√sNN = 5.36 TeV · Run 3 layout · L3 0.5 T · dipole 0.67 T
Event
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Centrality
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b (fm)
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Npart
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Ncoll
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Nch |η|<0.9
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ε₂
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v₂ (input)
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Ψ₂ (deg)
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Towers >0.1 GeV
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ΣE cal (GeV)
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γ in acc.
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MFT hits
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FT0 + FV0 hits
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FDD hits
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μ MCH / MID
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mμμ J/ψ (GeV)
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ZN-A / ZN-C (n)
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ZP-A / ZP-C (p)
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Model & references
Glauber MC: Pb Woods–Saxon R = 6.62 fm, a = 0.546 fm, σNN = 68 mb, σinelPbPb = 7.67 b (PRC 97, 054910, 2018).
Multiplicity: two-component dN/dη = 5.1[(1−x)Npart/2 + xNcoll], x = 0.12, tuned to ≈ 2000 for 0–5% (cf. ALICE, PRL 116, 222302, 2016).
Flow: v₂ = 0.23 ε₂ (participant plane), pT-dependent; pT spectra Γ-shaped with mass-ordered slopes (π, K, p) plus a power-law tail.
Tracking: helices with R[m] = pT/(0.3·B), hits on 7 ITS2 layers and TOF. Geometry after ALICE, JINST 3 S08002 (2008) and ITS upgrade TDR, J.Phys.G 41, 087002 (2014).
EMCal/DCal: 20 supermodules (EMCal 10 full + 2×⅓, DCal 6×⅔ + 2×⅓), 4416 modules, 17 664 Pb–scintillator towers, Δη×Δφ ≈ 0.0143×0.0143, projective; EMCal |η|<0.7, 80°<φ<187°; DCal 0.22<|η|<0.7, 260°<φ<320° and |η|<0.7, 320°<φ<327° (ALICE EMCal page). Front face at r = 4.28 m. σE/E = 1.7% ⊕ 11.3%/√E ⊕ 4.8%/E (test beam, arXiv:1008.0413; ALICE, JINST 18, P08007, 2023).
Neutrals: π⁰ (≈ π⁺ yield) and η (η/π⁰ ≈ 0.11) decay to γγ; photons shower over ~3×3 towers. Charged hadrons: 62% MIP (≈ 0.27 GeV), the rest a partial hadronic shower.
Run 3 layout: after ALICE, “ALICE upgrades during the LHC Long Shutdown 2”, JINST 19, P05062 (2024). Positions are approximate; the far-forward beam line is schematic.
PHOS (tick box, off by default): PbWO₄, 2.2 × 2.2 cm crystals at r = 4.6 m, |η| < 0.13, 250°–320° (3 full + 1 half module), CPV outline; σE/E = 1.1% ⊕ 3.3%/√E ⊕ 1.8%/E. HMPID: 7 RICH modules at r ≈ 4.9 m, 1.2°–58.8° in φ (schematic placement); tracks there end with a hit.
MFT: 5 disks × 2 planes at z = −46 to −77 cm, −3.6 < η < −2.5 (MFT TDR, CERN-LHCC-2015-001).
FIT: FT0-A (24 quartz modules, z = +3.35 m, 3.5 < η < 4.9), FT0-C (28 modules on a sphere of r = 0.84 m, −3.3 < η < −2.1), FV0 (5 rings × 8 sectors, z = +3.2 m, 2.2 < η < 5.0), FDD-A/C (z ≈ +17 m / −19.5 m, 4.7 < η < 6.3, −6.9 < η < −4.9; hits only).
Forward multiplicity: dN/dη flat to |η| ≈ 2.5, then falling as exp[−(|η|−2.5)²/8] (shape after ALICE, PLB 772, 567, 2017). Forward hadrons are drawn dimmed.
Muon spectrometer, −4 < η < −2.5: front absorber z = −0.9 to −5.03 m (C, concrete, steel; ≈ 10 λI), W beam shield, dipole 0.67 T (3 T·m) at z = −7.4 to −12.4 m, MCH 5 stations (10 planes), 1.2 m iron filter, MID 2 × 2 RPC planes at z ≈ −16 and −17 m (Muon TDR, CERN-LHCC-99-022). Muons: Lorentz-force stepping, mean dE/dx and multiple scattering; hadrons stop after an exponential depth (λ ≈ 0.43 m).
Muon sources: π/K → μν in flight before the absorber; heavy-flavour muons (toy: 1.5 × 10⁻³ per binary collision, pT > 1 GeV/c); one J/ψ → μ⁺μ⁻ per event (tick box), mμμ smeared by 70 MeV/c² when both muons cross ≥ 7 MCH planes.
ZDC: ZN (W, 0°) and ZP (brass, beside the outgoing beam pipe) at ±112.5 m, ZEM at +7.35 m (ZDC TDR, CERN-LHCC-99-005). Toy free-spectator fraction 0.3 + 0.5 Npart/416; neutrons 126/208; EZN = n × 2.68 TeV. Spectators accelerate on screen to reach the ZDCs about 3 display-seconds after impact.
Nuclei scale: drawn at true size by default (RPb ≈ 7.1 fm, far below a pixel at detector scale); the Nuclei zoom slider magnifies them, and the QGP fireball with them, up to ≈ 4.5×10¹³. Lorentz contraction drawn at γ = 12 (true γ ≈ 2.9×10³). Tch ≈ 156 MeV (Nature 561, 321, 2018).