Speaker
Description
The increase in luminosity and pileup at the High-Luminosity LHC (HL-LHC) will place unprecedented demands on the CMS experiment, requiring major advances in both detector technology and event reconstruction. Among the planned upgrades, the High-Granularity Calorimeter (HGCAL) will replace the current endcap calorimeters, providing fine spatial segmentation and precision timing. These features dramatically enhance physics capabilities but also introduce substantial reconstruction challenges due to the large number of hits per event and the stringent computing requirements. To address this, CMS is developing TICL (The Iterative CLustering), a modular and heterogeneous reconstruction framework integrated into the CMS software.
TICL is designed for parallelism and portability across heterogeneous architectures through the alpaka abstraction layer. It performs calorimetric pattern recognition through a sequence of clustering and linking stages that reduce several hundred thousand energy deposits to a compact set of high-quality particle candidates. The 2D clustering on each HGCAL layer and the 3D clustering across layers are heterogeneous, with the latter that prioritizes purity and therefore produces fragmented shower compoments. To recover these fragments, TICL employs multiple linking algorithms tailored to different shower types: a superclustering plugin optimized for electromagnetic showers and a geometric and topological linking for hadronic ones. Recently, a graph neural network approach has been introduced to further improve hadronic shower linking, enhancing completeness in dense environments. The linking between charged-particle tracks and calorimetric showers has also been refined: the current one is based on geometric compatibility, with requirements on time and energy, while the ongoing work targets a many-to-many linking strategy for a more coherent global event interpretation.
Beyond the endcaps, TICL is being extended to the barrel calorimeters, enabling a unified reconstruction approach across the entire CMS calorimeter system for the HL-LHC era.
This contribution will present the design principles of TICL, highlight the recent developments and performance studies. The results demonstrate the scalability and robustness of the framework and its readiness to meet the challenges of the forthcoming HL-LHC operations.