Rahool Kumar Barman, Dorival Gonçalves, Felix Kling
We explore the direct Higgs-top CP measurement via the $pp\to t\bar{t}h$ channel at the high-luminosity LHC. We show that a combination of machine learning techniques and efficient kinematic reconstruction methods can boost new physics sensitivity, effectively probing the complex $t\bar{t}h$ multi-particle phase space. Special attention is devoted to top quark polarization observables, uplifting the analysis from a raw rate to a polarization study. Through a combination of hadronic, semi-leptonic, and di-leptonic top pair final states in association with $h\to γγ$, we obtain that the HL-LHC can probe the Higgs-top coupling modifier and CP-phase, respectively, up to $|κ_t|\lesssim 8\%$ and $|α|\lesssim 13^{\circ}$ at $68\%$~CL.
Felix Kling, Laurence J. Nevay
With the upcoming Run 3 of the LHC, the FASERv and SND@LHC detectors will start a new era of neutrino physics using the far-forward high-energy neutrino beam produced in collisions at ATLAS. This emerging LHC neutrino physics program requires reliable estimates of the LHC's forward neutrino fluxes and their uncertainties. In this paper we provide a new fast-neutrino flux simulation, implemented as a RIVET module, to address this issue. We present the expected energy distributions going through the FASERv and SND@LHC detectors based on various commonly used event generators, analyze the origin of those neutrinos, and present the expected neutrino event rates.
Brian Batell, Jonathan L. Feng, Max Fieg, Ahmed Ismail, Felix Kling, Roshan Mammen Abraham, Sebastian Trojanowski
Models with light dark sector and dark matter particles motivate qualitatively new collider searches. Here we carry out a comprehensive study of hadrophilic models with U(1)$_B$ and U(1)$_{B-3L_τ}$ gauge bosons coupled to light dark matter. The new mediator particles in these models couple to quarks, but have suppressed couplings to leptons, providing a useful foil to the well-studied dark photon models. We consider current bounds from accelerator and collider searches, rare anomaly-induced decays, neutrino non-standard interactions, and dark matter direct detection. Despite the many existing constraints, these models predict a range of new signatures that can be seen in current and near future experiments, including dark gauge boson decays to the hadronic final states $π^+ π^- π^0$, $π^0 γ$, $K^+ K^-$, and $K_S K_L$ in FASER at LHC Run 3, enhancements of $ν_τ$ scattering rates in far-forward neutrino detectors, and thermal dark matter scattering in FLArE in the HL-LHC era. These models therefore motivate an array of different experiments in the far-forward region at the LHC, as could be accommodated in the proposed Forward Physics Facility.
Johann Brehmer, Felix Kling, Irina Espejo, Kyle Cranmer
Precision measurements at the LHC often require analyzing high-dimensional event data for subtle kinematic signatures, which is challenging for established analysis methods. Recently, a powerful family of multivariate inference techniques that leverage both matrix element information and machine learning has been developed. This approach neither requires the reduction of high-dimensional data to summary statistics nor any simplifications to the underlying physics or detector response. In this paper we introduce MadMiner, a Python module that streamlines the steps involved in this procedure. Wrapping around MadGraph5_aMC and Pythia 8, it supports almost any physics process and model. To aid phenomenological studies, the tool also wraps around Delphes 3, though it is extendable to a full Geant4-based detector simulation. We demonstrate the use of MadMiner in an example analysis of dimension-six operators in ttH production, finding that the new techniques substantially increase the sensitivity to new physics.
Felix Kling, Toni Mäkelä, Sebastian Trojanowski
The initiation of a novel neutrino physics program at the Large Hadron Collider (LHC) and the purpose-built Forward Physics Facility (FPF) proposal have motivated studies exploring the discovery potential of these searches. This requires resolving degeneracies between new predictions and uncertainties in modeling neutrino production in the forward kinematic region. The present work investigates a broad selection of existing predictions for the parent hadron spectra at FASER$ν$ and the FPF to parameterize expected correlations in the neutrino spectra produced in their decays and to determine the highest achievable precision for their observation based on Fisher information. This allows for setting constraints on various physics processes within and beyond the Standard Model, including neutrino non-standard interactions. We also illustrate how combining multiple neutrino observables could lead to experimental confirmation of the enhanced-strangeness scenario proposed to resolve the cosmic-ray muon puzzle already during the ongoing LHC Run 3.
Jonathan L. Feng, Alec Hewitt, Felix Kling, Daniel La Rocco
Heavy neutral leptons (HNLs) are motivated by attempts to explain neutrino masses and dark matter. If their masses are in the MeV to several GeV range, HNLs are light enough to be copiously produced at collider and accelerator facilities, but also heavy enough to decay to visible particles on length scales that can be observed in particle detectors. Previous studies evaluating the sensitivities of experiments have often focused on simple, but not particularly well-motivated, models in which the HNL mixes with only one active neutrino flavor. In this work, we accurately simulate models for HNL masses between 100 MeV and 10 GeV and arbitrary couplings to $e$, $μ$, and $τ$ leptons. We include over 150 HNL production channels and over 100 HNL decay modes, including all of the processes that can be dominant in some region of the general parameter space. The result is HNLCalc, a user-friendly, fast, and flexible library to compute the properties of HNL models. As examples, we implement HNLCalc to extend the FORESEE package to evaluate the prospects for HNL discovery at forward LHC experiments. We present sensitivity reaches for FASER and FASER2 in five benchmark scenarios with coupling ratios $|U_e|^2 : |U_μ|^2 : |U_τ|^2$ = 1:0:0, 0:1:0, 0:0:1, 0:1:1, and 1:1:1, where the latter two have not been studied previously. Comparing these to current constraints, we identify regions of parameter space with significant discovery prospects.
Dorival Goncalves, Tao Han, Felix Kling, Tilman Plehn, Michihisa Takeuchi
The measurement of the triple Higgs coupling is a key benchmark for the LHC and future colliders. It directly probes the Higgs potential and its fundamental properties in connection to new physics beyond the Standard Model. There exist two phase space regions with an enhanced sensitivity to the Higgs self-coupling, the Higgs pair production threshold and an intermediate top pair threshold. We show how the invariant mass distribution of the Higgs pair offers a systematic way to extract the Higgs self-coupling, focusing on the leading channel $pp\to hh+X\to b\bar b\ γγ+X$. We utilize new features of the signal events at higher energies and estimate the potential of a high-energy upgrade of the LHC and a future hadron collider with realistic simulations. We find that the high-energy upgrade of the LHC to 27 TeV would reach a 5$σ$ observation with an integrated luminosity of 2.5 ab$^{-1}$. It would have the potential to reach 15% (30%) accuracy at the 68% (95%) confidence level to determine the SM Higgs boson self-coupling. A future 100 TeV collider could improve the self-coupling measurement to better than 5% (10%) at the 68% (95%) confidence level.
Jonathan L. Feng, Felix Kling, Mary Hall Reno, Juan Rojo, Dennis Soldin, Luis A. Anchordoqui, Jamie Boyd, Ahmed Ismail, Lucian Harland-Lang, Kevin J. Kelly, Vishvas Pandey, Sebastian Trojanowski, Yu-Dai Tsai, Jean-Marco Alameddine, Takeshi Araki, Akitaka Ariga, Tomoko Ariga, Kento Asai, Alessandro Bacchetta, Kincso Balazs, Alan J. Barr, Michele Battistin, Jianming Bian, Caterina Bertone, Weidong Bai, Pouya Bakhti, A. Baha Balantekin, Basabendu Barman, Brian Batell, Martin Bauer, Brian Bauer, Mathias Becker, Asher Berlin, Enrico Bertuzzo, Atri Bhattacharya, Marco Bonvini, Stewart T. Boogert, Alexey Boyarsky, Joseph Bramante, Vedran Brdar, Adrian Carmona, David W. Casper, Francesco Giovanni Celiberto, Francesco Cerutti, Grigorios Chachamis, Garv Chauhan, Matthew Citron, Emanuele Copello, Jean-Pierre Corso, Luc Darmé, Raffaele Tito D'Agnolo, Neda Darvishi, Arindam Das, Giovanni De Lellis, Albert De Roeck, Jordy de Vries, Hans P. Dembinski, Sergey Demidov, Patrick deNiverville, Peter B. Denton, Frank F. Deppisch, P. S. Bhupal Dev, Antonia Di Crescenzo, Keith R. Dienes, Milind V. Diwan, Herbi K. Dreiner, Yong Du, Bhaskar Dutta, Pit Duwentäster, Lucie Elie, Sebastian A. R. Ellis, Rikard Enberg, Yasaman Farzan, Max Fieg, Ana Luisa Foguel, Patrick Foldenauer, Saeid Foroughi-Abari, Jean-François Fortin, Alexander Friedland, Elina Fuchs, Michael Fucilla, Kai Gallmeister, Alfonso Garcia, Carlos A. García Canal, Maria Vittoria Garzelli, Rhorry Gauld, Sumit Ghosh, Anish Ghoshal, Stephen Gibson, Francesco Giuli, Victor P. Gonçalves, Dmitry Gorbunov, Srubabati Goswami, Silvia Grau, Julian Y. Günther, Marco Guzzi, Andrew Haas, Timo Hakulinen, Steven P. Harris, Julia Harz, Juan Carlos Helo Herrera, Christopher S. Hill, Martin Hirsch, Timothy J. Hobbs, Stefan Höche, Andrzej Hryczuk, Fei Huang, Tomohiro Inada, Angelo Infantino, Ameen Ismail, Richard Jacobsson, Sudip Jana, Yu Seon Jeong, Tomas Ježo, Yongsoo Jho, Krzysztof Jodłowski, Dmitry Kalashnikov, Timo J. Kärkkäinen, Cynthia Keppel, Jongkuk Kim, Michael Klasen, Spencer R. Klein, Pyungwon Ko, Dominik Köhler, Masahiro Komatsu, Karol Kovařík, Suchita Kulkarni, Jason Kumar, Karan Kumar, Jui-Lin Kuo, Frank Krauss, Aleksander Kusina, Maxim Laletin, Chiara Le Roux, Seung J. Lee, Hye-Sung Lee, Helena Lefebvre, Jinmian Li, Shuailong Li, Yichen Li, Wei Liu, Zhen Liu, Mickael Lonjon, Kun-Feng Lyu, Rafal Maciula, Roshan Mammen Abraham, Mohammad R. Masouminia, Josh McFayden, Oleksii Mikulenko, Mohammed M. A. Mohammed, Kirtimaan A. Mohan, Jorge G. Morfín, Ulrich Mosel, Martin Mosny, Khoirul F. Muzakka, Pavel Nadolsky, Toshiyuki Nakano, Saurabh Nangia, Angel Navascues Cornago, Laurence J. Nevay, Pierre Ninin, Emanuele R. Nocera, Takaaki Nomura, Rui Nunes, Nobuchika Okada, Fred Olness, John Osborne, Hidetoshi Otono, Maksym Ovchynnikov, Alessandro Papa, Junle Pei, Guillermo Peon, Gilad Perez, Luke Pickering, Simon Plätzer, Ryan Plestid, Tanmay Kumar Poddar, Mudit Rai, Meshkat Rajaee, Digesh Raut, Peter Reimitz, Filippo Resnati, Wolfgang Rhode, Peter Richardson, Adam Ritz, Hiroki Rokujo, Leszek Roszkowski, Tim Ruhe, Richard Ruiz, Marta Sabate-Gilarte, Alexander Sandrock, Ina Sarcevic, Subir Sarkar, Osamu Sato, Christiane Scherb, Ingo Schienbein, Holger Schulz, Pedro Schwaller, Sergio J. Sciutto, Dipan Sengupta, Lesya Shchutska, Takashi Shimomura, Federico Silvetti, Kuver Sinha, Torbjörn Sjöstrand, Jan T. Sobczyk, Huayang Song, Jorge F. Soriano, Yotam Soreq, Anna Stasto, David Stuart, Shufang Su, Wei Su, Antoni Szczurek, Zahra Tabrizi, Yosuke Takubo, Marco Taoso, Brooks Thomas, Pierre Thonet, Douglas Tuckler, Agustin Sabio Vera, Heinz Vincke, K. N. Vishnudath, Zeren Simon Wang, Martin W. Winkler, Wenjie Wu, Keping Xie, Xun-Jie Xu, Tevong You, Ji-Young Yu, Jiang-Hao Yu, Korinna Zapp, Yongchao Zhang, Yue Zhang, Guanghui Zhou, Renata Zukanovich Funchal
Felix Kling, Yang Ma, Krzysztof Mękała, Jürgen Reuter, Zahra Tabrizi
In addition to their broad physics reach enabled by their high energies and precision, future multi-TeV muon colliders will also be the world's most intense sources of neutrinos. This offers the opportunity to search for new non-standard neutrino interactions, possible by installing a dedicated forward neutrino detector in the straight sections of the collision ring, which is then used to measure reactions initiated by neutrinos from the decaying beam muons. In this paper, we show that these searches can exceed current and upcoming bounds on non-standard neutrino interactions from low-energy precision experiments and the LHC. This is achieved by the large flux of high-energetic neutrinos, the precise knowledge of the neutrino flavor composition on each side of the interaction point and the chirality of the neutrinos. We further discuss the technical requirements of the proposed forward neutrino detector, \FASERmuC, to maximally exploit this physics potential.
FASER Collaboration, Roshan Mammen Abraham, Xiaocong Ai, Saul Alonso-Monsalve, John Anders, Claire Antel, Akitaka Ariga, Tomoko Ariga, Jeremy Atkinson, Florian U. Bernlochner, Tobias Boeckh, Jamie Boyd, Lydia Brenner, Angela Burger, Franck Cadoux, Roberto Cardella, David W. Casper, Charlotte Cavanagh, Xin Chen, Dhruv Chouhan, Sebastiani Christiano, Andrea Coccaro, Stephane Débieux, Monica D'Onofrio, Ansh Desai, Sergey Dmitrievsky, Radu Dobre, Sinead Eley, Yannick Favre, Jonathan L. Feng, Carlo Alberto Fenoglio, Didier Ferrere, Max Fieg, Wissal Filali, Elena Firu, Edward Galantay, Ali Garabaglu, Stephen Gibson, Sergio Gonzalez-Sevilla, Yuri Gornushkin, Carl Gwilliam, Daiki Hayakawa, Michael Holzbock, Shih-Chieh Hsu, Zhen Hu, Giuseppe Iacobucci, Tomohiro Inada, Luca Iodice, Sune Jakobsen, Hans Joos, Enrique Kajomovitz, Hiroaki Kawahara, Alex Keyken, Felix Kling, Daniela Köck, Pantelis Kontaxakis, Umut Kose, Rafaella Kotitsa, Peter Krack, Susanne Kuehn, Thanushan Kugathasan, Lorne Levinson, Botao Li, Jinfeng Liu, Yi Liu, Margaret S. Lutz, Jack MacDonald, Chiara Magliocca, Toni Mäkelä, Yasuhiro Maruya, Lawson McCoy, Josh McFayden, Andrea Pizarro Medina, Matteo Milanesio, Théo Moretti, Mitsuhiro Nakamura, Toshiyuki Nakano, Laurie Nevay, Ken Ohashi, Hidetoshi Otono, Hao Pang, Lorenzo Paolozzi, Pawan Pawan, Brian Petersen, Titi Preda, Markus Prim, Michaela Queitsch-Maitland, Juan Rojo, Hiroki Rokujo, André Rubbia, Jorge Sabater-Iglesias, Osamu Sato, Paola Scampoli, Kristof Schmieden, Matthias Schott, Anna Sfyrla, Davide Sgalaberna, Mansoora Shamim, Savannah Shively, Yosuke Takubo, Noshin Tarannum, Ondrej Theiner, Simon Thor, Eric Torrence, Oscar Ivan Valdes Martinez, Svetlana Vasina, Benedikt Vormwald, Yuxiao Wang, Eli Welch, Monika Wielers, Benjamin James Wilson, Jialin Wu, Johannes Martin Wuthrich, Yue Xu, Samuel Zahorec, Stefano Zambito, Shunliang Zhang, Xingyu Zhao
The FASER experiment at CERN has opened a new window in collider neutrino physics by detecting TeV-energy neutrinos produced in the forward direction at the LHC. Building on this success, this document outlines the scientific case and design considerations for an upgraded FASER neutrino detector to operate during LHC Run 4 and beyond. The proposed detector will significantly enhance the neutrino physics program by increasing event statistics, improving flavor identification, and enabling precision measurements of neutrino interactions at the highest man-made energies. Key objectives include measuring neutrino cross sections, probing proton structure and forward QCD dynamics, testing lepton flavor universality, and searching for beyond-the-Standard Model physics. Several detector configurations are under study, including high-granularity scintillator-based tracking calorimeters, high-precision silicon tracking layers, and advanced emulsion-based detectors for exclusive event reconstruction. These upgrades will maximize the physics potential of the HL-LHC, contribute to astroparticle physics and QCD studies, and serve as a stepping stone toward future neutrino programs at the Forward Physics Facility.
Felix Kling, Jui-Lin Kuo, Sebastian Trojanowski, Yu-Dai Tsai
Despite being mostly secluded, dark sector particles may feebly interact with photons via a small mass-dimension 4 millicharge, a mass-dimension 5 magnetic and electric dipole moment, or a mass-dimension 6 anapole moment and charge radius. If sufficiently light, the LHC may produce an intense and collimated beam of these particles in the far forward direction. We study the prospects of searching for such dark sector particles with electromagnetic form factors via their electron scattering signature in the Forward Liquid Argon Experiment (FLArE) detector at the Forward Physics Facility (FPF). We find that FLArE can provide new probes of sub-GeV dark particles with dipole moments and strong sensitivities for millicharged particles in the 100 MeV to 100 GeV region. This complements other search strategies using scintillation signatures or dark matter direct detection and allows for probing strongly interacting dark matter motivated by the EDGES anomaly. Along with the FORMOSA detector, this leads to a very diverse and leading experimental program in the search for millicharged particles in the FPF.
Asher Berlin, Felix Kling
Visible signals from the decays of light long-lived hidden sector particles have been extensively searched for at beam dump, fixed-target, and collider experiments. If such hidden sectors couple to the Standard Model through mediators heavier than $\sim 10$ GeV, their production at low-energy accelerators is kinematically suppressed, leaving open significant pockets of viable parameter space. We investigate this scenario in models of inelastic dark matter, which give rise to visible signals at various existing and proposed LHC experiments, such as ATLAS, CMS, LHCb, CODEX-b, FASER, and MATHUSLA. These experiments can leverage the large center of mass energy of the LHC to produce GeV-scale dark matter from the decays of dark photons in the cosmologically motivated mass range of $\sim 1-100$ GeV. We also provide a detailed calculation of the radiative dark matter-nucleon/electron elastic scattering cross section, which is relevant for estimating rates at direct detection experiments.
FASER Collaboration, Akitaka Ariga, Tomoko Ariga, Jamie Boyd, David W. Casper, Jonathan L. Feng, Iftah Galon, Shih-Chieh Hsu, Felix Kling, Hidetoshi Otono, Brian Petersen, Osamu Sato, Aaron M. Soffa, Jeffrey R. Swaney, Sebastian Trojanowski
FASER is a proposed small and inexpensive experiment designed to search for light, weakly-interacting particles at the LHC. Such particles are dominantly produced along the beam collision axis and may be long-lived, traveling hundreds of meters before decaying. To exploit both of these properties, FASER is to be located along the beam collision axis, 480 m downstream from the ATLAS interaction point, in the unused service tunnel TI18. We propose that FASER be installed in TI18 in Long Shutdown 2 in time to collect data from 2021-23 during Run 3 of the 14 TeV LHC. FASER will detect new particles that decay within a cylindrical volume with radius R= 10 cm and length L = 1.5 m. With these small dimensions, FASER will complement the LHC's existing physics program, extending its discovery potential to a host of new particles, including dark photons, axion-like particles, and other CP-odd scalars. A FLUKA simulation and analytical estimates have confirmed that numerous potential backgrounds are highly suppressed at the FASER location, and the first in situ measurements are currently underway. We describe FASER's location and discovery potential, its target signals and backgrounds, the detector's layout and components, and the experiment's preliminary cost estimate, funding, and timeline.
Johann Brehmer, Kyle Cranmer, Irina Espejo, Felix Kling, Gilles Louppe, Juan Pavez
One major challenge for the legacy measurements at the LHC is that the likelihood function is not tractable when the collected data is high-dimensional and the detector response has to be modeled. We review how different analysis strategies solve this issue, including the traditional histogram approach used in most particle physics analyses, the Matrix Element Method, Optimal Observables, and modern techniques based on neural density estimation. We then discuss powerful new inference methods that use a combination of matrix element information and machine learning to accurately estimate the likelihood function. The MadMiner package automates all necessary data-processing steps. In first studies we find that these new techniques have the potential to substantially improve the sensitivity of the LHC legacy measurements.
Luis A. Anchordoqui, Akitaka Ariga, Tomoko Ariga, Weidong Bai, Kincso Balazs, Brian Batell, Jamie Boyd, Joseph Bramante, Mario Campanelli, Adrian Carmona, Francesco G. Celiberto, Grigorios Chachamis, Matthew Citron, Giovanni De Lellis, Albert De Roeck, Hans Dembinski, Peter B. Denton, Antonia Di Crecsenzo, Milind V. Diwan, Liam Dougherty, Herbi K. Dreiner, Yong Du, Rikard Enberg, Yasaman Farzan, Jonathan L. Feng, Max Fieg, Patrick Foldenauer, Saeid Foroughi-Abari, Alexander Friedland, Michael Fucilla, Jonathan Gall, Maria Vittoria Garzelli, Francesco Giuli, Victor P. Goncalves, Marco Guzzi, Francis Halzen, Juan Carlos Helo, Christopher S. Hill, Ahmed Ismail, Ameen Ismail, Richard Jacobsson, Sudip Jana, Yu Seon Jeong, Krzysztof Jodlowski, Kevin J. Kelly, Felix Kling, Fnu Karan Kumar, Zhen Liu, Rafal Maciula, Roshan Mammen Abraham, Julien Manshanden, Josh McFayden, Mohammed M. A. Mohammed, Pavel M. Nadolsky, Nobuchika Okada, John Osborne, Hidetoshi Otono, Vishvas Pandey, Alessandro Papa, Digesh Raut, Mary Hall Reno, Filippo Resnati, Adam Ritz, Juan Rojo, Ina Sarcevic, Christiane Scherb, Holger Schulz, Pedro Schwaller, Dipan Sengupta, Torbjörn Sjöstrand, Tyler B. Smith, Dennis Soldin, Anna Stasto, Antoni Szczurek, Zahra Tabrizi, Sebastian Trojanowski, Yu-Dai Tsai, Douglas Tuckler, Martin W. Winkler, Keping Xie, Yue Zhang
The Forward Physics Facility (FPF) is a proposal to create a cavern with the space and infrastructure to support a suite of far-forward experiments at the Large Hadron Collider during the High Luminosity era. Located along the beam collision axis and shielded from the interaction point by at least 100 m of concrete and rock, the FPF will house experiments that will detect particles outside the acceptance of the existing large LHC experiments and will observe rare and exotic processes in an extremely low-background environment. In this work, we summarize the current status of plans for the FPF, including recent progress in civil engineering in identifying promising sites for the FPF and the experiments currently envisioned to realize the FPF's physics potential. We then review the many Standard Model and new physics topics that will be advanced by the FPF, including searches for long-lived particles, probes of dark matter and dark sectors, high-statistics studies of TeV neutrinos of all three flavors, aspects of perturbative and non-perturbative QCD, and high-energy astroparticle physics.
Ahmed Ismail, Felix Kling, Roshan Mammen Abraham
In detecting neutrinos from the Large Hadron Collider, FASER$ν$ will record the most energetic laboratory neutrinos ever studied. While charged current neutrino scattering events can be cleanly identified by an energetic lepton exiting the interaction vertex, neutral current interactions are more difficult to detect. We explore the potential of FASER$ν$ to observe neutrino neutral current scattering $νN \to νN$, demonstrating techniques to discriminate neutrino scattering events from neutral hadron backgrounds as well as to estimate the incoming neutrino energy given the deep inelastic scattering final state. We find that deep neural networks trained on kinematic observables allow for the measurement of the neutral current scattering cross section over neutrino energies from 100 GeV to several TeV. Such a measurement can be interpreted as a probe of neutrino non-standard interactions that is complementary to limits from other tests such as oscillations and coherent neutrino-nucleus scattering.
Kevin J. Kelly, Felix Kling, Douglas Tuckler, Yue Zhang
The Forward Physics Facility (FPF), planned to operate near the ATLAS interaction point at the LHC, offers exciting new terrain to explore neutrino properties at TeV energy scales. It will reach an unprecedented regime for terrestrial neutrino experiments and provide the opportunity to reveal new physics of neutrinos at higher energy scales. We demonstrate that future detectors at the FPF have the potential to discover new mediators that couple predominantly to neutrinos, with masses between 0.3 and 20 GeV and small couplings not yet probed by existing searches. Such a neutrinophilic mediator is well motivated for addressing the origin of several neutrino-portal dark matter candidates, including thermal freeze-out and sterile-neutrino dark matter scenarios. Experimentally, the corresponding signatures include neutrino charged-current scattering events associated with large missing transverse momentum, and excessive apparent tau-neutrino events. We discuss the FPF detector capabilities needed for this search, most importantly the hadronic energy resolution.
FASER Collaboration, Henso Abreu, Marco Andreini, Claire Antel, Akitaka Ariga, Tomoko Ariga, Caterina Bertone, Jamie Boyd, Andy Buckley, Franck Cadoux, David W. Casper, Francesco Cerutti, Xin Chen, Andrea Coccaro, Salvatore Danzeca, Liam Dougherty, Candan Dozen, Peter B. Denton, Yannick Favre, Deion Fellers, Jonathan L. Feng, Didier Ferrere, Jonathan Gall, Iftah Galon, Stephen Gibson, Sergio Gonzalez-Sevilla, Shih-Chieh Hsu, Zhen Hu, Giuseppe Iacobucci, Sune Jakobsen, Roland Jansky, Enrique Kajomovitz, Felix Kling, Umut Kose, Susanne Kuehn, Mike Lamont, Helena Lefebvre, Lorne Levinson, Ke Li, Josh McFayden, Sam Meehan, Dimitar Mladenov, Mitsuhiro Nakamura, Toshiyuki Nakano, Marzio Nessi, Friedemann Neuhaus, John Osborne, Hidetoshi Otono, Serge Pelletier, Brian Petersen, Francesco Pietropaolo, Michaela Queitsch-Maitland, Filippo Resnati, Marta Sabate-Gilarte, Jakob Salfeld-Nebgen, Francisco Sanchez Galan, Pablo Santos Diaz, Osamu Sato, Paola Scampoli, Kristof Schmieden, Matthias Schott, Holger Schulz, Anna Sfyrla, Savannah Shively, Jordan Smolinsky, Aaron M. Soffa, Yosuke Takubo, Eric Torrence, Sebastian Trojanowski, Serhan Tufanli, Dengfeng Zhang, Gang Zhang
FASERnu is a proposed small and inexpensive emulsion detector designed to detect collider neutrinos for the first time and study their properties. FASERnu will be located directly in front of FASER, 480 m from the ATLAS interaction point along the beam collision axis in the unused service tunnel TI12. From 2021-23 during Run 3 of the 14 TeV LHC, roughly 1,300 electron neutrinos, 20,000 muon neutrinos, and 20 tau neutrinos will interact in FASERnu with TeV-scale energies. With the ability to observe these interactions, reconstruct their energies, and distinguish flavors, FASERnu will probe the production, propagation, and interactions of neutrinos at the highest human-made energies ever recorded. The FASERnu detector will be composed of 1000 emulsion layers interleaved with tungsten plates. The total volume of the emulsion and tungsten is 25cm x 25cm x 1.35m, and the tungsten target mass is 1.2 tonnes. From 2021-23, 7 sets of emulsion layers will be installed, with replacement roughly every 20-50 1/fb in planned Technical Stops. In this document, we summarize FASERnu's physics goals and discuss the estimates of neutrino flux and interaction rates. We then describe the FASERnu detector in detail, including plans for assembly, transport, installation, and emulsion replacement, and procedures for emulsion readout and analyzing the data. We close with cost estimates for the detector components and infrastructure work and a timeline for the experiment.
Felix Kling, Sebastian Trojanowski
The search for light and long-lived particles at the LHC will be intensified in the upcoming years with a prominent role of the new FASER experiment. In this study, we discuss how FASER could independently probe such scenarios relevant for new physics searches at kaon factories. We put an emphasis on the proposed explanations for the recently observed three anomalous events in the KOTO experiment. The baseline of FASER precisely corresponds to the proposed lifetime solution to the anomaly that avoids the NA62 bounds on charged kaons. As a result, the experiment can start constraining relevant models within the first few weeks of its operation. In some cases, it can confirm a possible discovery with up to 10000 spectacular high-energy events in FASER during LHC Run 3. Further complementarities between FASER and kaon factories, which employ FASER capability to study di-photon signatures, are illustrated for the model with axion-like particles dominantly coupled to $SU(2)_W$ gauge bosons.
Felix Kling, Honglei Li, Shuailong Li, Adarsh Pyarelal, Huayang Song, Shufang Su, Wei Su
The exotic decay modes of non-Standard Model Higgses can serve as powerful search channels to explore the parameter space of extended Higgs sectors. In this Snowmass contribution, we illustrate this using the Two-Higgs Doublet Model (2HDM) as an example. We first review the current experimental constraints on the parameter space of a Type-II 2HDM arising from existing searches for the exotic Higgs decay mode $A/H\rightarrow HZ/AZ$. We then present the sensitivity of future colliders to discover addition Higgs bosons using the exotic decay channels $A\rightarrow HZ$, $A\rightarrow H^\pm W^\mp$ and $H^\pm\rightarrow H W^\pm$. We find that a 100 TeV collider can probe almost the entire region of the Type-II 2HDM parameter space that survives current theoretical and experimental constraints and would therefore be an ideal machine to search for heavier Higgses in hierarchical scalar sectors.