Datasets

In 2001, the RHIC collided gold nuclei at a center of mass energy of 200 GeV. Two UPC (Ultra Peripheral Collision) specific triggers were utilized, the UPC Minbias trigger and the UPC Topology trigger. The UPC Minbias trigger required at least one neutron in each Zero Degree Calorimeter and low multiplicity in the Central Trigger Barrel. Approximately 2.5 M events were collected in the Minbias data set. The integrated luminosity was 461.3 mb^-1. The following plot demonstrates the difference in the UPC Minbias vs. the Hadronic Minbias triggers.

An illustration of the CTB as divided for the UPC topology trigger.

The UPC Topology trigger utilized the Central Trigger Barrel divided into four quadrants. It required at least one track in the north and south quadrants; the top and bottom quadrants were used as vetos, to reject cosmic rays. Approximately 1.5 M events were collected in the Topology data set. The integrated luminosity was 7174 mb^-1.

A plot of ADC counts in the ZDCs vs the CTB for 2001 STAR triggers. The UPC Minbias triggered data is indicated by the purple region. The numbers on the plot represent trigger words.