The Forward Physics Facility at the High-Luminosity LHC (2203.05090v1)

Abstract: High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential.

Overview of the Forward Physics Facility at the High-Luminosity LHC

The proposal for the Forward Physics Facility (FPF) at the High-Luminosity Large Hadron Collider (HL-LHC) outlines the establishment of a new experimental site specifically designed to maximize the physics potential of high-energy particles produced in forward directions of LHC collisions. The FPF aims to address limitations of existing LHC detectors, offering unique opportunities to explore processes within the Standard Model (SM) and searching for signals of physics beyond the Standard Model (BSM). This facility, strategically located behind extensive shielding, is optimized for low-background conditions, facilitating precise measurements and innovative searches.

Civil Engineering and Detector Design

The FPF involves significant civil engineering undertakings to create a new cavern several hundred meters from the ATLAS interaction point. This space will host multiple experiments, each tailored to specific physics goals. These include:

• FASER2: Targeting long-lived particles like dark photons, axion-like particles, and other exotic states through decay signature observations.
• FASERν2 and Advanced SND: Designed to detect and paper neutrinos at energies up to several TeV, with a particular focus on tau neutrinos.
• FLArE (Forward Liquid Argon Experiment): A noble liquid detector searching for neutrinos and dark matter interactions.
• FORMOSA: Investigating millicharged particles with the potential for detecting extremely rare event signatures.

These experiments benefit from the FPF's location, directly aligned with the beam collision axis, allowing for detailed studies of particle behavior outside typical LHC detection capabilities. The facility's infrastructure includes advanced radiation shielding to diminish background noises, enhancing data integrity and interpretation.

Physics Potential and Research Implications

The FPF is projected to significantly advance our understanding of both SM and BSM phenomena through:

• BSM Searches: By exploiting forward production, FPF aims to investigate theoretical models proposing new particles like dark photons, scalars, and vectors linked with hidden-sector and dark matter theories. High-statistics analyses based on deviations from SM predictions can elucidate new interactions and symmetries.
• Neutrino Physics: With an unprecedented detection ability for TeV-scale neutrinos, experiments will improve knowledge on neutrino cross-sections and flavor oscillations. This data supports QCD studies and informs models of nuclear and hadron interaction dynamics.
• Astroparticle Synergies: By measuring particle flux in the forward direction, FPF contributes to cosmic ray and astrophysical neutrino research. These integrations enhance programs across astrophysics and particle colliders, aiding multi-messenger astrophysics.

Future Prospects and Challenges

The FPF aligns with strategic objectives from the European Strategy Update, focusing on maximizing LHC output potential. It promises valuable contributions to fundamental physics fields, nurturing collaborative intersections among high-energy particle physics and astronomy. The anticipated timeline suggests construction during Long Shutdown 3 (2026–28), with operational gearing by the next LHC run cycle.

In confronting challenges of implementation, the facility requires sophisticated design resolutions regarding muon background mitigation and efficient integration amidst existing LHC infrastructure. Research teams must also ready conceptual and technical designs to address anticipated financial and operational caveats effectively.

The Forward Physics Facility represents a bold leap forward in high-energy physics research, promising to push boundaries in neutrino physics and explore uncharted territories within BSM frameworks. This prospective advance bodes well for enriching LHC discoveries and illuminating the unknown facets of the universe, with implications stretching across theoretical and practical realms of modern physics.