Search

FASER is a new experiment designed to search for new light weakly-interactinglong-lived particles (LLPs) and study high-energy neutrino interactions in thevery forward region of the LHC collisions at CERN. The experimental apparatusis situated 480 m downstream of the ATLAS interaction-point aligned with thebeam collision axis. The FASER detector includes four identical trackerstations constructed from silicon microstrip detectors. Three of the trackerstations form a tracking spectrometer, and enable FASER to detect the decayproducts of LLPs decaying inside the apparatus, whereas the fourth station isused for the neutrino analysis. The spectrometer has been installed in the LHCcomplex since March 2021, while the fourth station is not yet installed. FASERwill start physics data taking when the LHC resumes operation in early 2022.This paper describes the design, construction and testing of the trackingspectrometer, including the associated components such as the mechanics,readout electronics, power supplies and cooling system.

FASERν at the CERN Large Hadron Collider (LHC) is designed to directly detect collider neutrinos for the first time and study their cross sections at TeV energies, where no such measurements currently exist. In 2018, a pilot detector employing emulsion films was installed in the far-forward region of ATLAS, 480 m from the interaction point, and collected 12.2 fb-1 of proton-proton collision data at a center-of-mass energy of 13 TeV. We describe the analysis of this pilot run data and the observation of the first neutrino interaction candidates at the LHC. This milestone paves the way for high-energy neutrino measurements at current and future colliders.

The FASER experiment is a new small and inexpensive experiment that is placed480 meters downstream of the ATLAS experiment at the CERN LHC. FASER isdesigned to capture decays of new long-lived particles, produced outside of theATLAS detector acceptance. These rare particles can decay in the FASER detectortogether with about 500-1000 Hz of other particles originating from the ATLASinteraction point. A very high efficiency trigger and data acquisition systemis required to ensure that the physics events of interest will be recorded.This paper describes the trigger and data acquisition system of the FASERexperiment and presents performance results of the system acquired duringinitial commissioning.

FASER$\nu$ at the CERN Large Hadron Collider (LHC) is designed to directlydetect collider neutrinos for the first time and study their cross sections atTeV energies, where no such measurements currently exist. In 2018, a pilotdetector employing emulsion films was installed in the far-forward region ofATLAS, 480 m from the interaction point, and collected 12.2 fb$^{-1}$ ofproton-proton collision data at a center-of-mass energy of 13 TeV. We describethe analysis of this pilot run data and the observation of the first neutrinointeraction candidates at the LHC. This milestone paves the way for high-energyneutrino measurements at current and future colliders.

FASERnu is a proposed small and inexpensive emulsion detector designed todetect collider neutrinos for the first time and study their properties.FASERnu will be located directly in front of FASER, 480 m from the ATLASinteraction point along the beam collision axis in the unused service tunnelTI12. From 2021-23 during Run 3 of the 14 TeV LHC, roughly 1,300 electronneutrinos, 20,000 muon neutrinos, and 20 tau neutrinos will interact in FASERnuwith TeV-scale energies. With the ability to observe these interactions,reconstruct their energies, and distinguish flavors, FASERnu will probe theproduction, propagation, and interactions of neutrinos at the highesthuman-made energies ever recorded. The FASERnu detector will be composed of1000 emulsion layers interleaved with tungsten plates. The total volume of theemulsion and tungsten is 25cm x 25cm x 1.35m, and the tungsten target mass is1.2 tonnes. From 2021-23, 7 sets of emulsion layers will be installed, withreplacement roughly every 20-50 1/fb in planned Technical Stops. In thisdocument, we summarize FASERnu's physics goals and discuss the estimates ofneutrino flux and interaction rates. We then describe the FASERnu detector indetail, including plans for assembly, transport, installation, and emulsionreplacement, and procedures for emulsion readout and analyzing the data. Weclose with cost estimates for the detector components and infrastructure workand a timeline for the experiment.

Neutrinos are copiously produced at particle colliders, but no collider neutrino has ever been detected. Colliders produce both neutrinos and anti-neutrinos of all flavors at very high energies, and they are therefore highly complementary to those from other sources. FASER, the Forward Search Experiment at the LHC, is ideally located to provide the first detection and study of collider neutrinos. We investigate the prospects for neutrino studies with FASERν, a proposed component of FASER, consisting of emulsion films interleaved with tungsten plates with a total target mass of 1.2 t, to be placed on-axis at the front of FASER. We estimate the neutrino fluxes and interaction rates, describe the FASERν detector, and analyze the characteristics of the signals and primary backgrounds. For an integrated luminosity of 150fb-1 to be collected during Run 3 of the 14 TeV LHC in 2021–23, approximately 1300 electron neutrinos, 20,000 muon neutrinos, and 20 tau neutrinos will interact in FASERν, with mean energies of 600 GeV to 1 TeV. With such rates and energies, FASER will measure neutrino cross sections at energies where they are currently unconstrained, will bound models of forward particle production, and could open a new window on physics beyond the standard model.

Neutrinos are copiously produced at particle colliders, but no colliderneutrino has ever been detected. Colliders, and particularly hadron colliders,produce both neutrinos and anti-neutrinos of all flavors at very high energies,and they are therefore highly complementary to those from other sources. FASER,the recently approved Forward Search Experiment at the Large Hadron Collider,is ideally located to provide the first detection and study of colliderneutrinos. We investigate the prospects for neutrino studies of a proposedcomponent of FASER, FASER$\nu$, a 25cm x 25cm x 1.35m emulsion detector to beplaced directly in front of the FASER spectrometer in tunnel TI12. FASER$\nu$consists of 1000 layers of emulsion films interleaved with 1-mm-thick tungstenplates, with a total tungsten target mass of 1.2 tons. We estimate the neutrinofluxes and interaction rates at FASER$\nu$, describe the FASER$\nu$ detector,and analyze the characteristics of the signals and primary backgrounds. For anintegrated luminosity of 150 fb$^{-1}$ to be collected during Run 3 of the 14TeV Large Hadron Collider from 2021-23, and assuming standard model crosssections, approximately 1300 electron neutrinos, 20,000 muon neutrinos, and 20tau neutrinos will interact in FASER$\nu$, with mean energies of 600 GeV to 1TeV, depending on the flavor. With such rates and energies, FASER will measureneutrino cross sections at energies where they are currently unconstrained,will bound models of forward particle production, and could open a new windowon physics beyond the standard model.

The ForwArd Search ExpeRiment (FASER) is an approved 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 and 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 briefly describe the FASER detector layout and the status of potential backgrounds. We then present the sensitivity reach for FASER for a large number of long-lived particle models, updating previous results to a uniform set of detector assumptions, and analyzing new models. In particular, we consider all of the renormalizable portal interactions, leading to dark photons, dark Higgs bosons, and heavy neutral leptons; light B-L and Li-Lj gauge bosons; axionlike particles that are coupled dominantly to photons, fermions, and gluons through nonrenormalizable operators; and pseudoscalars with Yukawa-like couplings. We find that FASER and its follow-up, FASER 2, have a full physics program, with discovery sensitivity in all of these models and potentially far-reaching implications for particle physics and cosmology.

FASER, the ForwArd Search ExpeRiment, is a proposed experiment dedicated tosearching for light, extremely weakly-interacting particles at the LHC. Suchparticles may be produced in the LHC's high-energy collisions in large numbersin the far-forward region and then travel long distances through concrete androck 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 extremelycompact and inexpensive detector, sensitive to decays in a cylindrical regionof radius R = 10 cm and length L = 1.5 m. FASER is planned to be constructedand installed in Long Shutdown 2 and will collect data during Run 3 of the 14TeV LHC from 2021-23. If FASER is successful, FASER 2, a much larger successorwith roughly R ~ 1 m and L ~ 5 m, could be constructed in Long Shutdown 3 andcollect data during the HL-LHC era from 2026-35. FASER and FASER 2 have thepotential to discover dark photons, dark Higgs bosons, heavy neutral leptons,axion-like particles, and many other long-lived particles, as well as providenew information about neutrinos, with potentially far-ranging implications forparticle physics and cosmology. We describe the current status, anticipatedchallenges, and discovery prospects of the FASER program.

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

FASER,the ForwArd Search ExpeRiment,is a proposed experiment dedicated tosearching for light, extremely weakly-interacting particles at the LHC. Suchparticles may be produced in the LHC's high-energy collisions and travel longdistances through concrete and rock without interacting. They may then decay tovisible particles in FASER, which is placed 480 m downstream of the ATLASinteraction point. In this work we briefly describe the FASER detector layoutand the status of potential backgrounds. We then present the sensitivity reachfor FASER for a large number of long-lived particle models, updating previousresults to a uniform set of detector assumptions, and analyzing new models. Inparticular, we consider all of the renormalizable portal interactions, leadingto dark photons, dark Higgs bosons, and heavy neutral leptons (HNLs); light B-Land $L_i - L_j$ gauge bosons; axion-like particles (ALPs) that are coupleddominantly to photons, fermions, and gluons through non-renormalizableoperators; and pseudoscalars with Yukawa-like couplings. We find that FASER andits follow-up, FASER 2, have a full physics program, with discovery sensitivityin all of these models and potentially far-reaching implications for particlephysics and cosmology.

FASER is a proposed small and inexpensive experiment designed to search forlight, weakly-interacting particles at the LHC. Such particles are dominantlyproduced along the beam collision axis and may be long-lived, travelinghundreds of meters before decaying. To exploit both of these properties, FASERis to be located along the beam collision axis, 480 m downstream from the ATLASinteraction point, in the unused service tunnel TI18. We propose that FASER beinstalled in TI18 in Long Shutdown 2 in time to collect data from 2021-23during Run 3 of the 14 TeV LHC. FASER will detect new particles that decaywithin a cylindrical volume with radius R= 10 cm and length L = 1.5 m. Withthese small dimensions, FASER will complement the LHC's existing physicsprogram, extending its discovery potential to a host of new particles,including dark photons, axion-like particles, and other CP-odd scalars. A FLUKAsimulation and analytical estimates have confirmed that numerous potentialbackgrounds are highly suppressed at the FASER location, and the first in situmeasurements are currently underway. We describe FASER's location and discoverypotential, its target signals and backgrounds, the detector's layout andcomponents, and the experiment's preliminary cost estimate, funding, andtimeline.

In this report, we compile empirical evidence regarding federal and state trends in the use of Supplemental Environmental Projects (SEPs). Our primary interest is in SEPs associated with enforcement of the federal Clean Water Act (CWA). We move from briefly examining the broadest trends—federal and state use of SEPs—to more particular emphasis on the experience of California’s State Water Resources Control Board (SWRCB) and Regional Water Quality Control Boards (RWQCB) with SEPs. Drawing on state and regional enforcement databases as well as extensive interviews with agency enforcement personnel, we evaluate the use of SEPs by the regional boards in California and offer recommendations for improving the use of this important policy tool.

Public lands and waters in the United States traditionally have been managed using frameworks and objectives that were established under an implicit assumption of stable climatic conditions. However, projected climatic changes render this assumption invalid. Here, we summarize general principles for management adaptations that have emerged from a major literature review. These general principles cover many topics including: (1) how to assess climate impacts to ecosystem processes that are key to management goals; (2) using management practices to support ecosystem resilience; (3) converting barriers that may inhibit management responses into opportunities for successful implementation; and (4) promoting flexible decision making that takes into account challenges of scale and thresholds. To date, the literature on management adaptations to climate change has mostly focused on strategies for bolstering the resilience of ecosystems to persist in their current states. Yet in the longer term, it is anticipated that climate change will push certain ecosystems and species beyond their capacity to recover. When managing to support resilience becomes infeasible, adaptation may require more than simply changing management practices—it may require changing management goals and managing transitions to new ecosystem states. After transitions have occurred, management will again support resilience—this time for a new ecosystem state. Thus, successful management of natural resources in the context of climate change will require recognition on the part of managers and decisions makers of the need to cycle between “managing for resilience” and “managing for change.”