Collider experiments can distinguish scalar from vector dark matter through characteristic production topologies, kinematic shapes, and angular correlations that reflect the particle’s spin and interaction portal. Scalar dark matter produced via the Higgs portal typically appears in events with an on- or off-shell Higgs leading to invisible Higgs decays and softer missing transverse energy spectra, while vector dark matter coupled through a gauge mediator such as a Z' produces harder MET and different associated visible activity because of polarization and longitudinal-mode effects.
Kinematic and angular signatures
Spin changes the angular distributions of visible recoils. For vector dark matter, the presence of longitudinal polarization components enhances production at high center-of-mass energy by the Goldstone equivalence mechanism, producing harder transverse momentum spectra for associated jets or photons. Scalar production lacks these polarization-driven enhancements, so mono-X pT and MET distributions tend to be softer and more centrally distributed. Experiments use shape fits of MET and leading-object pT, plus angular variables such as the azimuthal separation between jets and MET, to test templates corresponding to different spins. The ATLAS Collaboration CERN and the CMS Collaboration CERN have applied such techniques in monojet and mono-V searches to constrain simplified models that encode these differences.
Resonant and associated observables
The mediator and coupling structure add discriminating power. A Higgs-portal scalar often changes Higgs branching ratios and can be probed through precision measurements of Higgs invisible width, while a vector portal frequently leads to a resonant mediator visible in dilepton or dijet channels, or to kinetic mixing signatures. Theoretical studies by Yann Mambrini Université Paris-Saclay and other model builders show how combined fits to resonance searches, MET shape, and Higgs measurements can lift degeneracies between scalar and vector hypotheses. Nuanced model details such as mediator mass, coupling chiralities, and dark-sector multiplicity alter expected rates and must be included in experimental templates.
Discriminating spin has consequences beyond collider analyses: identification of a scalar or vector nature changes expectations for direct-detection cross sections, velocity dependence of annihilation relevant for indirect searches, and viable cosmological production mechanisms. It also shapes detector strategy and international research priorities, as experiments at CERN, national labs, and university groups coordinate to combine resonance, Higgs, and MET measurements into a coherent picture. Robust conclusions require global fits across channels and inputs from both experimental collaborations and vetted theoretical frameworks.