Experiment: DiCE (DiMuon and Charm Experiment, formerly NA60+) at the SPS (Super Proton Synchrotron), H8 line / EHN1: Pb beams 20–150 A GeV/c (√sNN ≈ 6.3–16.8 GeV), p beams 40–150 GeV/c on Be…Pb; ≈ 10⁶ Pb/s, ≈ 150 kHz Pb–Pb interaction rate. NA60+ LoI, arXiv:2212.14452; proposal CERN-SPSC-P-373; CERN detector seminar (2026).
Targets: 5 Pb disks, 1.5 mm thick, 12 mm apart (first Ø 6 mm, others Ø 1 mm), ≈ 15% interaction probability; the vertex is drawn on one disk at random.
VT (vertex telescope): 5 MAPS (monolithic active pixel sensor) planes at z = 7–38 cm, 30×30 cm with a 6 mm beam hole, ≈ 0.1–0.2% X₀ per plane, MOSAIX wafer-scale sensors (65 nm, from ALICE ITS3 R&D). Inside the MEP48 dipole: 1.47 T, 40 cm gap, Ø 1 m poles; B ∥ y, so tracks bend in x (use the Top view).
Absorber: BeO → Al₂O₃ → graphite, from z = 45 cm, with a tungsten plug on axis that stops the beam and spectators. Drawn lengths (0.6 / 0.3 / 2.65 m) are approximate; the real graphite length changes with beam energy.
MS (muon spectrometer): 6 MWPC (multi-wire proportional chamber) stations, MS0–MS1 before and MS2–MS3 after the MNP33 dipole (0.9 T·m, 2.45 × 2.4 m aperture), MS4–MS5 behind a graphite muon wall. Station z positions and sizes are approximate. A muon counts as triggered if it hits ≥ 5 stations, including MS4/5.
Muon transport: helix steps in By; continuous dE/dx (≈ 1.2× minimum ionising) and Highland multiple scattering (θ₀ = 13.6 MeV/p·√(x/X₀)) in the absorber and wall (PDG RPP, PRD 110, 030001, 2024). Hadrons are absorbed after an exponential path in λI; π, K can decay to μν first (the main single-μ background).
Glauber MC: Pb Woods–Saxon R = 6.62 fm, a = 0.546 fm; ⁹Be Gaussian, rms 2.5 fm; σNNinel ≈ 30–33 mb. Review: Miller et al., Ann. Rev. Nucl. Part. Sci. 57, 205 (2007).
Underlying event (UE): dNch/dη per participant pair ∝ s0.155 (cf. ALICE, PRL 116, 222302, 2016), Gaussian rapidity width σy = √ln(√s/2mp) (Landau), π/K/p with mass-ordered slopes and a double-humped proton y-distribution (baryon stopping). Toy, not a transport model.
Charm: σcc̄NN ≈ 4.4 µb at √s = 16.8 GeV, falling to ≈ 0.3 µb at 6.3 GeV (rough interpolation; cf. Lourenço & Wöhri, Phys. Rept. 433, 127, 2006), ⟨Ncc̄⟩ = σcc̄/σNN·Ncoll. Fragmentation D⁰ : D⁺ : Ds : Λc ≈ 56 : 24 : 10 : 10; dN/dmT ∝ mTe−mT/T, T = 0.27 GeV. Masses, cτ and branching fractions from PDG 2024. Semi-muonic decays use 3-body phase space (no form factors).
Signal forcing: charm is rare (≈ 0.1 cc̄ per central Pb–Pb collision at top energy), so the chosen signal is generated until it is in acceptance and embedded in a minimum-bias UE. "Signal tries" is that number. Mμμ is smeared with σM/M = 1.1% (11 MeV at ω, 33 MeV at J/ψ).
Freeze-out: Tch, μB from the parametrisation of Cleymans et al., PRC 73, 034905 (2006).
Scale: nuclei drawn at true size by default; Nuclei zoom magnifies them (and the fireball). Projectile contraction drawn at min(γ, 12); the target nucleus is at rest and stays spherical.