Calorimetry in Particle Physics Experiments
This page collects course material for the PhD course Calorimetry in particle physics experiments (University of Torino, Italy, AY 2025-2026).
Official course page: UniTo PhD Physics — Calorimetry course
Course synopsis and material
Lecture 1 — Why Calorimetry? Motivation and Historical Landscape
Calorimeter definition and operating principles; what particles can calorimeters measure?; why measure energy rather than momentum (resolution crossover); calorimeters in a collider detector system; missing transverse energy and hermetic coverage; intermezzo on collider kinematics and cross-sections; six physics-driven case studies tracing the history of electromagnetic and hadronic calorimeter design, from the Crystal Ball and NA48 to W-boson mass measurements, $H\to\gamma\gamma$ at the LHC, and the discovery of W/Z bosons at the $\mathrm{S\bar{p}pS}$.
Slides: Lecture 1 / Additional material
Lecture 2 — Electromagnetic Interactions and Shower Physics
Photon interactions: Beer–Lambert law, photoelectric effect, Compton scattering, pair production, and derivation of the radiation length; charged-particle interactions: Bethe–Bloch formula, Landau fluctuations, mean range; electron energy loss, bremsstrahlung, critical energy; Cherenkov radiation and its relevance to dual-readout calorimetry; electromagnetic shower development: Heitler toy model, longitudinal profiles ($\Gamma$-function parametrisation), electrons vs. photons, post-shower-maximum absorption argument; multiple Coulomb scattering and the Molière radius (first-principles derivation); 90/95/99% containment rules; design rules connecting $X_0$ and $R_M$ to calorimeter geometry; material reference table.
Slides: Lecture 2
Lecture 3 — Hadronic Interactions and Shower Physics
Hadronic interaction length $\lambda_I$ and its scaling; $X_0$ vs. $\lambda_I$ comparison table and consequences for detector layout; nuclear processes: elastic and inelastic cross-sections, spallation, evaporation neutrons, invisible energy budget; soft neutron detection in hydrogen-rich media; two-component shower structure: electromagnetic fraction $f_\mathrm{em}$, Groom parametrisation, energy dependence; event-by-event $f_\mathrm{em}$ fluctuations as the dominant hadronic resolution term; longitudinal and lateral shower development; the $e/h$ ratio, hadronic non-linearity, and energy-fraction decomposition; shower time evolution and implications for the LHC shaping gate; capstone exercise on the fundamental challenges of hadronic calorimetry.
Slides: Lecture 3
Lecture 4 — Calorimeter Performance: Energy Resolution
From shower physics to detector design: homogeneous vs. sampling calorimeters; the three-term energy resolution formula ($\sigma_E/E = a/\sqrt{E} \oplus b/E \oplus c$); stochastic term: total track-length argument, Fano factor, photo-electron statistics, sampling fluctuations, Wigmans relation; Landau fluctuations in thin active layers; noise term: electronic noise, bandwidth–noise trade-off, pile-up at the LHC; constant term: non-uniformity, temperature gradients, calibration residuals; leakage (longitudinal, lateral, upstream); $H\to\gamma\gamma$ as EM benchmark; hadronic energy resolution: $e/h \neq 1$, non-linearity, compensation theory; ZEUS uranium–scintillator, dual-readout (DREAM/RD52), software compensation; position reconstruction and logarithmic weighting; time resolution and the opening to 4D calorimetry.
Slides: coming soon
Lecture 5 — Calorimeter Technologies
Unified survey of detector technologies for electromagnetic and hadronic calorimetry at the level of operating principles and key performance parameters. Crystal calorimeters: the crystal zoo — NaI(Tl), BGO, CsI(Tl), $\mathrm{BaF_2}$, $\mathrm{PbWO_4}$, LYSO — with property tables; crystal detector examples (Crystal Ball at SPEAR, BaBar and Belle CsI(Tl), L3 BGO, CMS ECAL $\mathrm{PbWO_4}$); intermezzo on the Crystal Ball detector and lineshape function; noble-liquid calorimeters (LAr, LKr, LXe) and the NA48 liquid-krypton calorimeter; LAr accordion concept; sampling EM calorimeters; why hadronic calorimeters are always sampling; ZEUS uranium–scintillator as compensation proof-of-concept; ATLAS TileCal at overview level; CMS HCAL and CMS HF (Cherenkov in quartz fibres); ATLAS HEC and FCal; unified EM and HAD technology comparison table.
Slides: coming soon
Lecture 6 — Calorimeter Design
Implementation deep-dives into the ATLAS and CMS calorimeter systems. ATLAS LAr accordion: electrode structure (folded PCB, Pb absorbers, LAr gaps), accordion fold geometry, signal collection and drift, 3-gain readout concept, longitudinal segmentation (strips / middle / back layers). CMS ECAL in depth: APD readout, laser monitoring and radiation-damage quantification through Run 1–3, Phase-2 SiPM upgrade. Side-by-side ATLAS LAr vs. CMS $\mathrm{PbWO_4}$ comparison. TileCal design details: tile orientation trick, WLS fibre geometry, 3-layer segmentation. CMS HCAL design: brass absorber motivation, SiPM Phase-2 upgrade. Calorimeter design principles: depth requirements (25 $X_0$, 10 $\lambda_I$), granularity, longitudinal segmentation strategy, hermeticity. Presampler and dead material: upstream material budget, energy loss correction. Solenoid placement as the master design fork (EM calo before vs. after solenoid). Particle flow analysis: concept, hardware requirements, CALICE AHCAL, CMS HGCAL as realisation — bridge to Lecture 8. Design exercise.
Slides: coming soon
Lecture 7 — Signal Chain, Readout Electronics and Calibration
Signal formation in LAr (bipolar triangular ionisation pulse, ~450 ns drift) and crystal (exponential scintillation) calorimeters; charge/light collection and preamplifier; noise sources (series, parallel, 1/f); CR-RC shaping and noise–bandwidth trade-off; dynamic range and gain switching (ATLAS LAr 3-gain system); 40 MHz sampling and ADC; digital pulse reconstruction by optimal filtering (OFC coefficients, pile-up correction); trigger primitive generation. Calibration goals; hardware calibration (electronics pulse injection, laser monitoring, radioactive sources); test-beam calibration; in-situ calibration ($\pi^0/\eta \to \gamma\gamma$, $Z \to ee$, $E/p$ method, muons as MIPs); jet energy scale corrections and uncertainties.
Slides: coming soon
Lecture 8 — Future Calorimetry: New Technologies and Future Colliders
Challenges for the High-Luminosity LHC: pile-up up to 200 pp interactions per bunch crossing, extreme radiation doses, higher trigger rates. CMS HGCAL: silicon pad sensors and scintillator tiles, ~6 million channels, 3D shower imaging, CE-E and CE-H sections. Precision timing: LGAD technology, ~30 ps time resolution, CMS MTD concept, pile-up mitigation. 5D calorimetry (energy + 3D position + time). Particle flow with imaging calorimeters: CALICE programme, ILD and SiD concepts. Dual-readout calorimetry: RD52/DREAM — simultaneous scintillation and Cherenkov readout, $\sigma_E/E \approx 3\%/\sqrt{E}$ for hadrons. Crystal calorimetry for future lepton colliders: the IDEA concept at FCC-ee. Calorimetry at FCC-hh: radiation levels of $10^{17}\,\mathrm{n/cm^2}$, jets up to $p_T \sim 10$ TeV. Calorimetry at a muon collider: beam-induced background from muon decays, timing requirements. Closing synthesis: granularity, timing, dual-signal readout, and simulation-driven design as the recurring principles of next-generation calorimetry.
Slides: coming soon
Last update: April 20, 2026.