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: Lecture 4
Lecture 5 — Calorimeter Technologies
Unified survey of detector technologies for electromagnetic and hadronic calorimetry, organised by detection signal. Cherenkov calorimeters: threshold mechanism and photon yield; UV-extended SiPM; materials; CMS HF (quartz-fibre sampling Cherenkov in the forward region); Super-Kamiokande (homogeneous water Cherenkov, ring imaging for $e/\mu/\pi$ identification); future Cherenkov calorimeters. Scintillation calorimeters: crystal zoo — NaI(Tl), BGO, CsI(Tl), $\mathrm{BaF_2}$, $\mathrm{PbWO_4}$, LYSO — with property tables; optical characteristics, light output, and decay time; crystal calorimeters in particle physics experiments (Crystal Ball, BaBar, Belle, L3 BGO, CMS ECAL); $\mathrm{PbWO_4}$ engineering for the LHC; APD readout and radiation damage; LYSO and future crystal calorimetry. Ionisation calorimeters: noble liquids as active media (LAr, LKr, LXe); ionisation signal and charge collection; LAr accordion concept; NA48 liquid-krypton quasi-homogeneous calorimeter; ATLAS LAr EM overview; ATLAS LAr HEC and FCal. Semiconductor calorimeters: electron-hole pair creation in silicon; SiPM principle (from APD to G-APD) and key properties; HEP applications. Hadronic calorimeter technologies: why hadronic calorimeters are always sampling; ZEUS uranium–scintillator as compensation proof-of-concept; ATLAS TileCal (tile geometry, WLS fibres, calibration overview); CMS HCAL; CMS HF Cherenkov; ATLAS HEC and FCal as hadronic sub-systems; ATLAS vs. CMS hadronic comparison; unified EM and HAD technology comparison table.
Slides: Lecture 5
Lecture 6 — Calorimeter Design
Physics requirements for LHC calorimetry: speed, radiation hardness, and granularity constraints; $H\to\gamma\gamma$ as the electromagnetic resolution benchmark; TDR performance goals derived from physics; two coherent design answers to identical requirements (ATLAS LAr sampling vs. CMS $\mathrm{PbWO_4}$ homogeneous) and their trade-offs. Implementation deep-dives: ATLAS LAr accordion — electrode structure (folded PCB, Pb absorbers, LAr gaps), accordion fold geometry, granularity mechanism (strip etching in $\eta$), 3-gain readout, longitudinal segmentation (strips / middle / back), resolution budget, temperature sensitivity; CMS ECAL — APD readout, laser monitoring and radiation-damage correction through Run 1–3, readout electronics (MGPA 3-gain, 12-bit ADC); ATLAS TileCal and CMS HCAL — absorber choices (iron vs. brass), HCAL positioning consequences. Design principles: solenoid placement as the master design fork (EM calorimeter inside vs. outside solenoid); EM calorimeter size and granularity; detector hermeticity and $\eta$ coverage; signal collection in light vs. charge calorimeters; active-layer properties in sampling calorimeters; dead material, energy resolution impact, and presampler strategy; longitudinal segmentation and shower profile exploitation ($e/\gamma$ separation, $\pi^0/\gamma$ discrimination). Dual readout and particle flow: DREAM dual-readout concept (simultaneous scintillation and Cherenkov readout, event-by-event $f_\mathrm{em}$ correction); jet energy composition; particle flow analysis — 70/20/10 charged-hadron/photon/neutral-hadron decomposition, hardware granularity requirements; CALICE AHCAL and future particle-flow calorimeters.
Slides: Lecture 6
Lecture 7 — Signal Chain, Readout Electronics and Calibration
Signal formation in LAr (bipolar triangular ionisation pulse, ~450 ns drift) and crystal (scintillation) calorimeters; charge-sensitive preamplifier; noise sources (series, parallel, 1/f) and equivalent noise charge (ENC); CR-RC shaping and noise–bandwidth trade-off; in-time and out-of-time pile-up noise; dynamic range and 3-gain switching (ATLAS LAr ×64/×8/×1); 40 MHz sampling and ADC; digital amplitude and time reconstruction by optimal filtering (OFC coefficients, pile-up correction); OFC at HL-LHC (200 pile-up interactions); Level-1 trigger primitive generation. Cell and cluster energy calibration chain; hardware calibration (electronics pulse injection, laser monitoring, radioactive sources); test-beam calibration and absolute energy scale traceability (D0 cautionary tale). In-situ calibration: muons as MIPs (Landau MPV reference, longitudinal inter-calibration, time-stability monitoring); $\pi^0/\eta\to\gamma\gamma$ and $Z\to ee$ for the EM scale; $E/p$ method. Jet energy scale (JES): composite-jet calibration problem; $\gamma$+jet $p_T$ balance, $Z$+jet balance, $\eta$-intercalibration; JES uncertainty anatomy. Particle flow as the unifying reconstruction paradigm (closing synthesis).
Slides: Lecture 7
Lecture 8 — Future Calorimetry: New Technologies and Future Colliders
HL-LHC challenges: pile-up (up to 200 pp interactions per bunch crossing), radiation damage (up to ~10 MGy in the CMS endcap), higher trigger rates. CMS HGCAL: silicon pad sensors and scintillating tiles (~6 million channels), CE-E and CE-H sections, 3D shower imaging (longitudinal and transverse profiles, EM vs. hadronic shape discrimination), precision timing ($\sigma_t \sim 40\,\mathrm{ps}$ per hit in silicon layers). Physics-driven requirements for Higgs/Electroweak/Top (HET) lepton-collider factories (FCC-ee): energy coverage 200 MeV–180 GeV, jet-energy resolution $\sigma_E/E \lesssim 3$–4% at 50 GeV, extreme EM resolution for B and $\tau$ physics; all concepts targeting particle-flow reconstruction. Calorimeter technologies being developed for future lepton colliders: SiW ECAL (silicon–tungsten imaging calorimeter, ILC-originated, adapted for FCC-ee); ALLEGRO ECAL (inclined LAr/LKr Pb/W sampling with strip-electrode readout and turbine-like endcap); IDEA (dual-readout hybrid crystal ECAL + dual-readout fibre HCAL); GRAiNITA (scintillator grains in heavy liquid — near-homogeneous sampling granularity at lower cost than crystals). Recurring principles across all future designs: granularity, timing, multiple complementary signals, simulation-driven optimisation. Open questions and closing course synthesis.
Slides: Lecture 8
Last update: May 11, 2026.