Observations of beam losses due to bound-free pair production in a heavy-ion collider

We report the first observations of beam losses due tobound-free pair production at the interaction point of a heavy-ioncollider. This process is expected to be a major luminosity limit for theLarge Hadron Collider (LHC) when it operates with 208Pb82+ ions becausethe localized energy deposition by the lost ions may quenchsuperconducting magnet coils. Measurements were performed at theRelativistic Heavy Ion Collider (RHIC) during operation with 100GeV/nucleon 63Cu29+ ions. At RHIC, the rate, energy and magnetic fieldare low enough so that magnet quenching is not an issue. The hadronicshowers produced when the single-electron ions struck the RHIC beampipewere observed using an array of photodiodes. The measurement confirms theorder of magnitude of the theoretical cross section previously calculatedby others.