U.S. CMS passes CD-3b DOE checkpoint for detector upgrades

When Fermilab senior scientist Vaia Papadimitriou joined the CMS collaboration four years ago, it was like, “going back home.”

“I have been a member of the CDF collaboration at Fermilab since 1990,” Papadimitriou said. “After the Tevatron finished in 2011, the Large Hadron Collider continued this type of collider physics research at higher energies and luminosities. It is a natural place for me to be.”

The massive CMS detector collects data from the LHC, and the scientific collaborators reconstruct and analyze the data to search for new physics and phenomena. CMS was conceived in the 1990s and is expected to run through 2042. As the LHC physics program evolves, so does the CMS detector. On June 24, 2022, U.S. scientists working on CMS received CD-3b approval for $7.6 million from the U.S. Department of Energy to make time-critical purchases toward upgrading the CMS detector’s outer tracker and endcap calorimeter.

Project team and Purdue/CMSC personnel looking through the BTL-Tracker Support Tube prototype. Photo: Purdue University

“The DOE has these checkpoints where we present the project, costs, schedule and technical readiness,” said Petra Merkel, a senior scientist at Fermilab. “With the CD-3b approval, we now have the green light to buy more time-critical components for the outer tracker.”

The CMS experiment is composed of dozens of subdetectors that work together to photograph the paths of particles created during the LHC’s collisions. The tracker is the subdetector system closest to the point where the LHC makes particles collide.

“The tracker is at the very center of CMS—closest to the beam pipe,” said Merkel, who is the manager of the US CMS Outer Tracker subproject. “Because of its location, it needs the finest granularity, highest spatial resolution and lowest possible mass.”

This central location also means that the tracker is hit with a huge number of high-energy particles.

“As you hammer this detector, it dies a slow death,” Merkel said.

Merkel, Papadimitriou and their U.S. colleagues on CMS are currently planning and constructing a new outer tracker designed to thrive inside the High-Luminosity LHC, an accelerator upgrade that will increase the LHC’s collision rate by a factor of five. They plan to have this new detector—and many others—finished and installed inside CMS before the HL-LHC starts operation in 2029.

“Despite the pandemic and war [in Europe]—which put some breaks into the project schedule—we are still really making significant progress,” said Papadimitriou, who is deputy project manager for the US CMS HL-LHC Upgrade.

Now that the U.S. CMS team has passed this CD-3b checkpoint, the next steps are procuring the raw materials and starting construction on integral components, such as the outer tracker’s carbon fiber support structure. This support structure will eventually carry thousands of silicon sensors that will “photograph” passing particles, highlighting the particles’ trajectories. The next DOE checkpoint will be in January 2023. It will focus on baselining of the entire CMS upgrade project and green-lighting construction for significant part of it.

“We need to keep up the momentum to climb the next steps,” Papadimitriou said.