Deuteron Photodissociation in Ultraperipheral Relativistic Heavy-Ion on Deuteron Collisions

In ultraperipheral relativistic deuteron on heavy-ion collisions, a photon emitted from the heavy nucleus may dissociate the deuterium ion. We find deuterium breakup cross sections of 1.38 barns for deuterium-gold collisions at a center of mass energy of 200 GeV per nucleon, as studied at the Relativistic Heavy Ion Collider, and 2.49 barns for deuterium-lead collisions at a center of mass energy of 6.2 TeV, as proposed for the Large Hadron Collider. This cross section includes an energy-independent 140 mb contribution from hadronic diffractive dissociation. At the LHC, the cross section is as large as that of hadronic interactions. The estimated error is 5%. Deuteron dissociation could be used as a luminosity monitor and a ‘tag’ for moderate impact parameter collisions. Typeset using REVTEX 1 Deuterium-heavy ion collisions are of considerable interest at heavy ion colliders. Technically, they are much easier than proton-ion collisions because the deuteron charge-to-mass ratio, Z/A, is similar to that of heavy ions, greatly simplifying the magnetic optics around the collision point. Further, at the LHC, the matching Z/A of the two beams means that the nucleon-nucleon center-of-mass frame is closer to the lab frame than it would be in pA collisions. The similarity in proton:neutron ratios will also simplify the comparison of data from dA and AA collisions. For these reasons, dA collisions may be preferred over pA. Ultraperipheral dA collisions are also of interest. The strong electromagnetic field of the heavy ion acts as an intense photon beam which strikes the deuterium, producing very high energy γd collisions. In AA collisions, there is a two-fold ambiguity over which ion emitted the photon. However, in dA collisions, the photon almost always comes from the heavy ion, allowing a clean determination of the photon energy based on the final state rapidity. Some ultra-peripheral reactions are unique to dA. Here, we consider one example, photodissociation of deuterium. This reaction has a very large cross section and can serve as a luminosity monitor and as a ‘tag’ for moderate impact parameter UPCs. The photodissociation cross section is