Collider Spin Tomography with Missing Neutrinos

• URL: http://arxiv.org/abs/2607.28346v1
• Date: Thu, 30 Jul 2026 15:18:12 GMT
• Title: Collider Spin Tomography with Missing Neutrinos
• Abstract summary: We formulate the visible measurement under kinematic ambiguities arising from invisible particles as a coarse-grained positive-operator-valued measure on the production spin density matrix.<n>We show that information loss is governed by the null space of the resulting visible-data map, not by the number of kinematic solutions.
• Score: 23.51923401381968
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Missing neutrinos need not destroy collider spin tomography. We formulate the visible measurement under kinematic ambiguities arising from invisible particles as a coarse-grained positive-operator-valued measure on the production spin density matrix. We show that information loss is governed by the null space of the resulting visible-data map, not by the number of kinematic solutions. In $e^+e^-\toτ^+τ^-\toπ^+π^-+ν\barν$, the twofold ambiguity leaves only the antisymmetric spin-correlation combination $C_{nr}-C_{rn}$ unidentifiable, while the differential production rate and the remaining fourteen spin coefficients are identifiable. For practical reconstruction under kinematic ambiguities, we develop a self-consistent fixed-point unfolding method using only visible data, without assuming a theoretical production template. Closure tests in Standard Model and anomalous tau-dipole benchmarks show that the method reproduces the truth-level differential production rate and all identifiable spin coefficients, whereas the usual flat average over kinematic folds gives significantly biased reconstructions. When a nontrivial null space is present, the reconstructed identifiable subspace together with positivity yields controlled ranges for concurrence and the CHSH parameter.

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