FASER: ForwArd Search ExpeRiment at the LHC

TL;DR

FASER is a proposed experiment at the LHC designed to detect long-lived, weakly-interacting particles produced in high-energy collisions, with potential to discover new physics phenomena and improve understanding of particle physics and cosmology.

Contribution

This paper introduces the FASER experiment, detailing its design, planned implementation, and potential to discover new particles beyond the Standard Model.

Findings

FASER is planned for installation during LHC Run 3 (2021-23).

FASER 2 could significantly extend discovery potential during HL-LHC era.

FASER aims to detect particles like dark photons, heavy neutral leptons, and axion-like particles.

Abstract

FASER, the ForwArd Search ExpeRiment, is a proposed experiment dedicated to searching for light, extremely weakly-interacting particles at the LHC. Such particles may be produced in the LHC's high-energy collisions in large numbers in the far-forward region and then travel long distances through concrete and rock without interacting. They may then decay to visible particles in FASER, which is placed 480 m downstream of the ATLAS interaction point. In this work, we describe the FASER program. In its first stage, FASER is an extremely compact and inexpensive detector, sensitive to decays in a cylindrical region of radius R = 10 cm and length L = 1.5 m. FASER is planned to be constructed and installed in Long Shutdown 2 and will collect data during Run 3 of the 14 TeV LHC from 2021-23. If FASER is successful, FASER 2, a much larger successor with roughly R ~ 1 m and L ~ 5 m, could be constructed in Long Shutdown 3 and collect data during the HL-LHC era from 2026-35. FASER and FASER 2 have the potential to discover dark photons, dark Higgs bosons, heavy neutral leptons, axion-like particles, and many other long-lived particles, as well as provide new information about neutrinos, with potentially far-ranging implications for particle physics and cosmology. We describe the current status, anticipated challenges, and discovery prospects of the FASER program.