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This Letter presents the measurement of the energy-dependent neutrino-nucleon cross section in tungsten and the differential flux of muon neutrinos and antineutrinos. The analysis is performed using proton-proton collision data at a center-of-mass energy of 13.6 TeV and corresponding to an integrated luminosity of $(65.6\pm 1.4){\mathrm{fb}}^{-1}$. Using the active electronic components of the FASER detector, $338.1\pm 21.0$charged current muon neutrino interaction events are identified, with backgrounds from other processes subtracted. We unfold the neutrino events into a fiducial volume corresponding to the sensitive regions of the FASER detector and interpret the results in two ways: (i) we use the expected neutrino flux to measure the cross section, and (ii) we use the predicted cross section to measure the neutrino flux. Both results are presented in six bins of neutrino energy, achieving the first differential measurement in the TeV range. The observed distributions align with standard model predictions. Using this differential data, we extract the contributions of neutrinos from pion and kaon decays. Published by the American Physical Society2025 

A<sc>bstract</sc> The first FASER search for a light, long-lived particle decaying into a pair of photons is reported. The search uses LHC proton-proton collision data at$$ \sqrt{s} $$ $\sqrt{s}$= 13.6 TeV collected in 2022 and 2023, corresponding to an integrated luminosity of 57.7 fb⁻¹. A model with axion-like particles (ALPs) dominantly coupled to weak gauge bosons is the primary target. Signal events are characterised by high-energy deposits in the electromagnetic calorimeter and no signal in the veto scintillators. One event is observed, compared to a background expectation of 0.44 ± 0.39 events, which is entirely dominated by neutrino interactions. World-leading constraints on ALPs are obtained for masses up to 300 MeV and couplings to the Standard Model W gauge boson,g_aWW, around 10⁻⁴GeV⁻¹, testing a previously unexplored region of parameter space. Other new particle models that lead to the same experimental signature, including ALPs coupled to gluons or photons, U(1)_Bgauge bosons, up-philic scalars, and a Type-I two-Higgs doublet model, are also considered for interpretation, and new constraints on previously viable parameter space are presented in this paper. 

The Forward Search Experiment (FASER) at CERN’s Large Hadron Collider (LHC) has recently directly detected the first collider neutrinos. Neutrinos play an important role in all FASER analyses, either as signal or background, and it is therefore essential to understand the neutrino event rates. In this study, we update previous simulations and present prescriptions for theoretical predictions of neutrino fluxes and cross sections, together with their associated uncertainties. With these results, we discuss the potential for possible measurements that could be carried out in the coming years with the FASER neutrino data to be collected in LHC Run 3 and Run 4. 

The Forward Search Experiment (FASER) at CERN’s Large Hadron Collider (LHC) has recently directly detected the first collider neutrinos. Neutrinos play an important role in all FASER analyses, either as signal or background, and it is therefore essential to understand the neutrino event rates. In this study, we update previous simulations and present prescriptions for theoretical predictions of neutrino fluxes and cross sections, together with their associated uncertainties. With these results, we discuss the potential for possible measurements that could be carried out in the coming years with the FASER neutrino data to be collected in LHC Run 3 and Run 4. Published by the American Physical Society2024 

The first results of the study of high-energy electron neutrino (𝜈𝑒) and muon neutrino (𝜈𝜇) charged-current interactions in the FASER⁢𝜈 emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the FASER⁢𝜈 volume was analyzed after exposure to 9.5  fb−1 of √𝑠=13.6  TeV 𝑝⁢𝑝 data. Four (eight) 𝜈𝑒 (𝜈𝜇) interaction candidate events are observed with a statistical significance of 5.2⁢𝜎 (5.7⁢𝜎). This is the first direct observation of 𝜈𝑒 interactions at a particle collider and includes the highest-energy 𝜈𝑒 and 𝜈𝜇 ever detected from an artificial source. The interaction cross section per nucleon 𝜎/𝐸𝜈 is measured over an energy range of 560–1740 GeV (520–1760 GeV) for 𝜈𝑒 (𝜈𝜇) to be (1.2+0.8 −0.7)×10−38  cm2 GeV−1 [(0.5±0.2)×10−38  cm2 GeV−1], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges. 

The first results of the study of high-energy electron neutrino ( ${\nu }_e$) and muon neutrino ( ${\nu }_{\mu }$) charged-current interactions in the $\mathrm{FASER}\nu$emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the $\mathrm{FASER}\nu$volume was analyzed after exposure to $9.5{\mathrm{fb}}^{-1}$of $\sqrt{s}=13.6\mathrm{TeV}$ $pp$data. Four (eight) ${\nu }_e$( ${\nu }_{\mu }$) interaction candidate events are observed with a statistical significance of $5.2\sigma$( $5.7\sigma$). This is the first direct observation of ${\nu }_e$interactions at a particle collider and includes the highest-energy ${\nu }_e$and ${\nu }_{\mu }$ever detected from an artificial source. The interaction cross section per nucleon $\sigma /E_{\nu }$is measured over an energy range of 560–1740 GeV (520–1760 GeV) for ${\nu }_e$( ${\nu }_{\mu }$) to be $\left({1.2}_{-0.7}^{+0.8}\right)\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$[ $(0.5\pm 0.2)\times {10}^{-38}{\mathrm{cm}}^2{\mathrm{GeV}}^{-1}$], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges. Published by the American Physical Society2024 

Abstract FASER, the ForwArd Search ExpeRiment, is an experiment dedicated to searching for light, extremely weakly-interacting particles at CERN's Large Hadron Collider (LHC). Such particles may be produced in the very forward direction of the LHC's high-energy collisions and then decay to visible particles inside the FASER detector, which is placed 480 m downstream of the ATLAS interaction point, aligned with the beam collisions axis. FASER also includes a sub-detector, FASERν, designed to detect neutrinos produced in the LHC collisions and to study their properties. In this paper, each component of the FASER detector is described in detail, as well as the installation of the experiment system and its commissioning using cosmic-rays collected in September 2021 and during the LHC pilot beam test carried out in October 2021. FASER has successfully started taking LHC collision data in 2022, and will run throughout LHC Run 3. 

The statistical models used to derive the results of experimental analyses are of incredible scientific value andare essential information for analysis preservation and reuse. In this paper, we make the scientific case for systematically publishing the full statistical models and discuss the technical developments that make this practical. By means of a variety of physics cases -including parton distribution functions, Higgs boson measurements, effective field theory interpretations, direct searches for new physics, heavy flavor physics, direct dark matter detection, world averages, and beyond the Standard Model global fits -we illustrate how detailed information on the statistical modelling can enhance the short- and long-term impact of experimental results.