Probing some photon portals to new physics at intensity frontier experiments

TL;DR

This paper explores the detection prospects of light, long-lived particles predicted by extensions of the Standard Model at intensity frontier experiments, analyzing various production and decay signatures across multiple current and proposed detectors.

Contribution

It introduces a comprehensive study of three specific long-lived particles and evaluates their detectability at various beam dump and collider experiments, including novel signatures like electron scattering and Primakoff processes.

Findings

SHiP could provide the strongest constraints for displaced vertex searches.

FASER2/FPF could effectively probe the decay length region around 1 meter.

Multiple experiments offer complementary coverage for different parameter space regions.

Abstract

A number of extensions of the Standard Model predict the existence of new light, weakly-coupled particles that couple to the visible sector through higher-dimensional operators containing one or two photons, suppressed by a high new physics scale, and thus have long lifetimes. In this work, we study the prospects for detecting three $\sim\,$sub-GeV such long-lived particles (LLP) at intensity frontier experiments: a massive spin-2 mediator ($G$), a dark axion portal, and a light neutralino coupled to ALPino or gravitino. We consider the production and visible decays of these particles in several current and proposed beam dump experiments (CHARM, NuCal, SeaQuest, NA62, SHiP) as well as in the LHC detectors (FASER, FASER$\nu$, FLArE, MATHUSLA). In addition to the usual displaced vertex signature, we also examine the impact of electron scattering signature and the Primakoff-like process which leads to conversion of $G$ into a photon or to the secondary LLP production via upscattering of the lighter dark sector state on dense material put in front of the detector. In all cases, we find the SHiP experiment could provide the strongest constraints for the displaced vertex search, while FASER2/FPF could provide complementary coverage of the $\gamma c\tau \sim 1$ m decay length region of the parameter space.