The future 100 TeV FCC-hh hadron collider will give access to rare but clean final states which are out of reach of the HL-LHC. One such process is the $Zh$ production channel in the $(ν\barν / \ell^{+}\ell^{-})γγ$ final states. We study the sensitivity of this channel to the $\mathcal{O}_{φq}^{(1)}$, $\mathcal{O}_{φq}^{(3)}$, $\mathcal{O}_{φu}$, and $\mathcal{O}_{φd}$ SMEFT operators, which parametrize deviations of the $W$ and $Z$ couplings to quarks, or, equivalently, anomalous trilinear gauge couplings (aTGC). While our analysis shows that good sensitivity is only achievable for $\mathcal{O}_{φq}^{(3)}$, we demonstrate that binning in the $Zh$ rapidity has the potential to improve the reach on $\mathcal{O}_{φq}^{(1)}$. Our estimated bounds are one order of magnitude better than projections at HL-LHC and is better than global fits at future lepton colliders. The sensitivity to $\mathcal{O}_{φq}^{(3)}$ is competitive with other channels that could probe the same operator at FCC-hh. Therefore, combining the different diboson channels sizeably improves the bound on $\mathcal{O}_{φq}^{(3)}$, reaching a precision of $|δg_{1z}| \lesssim 2 \times 10^{-4}$ on the deviations in the $ZWW$ interactions.
The increase in luminosity and center of mass energy at the FCC-hh will open up new clean channels where BSM contributions are enhanced at high energy. In this paper we study one such channel, $Wh \to \ellνγγ$. We estimate the sensitivity to the $\mathcal{O}_{φq}^{(3)}$, $\mathcal{O}_{φ{W}}$, and $\mathcal{O}_{φ\widetilde {W}}$ SMEFT operators. We find that this channel will be competitive with fully leptonic $WZ$ production in setting bounds on $\mathcal{O}_{φq}^{(3)}$. We also find that the double differential distribution in the $p_T^h$ and the leptonic azimuthal angle can be exploited to e…
The production of axionlike particles (ALP) in ultraperipheral $PbPb$ collisions (UPHIC) is investigated considering the energies of the next run of the Large Hadron Collider (LHC) and of the future High Energy -- LHC (HE -- LHC) and Future Circular Collider (FCC). Assuming four different combinations for the ALP mass and coupling and the typical exclusivity cuts for central and forward detectors, we estimate the cross section and invariant mass, rapidity, transverse momentum and {acoplanarity} distributions associated to the diphoton final state produced in the $γγ\rightarrow a \rightarrow γγ…
We study the CP-conserving and CP-violating dimension-six operators of Higgs-gauge boson couplings via $pp\toγγ$+n-jet signal process in a strongly interacting light Higgs based effective field theory framework at the center of mass energy of 100 TeV. In order to perform a simulation which includes realistic detector effects, the signal events in the existence of $\bar{c}_γ $, $\tilde{c}_γ$, $\bar{c}_{g} $ and $\tilde{c}_{g}$ Wilson coefficients and the relevant SM background events are generated in MadGraph, then passed through Pythia 8 for parton showering and finally run Delphes with FCC-hh…
Precision measurements of the Drell-Yan (DY) cross section at the LHC constrain new physics scenarios that involve new states with electroweak (EW) charges. We analyze these constraints and apply them to models that can address the LHC diphoton excess at 750 GeV. We confront these findings with LEP EW precision tests and show that DY provides stronger constraints than the LEP data. While 8 TeV data can already probe some parts of the interesting region of parameter space, LHC14 results are expected to cover a substantial part of the relevant terrain. We derive the bounds from the existing data…
Elastic light-by-light scattering, $γγ\toγγ$, can be measured in electromagnetic interactions of lead (Pb) ions at the Large Hadron Collider (LHC) and Future Circular Collider (FCC), using the large (quasi)real photon fluxes available in ultraperipheral collisions. The $γγ\toγγ$ cross sections for diphoton masses m$_{γγ}>$ 5 GeV in pp, pPb, and PbPb collisions at LHC ($\sqrt{\rm s_{_{NN}}}$ = 5.5, 8.8, 14 TeV) and FCC ($\sqrt{\rm s_{_{NN}}}$ = 39, 63, 100 TeV) center-of-mass energies are presented. The measurement has controllable backgrounds in PbPb collisions, and one expects about 70 and 25…
We interpret the potential observation of the 750 GeV di-photon resonance at the LHC in models, in which an $SU(2)$ isospin-singlet scalar boson mixes with the Standard Model (SM) Higgs boson through an angle $α$. Allowing the singlet scalar boson to have renormalizable couplings to vector-like leptons and quarks and introducing sizable decay width of the 750 GeV di-photon resonance into non-SM particles such as dark matters, we can explain the large production cross section $σ(H_2) \times B(H_2 \to γγ)$ as well as the apparent large total width of the boson without conflicts from the results …
The design study of the Future Circular Colliders (FCC) in a 100-km ring in the Geneva area has started at CERN at the beginning of 2014, as an option for post-LHC particle accelerators. The study has an emphasis on proton-proton and electron-positron high-energy frontier machines. In the current plans, the first step of the FCC physics programme would exploit a high-luminosity e+e- collider called FCC-ee, with centre-of-mass energies ranging from below the Z pole to the t-tbar threshold and beyond, followed by 100\,TeV proton-proton collisions as ultimate goal. When combined, these two steps …
Due to the high anticipated experimental precision at the Future Circular Collider FCC-ee (or other proposed $e^+e^-$ colliders, such as ILC, CLIC, or CEPC) for electroweak and Higgs-boson precision measurements, theoretical uncertainties may have, if unattended, an important impact on the interpretation of these measurements within the Standard Model (SM), and thus on constraints on new physics. Current theory uncertainties, which would dominate the total uncertainty, need to be strongly reduced through future advances in the calculation of multi-loop radiative corrections together with impro…
The recently reported diphoton excess at the LHC may imply the existence of a new resonance with a mass of about 750 GeV which couples to photons via loops of new charged particles. In this letter, we study the possibility to test such models at the ILC, paying attention to the new charged particles responsible for the diphoton decay of the resonance. We show that they affect the scattering processes $e^+e^- \to f\bar{f}$ (with $f$ denoting Standard Model fermions) at the ILC, which makes it possible to indirectly probe the new charged particles even if they are out of the kinematical reach. W…
The proposed electron-proton collider experiments LHeC and FCC-eh at CERN are the highest resolution microscopes that can be realised in the present century and they would represent a really unique research facility. We exploit simulated neutral-current and charged-current deep-inelastic scattering data of the LHeC and the FCC-eh and examine their sensitivity for precision physics in the Electroweak sector of the Standard Model (SM), like the effective weak mixing angle $\sin^2θ_{\textrm{W},\ell}^\textrm{eff}$, or the light-quark weak-neutral-current couplings. Unique measurements are further …
The prospects for electroweak precision measurements at the Future Circular Collider with electron-positron beams (FCC-ee) are discussed. The Z mass and width, as well as the value of the electroweak mixing angle, can be measured with very high precision at the Z pole thanks to an instantaneous luminosity five to six order of magnitudes larger than LEP. At centre-of-mass energies around 160 GeV, corresponding to the WW production threshold, the W mass can be determined very precisely with high-statistics cross section measurements at several energy points. Similarly, a very precise determinati…
High precision experimental measurements of the properties of the Higgs boson at $\sim$ 125 GeV as well as electroweak precision observables such as the W -boson mass or the effective weak leptonic mixing angle are expected at future $e^+e^-$ colliders such as the FCC-ee. This high anticipated precision has to be matched with theory predictions for the measured quantities at the same level of accuracy. We briefly summarize the status of these predictions within the Standard Model (SM) and of the tools that are used for their determination. We outline how the theory predictions will have to be …
To exploit properly the precision physics program at the FCC-ee, the theoretical precision tag on the respective luminosity will need to be improved from the 0.054$\%$ (0.061$\%$) results at LEP to 0.01$\%$, where the former (latter) LEP result has (does not have) the pairs correction. We present an overview of the roads one may take to reach the required 0.01$\%$ precision tag at the FCC-ee and we discuss possible synergistic effects of the walk along these roads for other FCC precision theory requirements.
We compute the one-loop corrections to $σ(e^+ e^- \to Z h)$ arising from representative extended Standard Model scalar sector scenarios. According to the new scalar $\mathrm{SU(2)_L}$ representations, we consider the inert doublet, real and complex triplet, quintuplet, and septuplet models. With the sub-percent level precision expected for prospective future $e+e-$ collider measurements of $σ(e^+ e^- \to Z h)$, studies of the Higgsstrahlung process will probe extended scalar sector particle spectrum and interactions in a manner complementary to direct searches at the Large Hadron Collider and …
The Future Circular Collider (FCC) is a post-LHC project aiming at direct and indirect searches for physics beyond the SM in a new 100 km tunnel at CERN. In addition, the FCC-ee offers unique possibilities for high-precision studies of the strong interaction in the clean environment provided by $e^{+}e^{-}$ collisions, thanks to its broad span of center-of-mass energies ranging from the Z pole to the top-pair threshold, and its huge integrated luminosities yielding $10^{12}$ and $10^8$ jets from Z and W bosons decays, respectively, as well as $10^5$ pure gluon jets from Higgs boson decays. In …
The future FCC-ee collider is designed to deliver $\mathrm{e^+e^-}$ collisions to study with ultimate precision the Z, W, and Higgs bosons, and the top quark. In a high-statistics scan around the Z pole, $1.3\times 10^{11}$ events $\mathrm{Z}\toττ$ will be produced, the largest sample of $ττ$ events foreseen at any lepton collider. With their large boost, $τ$ leptons from Z decays are particularly well suited for precision measurements. The focus of this report is on tests of lepton universality from precision measurement of $\boldsymbolτ$ properties and on tests of charged lepton flavour viol…
Precision Higgs Boson Probe of Type-II Seesaw Models
Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；Washington University, Saint Louis（华盛顿大学圣路易斯分校）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）
When the measurements from the FCC-ee become available, an improved determination of the standard-model "input" parameters will be needed to fully exploit the new precision data towards either constraining or fitting the parameters of beyond-the-standard-model theories. Among these input parameters is the electromagnetic coupling constant estimated at the Z mass scale, alpha_QED(mZ). The measurement of the muon forward-backward asymmetry at the FCC-ee, just below and just above the Z pole, can be used to make a direct determination of alpha_QED(mZ) with an accuracy deemed adequate for an optim…
The renormalizable coloron model, which has previously been shown in the literature to be consistent with a wide array of theoretical and precision electroweak constraints, includes a pair of spinless bosons (one scalar, one pseudoscalar). We show that either of them, or both together if they are degenerate, could be responsible for the diphoton resonance signal for which both CMS and ATLAS have seen evidence. Because either of these bosons would be produced and decay through loops of spectator fermions, the absence of signals in dijet, $t\bar{t}$, and electroweak boson pair channels is not a …
We present pathways to the required theoretical precision for the luminosity targeted by the FCC-ee precision studies. We put the discussion in context by reviewing briefly the situation at the time of LEP. We then present the current status and routes to the desired 0.01\% targeted by the FCC-ee (as well as by the ILC).
Durham University（杜伦大学）；Institute for Particle Physics Phenomenology（粒子物理现象学研究所）
In this thesis, we present recent advances at the precision frontier of higher-order quantum chromodynamics (QCD) calculations. We consider massless two-loop five-point amplitudes, with a particular focus on diphoton-plus-jet production through gluon fusion. We build a library of infrared functions up to at most next-to-next-to-leading order (NNLO) in QCD, which can be used to validate amplitudes and construct counterterms in subtraction schemes at NNLO. We review progress in the novel use of machine learning technology to optimise the evaluation of amplitudes in hadron collider simulations. W…
Because of a luminosity of up to five orders of magnitude larger than at LEP, electroweak precision measurements at the FCC-ee -- the Future Circular Collider with electron-positron beams -- would provide improvements by orders of magnitude over the present status and constitute a broad search for the existence of new, weakly interacting particles up to very high energy scales. The FCC-ee will address centre-of-mass energies ranging from below the Z pole to the $\mathrm{t\bar{t}}$ threshold and above. At energies around the Z pole, the Z-boson mass and width can be measured to better than 100 …
IR-improvement based on amplitude-level resummation allows one to control unintegrable results in quantum field theory with arbitrary precision in principle. We illustrate such resummation in specific examples in precision LHC and FCC physics and in quantum gravity.
The Future Circular Collider (FCC) is a post-LHC project aiming at searches for physics beyond the SM in a new 80--100~km tunnel at CERN. Running in its first phase as a very-high-luminosity electron-positron collider (FCC-ee), it will provide unique possibilities for indirect searches of new phenomena through high-precision tests of the SM. In addition, by collecting tens of ab$^{-1}$ integrated luminosity in the range of center-of-mass energies $\sqrt{s}$~=90--350~GeV, the FCC-ee also offers unique physics opportunities for precise measurements of QCD phenomena and of photon-photon collision…
We present an overview of the use of IR-improvement of unintegrable singularities in the infrared regime via amplitude-based resummation in $\mathrm{QED} \times \mathrm{QCD}$ $\subset$ $\mathrm{SU}(2)_L \times \mathrm{U}_1 \times \mathrm{SU}(3)^c$. We work in the context of precision LHC/FCC physics. While illustrating such IR-improvement in specific examples, we discuss new results and new issues.
The current status of the theoretical precision for the Bhabha luminometry is critically reviewed and pathways are outlined to the requirement targeted by the FCC-ee precision studies. Various components of the pertinent error budget are discussed in detail -- starting from the context of the LEP experiments, through their current updates, up to prospects of their improvements for the sake of the FCC-ee. It is argued that with an appropriate upgrade of the Monte Carlo event generator BHLUMI and/or other similar MC programs calculating QED effects in the low angle Bhabha process, the total theo…
The hints for a new resonance at 750 GeV from ATLAS and CMS have triggered a significant amount of attention. Since the simplest extensions of the standard model cannot accommodate the observation, many alternatives have been considered to explain the excess. Here we focus on several proposed renormalisable weakly-coupled models and revisit results given in the literature. We point out that physically important subtleties are often missed or neglected. To facilitate the study of the excess we have created a collection of 40 model files, selected from recent literature, for the Mathematica pack…
The expected experimental precision of the rates and asymmetries in the Future Circular Collider with electron positron beams (FCC-ee) in the centre of the mass energy range 88-365GeV considered for construction in CERN, will be better by a factor 5-200. This will be thanks to very high luminosity, factor up to $10^5$ higher than in the past LEP experiments. This poses the extraordinary challenge of improving the precision of the Standard Model predictions by a comparable factor. In particular the perturbative calculations of the trivial QED effects, which have to be removed from the experimen…
The Future Circular Collider (FCC) at CERN, a proposed 100-km circular facility with several colliders in succession, culminates with a 100 TeV proton-proton collider. It offers a vast new domain of exploration in particle physics, with orders of magnitude advances in terms of Precision, Sensitivity and Energy. The implementation plan foresees, as a first step, an Electroweak Factory electron-positron collider. This high luminosity facility, operating between 90 and 365 GeV centre-of-mass energy, will study the heavy particles of the Standard Model, Z, W, Higgs, and top with unprecedented accu…
The future lepton colliders proposed for the High Energy and Precision Frontier set stringent demands on theory. The most ambitious, broad-reaching and demanding project is the FCC-ee. We consider here the present status and requirements on precision calculations, possible ways forward and novel methods, to match the experimental accuracies expected at the FCC-ee. We conclude that the challenge can be tackled by a distributed collaborative effort in academic institutions around the world, provided sufficient support, which is estimated to about 500 man-years over the next 20 years.
In this note, I will review the opportunities offered by the hint of a new resonance observed at LHC for future e+e- TeV linear collider (LC) projects. This discussion is mainly influenced by two specific scenarios of physics which assume either a (pseudo-)scalar or a tensor resonance, but these estimates can be used in most scenarios. I envisage either a photon collider, which has a guaranteed signal with the LHC observation, or a standard e+e- collider, more straightforward to implement. After a detailed study of the heavy graviton scenario, I conclude that at a TeV LC, high accuracy measure…
We present a new approach to the realization of hard fixed-order corrections in predictions for the processes probed in high energy colliding hadron beam devices, with some emphasis on the LHC and the future FCC devices. We show that the usual unphysical divergence of such corrections as one approaches the soft limit is removed in our approach, so that we would render the standard results to be closer to the observed exclusive distributions. We use the single Z/γ* production and decay to lepton pairs as our prototypical example, but we stress that the approach has general applicability. In thi…
This document provides a writeup of all contributions to the workshop on "High precision measurements of $α_s$: From LHC to FCC-ee" held at CERN, Oct. 12--13, 2015. The workshop explored in depth the latest developments on the determination of the QCD coupling $α_s$ from 15 methods where high precision measurements are (or will be) available. Those include low-energy observables: (i) lattice QCD, (ii) pion decay factor, (iii) quarkonia and (iv) $τ$ decays, (v) soft parton-to-hadron fragmentation functions, as well as high-energy observables: (vi) global fits of parton distribution functions, (…
With an eye toward the usual unphysical divergence of hard fixed-order corrections in predictions for the processes probed in high energy colliding hadron beam devices as one approaches the soft limit, we present a new approach to the realization of such corrections, with some emphasis on the LHC and the future FCC devices. We show that the respective divergence is removed in our approach. This means that we would render the standard results to be closer to the observed exclusive distributions. While we stress that the approach has general applicability, we use the single Z and virtual gamma p…
One may use amplitude-based resummation in QED $\otimes$ QCD to achieve IR-improvement of unintegrable singularities in the infrared regime to arbitrary precision in principle. We illustrate such improvement in specific examples in precision LHC/FCC physics.
Flavor-resolved four-fermion probes at the FCC-ee $Z$ pole
Institute for Advanced Research, Nagoya University（名古屋大学高等研究院）；Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University（名古屋大学小林-益川粒子宇宙起源研究所）
For both the FCC-ee and the ILC, to exploit properly the respective precision physics program, the theoretical precision tag on the respective luminosity will need to be improved from the analogs of the $ 0.054 \% (0.061\%)$ results at LEP at $M_Z$, where the former (latter) LEP result has (does not have) the pairs correction. At the FCC-ee at $M_Z$ one needs improvement to $0.01\%$, for example. We present an overview of the roads one may take to reach the required $0.01\%$ precision tag at the FCC-ee and of what the corresponding precision expectations would be for the FCC-ee$_{350}$, ILC$_{…
The top partner as a hallmark of the Littlest Higgs model with $T$-parity (LHT model) has been extensively searched for during the Large Hadron Collider (LHC) Run-1. With the increasing mass limits on the top partner, the single production of the top partner will be dominant over the pair production. Under the constraints from the Higgs data, the electroweak precision observables and $R_b$, we find that the mass of $T$-even top partner ($T_+$) has to be heavier than 730 GeV. Then, we investigate the observability of the single $T$-even top partner production through the process $pp \to T_+ j$ …
The FCC-ee offers powerful opportunities to determine the Higgs boson parameters, exploiting over $10^6$ ${\rm e^+e^- \to ZH}$ events and almost $10^5$ ${\rm WW \to H}$ events at centre-of-mass energies around 240 and 365 GeV. This essay spotlights the important measurements of the ZH production cross section and of the Higgs boson mass. The measurement of the total ZH cross section is an essential input to the absolute determination of the HZZ coupling -- a "standard candle" that can be used by all other measurements, including those made at hadron colliders -- at the per-mil level. A combina…
Circular colliders have the advantage of delivering collisions to multiple interaction points, which allow different detector designs to be studied and optimized - up to four for FCC-ee. On the one hand, the detectors must satisfy the constraints imposed by the invasive interaction region layout. On the other hand, the performance of heavy-flavour tagging, of particle identification, of tracking and particle-flow reconstruction, and of lepton, jet, missing energy and angular resolution, need to match the physics programme and the exquisite statistical precision offered by FCC-ee. During the FC…
The future of high-precision electroweak physics lies in e+e- collider measurements of properties of the Z boson, the W boson, the Higgs boson, and the top quark. We estimate the expected performance of three possible future colliders: the ILC, FCC-ee (formerly known as TLEP), and CEPC. In particular, we present the first estimates of the possible reach of CEPC, China's proposed Circular Electron-Positron Collider, for the oblique parameters S and T and for seven-parameter fits of Higgs couplings. These results allow the physics potential for CEPC to be compared with that of the ILC and FCC-ee…
Testing the idea of naturalness is and will continue to be one of the most important goals of high energy physics experiments. It will play a central role in the physics program of future colliders. In this paper, we present projections of the reach of natural SUSY at future lepton colliders: CEPC, FCC-ee and ILC. We focus on the observables which give the strongest reach, the electroweak precision observables (for left-handed stops), and Higgs to gluon and photon decay rates (for both left- and right-handed stops). There is a "blind spot" when the stop mixing parameter Xt is approximately equ…
We explore the indirect sensitivities to decoupled new physics of prospective precision electroweak measurements, triple-gauge-coupling measurements and Higgs physics at future $e^+e^-$ colliders, with emphasis on the ILC250 and FCC-ee. The Standard Model effective field theory (SM EFT) is adopted as a model-independent approach for relating experimental precision projections to the scale of new physics, and we present prospective constraints on the Wilson coefficients of dimension-6 operators. We find that in a marginalised fit ILC250 EWPT measurements may be sensitive to new physics scales $…
The physics program accessible in $e^+e^-$ collisions at the Future Circular Collider (FCC-ee) is summarized. The FCC-ee aims at collecting multi-ab$^{-1}$ integrated luminosities in $e^+e^-$ at $\sqrt{s}$ = 90, 160, 240, and 350 GeV, yielding 10$^{12}$ Z bosons, 10$^{8}$ W$^+$W$^-$ pairs, 10$^{6}$ Higgs bosons and $4\cdot 10^{5}$ top-quark pairs per year. Such huge data samples combined with a $\cal{O}(100 \rm keV)$ c.m. energy uncertainty will allow for Standard Model measurements with unparalleled precision and searches for new physics in regions not probed so far. The FCC-ee will be able t…
The FCC-ee physics program will deliver two complementary top-notch precision determinations of the W boson mass, and width. The first and main measurement relies on the rapid rise of the W-pair production cross section near its kinematic threshold. This method is extremely simple and clean, involving only the selection and counting of events, in all different decay channels. An optimal threshold-scan strategy with a total integrated luminosity of $12\,{\rm ab}^{-1}$ shared on energy points between 157 and 163 GeV will provide a statistical uncertainty on the W mass of 0.5 MeV and on the W wid…
Precision measurements of diphoton distributions at the LHC display some tension with theory predictions, obtained at next-to-next-to-leading order (NNLO) in QCD. We revisit the theoretical uncertainties arising from the approximation of the experimental photon isolation by smooth-cone isolation, and from the choice of functional form for the renormalisation and factorisation scales. We find that the resulting variations are substantial overall, and enhanced in certain regions. We discuss the infrared sensitivity at the cone boundaries in cone-based isolation in related distributions. Finally,…
Now that the mass of the Higgs boson is known, circular electron positron colliders, able to measure the properties of these particles with high accuracy, are receiving considerable attention. Design studies have been launched (i) at CERN with the Future Circular Colliders (FCC), of which an e+e- collider is a potential first step (FCC-ee, formerly caller TLEP) and (ii) in China with the Circular Electron Positron Collider (CEPC). Hosted in a tunnel of at least 50 km (CEPC) or 80-100 km (FCC), both projects can deliver very high luminosity from the Z peak to HZ threshold (CEPC) and even to the…
The next-generation lepton colliders, such as CEPC, FCC-ee, and ILC will make precision measurement of the Higgs boson properties. We first extract the Higgs coupling precision from Higgs observables at CEPC to illustrate the potential of future lepton colliders. Depending on the related event rates, the precision can reach percentage level for most couplings. Then, we try to estimate the new physics scales that can be indirectly probed with Higgs and electroweak precision observables. The Higgs observables, together with the existing electroweak precision observables, can probe new physics up…
