FCC-ee: Your Questions Answered

Blondel, Alain; Janot, Patrick; Tehrani, Niloufar Alipour; Azzi, Patrizia; Azzurri, Paolo; Bacchetta, Nicola; Benedikt, Michael; Blekman, Freya; Boscolo, Manuela; Dam, Mogens; De Curtis, Stefania; d'Enterria, David; Ellis, John; Ganis, Gerardo; Gluza, Janusz; Helsens, Clément; Jadach, Staszek; Koratzinos, Mike; Klute, Markus; Leonidopoulos, Christos; Locci, Elizabeth; Mangano, Michelangelo; Monteil, Stéphane; Oide, Katsunobu; Okorokov, Vitaly; Perez, Emmanuel; Riemann, Tord; Tenchini, Roberto; Selvaggi, Michele; Voutsinas, Georgios; Wenninger, Jörg; Zimmermann, Frank

doi:10.48550/arxiv.1906.02693

“…But they can also supplement the flavour programs of the LHCb and Belle in different ways: by producing b-flavoured hadrons in e + e − → Z → bb events. ILC operating at the Z pole is expected to produce around 10 9 Zs ("GigaZ") [70], and the FCC-ee is expected to deliver 10 12 Zs ("TeraZ") [71]; by searching for new particles responsible for the deviations, such as leptoquarks or Z bosons; by probing the effects of Wilson coefficients in the kinematical distributions sensible to virtual effects; and by improving the precision of the observables that enter our global fits. Due to the high number of Z bosons produced, EW observables are a prime example of the advantages of e + e − colliders.…”

Section: Global Fitsmentioning

confidence: 99%

Anomalies in B mesons decays: Present status and future collider prospects

Alda¹,

Guasch²,

Peñaranda³

2021

Preprint

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The experimental measurements on flavour physics, in tension with Standard Model predictions, exhibit large sources of Lepton Flavour Universality violation. This note summarises an analysis of the effects of the global fits to the Wilson coefficients assuming a model independent effective Hamiltonian approach, by including a proposal of different scenarios to include the New Physics contributions. Additionally, we include an overview of the impact of the future generation of colliders in the field of B-meson anomalies.

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“…Deviations from universality related with these scales will be searched for through the precise measurement of the couplings of each Send offprint requests to: fermion flavour to the Z. Separate access to the left-and right-handed components of the couplings will be available at FCC-ee even in the absence of polarised beams [8], as described below.…”

Section: Introductionmentioning

confidence: 99%

The Z lineshape challenge: ppm and keV measurements

Maestre

¹

,

Blondel

²

,

Dam³

et al. 2021

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The FCC-ee offers powerful opportunities for direct or indirect evidence for physics beyond the standard model, via a combination of high-precision measurements and searches for forbidden and rare processes and feebly coupled particles. A key element of FCC-ee physics program is the measurement of the Z lineshape from a total of $$5\times 10^{12}$$ 5 × 10 12 Z bosons and a beam-energy calibration with relative uncertainty of $$10^{-6}$$ 10 - 6 . With this exceptionally large event sample, five orders of magnitude larger than that accumulated during the whole LEP1 operation at the Z pole, the defining parameters—$$m_\mathrm{Z}$$ m Z , $$\Gamma _\mathrm{Z}$$ Γ Z , $$N_\nu $$ N ν , $$\sin ^2\theta _\mathrm{W}^\mathrm{eff}$$ sin 2 θ W eff , $$\alpha _\mathrm{S}(m_\mathrm{Z}^2)$$ α S ( m Z 2 ) , and $$\alpha _\mathrm{QED}(m^2_\mathrm{Z})$$ α QED ( m Z 2 ) —can be extracted with a leap in accuracy of up to two orders of magnitude with respect to the current state of the art. The ultimate goal that experimental and theory systematic errors match the statistical accuracy (4 keV on the Z mass and width, $$3\times 10^{-6}$$ 3 × 10 - 6 on $$\sin ^2\theta _\mathrm{W}^\mathrm{eff}$$ sin 2 θ W eff , a relative $$3\times 10^{-5}$$ 3 × 10 - 5 on $$\alpha _\mathrm{QED}$$ α QED , and less than 0.0001 on $$\alpha _\mathrm{S}$$ α S ) leads to highly demanding requirements on collider operation, beam instrumentation, detector design, computing facilities, theoretical calculations, and Monte Carlo event generators. Such precise measurements also call for innovative analysis methods, which require a joint effort and understanding between theorists, experimenters, and accelerator teams.

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“…result, although clearly short of an evidence for s-channel Higgs production, is still about 100 (30) times better [53] than that reachable at HL-LHC (FCC-hh [52]), and would imply setting a constraint on new physics affecting the electron-Higgs coupling above Λ bsm 110 TeV.…”

Section: Event Reconstruction and Preselectionmentioning

confidence: 84%

Measuring the electron Yukawa coupling via resonant s-channel Higgs production at FCC-ee

d'Enterria,

Poldaru,

Wojcik

2021

Preprint

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The Future Circular Collider (FCC-ee) offers the unique opportunity of studying the Higgs Yukawa coupling to the electron, y e , via resonant s-channel production, e + e − → H, in a dedicated run at √ s = m H . The signature for direct Higgs production is a small rise in the cross sections for particular final states, consistent with Higgs decays, over the expectations for their occurrence due to Standard Model (SM) background processes involving Z * , γ * , or t-channel exchanges alone. Performing such a measurement is remarkably challenging for four main reasons. First, the low value of the e ± mass leads to a tiny y e coupling, and correspondingly small cross section: σ ee→H ∝ m 2 e = 0.57 fb accounting for initial-state γ radiation. Second, the e + e − beams must be monochromatized such that the spread of their center-ofmass (c.m.) energy is commensurate with the narrow width of the SM Higgs boson, Γ H = 4.1 MeV, while keeping large beam luminosities. Third, the Higgs mass must also be known beforehand with a few-MeV accuracy in order to operate the collider at the resonance peak, √ s = m H . Last but not least, the cross sections of the background processes are many orders-of-magnitude larger than those of the Higgs decay signals. A preliminary generator-level study of 11 Higgs decay channels using a multivariate analysis, which exploits boosted decision trees to discriminate signal and background events, identifies two final states as the most promising ones in terms of statistical significance: H → gg and H → WW * → ν + 2 jets. For a benchmark monochromatization with 4.1-MeV c.m. energy spread (leading to σ ee→H = 0.28 fb) and 10 ab −1 of integrated luminosity, a 1.3σ signal significance can be reached, corresponding to an upper limit on the e ± Yukawa coupling at 1.6 times the SM value: |y e | < 1.6|y sm e | at 95% confidence level, per FCC-ee interaction point per year. Directions for future improvements of the study are outlined.

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FCC-ee: Your Questions Answered

Cited by 15 publications

References 41 publications

Anomalies in B mesons decays: Present status and future collider prospects

Anomalies in B mesons decays: Present status and future collider prospects

The Z lineshape challenge: ppm and keV measurements

Measuring the electron Yukawa coupling via resonant s-channel Higgs production at FCC-ee

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