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change pseudorapidity limits to Inf #42

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Merged
graeme-a-stewart merged 2 commits into from
May 4, 2026
Merged

change pseudorapidity limits to Inf #42

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906f4e4
change pseudorapidity limits to `Inf`
m-fila May 1, 2026
299994a
return Inf of appropriate type
m-fila May 4, 2026
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6 changes: 3 additions & 3 deletions src/coordinate_systems/XYZT.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -149,12 +149,12 @@ function eta(::XYZT, mom)
return zero(zcomp)
end

@warn "Pseudorapidity (η): transverse momentum is zero! return +/- 10e10"
@warn "Pseudorapidity (η): transverse momentum is zero! return ±Inf"
if zcomp > zero(zcomp)
return 10e10
return oftype(zcomp, Inf)
end

return -10e10
return oftype(zcomp, -Inf)
end

#######################
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6 changes: 5 additions & 1 deletion src/getter.jl
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Expand Up @@ -370,9 +370,13 @@ For a four-momentum `(px, py, pz, E)`, this function returns `log(tan(theta/2))`
!!! warning

If the transverse momentum (`pt`) is zero (i.e., the particle is aligned with the beam axis),
a warning is raised, and a large pseudorapidity value (±10e10) is returned as a convention.
a warning is raised, and `±Inf` (depending on the sign of the z-component) is returned as a convention.
This occurs because the pseudorapidity is ill-defined when `pt = 0`.

For compatibility with other software, the returned values might be clamped. In particular:
- With ROOT legacy vectors ([TLorentzVector](https://root.cern.ch/doc/master/classTLorentzVector.html)), use `clamp(eta(lv), -1e11, 1e11)`.
- With ROOT [GenVector](https://root.cern/doc/master/group__GenVector.html) classes (`ROOT::Math::LorentzVector`, `ROOT::Math::XYZTVector`), use `clamp(eta(lv), z(lv) - 22756, z(lv) + 22756)`.

# Notes
- Pseudorapidity is approximately equal to the rapidity ``y`` in the ultra-relativistic limit
(when the particle's mass is negligible compared to its energy).
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4 changes: 2 additions & 2 deletions test/XYZT.jl
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Expand Up @@ -113,8 +113,8 @@ end
@test isapprox(LorentzVectorBase.eta(lvec_non_zero), 0.5 * log((1 + cth) / (1 - cth)))

@test isapprox(LorentzVectorBase.eta(lvec_zero), 0.0)
@test isapprox(LorentzVectorBase.eta(CustomLVector(0.0, 0.0, 1.0, 0.0)), 10e10)
@test isapprox(LorentzVectorBase.eta(CustomLVector(0.0, 0.0, -1.0, 0.0)), -10e10)
@test LorentzVectorBase.eta(CustomLVector(0.0, 0.0, 1.0, 0.0)) == Inf
@test LorentzVectorBase.eta(CustomLVector(0.0, 0.0, -1.0, 0.0)) == -Inf
end

@testset "spherical coordinates consistence" for lvec in [lvec_non_zero, lvec_zero]
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