Future Circular Collider Research Articles

Impact of beam asymmetries at the Future Circular Collider e+e−

In this paper, we present detailed simulations with asymmetric initial beam settings in the context of the proposed Future Circular Collider e+e− (FCC-ee) using the framework. We compare simulated equilibrium bunch sizes and luminosities against an already existing analytical model, which shows remarkably good agreement for realistic small perturbations. We investigate the longitudinal top-up injection, the currently preferred injection scheme for the FCC-ee, using self-consistent simulations featuring beam-beam collisions with beamstrahlung and the injection process for the first time. We present and assess the sensitivity and required precision of the nominal beam parameters in a potential real-life operation by providing first estimates of the tolerances in the initial asymmetry of several machine parameters, with respect to the 3D flip-flop mechanism, obtained from parameter scan simulations. Published by the American Physical Society 2024

Assessing the Performance of Deep Learning Predictions for Dynamic Aperture of a Hadron Circular Particle Accelerator

Understanding the concept of dynamic aperture provides essential insights into nonlinear beam dynamics, beam losses, and the beam lifetime in circular particle accelerators. This comprehension is crucial for the functioning of modern hadron synchrotrons like the CERN Large Hadron Collider and the planning of future ones such as the Future Circular Collider. The dynamic aperture defines the extent of the region in phase space where the trajectories of charged particles are bounded over numerous revolutions, the actual number being defined by the physical application. Traditional methods for calculating the dynamic aperture depend on computationally demanding numerical simulations, which require tracking over multiple turns of numerous initial conditions appropriately distributed in phase space. Prior research has shown the efficiency of a multilayer perceptron network in forecasting the dynamic aperture of the CERN Large Hadron Collider ring, achieving a remarkable speed-up of up to 200-fold compared to standard numerical tracking tools. Building on recent advancements, we conducted a comparative study of various deep learning networks based on BERT, DenseNet, ResNet and VGG architectures. The results demonstrate substantial enhancements in the prediction of the dynamic aperture, marking a significant advancement in the development of more precise and efficient surrogate models of beam dynamics.

Searching for the vector-like X-quark at the future electron–proton colliders

In a simplified model including an exotic vector-like X-quark (VLQ-X) with electric charge 5/3, we investigate the process e+p→ν¯eX+ν¯eXt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e^{+}p \\rightarrow \\bar{\ u }_{e}X+\\bar{\ u }_{e}X\\bar{t}$$\\end{document} induced by the couplings between the VLQ-X and the first- and third-generation quarks at the future ep colliders. We further explore the prospects of discovering the VLQ-X via the X→tW\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$X\\rightarrow tW$$\\end{document} decay model at the electron–hadron Future Circular Collider (FCC-eh) with its proposed 60 GeV electron beam and 50 TeV proton beam. We focus our analysis on the final states, including two same-sign lepton (electrons or muons) or μμ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu \\mu $$\\end{document} pairs, at least one b-tagged jet, and large missing transverse momentum. By performing a detailed signal-to-background analysis and detector simulations, the 95% confidence level exclusion limits and 5σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$5\\sigma $$\\end{document} discovery reaches are presented in terms of parameter space regions.

High-tech guardians: Robotics at the heart of the Future Circular Collider.

A holistic robotic concept for inspection, maintenance, and emergency interventions for the Future Circular Collider is presented.

Quantum tomography with τ leptons at the FCC-ee: Entanglement, Bell inequality violation, sinθW , and anomalous couplings

The Future Circular Collider (FCC)—in its first incarnation as a lepton collider—will produce, according to the proposed design, more than 100 billion pairs of τ leptons after working for four years at the energy of the Z-boson resonance. The τ lepton is special because its relatively long lifetime makes it possible to reconstruct the momenta of neutrinos emitted in the single pion decay mode. The resulting large number of events is an ideal source for a full quantum tomography of the process that will test quantum entanglement and the violation of Bell inequality with unprecedented precision. In addition, the study of polarizations and spin correlations can provide a competitive determination of the Weinberg angle θW and constrain possible anomalous couplings in the neutral electroweak current. We utilize analytic results and Monte Carlo simulations to explore to what extent these goals might be accomplished. Published by the American Physical Society 2024

Simulation of a capillary tube, fibre dual-readout calorimeter in DD4hep

Over the past years the dual-readout method for calorimetry, which exploits complementary information from Scintillation and Cherenkov channels, has emerged as candidate to fulfil the requirements for precision physics at future circular lepton colliders. While the dual-readout approach has been tested experimentally quite extensively, this type of calorimeter has never been used in an experiment at a collider. In recent years dedicated studies in simulation have investigated various detector geometries based on a fibre dual-readout calorimeter. One variation of the geometry, relying on capillary tubes, promises easy assembly with excellent geometrical accuracy at a moderate cost. In these proceedings, we present the status and latest results from a full 4π detector geometry simulation in DD4hep. The simulation is used to estimate the performance of a dual-readout calorimeter for single electromagnetic and hadronic particles. The results for the dual-readout technique show an improvement in energy resolution for both electromagnetic and hadronic showers, with respect to single channel measurements.

Exposing a dual-readout fibre calorimeter to electron beams, in preparation for HiDRa: High-resolution calorimeter for [formula omitted] colliders

Among the proposed accelerators for the post-LHC era are the Future Circular Collider (FCC) and the Circular Electron–Positron Collider (CEPC). Both projects would take advantage of the clean environment and low radiation damage of electron–positron collisions, providing the highest precision studies of electroweak and Higgs physics. The relatively high branching fraction of W, Z and Higgs bosons into hadronic jets makes the precise measurements of these objects an essential aspect on detector development for experiments at future collider facilities. One of the most promising calorimetry techniques for improved hadron energy reconstruction is the dual-readout method, which exploits signals from two different physics processes to correct for the fem of hadron showers, therefore boosting the standalone calorimeter performance. The usage of compact photosensors (e.g. Silicon PhotoMultipliers) for the readout enables a very fine segmentation, opening to particle-flow and advanced neural networks software reconstruction of events. In this contribution, the results of testing a small-scale dual-readout calorimeter prototype, characterised by a mixed PMT and SiPM readout solution, with an electron beam at the CERN SPS facility in the energy range [10, 120] GeV are presented. It follows the description of a larger prototype of the same type, currently under construction in the context of the INFN HiDRa project, that will be large enough to fully contain hadron showers. The design, construction technique and expected performance, as estimated through a Geant4 simulation parameterised on the previous prototype, are presented.

Constraining Asymmetric Dark Matter using colliders and direct detection

We reappraise the viability of asymmetric dark matter (ADM) realized as a Dirac fermion coupling dominantly to the Standard Model fermions. Treating the interactions of such a DM particle with quarks/leptons in an effective-interactions framework, we derive updated constraints using mono-jet searches from the Large Hadron Collider (LHC) and mono-photon searches at the Large Electron-Positron (LEP) collider. We carefully model the detectors used in these experiments, which is found to have significant impact. The constraint of efficient annihilation of the symmetric part of the ADM, as well as other observational constraints are synthesized to produce a global picture. Consistent with previous work, we find that ADM with mass in the range 1–100 GeV is strongly constrained, thus ruling out its best motivated mass range. However, we find that leptophilic ADM remains allowed for ≳ 10 GeV DM, including bounds from colliders, direct detection, and stellar heating. We forecast that the Future Circular Collider for electron-positron collisions (FCC-ee) will improve sensitivity to DM-lepton interactions by almost an order of magnitude.

Forming limit diagram of annealed copper OFE thick sheets for optimized hydroforming of superconducting RF cavities

Coated superconducting radio-frequency (SRF) cavities are planned to be implemented in the Future Circular Collider (FCC) at the European Organization for Nuclear Research (CERN). The interest in industrialized and high-performance processes for fabrication of the corresponding copper substrates has thus risen. Tubular hydroforming is a well-known industrial process, but has not been thoroughly applied for ultra-pure oxygen-free electronic copper (Cu-OFE) thick products. To provide a feasibility analysis for the optimized fabrication process of copper substrate seamless cavities, a Forming Limit Diagram (FLD) of the material of interest was studied. In this paper, the methodology, test results and initial benchmark of the material model is presented, for 4 mm and 2 mm thick sheets.

Right-handed slepton bulk region for dark matter in generalized no-scale F -SU(5) with effective supernatural supersymmetry

We propose generalized no-scale supergravity, the simplest scenario for effective supernatural supersymmetry, naturally solving the supersymmetry electroweak fine-tuning problem and including natural dark matter. A light right-handed slepton bulk region is realized in F-SU(5) and the phenomenological minimal supersymmetric standard model. The bulk may be beyond the LHC reach, although it can be probed at the 1000-day LUX-ZEPLIN, Future Circular Collider at CERN, Circular Electron-Positron Collider, and Hyper-Kamiokande. Published by the American Physical Society 2024

Doubly heavy hadron production in ultraperipheral collision

We study the double heavy baryon ΞQQ′ and tetraquark TQQ production through photon-photon and photon-gluon fusion via ultraperipheral collisions at the LHC and Future Circular Collider (FCC) within the framework of nonrelativistic QCD factorization formalism. Various ion-ion collisions are taken into account, two cc(bb)-diquark configurations ([cc(bb),S31−3¯] and [cc(bb),S10−6]) and four bc-diquark configurations ([bc,S31−3¯], [bc,S31−6], [bc,S10−3¯], and [bc,S10−6]) are considered in the calculation. Numerical results indicate that the [cc,S31−3¯] diquark provides dominant contribution for Ξcc (Tcc) production, and a considerable number of Ξcc (Tcc) can be produced. Because the event topologies for ultraperipheral collision are very clear, the background from various QCD interactions can be suppressed, hence the experimental investigation for Ξcc and Tcc is feasible. The productions for Ξbc/bb are also discussed, leaving only a slight possibility for Ξbc through photon-gluon fusion with ultraperipheral collisions at the FCC. Published by the American Physical Society 2024

Single production of an exotic vectorlike Y quark at future high energy pp colliders

Vectorlike quarks have been predicted in various new physics scenarios beyond the Standard Model. In a simplified modelling of a (B,Y) doublet including a vectorlike quark Y, with charge −43e, there are only two free parameters: the Y coupling κY and mass mY. In the five flavor scheme, we investigate the single production of the Y state decaying into Wb at the Large Hadron Collider (LHC) run-III and High-Luminosity LHC (HL-LHC) operating at s=14 TeV, the possible High-Energy LHC (HE-LHC) with s=27 TeV as well as the Future Circular Collider in hadron-hadron mode (FCC-hh) with s=100 TeV. Through detailed signal-to-background analyses and detector simulations, we assess the exclusion capabilities of the Y state at the different colliders. We find that this can be improved significantly with increasing collision energy, especially at the HE-LHC and FCC-hh, both demonstrating an obvious advantage with respect to the HL-LHC in the case of high mY. Assuming a 10% systematic uncertainty on the background event rate, the exclusion capabilities are summarized as follows: (1) the LHC run-III can exclude the correlated regions of κY∈[0.06,0.5] and mY∈[1500 GeV,3800 GeV] with integrated luminosity L=300 fb−1; (2) the HL-LHC can exclude the correlated regions of κY∈[0.05,0.5] and mY∈[1500 GeV,3970 GeV] with L=3 ab−1; (3) the HE-LHC can exclude the correlated regions of κY∈[0.06,0.5] and mY∈[1500 GeV,6090 GeV] with L=3 ab−1; (4) the FCC-hh can exclude the correlated regions of κY∈[0.08,0.5] and mY∈[1500 GeV,10080 GeV] with L=3 ab−1. Published by the American Physical Society 2024

Testing lepton flavor universality at future Z factories

As one of the hypothetical principles in the Standard Model (SM), lepton flavor universality (LFU) should be tested with a precision as high as possible such that the physics violating this principle can be fully examined. The run of a Z factory at a future e+e− collider, such as the Circular Electron-Positron Collider or Future Circular Collider (electron/positron), provides a great opportunity to perform this task because of the large statistics and high reconstruction efficiencies for b hadrons at the Z pole. In this paper, we present a systematic study on the LFU test in future Z factories. The goal is threefold. First, we study the sensitivities of measuring the LFU-violating observables of b→cτν, i.e., RJ/ψ, RDs, RDs*, and RΛc, where τ decays muonically. For this purpose, we develop the strategies for event reconstruction, based on the track information significantly. Second, we explore the sensitivity robustness against detector performance and its potential improvement with the message of event shape or beyond the b-hadron decays. A picture is drawn on the variation of analysis sensitivities with the detector tracking resolution and soft photon detectability, and the impact of Fox-Wolfram moments is studied on the measurement of relevant flavor events. Finally, we interpret the projected sensitivities in the SM effective field theory, by combining the LFU tests of b→cτν and the measurements of b→sτ+τ− and b→sν¯ν. We show that the limits on the LFU-violating energy scale can be pushed up to ∼O(10) TeV for ≲O(1) Wilson coefficients at Tera-Z. Published by the American Physical Society 2024

Exploring nonstandard Hbb¯ interactions at future electron-proton colliders

In this paper, we use the charged-current Higgs boson production process at future electron-proton colliders, e−p→Hjνe, with the subsequent decay of the Higgs boson into a bb¯ pair, to probe the Standard Model effective field theory with dimension-six operators involving the Higgs boson and the bottom quark. The study is performed for two proposed future high-energy electron-proton colliders, the Large Hadron Electron Collider (LHeC) and the Future Circular Collider (FCC-he) at the center-of-mass energies of 1.3 TeV and 3.46 TeV, respectively. Constraints on the CP-even and CP-odd Hbb¯ couplings are derived by analyzing the simulated signal and background samples. A realistic detector simulation is performed and a multivariate technique using the gradient boosted decision trees algorithm is employed to discriminate the signal from background. Expected limits are obtained at 95% confidence level for the LHeC and FCC-he assuming the integrated luminosities of 1, 2 and 10 ab−1. We find that using 1 ab−1 of data, the CP-even and CP-odd Hbb¯ couplings can be constrained with accuracies of the order of 10−3 and 10−2, respectively, and a significant region of the unprobed parameter space becomes accessible. Published by the American Physical Society 2024

Production of fully-heavy tetraquark states through the double parton scattering mechanism in pp and pA collisions

The production of fully-heavy tetraquark states in proton–proton (pp) and proton–nucleus (pA) collisions at the center-of-mass energies of the Large Hadron Collider (LHC) and at the Future Circular Collider (FCC) is investigated considering that these states are produced through the double parton scattering mechanism. We estimate the cross sections for the T4c,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{4c},$$\\end{document}T4b\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{4b}$$\\end{document} and T2b2c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{2b2c}$$\\end{document} states and present predictions for pp, pCa and pPb collisions considering the rapidity ranges covered by central and forward detectors. We demonstrate that the cross sections for pA collisions are enhanced in comparison to the pp predictions scaled by the atomic number. Moreover, our results indicate that a search of these exotic states is, in principle, feasible in the future runs of the LHC and FCC.

SND@LHC: the scattering and neutrino detector at the LHC

SND@LHC is a compact and stand-alone experiment designed to perform measurements with neutrinos produced at the LHC in the pseudo-rapidity region of 7.2 < η < 8.4. The experiment is located 480 m downstream of the ATLAS interaction point, in the TI18 tunnel. The detector is composed of a hybrid system based on an 830 kg target made of tungsten plates, interleaved with emulsion and electronic trackers, also acting as an electromagnetic calorimeter, and followed by a hadronic calorimeter and a muon identification system. The detector is able to distinguish interactions of all three neutrino flavours, which allows probing the physics of heavy flavour production at the LHC in the very forward region. This region is of particular interest for future circular colliders and for very high energy astrophysical neutrino experiments. The detector is also able to search for the scattering of Feebly Interacting Particles. In its first phase, the detector is ready to operate throughout LHC Run 3 and collect a total of 250 fb-1.

Right-handed slepton bulk regions for dark matter in a generalized minimal supergravity

We study the light right-handed slepton bulk regions for dark matter from the generalized minimal supergravity (GmSUGRA) in the minimal supersymmetric Standard Model. In our comprehensive numerical studies, we show that Rϕ˜≳10% is a conservative criterion to formulate bulk region, where Rϕ˜≡(mϕ˜−mχ˜10)/mχ˜10. For right-handed stau as the next-to-the-lightest supersymmetric particle (NLSP), we find a large viable parameter space, consistent with the current LHC constraints, Planck2018 dark matter relic density bounds, and direct bounds on neutralino-nucleons scattering cross section that naturally supports the right-handed stau bulk regions for dark matter. In particular, the upper bounds on the masses of the lightest supersymmetric particle neutralino and right-handed stau are about 120.4 and 138 GeV, respectively. This bulk region may be beyond the current LHC reach and could be probed at LUX-ZEPLIN, a next-generation dark matter direct-detection experiment, the Future Circular Collider at CERN, and the Circular Electron Positron Collider. However, the scenario with the right-handed selectron as the NLSP is excluded by the LHC supersymmetry searches. Published by the American Physical Society 2024

Quantum collider probes of the fermionic Higgs portal

We explore the sensitivity of future hadron colliders to constrain the fermionic Higgs portal, with a focus on scenarios where the new fermions cannot be directly observed in exotic Higgs decays. This portal emerges in various models including twin-Higgs scenarios and dark matter models, posing significant challenges for collider tests. Working in an effective field theory (EFT), we determine the reach of the high-luminosity option of the Large Hadron Collider (HL-LHC), the high-energy upgrade of the LHC (HE-LHC) and a proposed Future Circular Collider (FCC) in probing the fermionic Higgs portal through off-shell and double-Higgs production. Notably, we find that quantum-enhanced indirect probes offer a better sensitivity than other direct Higgs measurements. We argue that this finding is valid in a wide class of ultraviolet realisations of the EFT. Our study presents a roadmap of a multifaceted search strategy for exploring the fermionic Higgs portal at forthcoming hadron machines.

Next-to-leading-order relativistic and QCD corrections to prompt pair photoproduction at future colliders* *Supported in part by the German Research Foundation DFG through Research Unit FOR 2926 "Next Generation Perturbative QCD for Hadron Structure: Preparing for the Electron-Ion Collider" (409651613). The work of X.B.J. was supported in part by National Natural Science Foundation of China (12061131006). The work of R.L. was

Within the framework of nonrelativistic-QCD factorization, we calculate both the next-to-leading-order relativistic and QCD corrections to prompt pair production, with feed-down from mesons, via photon-photon collisions at future colliders, including the Future Circular Lepton Collider (FCC-ee), the Circular Electron Positron Collider (CEPC), and the Compact Linear Collider (CLIC). We present total cross sections and distributions in single transverse momentum and rapidity, as well as in pair invariant mass. The relativistic and QCD corrections both turn out to be large and negative. However, the production rates are large enough for useful experimental studies.

Improved particle-flow event reconstruction with scalable neural networks for current and future particle detectors

Efficient and accurate algorithms are necessary to reconstruct particles in the highly granular detectors anticipated at the High-Luminosity Large Hadron Collider and the Future Circular Collider. We study scalable machine learning models for event reconstruction in electron-positron collisions based on a full detector simulation. Particle-flow reconstruction can be formulated as a supervised learning task using tracks and calorimeter clusters. We compare a graph neural network and kernel-based transformer and demonstrate that we can avoid quadratic operations while achieving realistic reconstruction. We show that hyperparameter tuning significantly improves the performance of the models. The best graph neural network model shows improvement in the jet transverse momentum resolution by up to 50% compared to the rule-based algorithm. The resulting model is portable across Nvidia, AMD and Habana hardware. Accurate and fast machine-learning based reconstruction can significantly improve future measurements at colliders.