High magnetic fields suppress cuprate superconductivity to reveal an unusual density wave (DW) state coexisting with unexplained quantum oscillations. Although routinely labeled a charge density wave (CDW), this DW state could actually be an electron-pair density wave (PDW). To search for evidence of a field-induced PDW, we visualized modulations in the density of electronic states ( ) within the halo surrounding Bi Sr CaCu O vortex cores. We detected numerous phenomena predicted for a field-induced PDW, including two sets of particle-hole symmetric ( ) modulations with wave vectors and , with the latter decaying twice as rapidly from the core as the former. These data imply that the primary field-induced state in underdoped superconducting cuprates is a PDW, with approximately eight CuO unit-cell periodicity and coexisting with its secondary CDWs.