Untangling the spin of a dark boson in $Z$ decays

Abstract

We analyze the $Z$-boson decay $Z\to \gamma X$ into a photon ($\gamma$) plus a hypothetical light boson ($X$) belonging to a dark or secluded sector. Due to its feeble interactions with Standard Model fields, this dark boson is behaving as missing energy in the detector. We consider for $X$ the cases of spin-1 (massless dark-photon), spin-0 (axion-like), and spin-2 (graviton-like) particles and explore the way to untangle its spin origin. All these scenarios predict a universal signature for this decay, characterized by a single mono-chromatic photon in the $Z$ center of mass, with energy about half of the $Z$ mass, plus a neutrino-like missing energy associated to the $X$ boson. We show that if the $Z\to \gamma X$ signal should be discovered at $e^{+}{e}^{-}$ colliders, the angular distribution of the mono-chromatic photon in $e^{+}{e}^{-}\to Z\to \gamma X$ can provide a clean probe to discriminate between the $J=1$ and alternative $J=0/2$ spin nature of the $X$ dark boson.

22 pages, 2 figures, improved text, new results added, same as PRD published version

References in corpus (9)

• Collider Probes of Axion-Like Particles
• Revised constraints and Belle II sensitivity for visible and invisible axion-like particles
• An M Theory Solution to the Strong CP Problem and Constraints on the Axiverse
• Review of short-range gravity experiments in the LHC era
• Dark Sectors 2016 Workshop: Community Report
• Dark photons and resonant monophoton signatures in Higgs boson decays at the LHC
• FCNC decays of SM fermions into a dark photon
• Z boson decay to photon plus Kaluza-Klein graviton in large extra dimensions
• $Z$-boson decays into an invisible dark photon at the LHC, HL-LHC and future lepton colliders

Cited by in corpus (3)

• $Z$-boson decays into an invisible dark photon at the LHC, HL-LHC and future lepton colliders
• Searching for the dark sector in two-body anti-muon decay with the polarization of monochromatic positrons
• Dark photon searches via Higgs boson production at the LHC and beyond