Probing naturally light singlets with a displaced vertex trigger

TL;DR

This paper explores the feasibility and physics potential of a dedicated displaced vertex trigger at the high luminosity LHC, focusing on light singlet particles and their exotic decay signatures.

Contribution

It proposes a minimal-cut trigger strategy for low-mass displaced vertices, enabling new searches for light resonances and exotic decays at the LHC.

Findings

Trigger rate can be reduced to kHz level with simple cuts

Displaced vertex trigger opens new parameter space for light resonances

Potential to detect exotic Higgs and B decays, and light scalar or axion-like particles

Abstract

We investigate the physics case for a dedicated trigger on a low mass, hadronic displaced vertex at the high luminosity LHC, relying on the CMS phase II track trigger. We estimate the trigger efficiency with a simplified simulation of the CMS track trigger and show that the L1 trigger rate from fake vertices, B meson decays and secondary interactions with the detector material can likely be brought down to the kHz level with a minimal set of cuts. While it would with any doubt be a severe experimental challenge to implement, we conclude that a displaced vertex trigger could open qualitatively new parameter space for exotic Higgs decays, exotic B decays and even direct production of light resonances. We parametrize the physics potential in terms of a singlet scalar mixing with the Standard Model Higgs and an axion-like particle with a coupling to gluons, and review a number or relevant models motivated by the hierarchy and strong CP problems, dark matter and baryogenesis.