Recent measurements at the Large Hadron Collider have observed entanglement in the spins of t t ¯ pairs. The effects of radiation, which are expected to lead to quantum decoherence and a reduction of entanglement, are generally neglected in such measurements. In this work we calculate the effects of decoherence from various different types of radiation for a maximally entangled pair of fermions—a bipartite system of qubits in a Bell state. We identify the Kraus operators describing the evolution of the open quantum system with the integrated Altarelli-Parisi splitting functions.
We study the impact of radiation on quantum systems defined by the spins of elementary fermion-antifermion pairs produced at colliders. We present predictions for several processes, showing that energetic final-state radiation can induce decoherence and significantly reduce the entanglement of quantum systems formed by elementary fermion pairs. We investigate the feasibility of observing this effect experimentally in exclusive samples with energetic radiation. A statistically significant signal can be obtained with current data in associated
pp→ttˉ(g) production at the LHC and in
e+e−→τ+τ−(γ) production at Belle 2. Future electron-positron colliders operated at the
Z pole or well above the
ttˉ production threshold will extend these prospects further.
We address momentum entanglement in Higgs decays to weak boson pairs,
H→WW,ZZ, by discretising momentum space. The momenta of the two weak bosons are entangled, as well as the degrees of freedom in momentum and spin spaces. For
H→ZZ in the four-lepton final state, we also estimate the statistical sensitivity of entanglement measures at the Large Hadron Collider and future upgrades. The discretisation method introduced here is broadly applicable, offering a framework for studies of momentum entanglement at the energy frontier.
Abstract In this article, we study quantum entanglement properties of the three-body
H→γllˉ H → γ l l ¯ decays (for
l=e,μ,τ l = e , μ , τ ) within the context of the Standard Model augmented with CP-violating interactions in the lepton Yukawa sector. Our aim is to elucidate the distribution of entanglement between the final photon, lepton and antilepton across the phase-space. These rare Higgs boson decays occur at 1-loop level, presenting a unique opportunity to scrutinize quantum correlations of fundamental interactions in tripartite systems by computing concurrence measures and investigating Bell non-locality. Moreover, we explore post-decay and autodistillation phenomena. Multipartite entanglement measures have much richer structure than those in the bipartite case, thus deserve more attention in collider phenomenology. In this line, we analyze here novel observables for these three-body Higgs boson decays, which can be extended to other multiparticle systems within the high-energy regime. We found that entanglement manifests among final particles, occasionally achieving a maximally entangled state in specific kinematical configurations. Also, these decay channels are promising for Bell non-locality tests but CP-effects are suppressed by lepton masses in this kind of observables.
We present a comprehensive theoretical framework for probing quantum entanglement in the decay angular distributions of a spin-
S particle-antiparticle pair
AAˉ, where each particle decays sequentially into a two-body final state,
A→B+C and
Aˉ→Bˉ+Cˉ, with
B(Bˉ) carrying spin
b and
C(Cˉ) being spinless. Starting from the most general polarized initial state, we derive the fully differential angular distribution
W(θ1,θ2,ϕ1,ϕ2) and identify observables
⟨cos(2S(ϕ1∓ϕ2))⟩ whose expectation values directly depend on the entanglement-sensitive coefficients
Re(α−S,∓SαS,±S∗) of the initial state. The proportionality factor
C(S,b) in these relations is computed explicitly. For bosonic decays (
b=0,1,2,…),
C(S,b) is universal and independent of decay dynamics; in particular,
C(S,0)=1/2 for any
S, and
C(1,1)=1/8, matching known results for
W+W− decays. For fermionic decays (
b=21,23,25…),
C(S,b) depends explicitly on the spin analysis powers
αA/Aˉ, making entanglement extraction more decay-dependent. We further demonstrate, within the context of
e+e−→γ∗→AAˉ production, how
αA/Aˉ can be determined experimentally using specific angular observables restricted to the beam-axis region. Our results highlight the special role of bosonic decays in providing clean, model-independent tests of quantum entanglement at colliders, while outlining a pathway for entanglement measurement in fermionic cases through supplementary polarization information.
In this article, we study quantum entanglement properties of the three-body
H→γllˉ decays (for
l=e,μ,τ) within the context of the Standard Model augmented with CP-violating interactions in the lepton Yukawa sector. Our aim is to elucidate the distribution of entanglement between the final photon, lepton and antilepton across the phase-space. These rare Higgs boson decays occur at 1-loop level, presenting a unique opportunity to scrutinize quantum correlations of fundamental interactions in tripartite systems by computing concurrence measures and investigating Bell non-locality. Moreover, we explore post-decay and autodistillation phenomena. Multipartite entanglement measures have much richer structure than those in the bipartite case, thus deserve more attention in collider phenomenology. In this line, we analyze here novel observables for these three-body Higgs boson decays, which can be extended to other multiparticle systems within the high-energy regime. We found that entanglement manifests among final particles, occasionally achieving a maximally entangled state in specific kinematical configurations. Also, these decay channels are promising for Bell non-locality tests but CP-effects are suppressed by lepton masses in this kind of observables.