Rare $Z$ Boson Decays to a Hidden Sector

Understand

We demonstrate that rare decays of the Standard Model $Z$ boson can be used to discover and characterize the nature of new hidden-sector particles.

• We propose new searches for these particles in soft, high-multiplicity leptonic final states at the Large Hadron Collider.
• The proposed searches are sensitive to low-mass particles produced in $Z$ decays, and we argue that these striking signatures can shed light on the hidden-sector couplings and mechanism for mass generation.