Dark Sectors 2016 Workshop: Community Report

TL;DR

The Dark Sectors 2016 Workshop advocates a broad, multi-pronged approach to uncover light dark matter and new forces that couple to the Standard Model via portal interactions, with emphasis on the vector portal. It surveys theory and a wide array of experimental strategies—from fixed-target beam dumps and missing-energy/missing-mass searches to direct detection and high-energy colliders—highlighting complementary sensitivities and the need to explore both simple and rich dark sectors. By defining thermal targets, outlining realistic constraints, and detailing near-term opportunities, the report argues that a coordinated program across facilities and detection techniques can decisively probe sub-GeV dark matter and dark forces within 5–10 years. Even in the absence of discovery, the proposed program will dramatically constrain viable dark-sector scenarios and guide future theory and experimentation. The overarching message is that discovery or falsification of a dark sector requires simultaneous investment in multiple, diverse experiments and robust theorist-experimenter collaboration.

Abstract

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years.

Figures (10)

• Figure 1: Visible dark photon decay branching ratios (figure from Ref. Liu:2014cma).
• Figure 2: Cartoon of $\varepsilon^2$ vs. $A^\prime$ mass parameter plane. Region A: bump hunts, visible or invisible modes. Region B: displaced vertex searches, short decay lengths; Region C: displaced vertex searches, long decay lengths.
• Figure 3: $A^\prime$ sensitivity for missing-mass experiments, allowing invisible decay modes. Existing exclusions, shown in gray, have been smoothed.
• Figure 4: Sensitivity to $A^\prime$ for exclusive experiments seeking visible decay modes $A^\prime\xspace\to\ell^{+}\ell^{-}\xspace$. Left: Experiments capable of delivering results over the next 5 years to 2021. Shaded regions show existing bounds. Green band shows $2\sigma$ region in which an $A^\prime$ can explain the discrepancy between the calculated and measured value for the muon $g-2$. Right: Longer term prospects beyond 2021 for experimental sensitivity. All projections on left plot are repeated in gray here. Note that LHCb and Belle-II can probe to higher masses than 2 GeV and SHIP can probe to lower values of $\epsilon$ than indicated.
• Figure 5: Schematic of the dual purpose LBNF beam-line that can simultaneously produce both a charged and neutral beam. The charged beam decays into neutrinos while the neutral beam can couple to LDM.