Letter of Intent: The Forward Physics Facility

TL;DR

The Forward Physics Facility (FPF) is a proposed extension of the HL-LHC to study high energy neutrinos and new particles with four detectors, aiming to expand discovery potential in particle physics.

Contribution

This paper proposes the construction and design of the FPF, detailing its physics goals, detector layout, collaboration, and implementation plan.

Findings

Supports a broad physics program including neutrino physics and dark matter searches.

Enables breakthrough measurements in quantum chromodynamics and astroparticle physics.

Plans for construction, integration, and installation of detectors at the FPF.

Abstract

The Forward Physics Facility (FPF) is a proposed extension of the HL-LHC program designed to exploit the unique scientific opportunities offered by the intense flux of high energy neutrinos, and possibly new particles, in the far-forward direction. Located in a well-shielded cavern 627 m downstream of one of the LHC interaction points, the facility will support a broad and ambitious physics program that significantly expands the discovery potential of the HL-LHC. Equipped with four complementary detectors -- FLArE, FASER$\nu$2, FASER2, and FORMOSA -- the FPF will enable breakthrough measurements that will advance our understanding of neutrino physics, quantum chromodynamics, and astroparticle physics, and will search for dark matter and other new particles. With this Letter of Intent, we propose the construction of the FPF cavern and the construction, integration, and installation of its experiments. We summarize the physics case, the facility design, the layout and components of the detectors, as well as the envisioned collaboration structure, cost estimate, and implementation timeline.