Phenomenology of Electroweak Portal Dark Showers: High Energy Direct Probes and Low Energy Complementarity

TL;DR

This paper explores how dark QCD sectors interacting via electroweak portals produce long-lived particles detectable through displaced decays at the LHC, offering new search strategies and constraints for dark sector models.

Contribution

It introduces a comprehensive phenomenological analysis of dark showers from electroweak portals, including current and future collider constraints, and proposes specific benchmark models for experimental testing.

Findings

Dark showers produce long-lived dark pions with displaced decays.

Current LHC data constrains some dark sector parameters.

Future high-luminosity runs and detectors can significantly improve sensitivity.

Abstract

We investigate the phenomenology of a dark QCD sector interacting with the Standard Model (SM) via the electroweak (EW) portals. The portal interactions allow SM bosons, such as $Z$ and $h$, or additional bosons that mix with them, to decay into dark quarks, producing dark showers. The light dark mesons are expected to be long-lived particles (LLPs), as their decays back to the SM states through the EW-portal interactions typically have macroscopic decay lengths. We focus on dark shower events initiated by various bosons at the Large Hadron Collider (LHC). The most prominent signal is the displaced decay of GeV-scale dark pions as LLPs. Current limits on dark shower signals at LHC detectors are recast from public data in a model-independent manner. Future limits in the high-luminosity phase and proposed auxiliary detectors are also projected. Additionally, we study the flavor-changing neutral current (FCNC) $B$ decays into dark pions, obtaining both current and projected constraints at the LHC and other facilities. These constraints can be combined for specific models, which are illustrated in two EW-portal benchmarks: one with the heavy doublet fermion mediation and another with the $Z^\prime$ mediator including a mass mixing. The collider reach shows significant potential to probe the parameter space unconstrained by EW precision tests, highlighting the necessity of dedicated LLP search strategies and facilities.