The Long Run to HGCAL

par Lourdes Urda (LLR / CNRS)

lundi 24 nov. 2025, 14:00 → 15:00 Europe/Paris

Salle de Conference (LLR)

Zoom: https://cern.zoom.us/j/64458678005?pwd=bzRZcWNYZit3aHNuSlVRMXViQmUwdz09

The High-Luminosity LHC (HL-LHC) sets the stage for a modern retelling of the fable of the hare and the tortoise. The “hare” is the sudden surge of luminosity, radiation, and occupancy—fast, overwhelming, and relentless. The “tortoise” is the HGCAL project: deliberate, methodical, and built to endure. The existing CMS endcap calorimeters, designed for the gentler pace of earlier LHC running, cannot keep up with the hare’s explosive acceleration. To win this new race and fully exploit the HL-LHC’s physics potential, CMS is replacing them with the High-Granularity Calorimeter.

Like the tortoise, HGCAL advances through precision and resilience. It is a sampling calorimeter with electromagnetic and hadronic sections, featuring unprecedented transverse and longitudinal segmentation and providing five-dimensional information—space, time, and energy. In regions of extreme radiation, the tortoise shields itself with silicon sensors; where conditions are more forgiving, it proceeds with plastic scintillator tiles coupled to silicon photomultipliers. Altogether, over six million silicon channels and 240,000 scintillator channels distributed across 47 layers per endcap form the robust shell that allows HGCAL to stay in the race.

This fine granularity enables particle-flow calorimetry, delivering detailed characterization of shower development and improvements in particle identification, energy resolution, and pileup mitigation. Yet the tortoise’s journey is not without challenges: the scale and complexity of HGCAL demand innovations in mechanics, infrastructure, and readout electronics capable of handling immense channel density and data volume. As testing, integration, and large-scale production move forward, the accumulated experience is distilled into calibration strategies and operational procedures.

Just as in the fable, the tortoise succeeds not through speed but through endurance, ingenuity, and careful design. HGCAL lays the groundwork for future generations of high-granularity calorimeters. In this talk, I will present its design, outline the readout system, and summarize the latest results from system validation and integration tests.