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Abstract

We present new exclusion bounds obtained at the European X-Ray Free Electron Laser facility (EuXFEL) on axionlike particles in the mass range 10⁻³  eV≲m_a≲10⁴  eV. Our experiment exploits the Primakoff effect via which photons can, in the presence of a strong external electric field, decay into axions, which then convert back into photons after passing through an opaque wall. While similar searches have been performed previously at a third-generation synchrotron [Yamaji et al., Phys. Lett. B 782, 523 (2018)], our work demonstrates improved sensitivity, exploiting the higher brightness of x-rays at EuXFEL.