Vertical emittance growth from IBS diffusion via beam-beam coupling in the EIC

We investigate vertical emittance growth in the Electron-Ion Collider (EIC) arising from intrabeam scattering (IBS) diffusion through beam-beam interactions. Using weak-strong simulations, we demonstrate that when horizontal noise is introduced, vertical emittance increases even in the absence of direct vertical diffusion. This behavior is attributed to resonance streaming around the synchro-betatron resonance 2𝜈_x − 2𝜈_y + p𝜈_z = 0, which enables unidirectional emittance transfer from the horizontal to the vertical plane. We further show that horizontal cooling alone cannot suppress the vertical growth, confirming that dedicated vertical cooling is essential for preserving the flat beam profile in high-luminosity EIC operation.