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The axion, a theoretical particle arising from the breaking of Peccei-Quinn (PQ) symmetry, was proposed to explain the absence of CP violation in quantum chromodynamics (QCD). Axion-like particles (ALPs) are similarly predicted in string theory and could account for cold dark matter if their mass falls within the range of 10-6 – 10-4 eV. While most experimental searches target this "light axion window," heavy axions with masses exceeding 10-2 eV have recently gained attention. These “heavy” 

axions are associated with a low scale breaking of Peccei-Quinn so are less susceptible to the “axion quality problem”, namely destabilizing effects from quantum gravity on global symmetries. The most sensitive experimental bounds on these heavy axions are from various searches which aim to detect axions from the sun. This entails a degree of model dependence due to the high temperatures and plasma frequencies associated with this generation mechanism. So-called “direct detection” experiments, which aim to generate and detect axions in the laboratory have been proposed as a search strategy which negates this model dependence.

In this seminar, we describe a novel direct-detection experiment, conducted at EuXFEL (European X-Ray Free Electron Laser). Our experiment exploits the Primakoff effect via which photons can decay into axions in the presence of a strong external electric field and then reconvert back into photons after passing through an opaque wall. This was previously employed in so-called “light shining through wall experiments” with optical lasers and external magnetic fields. However, in our work we used a free electron laser combined with a pair of germanium crystals. Within these crystals, the electric fields can be as high as 10^11 V/m, corresponding to a magnetic field ~1 kT – much higher than the field strengths accessible using the best electromagnets. In our initial experiment we were able to probe down to coupling constants on the order of 10^-3/GeV, however we will describe modifications to this setup capable of bringing the estimated bounds down to ~10^6/GeV.  This is close to the expectation for QCD axions to be dark matter.