A flavoured dark sector

TL;DR

This paper investigates a QCD-like dark sector with a flavour structure, focusing on dark pions as decay products, their phenomenology, and how they can be detected in experiments like NA62, SHiP, and the LHC.

Contribution

It provides the first calculation of dark pion decays to SM mesons below 1.5 GeV using a chiral Lagrangian and explores experimental constraints and detection prospects.

Findings

Dark pions can decay with lengths from millimetres to hundreds of metres.

Constraints from BBN, dark matter detection, and flavour restrict the parameter space.

Dark pions can be effectively searched for at fixed target experiments and the LHC.

Abstract

We explore the phenomenology of a QCD-like dark sector which confines around the GeV scale. The dark sector inherits a flavour structure from a coupling between dark quarks and SM quarks via a heavy mediator, which leads to exciting new phenomena. While stable baryonic bound states are the dark matter candidates, the phenomenology is dominated by the lightest composite mesons, the dark pions, which can have decay lengths ranging from millimetres to hundreds of meters. For masses below 1.5 GeV, their exclusive decays to SM mesons are calculated for the first time by matching both dark and visible sectors to a chiral Lagrangian. Constraints from big bang nucleosynthesis, dark matter direct detection and flavour single out a small region of allowed parameter space for dark pion masses below 5 GeV. It is best probed by the fixed target experiments NA62 and SHiP, where dark pions can be produced copiously in rare decays like B to K piD. Heavier dark pions are best searched for at the LHC, where they decay after hadronisation to produce jets which emerge into SM states within the detector. Here the flavour structure ensures different flavours emerge on different length scales, leading to a striking new feature in the emerging jets signature.