High Granular Calorimetry for Higgs Factories and other applications
Sandwich and Compact High Granular calorimeters with integrated electronics
To meet the high precision levels foreseen by future lepton collider experiments, the detectors will be based on Particle Flow (PF) techniques. These techniques consist of choosing the best information available to measure the energy of the final state objects (i.e. measuring the charged particle momentum with tracking devices, where the resolution is better than in the calorimeters). Therefore, PF techniques rely on single-particle separation. For this purpose, PF algorithms require highly granular and compact calorimeter systems featuring minimum dead material.
The R&D of highly granular calorimeters, with FCC-ee as one of its main target applications, is currently pursued within the CERN DRD Calo and FCAL collaborations, also addressing the requirements of other future lepton collider projects such as the Linear Collider Facility (LCF). The technological developments originally conducted within the CALICE collaboration are now integrated into DRD Calo, while FCAL provides a complementary framework particularly focused on compact forward calorimetry, luminometry and related physics applications.
IFIC (AITANA) participates in DRD Calo and FCAL, with A. Irles as IFIC institutional board representative for both collaborations.
DRD Calo
The Detector R&D Collaboration on Calorimetry, DRD Calo, is a CERN-based collaboration established in 2024 following the recommendations of the ECFA Detector R&D Roadmap. Its main mission is to foster and develop calorimeter concepts required for future high-energy physics experiments and to provide a common framework for the development of technologies, tools and infrastructures shared among different projects.
A major target for these developments is the next generation of experiments at FCC-ee, which will require highly performant calorimeter systems capable of meeting the demanding precision goals of a future Higgs, electroweak and top factory. The technologies developed within DRD Calo are also applicable to other future collider projects, including the Linear Collider Facility (LCF).
Electromagnetic and hadronic calorimeter developments are pursued within a unified R&D framework. The activities and technological developments previously organised within the CALICE collaboration have been fully integrated into DRD Calo.
The AITANA group contributes in particular to the development of highly granular silicon-based electromagnetic calorimeters and associated detector technologies.
FCAL
The FCAL Collaboration, re-established in its current form in 2025, provides a complementary framework for R&D and physics studies related to very-forward calorimetry and precision luminometry for future lepton colliders, with FCC-ee and LCF among its main applications.
FCAL works in close coordination with the CERN Detector R&D programme. Part of its detector R&D shares scientific forums, person-power and experimental infrastructure with DRD Calo, while FCAL also maintains dedicated activities in detector optimisation and in the physics enabled by forward calorimeters and luminometers.
Its activities include:
Hardware development for detector prototypes, their readout electronics and data acquisition, partly carried out in coordination with the DRD R&D working groups.
Development and optimisation of very-forward calorimeters and luminometers for future lepton colliders, including studies of luminosity determination, beam polarisation and other precision measurements.
Studies of the physics potential of these detector systems at future colliders and in the Strong-Field QED (SFQED) domain, including the transition between perturbative and non-perturbative QED.
Development of compact highly granular calorimeters for experiments such as LUXE, together with the associated physics programme.
Detector simulation and optimisation studies, including software development for event generation, detector simulation, event reconstruction and analysis.
The design and R&D of this prototype is conducted by CALICE and it is oriented at the baseline design of the ILD ECAL. The ILD ECAL is a sampling calorimeter of 24X0 of thickness (in the barrel region) and it uses silicon (Si) as active material and tungsten (W) as absorber material. The choice of Si and W allows the construction of a very compact calorimeter made up of compact active layers with small cell size (high granularity) in the transverse and longitudinal planes. It will consist of an alveolar structure of carbon fiber into which the slabs made up of tungsten plates and active sensors will be inserted. The very-front-end (VFE) electronics will be embedded in the slabs. The silicon sensors will be segmented in squared cells of 5×5 mm², featuring a total of∼100 million channels for the ECAL of the ILD. To reduce overall power consumption, the ILD ECAL will exploit the pulsed bunch structure foreseen for the ILC: the lepton bunchs trains will arrive within acquisition windows of∼1-2 ms width separated by ∼200 ms. During the idle time,∼99% of the time, the bias currents of the electronics will be shut down. This technique is usually denominated power pulsing. In addition, as the PF techniques demands minimum dead material in the detector, the design of the ILD foresees the calorimeters (hadronic and electromagnetic) to be placed inside the magnetic coil that provides magnetic fields of 3-4 T.
Members of the AITANA group are involved in the silicon-tungsten electromagnetic calorimeter, SiW-ECAL group. The SiW-ECAL team is composed by several groups from: France (IJCLab – ex LAL, OMEGA, LPNHE, LLR, LPSC), Japan (Kyushu University, KEK ), South Korea (SKK University) and Spain (the AITANA group from IFIC and the CIEMAT).
Compact silicon-tungsten calorimeters provide a highly granular and mechanically compact solution for precision electromagnetic calorimetry. Their small Molière radius, fine transverse segmentation and reduced dead material make them particularly well suited for applications requiring efficient particle separation, precise energy measurements and operation in very forward detector regions.
Within the FCAL Collaboration, these technologies are developed primarily for very-forward calorimetry and precision luminometry at future electron-positron colliders, with direct relevance for FCC-ee and the Linear Collider Facility (LCF). In these environments, compact silicon calorimeters can provide precise luminosity measurements and contribute to beam-related and electroweak precision observables under challenging occupancy and radiation conditions.
The same detector concepts also provide attractive solutions for experiments beyond collider luminometry. A prominent example is LUXE, where compact silicon-tungsten calorimeters are used to measure the spectra and multiplicities of electrons and positrons produced in strong-field QED interactions. These measurements are essential to probe non-linear and non-perturbative QED effects at effective field strengths approaching and exceeding the Schwinger limit.
For LUXE, two complementary electromagnetic calorimeter concepts are being developed. ECAL-P is based on compact calorimeter technologies developed within FCAL, while ECAL-E builds on highly granular silicon-tungsten calorimeter technologies originating from CALICE and now pursued within the CERN DRD Calo Collaboration. Together with the tracking system, these calorimeters provide independent measurements of particle multiplicities and energy spectra, improve control of beam-related backgrounds and enable in situ cross-calibration of the detector system.
These developments therefore establish a strong technological link between precision luminometry at FCC-ee and LCF, detector R&D within FCAL and DRD Calo, and compact calorimetry for experiments such as LUXE.
The AITANA group is involved in the design, optimisation, construction and test of compact silicon calorimeters, with activities spanning detector R&D for future collider experiments and their application to the LUXE physics programme.
A. Irles is the institutional representative of the IFIC in the following collaborations:
- DRD Calo
- FCAL
A. Irles es deputy coordinator of the DRD Calo-WP1 package
Around the world with CALICE
The SiW-ECAL Technological Prototype
The group acknowledges the financial support from the MCIN with funding from the European Union NextGenerationEU and Generalitat Valenciana in the call Programa de Planes Complementarios de I+D+i (PRTR 2022). Project (Si4HiggsF), reference ASFAE/2022/015
