FASER2 logo small.png


FPF Cavern FASER2 logo.png


Welcome to the FASER2 webpage. This page documents information related to the FASER2 detector for the Forwards Physics Facility (FPF). FASER2 is primarily focused on searching for exotic and long-lived beyond the Standard Model particles, which, along with other motivations, are possible candidates for Dark Matter.
FASER2 is a detector proposed to be housed in the FPF. It's physics goals are similar to that of the existing FASER (ForwArd Search ExpeRiment), however although FASER is already set to probe new parameter space in the search for BSM physics the overall size of FASER is been heavily constrained by the available space underground. This restricts the size of the possible decay volume and therefore sensitivity to various new physics models, which for many representative BSM models is directly related to the length and radius of the decay volume. This strongly motivates the case for an enlarged detector, FASER2, which would be housed in the dedicated cavern of the FPF where significantly more space is available.

Contact information and useful links




Regular meetings are held every other Thursday at 1pm CERN time.

Meetings can be found in the FASER2 indico category.

Recent meetings

Physics Priorities and Milestones

FASER2 is expected to have sensitivity to a number of physics models not accessible to FASER, as summarised in this table from the FASER Physics Reach Paper:

FASER2 benchmarks table.png

The larger volume of FASER2 and the richer phenomenology means that there are several important design considerations:

  • Larger aperture imposes strong restrictions on possible magnet technology.
  • Larger radius means being on-axis is less important.
  • More LLP decay channel means particle ID will be important.
  • A larger detector means a larger background rate, may required different detector technology.
  • More sophisticated signal reconstruction strongly desirable (mass and pointing).
  • Link to FASERν2 - need to be able to measure muon charge (and momentum) from (τ and μ) neutrino interactions.


  • FPF5: 15-16th Nov 2022
  • P5 committee?: Q3 2022?
  • CDR: Q1 2023
  • LHCC discussion? Q2 2023

HL-LHC timeline:

HLLHC FPF Timeline.png

Activity areas

Activity area Sub-area Responsible Comments
Magnet   Jamie/Hide  
Tracker SciFi Sune  
Other R&D Monica  
Interface Tracker SCT Hide/Yosuke  
Scintillator   Sune  
Calorimeter Dual-readout Josh, Iacopo  
Support structures      
TDAQ   Anna/Claire  
Physics Sim studies Size/Shape Josh/Alan/Olivier  
Physics signatures Anna/Monica  
Generation Josh/Carl  

Person power

Open studies

Study Responsible Timescale Comments Status
Magnet aperture Josh/Olivier Nov 2022 FORESEE In progress
Magnet manufacturer Jamie/Hide/Monica/Alan/Anna Nov 2022 FORESEE In progress
Overall detector layout Josh/Olivier Nov 2022 FORESEE In progress
Tracker pT resolution Yosuke Dec 2022 Important for FASERnu2 but also mass reco Not started
Trigger rate / deadtime Anna / Claire Dec 2022   Not started
Use of old SCT modules Hide Dec 2022 Radiation study etc.. Not started
Usefulness of timing TBD Dec 2022   Not started
Possibility of mass reco Alan/Olivier Dec 2022 Using ACTS Not started
Pointing capability Alan/Olivier Dec 2022 Using ACTS Not started
SciFi specs. Sune Dec 2022 Number of layers, etc… Not started
Calorimeter requirements Josh/Iacopo Dec 2022   Early stages
Muons system requirements   Jan 2023   Not started

Baseline Geometry

A possible FASER2 geometry very similar to FASER but with larger dimensions was already explored in the LoI, Technical Proposal and Physics Reach publications from FASER.

This geometry had a decay volume of dimensions: Length=5m, Diameter=2m. This results in 4 orders of magnitude improvement in sensitivity reach and the angular acceptance of of all neutral pions goes from 0.6% in FASER to 10% in FASER2. It also improves sensitivities to LLPs produced in decays of heavy mesons and in general improves sensitivity to larger LLP masses.

However, further investigations of the available technology have indicated that such long and wide-aperture superconducting magnets are infeasible for the expected cost envelope for FASER2. Therefore, several other proposals have been considered for slightly reduced size and different shape magnet apertures have been studied which look promising. As a result, an updated baseline FASER2 geometry has been defined, as shown in the figure below:

FASER2 schema v1.png

This new baseline uses a single magnet, it does not immerse the decay volume in a magnetic field and in general has a significantly reduced length of magnetic field. However, the charged particle separations required still appear to be feasible due to the longer detector length. The baseline has a rectangular aperture of 1m x 3m in the transverse plane and the decay volume is 10m long. The effect of different scenarios on the Dark Higgs reach is shown in the following figure, the new baseline scenario corresponds to the magenta dashed line ("R1 L=10m X=3m Y=1m"), where it can be seen that the expected sensitivity is similar to that of the old default FASER2 geometry shown in dark red ("F2 L=5m D=2m"):

FASER2 RandD DarkHiggs v1.png



Developed by Felix Kling and Sebastian Trojanowski, FORESEE (FORward Experiment SEnsitivity Estimator) is a package for simulating the expected sensitivity reach of experiments placed in the far-forward direction from the proton-proton interaction point to new physics models. It can also be used to create HepMC files of these models for input into e.g. Geant4 simulations.

Simple FORESEE+Geant4 simulation

To test different magnet and detector geometries the FORESEE package was slightly adapted to produce HepMC output files and a platform for creating simple Geant4 geometries has been developed for FASER2 R&D studies:

Detector technologies


Add magnet resources/studies here


Add magnet resources/studies here

Dual-readout calorimeter

Add dual-readout resources/studies here

Background estimates

TODO: Add FLUKA estimates of the muon flux as a function of position in the FPF. Can be used for background and trigger studies.


-- JoshMcFayden - 2022-10-11

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng FASER2_RandD_DarkHiggs_v1.png r1 manage 352.3 K 2022-11-15 - 00:00 JoshMcFayden  
PNGpng FASER2_benchmarks_table.png r1 manage 1143.1 K 2022-11-14 - 23:58 JoshMcFayden  
PNGpng FASER2_logo_small.png r1 manage 187.0 K 2022-11-14 - 23:56 JoshMcFayden  
PNGpng FASER2_schema_v0.png r1 manage 2047.7 K 2022-11-14 - 23:59 JoshMcFayden  
PNGpng FASER2_schema_v1.png r1 manage 212.9 K 2022-11-15 - 00:00 JoshMcFayden  
PNGpng FPF_Cavern_FASER2_logo.png r1 manage 1174.6 K 2022-11-14 - 23:57 JoshMcFayden  
PNGpng HLLHC_FPF_Timeline.png r1 manage 1385.5 K 2022-11-14 - 23:59 JoshMcFayden  
Edit | Attach | Watch | Print version | History: r3 < r2 < r1 | Backlinks | Raw View | WYSIWYG | More topic actions
Topic revision: r3 - 2023-02-02 - JoshMcFayden
    • Cern Search Icon Cern Search
    • TWiki Search Icon TWiki Search
    • Google Search Icon Google Search

    FASER All webs login

This site is powered by the TWiki collaboration platform Powered by PerlCopyright &© 2008-2023 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
or Ideas, requests, problems regarding TWiki? use Discourse or Send feedback