Study of electromagnetic dissociation of heavy nuclei at the relativistic heavy ion collider

Abstract

The work presented here is devoted to research which I have done within the BRAHMS collaboration at Brookhaven National Laboratory in the period from January 1999 until October 2001. The Texas A&M group in the BRAHMS experiment is responsible for the zero-degree calorimeters (ZDCs) - an important part of the experiment's global detector system. The two BRAHMS ZDCs were built at Texas A&M. The ZDCs measure forward going neutrons at RHIC and are used for beam luminosity monitoring, determining the interaction vertex, making collision centrality measurements, forming triggers, rejecting background and are also used for a number of physics measurements. The experimental data from the BRAHMS zero-degree calorimeters, beam-beam counters and tile multiplicity array were used to study the process of the mutual Coulomb dissociation of gold nuclei during the two runs which have taken place at RHIC in the summer of 2000, at [] = 130 GeV, and in the summer 2001, at [] = 200 GeV. This process is a well-known phenomenon at heavy-ion colliders. When two ultrarelativistic heavy nuclei pass near each other at the impact parameter larger than sum of nuclear radii, the long-ranged Lorentz-contracted electromagnetic field of one nucleus can excite another nucleus by exchange of one or more photons, which usually results in excitation of giant dipole resonance. Resonance de-excitation occurs primarily by emission of neutrons. The transverse momenta of such neutrons are usually less then 250 MeV/c and therefore the neutrons are spread within very narrow cone about the beam direction.