From 906f4e42f05acb2d912631d793450ee148dae3fe Mon Sep 17 00:00:00 2001
From: Mateusz Jakub Fila <mateusz.jakub.fila@cern.ch>
Date: Fri, 1 May 2026 17:11:03 +0200
Subject: [PATCH 1/2] change pseudorapidity limits to `Inf`

---
 src/coordinate_systems/XYZT.jl | 6 +++---
 src/getter.jl                  | 6 +++++-
 test/XYZT.jl                   | 4 ++--
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/coordinate_systems/XYZT.jl b/src/coordinate_systems/XYZT.jl
index 8442e56..967ccb1 100644
--- a/src/coordinate_systems/XYZT.jl
+++ b/src/coordinate_systems/XYZT.jl
@@ -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 Inf
   end
 
-  return -10e10
+  return -Inf
 end
 
 #######################
diff --git a/src/getter.jl b/src/getter.jl
index 681ab48..b31543b 100644
--- a/src/getter.jl
+++ b/src/getter.jl
@@ -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).
diff --git a/test/XYZT.jl b/test/XYZT.jl
index 8daef7f..cee5f53 100644
--- a/test/XYZT.jl
+++ b/test/XYZT.jl
@@ -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]

From 299994a7ecea18251007bbabc6f69b980177bf7a Mon Sep 17 00:00:00 2001
From: Mateusz Jakub Fila <mateusz.jakub.fila@cern.ch>
Date: Mon, 4 May 2026 09:04:54 +0200
Subject: [PATCH 2/2] return Inf of appropriate type

---
 src/coordinate_systems/XYZT.jl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/coordinate_systems/XYZT.jl b/src/coordinate_systems/XYZT.jl
index 967ccb1..3bdb4e1 100644
--- a/src/coordinate_systems/XYZT.jl
+++ b/src/coordinate_systems/XYZT.jl
@@ -151,10 +151,10 @@ function eta(::XYZT, mom)
 
   @warn "Pseudorapidity (η): transverse momentum is zero! return ±Inf"
   if zcomp > zero(zcomp)
-    return Inf
+    return oftype(zcomp, Inf)
   end
 
-  return -Inf
+  return oftype(zcomp, -Inf)
 end
 
 #######################