FASER Technical Proposal

Draft: LHCC, 3 December 2018

Contact: FASER email list
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e-print: arXiv: pdf from arXiv
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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.
Figures
Figure 01:
See Fig. (???). Schematic view of the far-forward region downstream of ATLAS and various particle trajectories. Upper panel: FASER is located 480 m downstream of ATLAS along the beam collision axis (dotted line) after the main LHC tunnel curves away. Lower left panel: High-energy particles produced at the IP in the far-forward direction. Charged particles are deflected by LHC magnets, and neutral hadrons are absorbed by either the TAS or TAN, but LLPs pass through the LHC infrastructure without interacting. Note the extreme difference in horizontal and vertical scales. Lower right panel: LLPs may then travel ∼ 480 m further downstream, passing through 10 m of concrete and 90 m of rock, and decay within FASER in TI12. f.

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Figure 02:
Layout of the proposed FASER detector. LLPs enter from the left. The detector components include scintillators (gray), dipole magnets (red), tracking stations (blue), and a calorimeter (dark purple). f.

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Figure 03:
A model of the FASER detector situated at the proposed location (centered on the nominal LOS) in the TI12 tunnel. f.

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Figure 04a:
FLUKA simulation estimation of the particle flux as a function of energy at the FASER location: (top) for negative and positive muons; (bottom) for different neutrino species. These are normalized to a luminosity of 2 × 1034 cm-2 s-1. f.

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Figure 04b:
FLUKA simulation estimation of the particle flux as a function of energy at the FASER location: (top) for negative and positive muons; (bottom) for different neutrino species. These are normalized to a luminosity of 2 × 1034 cm-2 s-1. f.

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Figure 05a:
FLUKA simulation estimates of negative muon fluxes (top left) and positive muon fluxes (top right) in the transverse plane at the FASER location. These results assume the TI18 location, 485 m from the IP. The diagram at the bottom shows the geometry used in the simulations. The FASER detector is visible as a small, partially-cut circle of radius 20 cm at the bottom right of the tunnel. f.

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Figure 05b:
FLUKA simulation estimates of negative muon fluxes (top left) and positive muon fluxes (top right) in the transverse plane at the FASER location. These results assume the TI18 location, 485 m from the IP. The diagram at the bottom shows the geometry used in the simulations. The FASER detector is visible as a small, partially-cut circle of radius 20 cm at the bottom right of the tunnel. f.

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Figure 05c:
FLUKA simulation estimates of negative muon fluxes (top left) and positive muon fluxes (top right) in the transverse plane at the FASER location. These results assume the TI18 location, 485 m from the IP. The diagram at the bottom shows the geometry used in the simulations. The FASER detector is visible as a small, partially-cut circle of radius 20 cm at the bottom right of the tunnel. f.

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Figure 06a:
In situ measurements by emulsion detectors at the TI18 location (upper panels) and TI12 location (lower panels). We show photos of the installed detectors (left), maps of the installation locations (center), and angular distributions of the detected particles (right). f.

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Figure 06b:
In situ measurements by emulsion detectors at the TI18 location (upper panels) and TI12 location (lower panels). We show photos of the installed detectors (left), maps of the installation locations (center), and angular distributions of the detected particles (right). f.

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Figure 06c:
In situ measurements by emulsion detectors at the TI18 location (upper panels) and TI12 location (lower panels). We show photos of the installed detectors (left), maps of the installation locations (center), and angular distributions of the detected particles (right). f.

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Figure 06d:
In situ measurements by emulsion detectors at the TI18 location (upper panels) and TI12 location (lower panels). We show photos of the installed detectors (left), maps of the installation locations (center), and angular distributions of the detected particles (right). f.

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Figure 06e:
In situ measurements by emulsion detectors at the TI18 location (upper panels) and TI12 location (lower panels). We show photos of the installed detectors (left), maps of the installation locations (center), and angular distributions of the detected particles (right). f.

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Figure 06f:
In situ measurements by emulsion detectors at the TI18 location (upper panels) and TI12 location (lower panels). We show photos of the installed detectors (left), maps of the installation locations (center), and angular distributions of the detected particles (right). f.

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Figure 07a:
Angular distributions, projected into the x-axis, by three emulsion films with and without tungsten plates, corresponding to energy cutoffs of about 1 GeV and 50 MeV, due to multiple Coulomb scattering, respectively. f.

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Figure 07b:
Angular distributions, projected into the x-axis, by three emulsion films with and without tungsten plates, corresponding to energy cutoffs of about 1 GeV and 50 MeV, due to multiple Coulomb scattering, respectively. f.

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Figure 08a:
Measured temperature and humidity. Top: during the period when the emulsion detector was installed on the LOS in TI12 (between mid-September and mid-October). Bottom: in the LHC tunnel close to TI12 (in the UJ12 region) from LHC monitoring, over about 1 year. For the top plot the humidity is shown, whereas for the bottom it is the dew point of the air. f.

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Figure 08b:
Measured temperature and humidity. Top: during the period when the emulsion detector was installed on the LOS in TI12 (between mid-September and mid-October). Bottom: in the LHC tunnel close to TI12 (in the UJ12 region) from LHC monitoring, over about 1 year. For the top plot the humidity is shown, whereas for the bottom it is the dew point of the air. f.

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Figure 09a:
Left: a sketch of the magnet design. Right: the field lines in the magnet. f.

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Figure 09b:
Left: a sketch of the magnet design. Right: the field lines in the magnet. f.

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Figure 10a:
Left) The magnetic field (in mT) outside of the magnet estimated from the magnet design model 10 cm from the magnet end. Right) The vertical field along the center of the magnet and beyond; the red line indicates the end of the magnet. The closest scintillator PMT is located 35cm from center. f.

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Figure 10b:
Left) The magnetic field (in mT) outside of the magnet estimated from the magnet design model 10 cm from the magnet end. Right) The vertical field along the center of the magnet and beyond; the red line indicates the end of the magnet. The closest scintillator PMT is located 35cm from center. f.

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Figure 11:
Timeline for magnet construction for the FASER experiment. f.

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Figure 12:
Illustration of the ATLAS SCT barrel module to be used in FASER. f.

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Figure 13:
Chimaera digital board (right) with the Tengja card (left). f.

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Figure 14a:
Module QA setup at CERN. f.

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Figure 14b:
Module QA setup at CERN. f.

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Figure 15:
Left: A full FASER tracker plane, with two rows of four SCT modules. Right: To allow the edges to overlap, modules are staggered in and out of the plane by several millimeters. f.

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Figure 16:
SCT module with its cooling pipe (dark blue). f.

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Figure 17:
An SCT module in its holding frame and close-up of the hybrid part. f.

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Figure 18:
Left: Module frame with a tracker plane mounted inside. Center: Three module frames assembled into a tracking station. Right: The module frame itself (holes for alignment and attachment are not shown). f.

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Figure 19:
A tracking station with module frame spacers, showing cooling and electronic connectors. f.

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Figure 20:
A tracking station in its outer box between two magnet segments. Nearby scintillators are not shown. f.

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Figure 21:
The tracking station outer box showing the locations of the patch panel and aluminized mylar windows (to minimize material and multiple scattering). f.

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Figure 22:
Chiller data sheet. f.

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Figure 23:
HRS030 with cooling capacity and dimensions. f.

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Figure 24:
HRS030 Monitoring via PC. f.

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Figure 25:
Tracker readout hardware architecture. f.

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Figure 26:
Schedule of Tracker stations f.

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Figure 27a:
Design of the two types of scintillator layers. f.

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Figure 27b:
Design of the two types of scintillator layers. f.

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Figure 28:
Timeline for the construction of the scintillator system. f.

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Figure 29:
Design of the LHCb outer ECAL modules [29]. f.

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Figure 30:
Timeline for the preparation of the calorimeter system. f.

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Figure 31:
Detector support overview f.

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Figure 32:
Base plate with detector resting blocks. f.

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Figure 33:
Close up of magnet and Tracker station alignment. f.

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Figure 34:
Schedule for FASER Support structure. f.

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Figure 35:
Schematic diagram of the Trigger and DAQ system. f.

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Figure 36:
Architecture of the ``UniGe USB3 GPIO" board. f.

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Figure 37:
The ``UniGe USB3 GPIO" board. f.

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Figure 38:
DAQ framework for USB3 GPIO board. f.

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Figure 39:
UniGe VHDL library and application firmware overview. f.

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Figure 40:
Schematic diagram of the functionality implemented in the Trigger Logic Board f.

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Figure 41:
Schematic diagram of the functionality implemented in the Chimaera board for reading out four SCT modules. f.

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Figure 42:
Timeline for the Trigger and DAQ construction and commissioning. f.

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Figure 43:
Location plan showing the proposed situation of FASER in TI12 f.

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Figure 44:
As-built typical section of tunnel TI12 showing form of construction. f.

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Figure 45:
As-built plan view of tunnel showing arrangement of existing drainage infrastructure. f.

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Figure 46:
Section showing trench and experiment in relation to TI12 floor and LOS. f.

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Figure 47:
View showing extents of trench and proposed drainage in relation to tunnel TI12. f.

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Figure 48:
Plan view showing proposed arrangement. f.

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Figure 49:
Proposed sections showing depth of experiment along LOS in relation to the structure and drainage of tunnel TI12 (trench omitted). f.

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Figure 50a:
(left) Example of the SAS dust protection system as used in CE works at the AWAKE experimental area at CERN. (right) Example of the coring tool to be used for the CE works. f.

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Figure 50b:
(left) Example of the SAS dust protection system as used in CE works at the AWAKE experimental area at CERN. (right) Example of the coring tool to be used for the CE works. f.

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Figure 51:
Draft schedule for civil engineering work to be done in 2019. f.

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Figure 52a:
Pictures from the study of transporting the detector components of FASER to the detector location. Both pictures show the transport of the largest magnet. The top picture shows how this will be lifted over the LHC machine from one tractor to another. The bottom picture shows how this will be transported into position in the TI12 tunnel. f.

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Figure 52b:
Pictures from the study of transporting the detector components of FASER to the detector location. Both pictures show the transport of the largest magnet. The top picture shows how this will be lifted over the LHC machine from one tractor to another. The bottom picture shows how this will be transported into position in the TI12 tunnel. f.

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Figure 53:
A preliminary design of the protection to be installed over the QRL cryogenic line, and the LHC dipole magnets for safety during the transport of FASER components over the machine. f.

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Figure 54a:
Pictures from 3D model of integration of the experiment in the TI12 tunnel. The model includes: the detector, the mini-crate for the tracker readout electronics, a VME crate for the TDAQ and power supplies, and the chillers (one is the spare). The green space is 1.2 m reserved for access. f.

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Figure 54b:
Pictures from 3D model of integration of the experiment in the TI12 tunnel. The model includes: the detector, the mini-crate for the tracker readout electronics, a VME crate for the TDAQ and power supplies, and the chillers (one is the spare). The green space is 1.2 m reserved for access. f.

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Figure 55:
Draft schedule for the infrastructure work. The exact scheduling of the various preparatory work still has to be integrated in the LS2 schedule, but is expected to be able to take place in the indicated time intervals in 2019 while the services will be installed in the first half of 2020. f.

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Figure 56:
Schedule for FASER commissioning on surface and in TI12 as well as for installation in TI12. f.

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Figure 57a:
Two views of a simulated dark photon decay to e+ e- recorded in FASER. Above: Top view showing the two charged tracks separating in the magnetic field as they pass through the tracker and enter the calorimeter at top right. Below: Close-up showing the silicon strips fired in the first planes of the three tracking stations. f.

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Figure 57b:
Two views of a simulated dark photon decay to e+ e- recorded in FASER. Above: Top view showing the two charged tracks separating in the magnetic field as they pass through the tracker and enter the calorimeter at top right. Below: Close-up showing the silicon strips fired in the first planes of the three tracking stations. f.

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Figure 58:
Two-track separation efficiency based on isolated space-points in the first tracker plane for the indicated dark photon masses and momenta. Dark photon decays are uniformly distributed over the length of the 1.5 m decay volume. Because most of the separation comes from magnetic bending, rather than the transverse momenta of the decay products, the separation efficiency does not depend on the dark photon mass. Higher dark-photon energies, on the other hand, significantly degrade efficiency. f.

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Figure 59a:
Spatial resolution of reconstructed space-points in the magnetic bending direction (left) and along the strip direction (right), with respect to Monte Carlo truth, for the first detector plane. f.

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Figure 59b:
Spatial resolution of reconstructed space-points in the magnetic bending direction (left) and along the strip direction (right), with respect to Monte Carlo truth, for the first detector plane. f.

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Figure 60:
Fractional momentum resolution (σp/p) for reconstructed muon tracks as a function of momentum, compared to the predicted resolution from Karimaki [40]. f.

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Figure 61:
Overall schedule for FASER construction, installation and commissioning in TI12. f.

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Tables
Table 01:
The expected charge particle flux at the FASER location from FLUKA simulations for different energy thresholds, normalized to the expected Run 3 luminosity of 2 × 1034 cm-2 s-1. The rate is entirely from muons. The expected charge particle flux at the FASER location from FLUKA simulations for different energy thresholds, normalized to the expected Run 3 luminosity of 2 × 1034 cm-2 s-1. The rate is entirely from muons. f.

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Table 02:
Measured fluxes from emulsion detector data. The fluxes in the main peak (within 10 mrad) should be compared with the FLUKA simulation. f.

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Table 03:
Preliminary results from the TimePix detector installed in TI18, indicating that the main particle rate is proportional to luminosity in IP1. This also shows a small, but significant, increase in rate with non-colliding beam, compared to no beam in the machine. Beam (no collisions) corresponds to a full machine (2556 bunches) at the start of a physics fill, providing a total intensity of 2.7× 1014 protons per beam. f.

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Table 04:
Main magnet parameters for the FASER magnet design. Main magnet parameters for the FASER magnet design. f.

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Table 05:
Budget for magnet construction for the FASER experiment. f.

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Table 06:
Budget for tracker station mechanical assembly. f.

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Table 07:
Budget for other tracker-related hardware. Budget for other tracker-related hardware. f.

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Table 08:
Budget for scintillator system for the FASER experiment. f.

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Table 09:
Budget for the calorimeter system for the FASER experiment. f.

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Table 10:
Budget for Detector support for FASER experiment. f.

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Table 11:
Expected trigger rate per trigger source at a instantaneous luminosity of 2 × 1034 cm-2 s-1. Note that since the primary source of triggers is high-energy muons passing through the full detector, the rates are highly correlated. The random trigger rate is meant for pedestal calibration and noise monitoring. f.

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Table 12:
Average expected event sizes. The PMT size assumes a 1 μs readout window (500 samples of 2 ns).Average expected event sizes. The PMT size assumes a 1 μs readout window (500 samples of 2 ns). f.

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Table 13:
Comparison of Xilinx XC6 and Intel Cyclone V. The usage of Logic and RAM was estimated from ratio between XC6 and Intel Cyclone V. f.

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Table 14:
Budget for trigger/DAQ system for the FASER experiment. f.

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Table 15:
Expected power consumption of FASER experiment in TI12. f.

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Table 16:
Overall budget for FASER experiment hardware. The TDAQ system includes the readout for all detectors (including the Tracker).Overall budget for FASER experiment hardware. The TDAQ system includes the readout for all detectors (including the Tracker). f.

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Table 17:
Budget for infrastructure work and computing support whose cost is assumed to be borne by CERN. Items marked by a * are not full quotes but are rough cost estimates, whereas items marked with ** have parts that have been fully costed, but an additional part that is a more rough cost estimate. f.

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© 2018-2019 CERN for the benefit of the FASER Collaboration.
Reproduction of the article, figures and tables on this page is allowed as specified in the CC-BY-4.0 license.
Thank you to Zach Marshall for sharing the script for extracting figures and tables from ATLAS documents.