[论文解读] Technical Proposal for FASER: ForwArd Search ExpeRiment at the LHC

FASER Collaboration, A. Ariga+34 more|arXiv (Cornell University)|Dec 21, 2018

Particle physics theoretical and experimental studies参考文献 26被引用 84

一句话总结

本论文提出在 ATLAS IP 下游 480 m 的 TI12 放置 FASER 实验，用于搜索轻型、弱相互作用的 LLP；描述探测器组件、环境以及包括成本与进度的实施计划。

ABSTRACT

FASER is a proposed small and inexpensive experiment designed to search for light, weakly-interacting particles during Run 3 of the LHC from 2021-23. Such particles may be produced in large numbers along the beam collision axis, travel for hundreds of meters without interacting, and then decay to standard model particles. To search for such events, FASER will be located 480 m downstream of the ATLAS IP in the unused service tunnel TI12 and be sensitive to particles that decay in a cylindrical volume with radius R=10 cm and length L=1.5 m. FASER will complement the LHC's existing physics program, extending its discovery potential to a host of new, light particles, with potentially far-reaching implications for particle physics and cosmology. This document describes the technical details of the FASER detector components: the magnets, the tracker, the scintillator system, and the calorimeter, as well as the trigger and readout system. The preparatory work that is needed to install and operate the detector, including civil engineering, transport, and integration with various services is also presented. The information presented includes preliminary cost estimates for the detector components and the infrastructure work, as well as a timeline for the design, construction, and installation of the experiment.

研究动机与目标

• Motivate a complementary search for light, weakly interacting particles at the LHC beyond ATLAS/CMS capabilities.
• Describe a small, cost-effective detector located along the beam line 480 m from the ATLAS interaction point to catch LLP decays.
• Outline the detector components (magnets, tracker, scintillators, calorimeter) and the trigger/readout and integration requirements.
• Assess the detector environment (flux, radiation, temperature, vibrations) and civil/inaction commissioning needs.
• Provide preliminary cost estimates and a schedule for design, construction, installation, and commissioning.

提出的方法

• Present the detector design: a 0.5 T permanent magnet decay volume with a 10 cm radius, followed by a tracking spectrometer and an electromagnetic calorimeter.
• Quantify particle fluxes and backgrounds using FLUKA simulations and in situ measurements in TI18/TI12 to validate the model.
• Analyze the impact of beam configuration (crossing angle, divergence, filling scheme) on LOS and acceptance.
• Describe the trigger and readout system, data acquisition, and alignment/calibration strategies.
• Outline civil engineering, installation, integration, safety, and commissioning plans.
• Provide preliminary costing and scheduling for the full detector and infrastructure.

实验结果

研究问题

• RQ1 What is FASER’s sensitivity to a range of light, weakly interacting particles (e.g., dark photons, dark Higgs, heavy neutral leptons, axion-like particles) given Run 3 LHC conditions?
• RQ2 What are the expected background rates and particle fluxes at the FASER location, and how do they affect signal efficiency and triggering?
• RQ3 How do LHC beam parameters (crossing angle, divergence, filling scheme) influence the LOS, acceptance, and physics reach of FASER?
• RQ4 What are the practical feasibility, costs, and timeline for installing and commissioning FASER in TI12 during Long Shutdown 2?

主要发现

• FLUKA simulations predict a charged particle flux through FASER of about 0.40 cm^-2 s^-1 for E>10 GeV, 0.20 cm^-2 s^-1 for E>100 GeV, and 0.06 cm^-2 s^-1 for E>1000 GeV at Run 3 luminosity.
• In situ emulsion measurements at TI12 (main peak) yield fluxes of (1.9–3.0)×10^4 fb cm^-2, in good agreement with FLUKA expectations (2.0×10^4 fb cm^-2 for E>10 GeV).
• The main angular peak width measured by emulsions is 2.3 mrad, indicating high-energy particles entering from the ATLAS IP direction with minimal multiple scattering.
• Radiation environment estimates show dose less than 5×10^-3 Gy per year and 1 MeV neutron-equivalent fluence below 5×10^7 per year, compatible with non-radiation-hard electronics.
• TI12 allows a longer detector (~5 m) compared to TI18 (~3 m) due to tunnel geometry and floor lowering, enhancing sensitivity to LLP decays.
• Measured radiation and flux measurements in TI12 are consistent with simulations, supporting feasibility of non-radiation-hard electronics and the overall detector design.