CERN Develops Prototype Cassettes for Cutting-Edge Calorimeter

Researchers at CERN have made a significant advancement in particle detection technology by developing the first prototype cassettes for the new CMS High-Granularity Calorimeters (HGCALs). These cassettes are crucial components of the upcoming calorimeters, which will be integrated into the Compact Muon Solenoid (CMS) experiment as part of preparations for the High-Luminosity LHC (HL-LHC), scheduled to commence operations in 2030.

Innovative Design and Functionality

The newly developed cassettes, shaped like wedges, are designed to form the building blocks of the HGCALs. Once completed, the HGCAL will be the largest silicon-based detectors ever constructed, with two endcaps set to replace the existing ones on either side of the CMS. According to Dimitra Tsionou, a physicist from National Taiwan University, the HGCAL represents a leap forward in detection capabilities. “HGCAL is effectively a 5D calorimeter,” she stated, highlighting its ability to perform three-dimensional spatial reconstruction alongside energy reconstruction and high timing resolution.

This advanced technology is essential for managing the increased particle collisions expected from the HL-LHC, which will produce 4 to 5 times more simultaneous collisions than the current LHC. Specifically, the new setup anticipates around 140–200 collisions occurring every second, generating a level of activity that the existing CMS endcaps cannot adequately measure. The HGCAL is engineered to withstand the heightened radiation levels resulting from these more frequent collisions.

Technical Specifications and Collaboration Efforts

The HGCAL will not only endure harsher conditions but will also enhance the energy resolution, particle identification, and triggering performance compared to the current endcaps. Following a particle collision, numerous secondary particles will enter the endcaps for detection by the HGCAL. As these collisions occur simultaneously but at distances of up to 10 cm apart, the HGCAL will precisely measure the timing of each particle, allowing it to trace their origins back to the collision point.

To achieve this level of precision, the HGCAL requires a high density of sensors, which contributes to its “high granularity” designation. Each cassette is equipped with sensors that record energy, position, and timing across 47 layers of the detector. CERN will construct the 26 layers closest to the collision points, forming the electromagnetic section to detect electrons and photons. In parallel, Fermilab will develop the 21 layers further away, which will measure particles like protons and neutrons in the hadronic section. Each complete endcap will encompass roughly 500 square meters of active sensor area—equivalent to nearly two tennis courts—and will feature more than 3 million detector channels.

“It’s very ambitious,” noted Ludivine Ceard, another physicist from National Taiwan University and the project’s logistics manager. “This is the first time that a detector using this technology will be built on this scale and have to operate in such challenging conditions.”

Once Fermilab finalizes the construction and testing of the hadronic cassettes, they will be transported to CERN for integration into steel structures. The first of these structures was produced in Pakistan and is currently being reassembled at CERN. The electromagnetic section will subsequently be joined with the hadronic section to create a complete HGCAL endcap.

Despite the numerous challenges ahead, Ceard emphasized the importance of the project. “HGCAL is really special, the first of its kind,” she stated, expressing the team’s commitment to overcoming the obstacles they face in this pioneering endeavor.