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Optimizing Higgs factories by modifying the recoil mass

Jiayin Gu; Ying-Ying LiSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

It is difficult to measure the WW-fusion Higgs production process (e+e? ! ? h) at a lepton collider with a center of mass energy of 240-250 GeV due to its small rate and the large background from the Higgsstrahlung process with an invisible Z(e+e? ! hZ, Z ! ? ). We construct a modified recoil mass variable, mp recoil,defined using only the 3-momentum of the reconstructed Higgs particle, and show that it can better separate the WW-fusion and Higgsstrahlung events than the original recoil mass variable mrecoil. Consequently, the mp recoil variable can be used to improve the overall precisions of the extracted Higgs couplings, in both the conventional framework and the effective-field-theory framework. We also explore the application of the mp recoil variable in the inclusive cross section measurements of the Higgsstrahlung process, while a quantitive analysis is left for future studies. |

Learning from Higgs Physics at Future Higgs Factories

Jiayin Gu; Honglei Li; Zhen Liu; Shufang Su; Wei SuSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Future Higgs factories can reach impressive precision on Higgs property measurements.In this paper, instead of conventional focus of Higgs precision in certain interaction bases, we explored its sensitivity to new physics models at the electron-positron colliders. In particular, we studied two categories of new physics models, Standard Model (SM) with a real scalar singlet extension, and Two Higgs Double Model (2HDM) as examples of weaklyinteracting models, Minimal Composite Higgs Model (MCHM) and three typical patterns of the more general operator counting for strong nteracting models as examples of strong dynamics. We performed a global t to various Higgs search channels to obtain the 95% C.L.constraints on the model parameter space. In the SM with a singlet xtension, we obtained the limits on the singlet-doublet mixing angle sin , as well as the more general Wilson coe cients of the induced higher dimensional operators. In the 2HDM, we analyzed tree level e ects in tan vs. cos(β-α) plane, as well as the one-loop contributions from the heavy Higgs bosons in the alignment limit to obtain the constraints on heavy Higgs masses for di erent types of 2HDM. In strong dynamics models, we obtained lower limits on the strong dynamics scale. In addition, once deviations of Higgs couplings are observed, they can be used to distinguish di erent models. We also compared the sensitivity of various future Higgs factories,namely Circular Electron Positron Collider (CEPC), Future Circular Collider (FCC)-ee and International Linear Collider (ILC). |

Beyond Higgs Couplings: Probing the Higgs with Angular Observables at Future e$^+$ e$^?$ Colliders

Nathaniel Craig; Jiayin Gu; Zhen Liu; Kechen WangSubjects: Physics >> Nuclear Physics

We study angular observables in the?e+e?→ZH→?+??bb??channel at future circular?e+e??colliders such as CEPC and FCC-ee. Taking into account the impact of realistic cut acceptance and detector effects, we forecast the precision of six angular asymmetries at CEPC (FCC-ee) with center-of-mass energy?s√=?240 GeV and 5 (30)?ab?1?integrated luminosity. We then determine the projected sensitivity to a range of operators relevant for the Higgs-strahlung process in the dimension-6 Higgs EFT. Our results show that angular observables provide complementary sensitivity to rate measurements when constraining various tensor structures arising from new physics. We further find that angular asymmetries provide a novel means of both probing BSM corrections to the?HZγ?coupling and constraining the "blind spot" in indirect limits on supersymmetric scalar top partners. |

The $ Zb\overlineb $ couplings at future e$^+$ e$^?$ colliders

Stefania Gori; Jiayin Gu; Lian-Tao Wang(c; d)Subjects: Physics >> Nuclear Physics

Many new physics models predict sizable modifications to the SM Zbb couplings, while the corresponding measurements at LEP and SLC exhibit some discrepancy with the SM predictions. After updating the current results on the Zbb coupling constraints from global fits, we list the observables that are most important for improving the Zbb coupling constraints and estimate the expected precision reach of three proposed future e+e- colliders, CEPC, ILC and FCC-ee. We consider both the case that the results are SM-like and the one that the Zbb couplings deviate significantly from the SM predictions. We show that, if we assume the value of the Zbb couplings to be within 68% CL of the current measurements, any one of the three colliders will be able to rule out the SM with more than 99.9999% CL (5 sigma). We study the implications of the improved Zbb coupling constraints on new physics models, and point out their complementarity with the constraints from the direct search of new physics particles at the LHC, as well as with Higgs precision measurements. Our results provide a further motivation for the construction of future e+e- colliders. |

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