Physics — Particle Decay Chain (Cosmic-Ray Air Shower)

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      "type": "rounded",
      "label": "Primary cosmic ray — a proton at ~10¹⁵ eV",
      "x": 620,
      "y": 60,
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      "fill": "#e0f2fe",
      "stroke": "#0369a1"
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    {
      "id": "pd-first",
      "type": "hexagon",
      "label": "First interaction with an air nucleus (N, O) at ≈ 20 km",
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      "y": 235,
      "width": 240,
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      "fill": "#fef3c7",
      "stroke": "#b45309"
    },
    {
      "id": "pd-pip",
      "type": "stadium",
      "label": "π⁺  ·  139.6 MeV/c²  ·  τ = 26.0 ns",
      "x": 60,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#ede9fe",
      "stroke": "#6d28d9"
    },
    {
      "id": "pd-pi0",
      "type": "stadium",
      "label": "π⁰  ·  135.0 MeV/c²  ·  τ = 8.5 × 10⁻¹⁷ s",
      "x": 620,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#ede9fe",
      "stroke": "#6d28d9"
    },
    {
      "id": "pd-pim",
      "type": "stadium",
      "label": "π⁻  ·  the charge-conjugate chain",
      "x": 1180,
      "y": 410,
      "width": 240,
      "height": 117,
      "fill": "#ede9fe",
      "stroke": "#6d28d9"
    },
    {
      "id": "pd-mup",
      "type": "stadium",
      "label": "µ⁺  ·  105.7 MeV/c²  ·  τ = 2.20 µs",
      "x": 60,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#fce7f3",
      "stroke": "#be185d"
    },
    {
      "id": "pd-numu",
      "type": "ellipse",
      "label": "ν_µ  ·  escapes, effectively undetectable",
      "x": 340,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#dbeafe",
      "stroke": "#1d4ed8"
    },
    {
      "id": "pd-gg",
      "type": "stadium",
      "label": "2γ  ·  back-to-back, 67.5 MeV each in the π⁰ frame",
      "x": 620,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#dcfce7",
      "stroke": "#15803d"
    },
    {
      "id": "pd-pair",
      "type": "hexagon",
      "label": "e⁺e⁻ pair production in a nuclear Coulomb field",
      "x": 900,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#fef3c7",
      "stroke": "#b45309"
    },
    {
      "id": "pd-mum",
      "type": "stadium",
      "label": "µ⁻ + ν̄_µ  ·  mirror of the π⁺ branch",
      "x": 1180,
      "y": 585,
      "width": 240,
      "height": 117,
      "fill": "#fce7f3",
      "stroke": "#be185d"
    },
    {
      "id": "pd-ep",
      "type": "ellipse",
      "label": "e⁺  ·  annihilates on the first electron it meets",
      "x": 60,
      "y": 760,
      "width": 240,
      "height": 117,
      "fill": "#dcfce7",
      "stroke": "#15803d"
    },
    {
      "id": "pd-nue",
      "type": "ellipse",
      "label": "ν_e + ν̄_µ  ·  carry off most of the muon's energy",
      "x": 340,
      "y": 760,
      "width": 240,
      "height": 117,
      "fill": "#dbeafe",
      "stroke": "#1d4ed8"
    },
    {
      "id": "pd-shower",
      "type": "layers",
      "label": "Electromagnetic cascade — bremsstrahlung ⇄ pair production",
      "x": 620,
      "y": 760,
      "width": 240,
      "height": 117,
      "fill": "#fef3c7",
      "stroke": "#b45309"
    },
    {
      "id": "pd-detect",
      "type": "gauge-chart",
      "label": "Sea level: muon flux ≈ 1 cm⁻² min⁻¹ (the hard component)",
      "x": 900,
      "y": 760,
      "width": 240,
      "height": 117,
      "fill": "#fce7f3",
      "stroke": "#be185d"
    },
    {
      "id": "pd-charge",
      "type": "note",
      "label": "Charge is conserved at every vertex: π⁺(+1) → µ⁺(+1) + ν_µ(0); π⁰(0) → γ(0) + γ(0); µ⁺(+1) → e⁺(+1) + ν_e(0) + ν̄_µ(0).",
      "x": 60,
      "y": 935,
      "width": 520,
      "height": 117,
      "fill": "#fef9c3",
      "stroke": "#ca8a04"
    },
    {
      "id": "pd-lepton",
      "type": "note",
      "label": "Lepton number is conserved per flavour. In µ⁺ → e⁺ + ν_e + ν̄_µ: L_e goes 0 → (−1) + (+1) = 0, and L_µ goes −1 → −1. Both hold.",
      "x": 620,
      "y": 935,
      "width": 520,
      "height": 117,
      "fill": "#fef9c3",
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    },
    {
      "id": "pd-dilation",
      "type": "note",
      "label": "cτ for the muon is only 659 m, yet muons made at 15 km reach the ground. At γ ≈ 20 the lab decay length is 13 km — special relativity, observed daily.",
      "x": 1180,
      "y": 935,
      "width": 240,
      "height": 117,
      "fill": "#fef9c3",
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  ],
  "edges": [
    {
      "id": "pd-e1",
      "source": "pd-primary",
      "target": "pd-first",
      "label": "hadronic interaction at ≈ 20 km"
    },
    {
      "id": "pd-e2",
      "source": "pd-first",
      "target": "pd-pip",
      "label": "pion production"
    },
    {
      "id": "pd-e3",
      "source": "pd-first",
      "target": "pd-pi0"
    },
    {
      "id": "pd-e4",
      "source": "pd-first",
      "target": "pd-pim"
    },
    {
      "id": "pd-e5",
      "source": "pd-pip",
      "target": "pd-mup",
      "label": "BR 99.99 %"
    },
    {
      "id": "pd-e6",
      "source": "pd-pip",
      "target": "pd-numu"
    },
    {
      "id": "pd-e7",
      "source": "pd-pim",
      "target": "pd-mum",
      "label": "charge conjugate"
    },
    {
      "id": "pd-e8",
      "source": "pd-pi0",
      "target": "pd-gg",
      "label": "BR 98.8 %, τ = 8.5 × 10⁻¹⁷ s"
    },
    {
      "id": "pd-e9",
      "source": "pd-gg",
      "target": "pd-pair",
      "label": "above the 1.02 MeV threshold"
    },
    {
      "id": "pd-e10",
      "source": "pd-pair",
      "target": "pd-shower"
    },
    {
      "id": "pd-e11",
      "source": "pd-mup",
      "target": "pd-ep",
      "label": "τ = 2.20 µs"
    },
    {
      "id": "pd-e12",
      "source": "pd-mup",
      "target": "pd-nue"
    },
    {
      "id": "pd-e13",
      "source": "pd-mup",
      "target": "pd-detect",
      "label": "survives to sea level"
    },
    {
      "id": "pd-e14",
      "source": "pd-mum",
      "target": "pd-detect"
    },
    {
      "id": "pd-e15",
      "source": "pd-ep",
      "target": "pd-shower",
      "label": "annihilation photons feed the cascade"
    }
  ]
}