ALICE, CERN’s dedicated heavy ion physics experiment, is upgrading its internal tracking system and adding a forward calorimeter for the next phase of the Large Hadron Collider upgrade
Two detector upgrades to ALICE, the Large Hadron Collider’s (LHC) dedicated heavy ion physics experiment, have recently been approved for installation during the LHC’s next long-term outage, which will last from 2026 to 2028.
High-energy collisions of heavy ions such as lead nuclei at the Large Hadron Collider have recreated quark-gluon plasma: the hottest, densest fluid ever studied in a laboratory. In addition to studying the properties of quark-gluon plasma, the ALICE project also covers a wide range of topics involving strong interactions, such as determining the structure of atomic nuclei and interactions between unstable particles, such as “quark-gluon plasma and beyond” journey”.
Internal Tracking System (ITS3)
ALICE’s current in-house tracking system, installed for ongoing Large Hadron Collider operations, is the world’s largest pixel detector to date, with 10 square meters of active silicon area and nearly 13 billion pixels. The new in-house tracking system ITS3 builds on the successful use of monolithic active pixel sensors and takes this concept to a new level.
ALICE acts like a high-resolution camera, capturing the intricate details of particle interactions. ITS3 project leaders Alex Kluge and Magnus Mager said that ITS3 aims to increase the pointing resolution of the orbit by a factor of 2 compared to current ITS detectors. This will greatly enhance measurements of thermal radiation emitted by quark-gluon plasmas and provide insights into the interactions of charm and beauty quarks as they propagate through the plasma.
The ITS3 sensor is 50 m thick and has an area of 2610 cm2. To achieve this, a novel stitching technique is used to connect individual sensors together into a large structure. These sensors can now be bent into a true cylindrical shape around the beam tube. The first layer will be placed just 2 mm from the bundle tube and 19 mm from the interaction point. It can now be cooled by air instead of water and has a lighter support structure, significantly reducing the material and its impact on the particle trajectories seen in the detector.
Positive calorimeter (FoCal)
The FoCal detector consists of an electromagnetic calorimeter (FoCal-E) and a hadron calorimeter (FoCal-H). FoCal-E is a highly sophisticated calorimeter consisting of 18 layers of silicon pad sensors (each layer is as small as 11 cm2) and two additional special layers with 3030 m2 pixels. FoCal-H is made of copper capillaries and scintillation fibers.
By measuring inclusive photons and their correlation with neutral mesons, as well as the production of jets and chamonias, FoCal offers unique possibilities for the systematic exploration of QCD of small Bjorken-x. Constantin Loizides, head of FoCal’s ALICE collaboration program, said FoCal has expanded the scope of ALICE by adding new capabilities to explore the small molecule structure of nucleons and atomic nuclei.
The newly built FoCal prototype recently underwent beam testing at the CERN accelerator complex, the Proton Synchrotron and the Super Proton Synchrotron, demonstrating that its performance is in line with expectations from detector simulations.
The ITS3 and FoCal projects have reached the important milestone of completing the technical design report, which was approved by the CERN Review Committee in March 2024. Be prepared for data collection.
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