Detector (as operated in Runs 23–25, sPHENIX frame: +z = North, +y = up). Former BaBar superconducting solenoid, 1.4 T, cryostat r ≈ 1.40–1.73 m, length ≈ 3.85 m. MVTX (MAPS, Monolithic Active Pixel Sensors; ALICE ITS-2 staves): 3 layers at r = 2.5, 3.2, 4.0 cm, 12/16/20 staves, |z| < 13.5 cm. INTT (Intermediate Silicon Tracker, strips): 2 barrels / 4 ladder layers, r ≈ 7–10 cm. TPC (Time Projection Chamber): 20 < r < 78 cm (pads 30–78 cm), |z| < 1.05 m, |η| < 1.1, Ne–CF₄, 72 quad-GEM (Gas Electron Multiplier) modules, 3 radial × 12 φ per end. TPOT (TPC Outer Tracker): 8 Micromegas modules in 3 sectors below the TPC (sPHENIX, arXiv:2410.18031; Klest et al., arXiv:2110.02082).
Calorimetry, |η| < 1.1, full φ: EMCal W/SciFi SPACAL, r ≈ 0.90–1.16 m, 256 φ × 96 η towers of Δη×Δφ ≈ 0.024×0.024, 18 X₀, σE/E ≈ 14%/√E ⊕ 3% here (Aidala et al., IEEE TNS 65, 2901, 2018, arXiv:1704.01461). Inner HCal (Al, inside the cryostat) r ≈ 1.16–1.37 m and Outer HCal (steel, also the flux return) r ≈ 1.82–2.69 m, each 24 η × 64 φ towers of 0.1×0.1 with tilted plates; ≈ 4.9 λI total (sPHENIX TDR, 2019).
Forward / trigger: MBD (Minimum-Bias Detector, ex-PHENIX BBC) 2 × 64 quartz + PMT at |z| = 2.50 m, 3.61 < |η| < 4.51. sEPD (sPHENIX Event-Plane Detector) 2 scintillator wheels at |z| ≈ 3.16 m, 2.0 < |η| < 4.9, 24 sectors × 31 tiles drawn as 16 rings. ZDCs at ±18 m behind the DX magnets (arXiv:2410.18031). Dimensions are approximate published values, not the GEANT4 geometry.
Glauber MC: Woods–Saxon Au (R = 6.38, a = 0.535 fm), σNNinel = 42 mb (Miller et al., Ann. Rev. Nucl. Part. Sci. 57, 205, 2007). Bulk: two-component dN/dη tuned to ≈ 690 for 0–5% Au+Au (PHOBOS, PRC 83, 024913, 2011), ≈ 2.3 in p+p; v₂ from ε₂.
Hard probes (embedded): dijet with leading pT 15–45 GeV, toy fragmentation (≈ 60% charged, 30% π⁰ → γγ, 10% n/K⁰L); in Au+Au the recoil jet loses energy with centrality and radiates soft particles at large angle, giving xJ imbalance (qualitatively after ATLAS, PRL 105, 252303, 2010). Υ(1S) → e⁺e⁻ (m = 9.46 GeV), |y| < 1. Jet cones drawn with R = 0.4.
Response: helices in uniform 1.4 T up to the EMCal face (R[m] = pT/(0.42·GeV)); e/γ shower in the EMCal; hadrons start a shower in the EMCal with P ≈ 1 − e−0.83, otherwise leave a MIP and shower in the iHCal / oHCal. Toy shares, not a GEANT simulation.