAS hint of a light axion-like particle coupled to photons. It details the theoretical framework of photon-axion oscillations, the experimental design around a single 5 T magnet, and the key components (MIU, high-power infrared laser, and InGaAs detector), including buffer-gas tuning to optimize coherence. It then estimates the experimental reach, showing potential to confirm or exclude the PVLAS region and to measure or constrain the mass and coupling of the particle, though QCD axions remain out of reach in this configuration. The work outlines a feasible near-term program with concrete sensitivity expectations and configurations, aiming for a rapid clarification of the axion-like particle interpretation of the PVLAS anomaly and a measurement of its properties.

Abstract

Recently, the PVLAS collaboration has reported evidence for an anomalous rotation of the polarization of light in vacuum in the presence of a transverse magnetic field. This may be explained through the production of a new light spin-zero (axion-like) neutral particle coupled to two photons. In this letter-of-intent, we propose to test this hypothesis by setting up a photon regeneration experiment which exploits the photon beam of a high-power infrared laser, sent along the transverse magnetic field of a superconducting HERA dipole magnet. The proposed ALPS (Axion-Like Particle Search) experiment offers a window of opportunity for a rapid firm establishment or exclusion of the axion-like particle interpretation of the anomaly published by PVALS. It will also allow for the measurement of mass, parity, and coupling strength of this particle. [The experiment has been approved by the DESY directorate on January 11, 2007.]

Figures (11)

• Figure 1: Schematic view of (pseudo-)scalar production through photon conversion in a magnetic field (left), subsequent travel through a wall, and final detection through photon regeneration (right).
• Figure 2: Two photon coupling $g$ of the (pseudo-)scalar versus its mass $m_\phi$. Top panel: 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. Bottom panel: Three sigma allowed region from PVLAS data on rotation plus BFRT data on rotation, ellipticity, and regeneration Ahlers:priv.
• Figure 3: Two photon coupling $g$ of the (pseudo-)scalar versus its mass $m_\phi$. The 3 sigma allowed region from PVLAS data on rotation plus BFRT data on rotation, ellipticity, and regeneration is shown in red Ahlers:priv. Top panel: Iso-contours of the regeneration probability probability $P_{\gamma\to\phi\to\gamma}$, Eq. (\ref{['regpropab']}), for the parameters of the HERA dipole magnet, $B_1=B_2=5$ T, $\ell_1=\ell_2=4.21$ m, exploiting an infrared photon beam, $\lambda =1064$ nm, corresponding to $\omega =1.17$ eV, in vacuum ($n_\gamma =1$). Bottom panel: Same as top panel, but in buffer gas with $n_\gamma -1=5\times 10^{-7}$.
• Figure 4: Schematic view of the experimental setup with the laser on the left, followed by the laser injector/extractor system, the magnet and the detector table. An intensity-reduced reference beam of the laser is guided parallel to the magnet for constant alignment monitoring between laser and detector.
• Figure 5: HERA dipole at the magnet test stand.