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9th Forward Physics Facility Meeting

→ Europe/Zurich
6/R-012 - conference room (CERN)

6/R-012 - conference room

CERN

40
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Description

Luis Anchordoqui, Jamie Boyd, Albert De Roeck, Jonathan Feng, Felix Kling, Juan Rojo
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  • Thursday 5 March
    • 09:00 → 11:10
      Welcome and Physics Overview 6/R-012 - conference room

      6/R-012 - conference room

      CERN

      40
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      • 09:00
        Opening Remarks by Organizers 10m
        Speakers: Alan Barr (University of Oxford (GB)), Brian Thomas Batell, Felix Kling (DESY), Juan Salvador Tafoya Vargas (University of California Davis (US))
        Intro.pdf
      • 09:15
        Opening Remarks 10m
        Speaker: Urs Wiedemann (CERN)
      • 09:30
        European Strategy Update 10m
        Speaker: Matthew Philip Mccullough (CERN)
        EuropeanStrategyUpdate.pdf
      • 09:45
        New Results from FASER/SND 20m
        Speaker: Dr Umut Kose (ETH-Zurich)
        FPF09_March2026_UKose.pdf
      • 10:10
        FPF Implications and Opportunities for BSM and Neutrino Physics 20m
        Speaker: Ryan Plestid (CERN)
        FPF-Talk-Plestid.pdf
      • 10:35
        FPF Implications and Opportunities for QCD and Astroparticle 20m
        Speaker: Dr Tanguy Pierog
        Pierog_FPF_QCD.pdf
    • 11:30 → 12:30
      Facility 6/R-012 - conference room

      6/R-012 - conference room

      CERN

      40
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    • 14:30 → 18:00
      Parallel Session: Dark Sectors 6/2-004

      6/2-004

      CERN

      Room 6/2-004
      40
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      • 14:30
        Right handed neutrino production from $Z^\prime$ interactions in forward search experiments 15m

        We study two general $U(1)$ extensions of the Standard Model (SM) those generate tiny neutrino masses via the seesaw mechanism after general $U(1)$ breaking. These models predict a new neutral gauge boson ($Z'$) and right-handed neutrinos (RHNs), the latter introduced for anomaly cancellation and neutrino mass generation. In both scenarios, left- and right-handed fermions couple differently to the $Z'$, and RHNs mix with light neutrinos, enabling variety of decay modes. Focusing on the high-luminosity LHC (HL-LHC) and the future FASER2 experiment, we explore RHN pair production from $Z'$ decays in two cases: (i) long-lived $Z'$ decays to visible modes and long-lived RHNs, and (ii) short-lived $Z'$ decays to long-lived RHNs, which further decay visibly inside FASER2. We estimate projected limits on the general $U(1)$ gauge coupling, $Z'$ mass, RHN mass, and light--heavy neutrino mixing for various $U(1)$ charge assignments, and compare them with current experimental bounds.

        Speaker: Arindam Das (Hokkaido University)
        ADas_Forward_Physics_meeting.pdf
      • 14:50
        Long-lived particle searches Beyond B meson 15m

        In this talk I will show our recent study about the LLP searches af FASER. There are two kinds of modes, with the production from the usual mesons, and from the PP collision directly.

        For the meson production mode, we study the prospect of detecting light CP-even and CP-odd scalars. We develop the general formalism for the scalar production and decay from mesons at LHC, given modified couplings of the scalars to the SM particles. We then analyze the complete long-lived particle of 2HDM at FASER.

        For the PP collision, we take the compressed neutral Higgsino as examples. The results show the NLSP, as the LLP, can be probed up to 100 GeV scale.

        Speaker: Wei Su (Sun Yat-sen University)
        FPF2026-weisu-20260305.pdf
      • 15:10
        Single Photon Signature of Light Long-Lived Particles 15m

        We have investigated single photon signatures of a light long-lived neutralino in supersymmetric models with broken R-parity. We consider the sensitivities at the detectors: ANUBIS, CODEXb, FACET, FASER, MAPP, MATHUSLA.

        Speaker: Herbi Dreiner
      • 15:30
        Exploring Neutrino Compositeness: Emerging and Invisible Jets at Neutrino and Charged Lepton Beams 15m

        The origin of neutrino masses suggests the existence of a sterile neutrino sector, which may be either too heavy or too weakly coupled to the Standard Model (SM) to be detected in the near future. The inverse seesaw mechanism provides a testable framework where the coupling between the sterile sector and the SM is large enough to allow direct experimental probes. In this context, it is crucial to explore whether the sterile sector is a weakly or strongly coupled theory and to identify methods to distinguish between these possibilities.
        We propose a novel experimental probe for neutrino coupling with a strongly coupled sterile sector, based on the distinctive signature of neutrino disintegration into ``dark jets'' in high-energy neutrino scattering with electrons and nucleons. If the confinement scale of the sterile sector is below the center of mass energy of the collisions the neutrinos disintegrate into dark-sector jets. As the dark shower evolves, dark bound states form and eventually decay into Standard Model particles with finite lifetimes. If these decays occur outside the detector, the resulting invisible jet manifests as missing energy. Alternatively, if decays happen at macroscopic distances from the interaction point, they generate a distinctive signature known as an emerging jet. These jets are semi-visible, containing missing energy from Standard Model neutrinos, and their detailed structure is determined by the nature of the portal connecting the visible and dark sectors. We compute the expected signal rates for such events at various upcoming neutrino beamline experiments, as well as at charged lepton beams highlighting their sensitivity to the compositeness of the neutrino sector.
        The unique signals discussed here offer a new experimental signature for future neutrino experiments, presenting both challenges in optimizing signal-to-background discrimination and a promising avenue for identifying composite neutrino interactions.

        Speaker: Matteo Borrello (University of Florence, INFN of Florence)
        fpfmeeting_borrello.pdf
      • 16:00
        Characterizing Heavy Neutral Leptons: Measuring Parameters, Discriminating Majorana versus Dirac, and Using FASER2 as a Trigger for ATLAS 15m

        Heavy Neutral Leptons (HNLs) are a well-motivated extension of the Standard Model which may provide explanations for observed neutrino masses, dark matter, and baryogengesis via leptogenesis. In the event that a HNL signal is actually detected, much work will be dedicated to identifying the underlying nature of the observed signal excess. In this talk, we will use Monte-Carlo simulations of HNLs generated in FORESEE to explore the potential of the proposed FASER2 experiment at the LHC to determine the properties of a discovered HNL, including its mass, couplings, and whether it is a Majorana or Dirac fermion. We consider the ability of FASER2 to make these measurements from kinematics alone and additionally explore the possibility of using FASER2 as a trigger for ATLAS and measuring the charge of muons produced in association with the HNL at ATLAS to search for lepton number violation. These results show that FASER2, sometimes in coordination with ATLAS, can precisely determine the HNL properties and showcases that main LHC detectors and proposed auxiliary detectors can have a synergistic relationship on an event-by-event basis.

        Speaker: Daniel La Rocco
        FPF9.pdf
      • 16:20
        Spin Correlations in Dark Photon Searches 15m

        We investigate the spin correlations between production and decay in the process where dark photons $A'$ are produced in pseudoscalar meson decays, for example, $\pi^0, \eta \to \gamma A'$, and then decay to fermion pairs, $A' \to f \bar{f}$. This process is the focus of many experimental searches, but spin correlations are typically ignored. We derive analytic results that allow us to quickly scan parameter space and quantify the error made in neglecting spin correlations. In particular, we define a discrepancy parameter and find that this parameter is always less than $\frac{1}{6\sqrt{3}} \approx 9.6\%$, which provides a rough measure of the size of spin correlation effects. However, these effects may be enhanced or suppressed by cuts in realistic experimental analyses, and so we also consider two representative examples, including current FASER analyses and possible future searches at SHiP. We find that the effects of spin correlations are negligible for existing FASER analyses, but can significantly reduce event rates at upcoming SHiP searches.

        Speaker: Misa Toman
        FPF9 meeting - Misa Toman.ppsx
      • 16:40
        Millicharged Particles with FORMOSA via Forward Neutron-Induced Showers at the LHC 15m

        We study the sensitivity of the FORMOSA experiment at the LHC Forward Physics Facility to millicharged particles (mCPs), focusing on a previously unexplored production mechanism associated with the forward neutron flux. Existing studies mainly consider mCP production from forward mesons directly produced in pp collisions.
        We point out that pp collisions also generate an intense flux of highly forward, TeV-scale neutrons, which are absorbed by materials located hundreds of meters downstream of the interaction point. These neutron-induced beam-dump interactions initiate hadronic showers, producing secondary mesons such as neutral pions that can subsequently decay into mCPs.
        We model this neutron-induced meson shower and evaluate its contribution to the mCP flux reaching FORMOSA. We find that this secondary production channel enhances the total mCP flux by up to about 60%, significantly improving FORMOSA’s sensitivity. Our results highlight the importance of beam-dump–like effects from forward neutral hadrons in assessing the discovery potential of forward experiments at the LHC.

        Speaker: Peiran Li (University of Minnesota)
        mCP_LHC_FPF.pdf
      • 17:00
        Cosmic Millicharged Background, Reheating, and Arithmetica Electrōrum 15m

        We demonstrate that the searches for dark sector particles can provide probes of reheating scenarios, focusing on the cosmic millicharge background produced in the early universe. We discuss two types of millicharge particles (mCPs): either with, or without, an accompanying dark photon. These two types of mCPs have distinct theoretical motivations and cosmological signatures. We discuss constraints from the overproduction and mCP-baryon interactions of the mCP without an accompanying dark photon, with different reheating temperatures. We also consider the ΔNeff constraints on the mCPs from kinetic mixing, varying the reheating temperature. The regions of interest in which the accelerator and other experiments can probe the reheating scenarios are identified in this paper for both scenarios. These probes can potentially allow us to set an upper bound on the reheating temperature down to ∼10 MeV, much lower than the previously considered upper bound from inflationary cosmology at around ∼10^16 GeV. In addition, we find parameter regions in which the two mCP scenarios may be differentiated by cosmological considerations. Finally, we discuss the implications of dedicated mCP searches and future CMB-S4 observations.

        Speaker: Yu-Dai Tsai (University of California, Irvine)
    • 14:30 → 18:00
      Parallel Session: Neutrinos 6/R-012 - conference room

      6/R-012 - conference room

      CERN

      40
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      • 14:30
        Transverse-momentum distributions in neutrino-nucleon scattering 15m

        One of the main goals of physics is to understand the inner structure of matter. To achieve this result, studying the composition of protons and neutrons (nucleons) is essential. In nonperturbative QCD the internal structure of nucleons can be described in terms of parton distribution functions (PDF). PDFs can in turn be investigated using deep-inelastic-scattering processes (DIS).

        Experimental data from neutrino-nucleon DIS are normally used in order to reduce the uncertainties in the determination of collinear PDFs. It is therefore natural to ask ourselves if the same still holds true for transverse-momentum-dependent PDFs (TMDs) in the Semi-Inclusive DIS (SIDIS). To address this question we first need to define neutrino-proton SIDIS structure functions, then we have to compute their expressions in terms of TMDs. Finally, we can produce estimates for these functions based on existing extractions of TMDs.
        These steps are essential for an assessment of the impact that future experiments (such as the FASER$\nu$2 at the LHC) would have on the determination of TMDs.

        Speaker: Mattia Bellotti (Università di Cagliari)
        SIDIS_FPF9.pptx
      • 14:50
        The First Determination of the LHC Neutrino Fluxes from FASER Data 15m

        The recent detection of TeV neutrinos at FASER has launched a new era of collider physics. Measuring the flavor, energy and rapidity of these neutrinos allows for an unprecedented extraction of the full energy-dependence of far-forward neutrino production in p-p collisions. Analogous to PDF extractions from collider data, we determine the energy distribution of the (anti) muon neutrino flux at FASER using the Monte Carlo (MC) replica method, in conjunction with machine learning tools. We validate our methodology using closure tests, provide projections for future FASER(v,v2) data and show how our results can be used to verify MC event generators at the p-p level. Finally, we investigate the extent to which intrinsic charm in the proton can be constrained at FASER detectors.

        Speaker: Jelle Koorn (Nikhef National institute for subatomic physics (NL))
        Slides_Jelle-3.pdf
      • 15:10
        Latest neutrino results from the FASER experiment and their implications for cosmic ray physics 15m

        The muon puzzle --- an excess of muons relative to simulation predictions in ultra-high-energy cosmic-ray air showers --- has been reported by many experiments.
        This suggests that forward particle production in hadronic interactions is not fully understood.
        Some of the scenarios proposed to resolve this predict reduced production of forward neutral pions and enhanced production of forward kaons (or other particles).
        The FASER experiment at the LHC is located 480~m downstream of the ATLAS interaction point and is sensitive to neutrinos and muons, which are the decay products of forward charged pions and kaons.
        In this study, the latest measurements of electron and muon neutrino fluxes are presented using the data corresponding to 9.5~$\mathrm{fb^{-1}}$ and 65.6~$\mathrm{fb^{-1}}$ of proton-proton collisions with $\sqrt{s}=13.6~\mathrm{TeV}$ by the FASER$\nu$ and the FASER electronic detector, respectively. These fluxes are compared with predictions from recent hadronic interaction models, including \texttt{EPOS-LHCr}, \texttt{SIBYLL 2.3e}, and \texttt{QGSJET 3}.
        The predictions are generally consistent with the measured fluxes from FASER, although some discrepancies appear in certain energy bins.
        More precise flux measurements with additional data will follow soon, enabling validation of pion, kaon, and charm meson production with finer energy binning, reduced uncertainties, and multi-differential analyses.

        Speaker: Ken Ohashi (Universitaet Bern (CH))
        FASER_astroparticle_FPF9_KenOhashi.pdf
      • 15:30
        Tau tridents at accelerator neutrino facilities 15m

        We present the first detailed study of Standard Model neutrino tridents involving tau leptons at the near detectors of accelerator neutrino facilities. The rates of these processes were previously thought to be negligible, even at future facilities. Our full $2\to4$
        calculation, including both coherent and incoherent scatterings, reveals that the DUNE near detector could observe a considerable number of tau tridents, an important background to new physics searches. We identify promising kinematic features that may allow distinction of tau tridents from the usual neutrino charged-current background at DUNE, and thus establish the observation of tau tridents for the first time. We also comment on the detection prospects at other accelerator and collider neutrino experiments including the FASER$\nu$ experiment.

        Speaker: Diego Lopez Gutierrez (Washington University in St Louis)
        Presentation.pdf
      • 16:00
        Muon trident process at FASER$\nu$ and FASER$\nu$2 detectors 15m

        The electromagnetic production of a dilepton pair in the muon - ion scattering, usually denoted as muon trident process, is investigated considering the feasibility of studying processes induced by muons at LHC using FASER$\nu$ and FASER$\nu$2 detectors. The total and differential cross - sections are estimated taking into account of the Bethe-Heitler and bremsstrahlung channels, and predictions for the event rates expected for muon - tungsten ($\mu W$) collisions at the LHC energies are calculated. Our results indicate that the observation of the muon trident process is feasible at these detectors. In particular, our results indicate that the electromagnetic production of $\tau^+ \tau^-$ pairs in the $\mu W$ scattering can, in principle, be observed for the first time ever at the LHC. In addition, we made predictions for the production of QED bound states.

        Speaker: Gabriel Rabelo-Soares
        9th_FPF_Meeting_GRS.pdf
      • 16:20
        Anti-Electron Neutrinos: Identification Strategies and Physics Potential 15m

        Most existing and proposed high energy neutrino experiments have excellent muon charge identification capabilities, enabling the distinction of $\nu_\mu$ and $\bar \nu_\mu$ charged current interactions. In contrast, distinguishing electrons and positrons from $\nu_e$ and $\bar \nu_e$ interactions is typically impossible, as they quickly interact within dense detector materials and do not reach the spectrometer. We propose a compact and cost-effective plastic target, placed right before the spectrometer, to maximize the rate of electrons and positrons that reach the spectrometer before interacting. When installed at the FASER or FASER2 experiments, the setup is demonstrated to enable the first separate measurement of $\nu_e$ and $\bar\nu_e$ cross sections at high energy. Furthermore, it opens new opportunities for studying forward particle production, such as constraining forward $\Lambda$ hyperons, and, by reducing flux uncertainties, improving limits on non-standard neutrino interactions in neutral currents.

        Speaker: Dr Toni Makela (University of California, Irvine)
        anti-nue_identification_strategies_and_physics_potential.pdf
      • 16:40
        Simulated Neutrino Fluxes at the Forward Physics Facility 15m

        Measurements of neutrino fluxes at the Forward Physics Facility can be used to study predictions of hadronic interaction models. These advancements are critical for astroparticle physics, linking forward scattering processes to extensive air showers and improving our understanding of cosmic-ray interactions. This work investigates simulated neutrino fluxes at the FPF, focusing in particular on the ratio of electron neutrino to muon neutrino fluxes. Due to their distinct origin and energy spectra, these fluxes may be differentiated, providing an indirect method for determining the ratio of charged kaons to pions. We present simulation studies of the theoretical expectations of the neutrino fluxes at FASER𝝂2 and FLArE. These results will offer insights to refine hadronic interaction models, including the most recently developed, and better estimate atmospheric neutrino backgrounds in astrophysical neutrino telescopes.

        Speaker: Isabella Coronado
        FPF9_ICoronado.pdf
      • 17:00
        Testing hadronic interaction models in the far forward direction using simulations of muon fluxes at FASER 15m

        Our goal is to constrict hadronic interaction models in the far-forward region. To do this, we produce simulations of the muon fluxes produced from the decay of different hadrons using BDSIM with different event generators. We will present studies of the energy spectra and x-y position of the muon flux at FASER for different parent particles to constrain various hadronic interaction models.

        Speaker: Kemuel Cullimore (University of Utah)
  • Friday 6 March