Physics analysis of peripheral and ultraperipheral high-energy nuclear collisions with the ATLAS detector.

At the Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC), relativistic heavy ion collisions such as lead on lead (Pb+Pb) are used to create droplets of quark-gluon plasma (QGP). The defining signals of QGP diminish as the overlapping area of the colliding nuclei decreases. However, small systems like proton on proton (p+p) and proton on lead (p+Pb) exhibit hydrodynamic behavior, suggesting that QGP may still be created in smaller systems including in peripheral heavy ion collisions. Ultra-peripheral collisions (UPC's) may form a background to the peripheral A+A collisions of interest and thus peripheral event data should be corrected for their contributions. In this study we have investigated methods of detecting and removing the contributions of UPC's. We will show how we have used the Monte Carlo simulation programs, EPOS, HIJING, and DPMJET to estimate the contributions of different processes. The simulation outputs are compared against real peripheral 5.02 TeV Pb+Pb data recorded by the ATLAS detector at the Large Hadron Collider.