Family reunion for the UA2 calorimeter

After many years in CERN’s Microcosm exhibition, the last surviving UA2 central calorimeter module has been moved to Hall 175, the technical development laboratory of the ATLAS Tile Hadronic Calorimeter (Tilecal). The UA2 and ATLAS calorimeters are cousins, as both were designed by Otto Gildemeister. Now side by side, the calorimeters illustrate the progress made in sampling organic scintillator calorimeters over the past 35 years.


The ATLAS Tile Calorimeter prototypes (left) and the UA2 central calorimeter (right) in Hall 175. (Image: Mario Campanelli/ATLAS.)

From 1981 to 1990, the UA2 experiment was one of the two detectors on CERN’s flagship accelerator, the SPS. At the heart of the UA2 detector was the central calorimeter. It was made up of 24 slices – each weighing four tonnes – arranged like orange segments around the collision point. These calorimeter slices played a central role in the research carried out by UA2 for the discovery of W bosons, as well as in the detection of hadronic jets. Once UA2 was taken offline, 23 of the slices were dismantled and their materials repurposed – leaving one slice for the history books.

Since the end of June, the UA2 calorimeter slice has had a new home in Hall 175, where the Tilecal calorimeter currently used in the ATLAS detector continues to be developed. “The Tilecal geometry is the natural evolution of the UA2 calorimeter concept,” says Irene Vichou, ATLAS Tilecal project leader.

Otto Gildemeister with two colleagues from UA2, Luigi Di Lella (left) and Peter Jenni (right), in front of the UA2 central calorimeter ‘orange slice’ module.

“For example,” explains Ana Henriques, former Tilecal project leader, “the Tilecal has scintillating tiles oriented perpendicular to the colliding beams instead of the traditional parallel orientation, and it uses wavelength-shifting fibres instead of light-guide plates.” 

Otto Gildemeister, the expert who designed both calorimeters, visited Hall 175 recently during a trip to CERN. “It was nice to visit the well-conserved UA2 calorimeter ‘orange slice’ module, which, after so many years, still appears quite familiar to me,” he said. “To see it alongside the present and future ATLAS Tile Calorimeter developments was touching.”

by Abha Eli Phoboo