The UA1 high energy physics experiment ran at CERN from 1981 until 1993 on the SPS collider. The discovery of the W and Z bosons by this experiment and UA2 in 1982 led to the Nobel Prize for physics being awarded to Carlo Rubbia and Simon Van der Meer in 1984.
It was named as the first experiment in the CERN "Underground Area", i.e. located underground outside of the two main CERN sites at an interaction point on the underground SPS accelerator which was modified at the same time to convert it into a collider.