Equivalent g beams in UPC A+A collisions

• Heavy-ions (w/ charge Z) produce stronger

• electromagnetic fields than e± beams due to

• the coherent action of all proton charges.

• EPA formula for flux of photons in electromagnetic

• (i.e. ultraperipheral, b>bmin~ 2RA ) A+A collisions:

• Characteristics of photon beams:

  • Flux ~ Z2 (~7·103 for Pb) and s(gg) ~ Z4 (i.e. ~4·107) larger than e± beams !
  • “Coherence condition” : g wavelength > nucleus size since all protons