We present a tool to compute the sensitivity of the Future Circular Electron-Positron Collider (FCC-ee) to the interactions of new, heavy particles via publicly available extensions to the smelli and flavio computer programs. We parametrize new particles’ effects without any flavor assumptions and take into account the projected experimental and correlated theoretical uncertainties of various electroweak and Higgs observables at the proposed collider. We illustrate a use of the tool by estimating the sensitivity of the FCC-ee to a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> model with flavor-specific couplings, which explains anomalies inferred from present-day measurements and Standard Model predictions of observables that involve the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi><mo stretchy="false">→</mo><mi>s</mi><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup></math> transition.

United Kingdom

Ben Allanach

Eetu Loisa

Computation of FCC-ee sensitivity to heavy new physics with interactions of any flavor structure

We investigate how extensions of the Standard Model (SM) involving heavy neutral leptons (HNLs) can be probed at FCC-ee, the proposed high-energy circular $\textit{e}$ $\textit{e}$ collider. Using the effective field theory (EFT) approach, we determine the impact of new interactions on the production and decay of HNLs at FCC-ee. In particular, we consider $\textit{d}$ ≤ 7 $\textit{ν}$SMEFT operators which induce vector, scalar and tensor four-fermion and effective charged- and neutral-current interactions of HNLs, that may also mix with the active neutrinos of the SM. We consider sensitivities to the active-sterile mixing and EFT Wilson coefficients from monophoton searches and displaced vertex decay signatures. In both analyses, we consider the scenarios where HNLs are Majorana or Dirac fermions. We translate the upper bounds on the Wilson coefficients to lower limits on the scale of new physics.

Slovenia

Italy

Patrick Bolton

Frank Deppisch

Austria

Suchita Kulkarni

Chayan Majumdar

Hungary

Wenna Pei

Constraining the SMEFT extended with sterile neutrinos at FCC-ee

The sensitivity of the CERN FCC-ee collider to the production of heavy neutral leptons (HNL) is investigated. The study focuses on a simplified model with a single low-mass HNL mixing with a muon, and addresses the fully leptonic and semileptonic decay modes of the HNL. Complete Monte Carlo analyses of signal and background based on a parametrised detector simulation are performed for the FCC-ee run at the $\textit{Z}$ pole, resulting in an estimate of the intervals of the mixing parameter for which the FCC-ee will have a 95% CL sensitivity as a function of the HNL mass.

L. Bellagamba

G. Polesello

N. Valle

Searches for heavy neutral leptons at FCC-ee in final states including a muon

The rare semi-leptonic decays $$B\rightarrow K^*\ell ^+\ell ^-$$ , with $$\ell =e, \mu $$ , are highly sensitive to new physics (NP) due to their suppression in the Standard Model (SM). Current LHCb measurements in the muon channel exhibit a significant tension with state-of-the-art SM theory predictions. The proposed tera-$\textit{Z}$ run at FCC-ee provides a unique opportunity to untangle the origin of this tension by producing a very large sample of $\textit{B}$-mesons in a clean $$e^+e^-$$ environment. We explore the expected precision of $$B\rightarrow K^*\ell ^+\ell ^-$$ ( $$\ell =e, \mu $$ ) measurements at FCC-ee, complementing existing studies with $$\tau ^+\tau ^-$$ in the final state, and compare with HL-LHC projections. For the case of muons in the final state, we show that HL-LHC and FCC-ee are expected to deliver a similar number of events, while the latter performs much better in the case of final state electrons. Regardless of the lepton flavour, we expect the FCC-ee environment to be much cleaner than at HL-LHC, with subleading systematics. We also find that a significant reduction in theory uncertainties on the SM predictions is required to capitalize on the advantage going from HL-LHC to FCC-ee. We demonstrate the power of such measurements at FCC-ee to extract information on the long-distance contribution to these decays, and to reveal evidence for new physics even if no deviations are seen in electroweak precision tests.

Switzerland

Marzia Bordone

Claudia Cornella

Joe Davighi

Precision tests in $$\varvec{b\rightarrow s\ell ^+\ell ^-}$$ ( $$\varvec{\ell =e,\mu }$$ ) at FCC-ee

This paper presents a novel tagging technique to measure the beauty-quark partial decay-width ratio $$R_b$$ and its forward–backward asymmetry $$A_{\textrm{FB}}^b$$ at the FCC-ee, using $$\mathcal {O}(10^{12})$$ $\textit{Z}$-boson decays. The method is based on the exclusive reconstruction of a selected list of $\textit{b}$-hadron decay modes in $$Z\rightarrow b\bar{b}$$ events at the $\textit{Z}$ pole, which can provide the flavour and possibly the charge of the hemisphere. This approach effectively eliminates the contamination from light-quark physics events and reduces the leading systematic uncertainties arising from background contamination, tagging-efficiency correlations, and gluon-radiation corrections by exploiting the geometric and kinematic properties of beauty hadrons. This results in a total relative uncertainty of the order of 0.01 % for both observables. Furthermore, this precision allows to obtain a commensurate precision on the weak mixing angle $$\sin ^2(\theta _\text {W}^{\text {eff}})$$ compared to the muon forward–backward asymmetry on the order of 0.002 %.

Germany

France

Lars Röhrig

Kevin Kröninger

Romain Madar

Stéphane Monteil

Fabrizio Palla

Emmanuel Perez

Measuring $$A_\textrm{FB}^b$$ and $$R_b$$ with exclusive $\textit{b}$-hadron decays at the FCC-ee

We present a search for new scalar bosons predicted by the Inert Doublet Model at an $$e^+e^-$$ machine with centre-of-mass energies $$\sqrt{s} $$ of 240 and 365 $$\text {G}\text {eV}$$ . Within this model, four additional scalar bosons ( $$H,\, A,\, H^+$$ and $$H^-$$ ) are predicted. Due to an additional symmetry, the lightest new scalar, here chosen to be $\textit{H}$, is stable and provides an adequate dark matter candidate. The search for pair production of the new scalars is investigated in final states with two electrons or two muons, in the context of the future circular collider proposal, FCC-ee. Building on previous studies in the context of the CLIC proposal, this analysis extends the search to detector-level objects, using a parametric neural network to enhance the signal contributions over the Standard Model backgrounds, and sets projected exclusion and discovery contours in the $$M_A-M_H$$ vs. $$M_H$$ plane. With a total integrated luminosity of 10.8 (2.7) $$\,\hbox {ab}^{-1}$$ for $$\sqrt{s} =$$ 240 (365) $$\text {G}\text {eV}$$ , the discovery reach for the model goes up to $$M_H$$ $$= 108\,(157)\,\text {G}\text {eV}$$ for $$M_A-M_H$$ $$=15$$ $$\text {G}\text {eV}$$ at $$\sqrt{s} =$$ 240 (365) $$\text {G}\text {eV}$$ . For exclusion, almost the entire phase-space available in the $$M_A-M_H$$ vs. $$M_H$$ plane is expected to be ruled out at 95% CL, reaching up to $$M_H$$ $$=110\,(165)$$ $$\text {G}\text {eV}$$ .

Anubha Bal

Edward Curtis

Anne-Marie Magnan

Benedikt Maier

Croatia

Tania Robens

Nicholas Wardle

Search for additional scalar bosons within the Inert Doublet Model in a final state with two leptons at the FCC-ee

We present predictions for the DIS 1-jettiness event shape $$ {\tau}_1^b $$ , or DIS thrust, using the framework of Soft Collinear Effective Theory (SCET) for factorization, resummation of large logarithms, and rigorous treatment of nonperturbative power corrections, matched to fixed-order QCD away from the resummation region. Our predictions reach next-to-next-to-next-to-leading-logarithmic (N LL) accuracy in resummed perturbation theory, matched to $$ \mathcal{O} $$ ( $$ {\alpha}_s^2 $$ ) fixed-order QCD calculations obtained using the program NLOJet++. We include a rigorous treatment of hadronization corrections, which are universal across different event shapes and kinematic variables $\textit{x}$ and $\textit{Q}$ at leading power, and supplement them with a systematic scheme to remove $$ \mathcal{O} $$ (Λ ) renormalon ambiguities in their definition. The framework of SCET allows us to connect smoothly the nonperturbative, resummation, and fixed-order regions, whose relative importance varies with $\textit{x}$ and $\textit{Q}$, and to rigorously estimate theoretical uncertainties, across a broad range of $\textit{x}$ and $\textit{Q}$ covering existing experimental results from HERA as well as expected new measurements from the upcoming Electron- Ion-Collider (EIC). Our predictions will serve as an important benchmark for the EIC program, enabling the precise determination of the QCD strong coupling $\textit{α}$ and the universal nonperturbative first moment parameter Ω .

United States

June-Haak Ee

South Korea

China

Daekyoung Kang

Christopher Lee

Iain Stewart

Precision DIS thrust predictions for HERA and EIC

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

Jaco ter Hoeve

Spain

Luca Mantani

Netherlands

Juan Rojo

Alejo N. Rossia

Eleni Vryonidou

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

The decay of the $\textit{Z}$ boson into axion-like particles (ALP) at the $\textit{Z}$-pole run of the proposed CERN FCC-ee collider is investigated. We perform a detailed study of final states with three photons or with a single photon and missing energy, yielding an evaluation of the accessible values of the ALP coupling to the photon for ALP masses between 0.1 and 85 GeV. Special attention is paid to the experimental implications of detecting the three-photon signature for the ALP mass region below 10 GeV. The FCC-ee run will be able to detect the ALP for couplings down to a few 10 TeV over the considered mass range in an effective model where the ALP only couples to the U(1) boson of the Standard Model.

Sensitivity of the FCC-ee to decay of an axion-like particle into two photons

This paper investigates the search for long-lived dark scalars from exotic Higgs boson decays at the Future Circular Collider in its $\textit{e}$ $\textit{e}$ stage, FCC-ee, considering an integrated luminosity of 10$\textit{.}$8 ab collected during the ZH run at a center-of-mass energy $$ \sqrt{s} $$ = 240 GeV. The work considers $\textit{Zh}$ events where the $\textit{Z}$ boson decays leptonically and the Higgs boson $\textit{h}$ decays into two long-lived dark scalars $\textit{s}$ which further decay into bottom anti-bottom quark pairs. The analysis is performed using a parametrized simulation of the IDEA detector concept and targets dark scalar decays in the tracking volume, resulting in multiple displaced vertices in the final state. The sensitivity towards long-lived dark scalars at FCC-ee is estimated using an event selection requiring two opposite-charge, same-flavor leptons compatible with the $\textit{Z}$ boson, and at least two displaced vertices in the final state. The selection is seen to efficiently remove the Standard Model background, while retaining sensitivity for dark scalar masses between $\textit{m}$ = 20 GeV and $\textit{m}$ = 60 GeV and mean proper lifetimes $\textit{cτ}$ between approximately 10 mm and 10 m. The results show that the search strategy has potential to probe Higgs to dark scalar branching ratios as low as 10 for a mean proper lifetime $\textit{cτ}$ ≈ 1 m. The results provide the first sensitivity estimate for exotic Higgs decays at FCC-ee with the IDEA detector concept, using the common FCC framework.