The detection of TeV neutrinos from the LHC by the far-forward detectors FASER and SND@LHC enables a plethora of novel physics opportunities. Among these, the measurement of the flavour, energy, and rapidity dependence of the LHC forward neutrino fluxes provides unique constraints on theoretical predictions of forward particle production in hadronic collisions. We demonstrate that neutrino event yield measurements at FASER from Run 3 and at its HL-LHC upgrades enable a theory-agnostic extraction of the LHC forward neutrino fluxes. We exploit the equivalence of the problem with the determination of parton distributions from deep-inelastic structure functions to apply the NNPDF approach, based on machine learning regression and the Monte Carlo replica method, to LHC neutrino fluxes. The resulting NN$\textit{ν}$flux methodology is validated through closure tests and applied to a first extraction of the LHC muon neutrino flux from the FASER 2024 data. We show how NN$\textit{ν}$flux can discriminate between event generators of forward hadron production; scrutinize a possible intrinsic charm component in the proton; and constrain BSM scenarios with enhanced decays of neutral hadrons into neutrinos.

Netherlands

Jukka John

United States

Germany

Felix Kling

Jelle Koorn

Peter Krack

Juan Rojo

A first determination of the LHC neutrino fluxes from FASER data

The LHC far-forward experiments FASER and SND@LHC have pioneered the detection of TeV-energy neutrinos produced in hard-scattering proton-proton collisions at the LHC. In addition to neutrinos, an intense flux of TeV-energy muons reaches these detectors, representing a dominant background for both neutrino studies and beyond the Standard Model searches. Here we demonstrate that this forward muon flux enables a comprehensive neutral-current deep-inelastic scattering (DIS) program at FASER with a strong kinematical overlap with the Electron Ion Collider. For the Run 3 luminosity of $${\mathcal {L}}_{{\textrm{pp}}}=250$$ fb $$^{-1},$$ more than $$10^5$$ inclusive muon DIS events, of which up to $$10^4$$ from charm production, are expected at FASER $$\nu .$$ As a representative application, we demonstrate the sensitivity of muon DIS at FASER $$\nu $$ to probe the (intrinsic) charm content of the proton at large-$\textit{x}$. We also provide predictions for event yields of muon DIS for future FASER runs and for the proposed Forward Physics Facility.

Brazil

Reinaldo Francener

Victor Gonçalves

Deep-inelastic scattering at TeV energies with LHC muons

We present a determination of the strong coupling $$\alpha _s(m_Z)$$ from a global dataset including both fixed-target and collider data from deep-inelastic scattering and a variety of hadronic processes, with a simultaneous determination of parton distribution functions (PDFs) based on the NNPDF4.0 methodology. This determination is performed at NNLO and approximate $${\textrm{N}}^3$$ LO ( $${\textrm{aN}}^3$$ LO) perturbative QCD accuracy, including QED corrections and a photon PDF up to NLO accuracy. We extract $$\alpha _s$$ using two independent methodologies, both of which take into account the cross-correlation between $$\alpha _s$$ and the PDFs. The two methodologies are validated by closure tests that allow us to detect and remove or correct for several sources of bias, and lead to mutually consistent results. We account for all correlated experimental uncertainties, as well as correlated theoretical uncertainties related to missing higher order perturbative corrections (MHOUs). We study the perturbative convergence of our results and the impact of QED corrections. We assess individual sources of uncertainty, specifically MHOUs and the value of the top quark mass. We provide a detailed appraisal of methodological choices, including the choice of input dataset, the form of solution of evolution equation, the treatment of the experimental covariance matrix, and the details of Monte Carlo data generation. We find $$\alpha _s(m_Z)=0.1194^{+0.0007}_{-0.0014}$$ at $${\textrm{aN}}^3$$ $${\textrm{LO}}_{\textrm{QCD}}\otimes {\textrm{NLO}}_{\textrm{QED}}$$ accuracy, consistent with the latest PDG average and with recent lattice results.

United Kingdom

Richard Ball

Italy

Andrea Barontini

Switzerland

Juan Cruz-Martinez

Stefano Forte

Finland

Felix Hekhorn

Emanuele Nocera

Roy Stegeman

A determination of $$\alpha _s(m_Z)$$ at $${{\textrm{aN}}}^3{{\textrm{LO}}}_{{\textrm{QCD}}}\otimes {{\textrm{NLO}}}_{{\textrm{QED}}}$$ accuracy from a global PDF analysis

We present NNPDF 2.0, a new set of collinear helicity parton distribution functions (PDFs) of the proton based on legacy measurements of structure functions in inclusive neutral-current longitudinally polarised deep-inelastic scattering (DIS), and of $\textit{W}$ -boson, single-inclusive, and di-jet production asymmetries in longitudinally polarised proton-proton collisions. The determination is accurate to next-to-next-to-leading order in the strong coupling, and includes heavy quark mass corrections in the analysis of DIS data. Uncertainties due to missing higher-order corrections are systematically incorporated by means of a covariance matrix determined by scale variations. NNPDF 2.0 is based on a machine learning methodology, that makes use of Monte Carlo sampling for the representation of uncertainties into PDFs, of a neural network for the parametrisation of PDFs, of stochastic gradient descent for the optimisation of PDF parameters, and of hyperoptimisation for the selection of the best fitting model. We study the impact on PDFs of higher-order corrections, of the positivity constraint, and of the data. We demonstrate two phenomenological applications of NNPDF 2.0, specifically the determination of the proton spin fraction carried by gluons and quarks, and of theoretical predictions for single-hadron production in longitudinally polarised DIS and proton-proton collisions.

Toon Hasenack

Giacomo Magni

Tanjona Rabemananjara

Tanishq Sharma

Gijs Seeventer

NNPDF

<p>Motivated by the updated high luminosity (HL)-LHC projections for Higgs pair production from ATLAS and CMS and by the release of the FCC-ee feasibility study, we critically revisit the sensitivity of the global standard model effective field theory (SMEFT) analysis to deformations of the Higgs self-coupling modifier <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>κ</mi><mn>3</mn></msub></math>. To this end, we quantify the impact of SMEFT operators modifying double Higgs production at the LHC and single Higgs production, including loop corrections, at the FCC-ee, and include renormalization group evolution throughout. We demonstrate that significantly improving on the legacy HL-LHC constraints on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>κ</mi><mn>3</mn></msub></math> at the FCC-ee is not possible without the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>365</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> run; that individual and marginalized determinations are similar at the HL-LHC while differing by up to a factor 3 at the FCC-ee; and that quadratic EFT corrections cannot be neglected, especially at the (HL-)LHC. This finding fundamentally alters the picture compared to strategic planning often based on one-parameter projections. Overall, the combination of HL-LHC and FCC-ee data offers unique potential to pin down the Higgs self-coupling with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><mn>15</mn><mo>%</mo></math> precision.</p>

Jaco ter Hoeve

Spain

Luca Mantani

Alejo N. Rossia

Eleni Vryonidou

Higgs trilinear coupling in the standard model effective field theory at the high luminosity LHC and the FCC-ee

We present a systematic comparison of theoretical predictions and various high-precision experimental measurements, specifically of differential cross sections performed by the LHC run II for Drell-Yan gauge boson, top-quark pair, single-inclusive jet and di-jet production, and by HERA for single-inclusive jet and di-jet production. Theoretical predictions are computed at next-to-next-to-leading order (NNLO) accuracy in perturbative Quantum Chromodynamics. The most widely employed sets of Parton Distribution Functions (PDFs) are used, and PDF, strong coupling, and missing higher order uncertainties are taken into account. We quantitatively assess the predictive power of each PDF set and the contribution of the different sources of experimental and theoretical uncertainty to the agreement between data and predictions. We show that control over all of these aspects is crucial to precision physics studies, such as the determination of Standard Model parameters at the LHC.

Amedeo Chiefa

Mark Costantini

Maria Ubiali

Parton distributions confront LHC Run II data: a quantitative appraisal

Global interpretations of particle physics data within the framework of the Standard Model Effective Field Theory (SMEFT), including their matching to UV-complete models, involve energy scales potentially spanning several orders of magnitude. Relating these measurements among them in terms of a common energy scale is enabled by the Renormalisation Group Equations (RGEs). Here we present a systematic assessment of the impact of RGEs, accounting for QCD, electroweak, and Yukawa corrections, in a global SMEFT fit of LEP and LHC data where individual cross-sections are assigned a characteristic energy scale. We also quantify the impact of the RGE effects in projected global fits at the HL-LHC and the FCC-ee. Finally, we assess the role that RGEs play on the sensitivity at HL-LHC and FCC-ee to representative one-particle UV models matched onto SMEFT either at tree and one-loop level. Our study emphasizes the importance of a consistent treatment of energy scales to achieve the best precision and accuracy in indirect searches for heavy new physics through precision measurements.

Jaco Hoeve

Alejo Rossia

Connecting scales: RGE effects in the SMEFT at the LHC and future colliders

The recent direct detection of neutrinos at the LHC has opened a new window on high-energy particle physics and highlighted the potential of forward physics for groundbreaking discoveries. In the last year, the physics case for forward physics has continued to grow, and there has been extensive work on defining the Forward Physics Facility and its experiments to realize this physics potential in a timely and cost-effective manner. Following a 2-page Executive Summary, we first present the status of the FPF, beginning with the FPF’s unique potential to shed light on dark matter, new particles, neutrino physics, QCD, and astroparticle physics. We then summarize the current designs for the Facility and its experiments, FASER2, FASER $$\nu $$ 2, FORMOSA, and FLArE.

Poland

Jyotismita Adhikary

Luis Anchordoqui

Japan

Akitaka Ariga

Tomoko Ariga

Alan Barr

Brian Batell

Jianming Bian

Jamie Boyd

Matthew Citron

Albert Roeck

Milind Diwan

Jonathan Feng

Christopher Hill

Yu Jeong

Steven Linden

Toni Mäkelä

Kostas Mavrokoridis

Josh McFayden

Hidetoshi Otono

Dennis Soldin

Anna Stasto

Sebastian Trojanowski

Matteo Vicenzi

Wenjie Wu

Scientific program for the Forward Physics Facility

Proton-proton collisions at energy-frontier facilities produce an intense flux of high-energy light particles, including neutrinos, in the forward direction. At the LHC, these particles are currently being studied with the far-forward experiments FASER/FASER and SND@LHC, while new dedicated experiments have been proposed in the context of a Forward Physics Facility (FPF) operating at the HL-LHC. Here we present a first quantitative exploration of the reach for neutrino, QCD, and BSM physics of far-forward experiments integrated within the proposed Future Circular Collider (FCC) project as part of its proton-proton collision program (FCC-hh) at $$ \sqrt{s} $$ ≃ 100 TeV. We find that 10 electron/muon neutrinos and 10 tau neutrinos could be detected, an increase of several orders of magnitude compared to (HL-)LHC yields. We study the impact of neutrino DIS measurements at the FPF@FCC to constrain the unpolarised and spin partonic structure of the nucleon and assess their sensitivity to nuclear dynamics down to ∼ 10 with neutrinos produced in proton-lead collisions. We demonstrate that the FPF@FCC could measure the neutrino charge radius for and and reach down to five times the SM value for . We fingerprint the BSM sensitivity of the FPF@FCC for a variety of models, including dark Higgs bosons, relaxion-type scenarios, quirks, and millicharged particles, finding that these experiments would be able to discover LLPs with masses as large as 50 GeV and couplings as small as 10 8 , and quirks with masses up to 10 TeV. Our study highlights the remarkable opportunities made possible by integrating far-forward experiments into the FCC project, and it provides new motivation for the FPF at the HL-LHC as an essential precedent to optimize the forward physics experiments that will enable the FCC to achieve its full physics potential.

Roshan Mammen Abraham

Max Fieg

China

Jinmian Li

Junle Pei

FPF@FCC: neutrino, QCD, and BSM physics opportunities with far-forward experiments at a 100 TeV Proton Collider

We perform a detailed phenomenological study of high-energy neutrino deep inelastic scattering (DIS) focused on LHC far-forward experiments such as FASER $$\nu $$  <math> <mi>ν</mi> </math>   and SND@LHC. To this aim, we parametrise the neutrino fluxes reaching these LHC far-forward experiments in terms of ‘neutrino PDFs’ encoding their energy and rapidity dependence by means of the LHAPDF framework. We integrate these neutrino PDFs in the recently developed POWHEG-BOX-RES implementation of neutrino-induced DIS to produce predictions accurate at next-to-leading order (NLO) in the QCD coupling matched to parton showers (PS) with Pythia8. We present NLO+PS predictions for final-state distributions within the acceptance for FASER $$\nu $$  <math> <mi>ν</mi> </math>   and SND@LHC as well as for two experiments of the proposed Forward Physics Facility (FPF), FASER $$\nu $$  <math> <mi>ν</mi> </math>  2 and FLArE. We quantify the impact of NLO QCD corrections, of the parton showering and hadronisation settings in Pythia8, of the QED shower, and of the incoming neutrino flavour for the description of these observables, and compare our predictions with the GENIE neutrino event generator. Our work demonstrates the relevance of modern higher-order event generators to achieve the key scientific targets of the LHC neutrino experiments.

Melissa Beekveld

CERN

Silvia Ferrario Ravasio

Eva Groenendijk

Valentina Schütze Sánchez

A phenomenological analysis of LHC neutrino scattering at NLO accuracy matched to parton showers