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Prospects for Triple Gauge Coupling Measurements at Future Lepton Colliders and the 14 TeV LHC

Ligong Bian; Jing Shu; Yongchao ZhangSubjects: Physics >> The Physics of Elementary Particles and Fields

The WW production is the primary channel to directly probe the triple gauge couplings. We first analyze the e+e?→W+W? process at the future lepton collider, China’s proposed Circular Electron-Positron Collider (CEPC). We use the five kinematical angles in this process to constrain the anomalous triple gauge couplings and relevant dimension six operators at the CEPC up to the order of magnitude of 10-4. The most sensible information is obtained from the distributions of the production scattering angle and the decay azimuthal angles. We also estimate constraints at the 14 TeV LHC, with both 300 fb?1 and 3000 fb?1 integrated luminosity from the leading lepton pT and azimuthal angle difference ? φll distributions in the di-lepton channel. The constrain is somewhat weaker, up to the order of magnitude of 10?3. The limits on the triple gauge couplings are complementary to those on the electroweak precision observables and Higgs couplings. Our results show that the gap between sensitivities of the electroweak and triple gauge boson precision can be significantly decreased to less than one order of magnitude at the 14 TeV LHC, and that both the two sensitivities can be further improved at the CEPC. |

Subjects: Physics >> The Physics of Elementary Particles and Fields

In this work, we introduce an extra singlet pseudoscalar into the Type-III two Higgs doublet model (2HDM) which is supposed to solve a series of problems in the modern particle-cosmology. With existence of a light pseudoscalar, the h → ?τ excess measured at CMS and as well as the (g ? 2)? anomaly could be simultaneously explained within certain parameter spaces that can also tolerate the data on the flavor-violating processes τ → ?γ and Higgs decay gained at LHC. Within the same parameter spaces, the DM relic abundance is well accounted. Moreover, the recently observed Galactic Center gamma ray excess(GCE) is proposed to realize through dark matter(DM) pair annihilations, and in this work, the scenario of the annihilation being mediated by the pseudoscalar is also addressed. |

Interference E#11;ect on Resonance Studies in Searches of Heavy Particles

Ligong Bian; Da Liu; Jing Shu; Yongchao ZhangSubjects: Physics >> The Physics of Elementary Particles and Fields

The interference between resonance signal and continuum background can be either constructive or destructive, depending on the relative sign of couplings between the signal and background amplitudes. Different interference schemes lead to asymmetric distortions of the resonance line shape, which could be distinguished in experiments, when the internal resonance width is larger than the detector resolution. Interpreting the ATLAS diboson excesses by means of a toy W' model as an illustrative example (though it is disfavored by the 13 TeV data), we find that the signs of resonance couplings can only be revealed in the line shape measurements up to a high confidence level at a high luminosity, which could bring us further information on the underlying theory beyond resonance searches at future lepton and hadron colliders. |

A hidden confining world on the 750 GeV diphoton excess

Ligong Bian; Ning Chen; Da Liu; Jing ShuSubjects: Physics >> The Physics of Elementary Particles and Fields

We explain the recent diphoton excesses around 750 GeV by both ATLAS and CMS as a singlet scalar Φ which couples to SM gluon and neutral gauge bosons only through higher dimensional operators. A natural explanation is that Φ is a pseudo-Nambu-Goldstone boson (pNGB) which receives parity violation through anomaly if there exists a hidden strong dynamics. The singlet and other light pNGBs will decay into two SM gauge bosons and even serves as the meta-stable coloured states which can be probed in the future. By accurately measuring their relative decay and the total production rate in the future, we will learn the underlying strong dynamics parameter. The lightest baryon in this confining theory could serve as a viable dark matter candidate. |

The Maximally Symmetric Composite Higgs

Csaba Cs?aki; Teng Ma; Jing ShuSubjects: Physics >> The Physics of Elementary Particles and Fields

We present a novel class of calculable four dimensional composite pseudo-Goldstone boson Higgs models based on symmetric G/H coset spaces which contain a Higgs-parity operator V as well as a linear representation Σ0 for the Goldstone bosons. For such cosets the low-energy effective Lagrangian for the Standard Model fields can have an enhanced global symmetry which we call the maximal symmetry. We show that such a maximally symmetric case leads to a finite and fully calculable Higgs potential, which also minimizes the tuning by eliminating double tuning and reducing the Higgs mass. We present a detailed analysis of the Maximally Symmetric SO(5)/SO(4) model, and comment on its observational consequences. |

Interference effects on Higgs mass measurement in $e^+e^-\to H(\gamma\gamma) Z$ at CEPC

Xu Guang-Zhi; Li Gang; Li Yi-Jie; Liu Kui-Yong; Zhang Yu-JieSubjects: Physics >> Nuclear Physics

A high luminosity Circular Electron Positron Collider (CEPC) as a Higgs Factory will be helpful to the precision measurement of the Higgs mass. The signal-background interference effect is carefully studied for the Higgs diphoton decay mode in the associated Z boson production at the future?e+e??colliders at energy?246GeV. The mass shifts go up from about?20MeV?to?50MeV?for the experimental mass resolution ranging from?0.8GeV?to?2GeV. |

Combined estimation for multi-measurements of branching ratio

LIU Xiao-Xia; LYU Xiao-Rui; ZHU Yong-ShengSubjects: Physics >> Nuclear Physics

A maximum likelihood method is used to deal with the combined estimation of multi-measurements of a branching ratio, where each result can be presented as an upper limit. The joint likelihood function is constructed using observed spectra of all measurements and the combined estimate of the branching ratio is obtained by maximizing the joint likelihood function. The Bayesian credible interval, or upper limit of the combined branching ratio, is given in cases both with and without inclusion of systematic error. |

Probe Higgs boson pair production via the 3?2j+$\notE$ mode

Qiang Li; Zhao Li; Qi-Shu Yan; Xiaoran ZhaoSubjects: Physics >> Nuclear Physics

We perform a detailed hadron-level study on the sensitivity of Higgs boson pair production via the?WW?WW?channel with the final state?3?2j?+ missing?ET?at the LHC with the collision energy?S√=14?TeV and a future 100 TeV collider. To avoid the huge background from?pp→ZW+jets?processes, we confine to consider the four lepton patterns:?e±e±μ??and?μ±μ±e?. We propose a partial reconstruction method to determine the most reliable combination. After that, we examine a few crucial observables which can discriminate efficiently signal and background events, especially we notice that the observable?mT2?is very efficient. For the LHC 14 TeV collisions, with an accumulated 3000 fb?1?dataset, we find that the sensitivity of this mode can reach up to 1.5?σ?for the Standard Model and the triple coupling of Higgs boson?λ3?in the simplest effective theory can be constrained into the range [-1, 8] at?95%?confidence level; at a 100 TeV collider with the integrated luminosity 3000 fb?1, the sensitivity can reach up to 13?σ?for the Standard Model and we find that all values of?λ3?in the effective theory can be covered up to 3σ?even without optimising signals. To precisely measure the triple coupling of Higgs boson?λ3=1?of the Standard Model at a 100 TeV collider, by using the invariant mass of three leptons which is robust to against the contamination of underlying events and pileup effects and by performing a?χ2?analysis, we find that it can be determined into a range [0.8, 1.5] at?95%?confidence level. |

Two-loop QCD Corrections to $B_c$ Meson Leptonic Decays

Long-Bin Chen; Cong-Feng QiaoSubjects: Physics >> Nuclear Physics

The two-loop QCD radiative corrections to the?Bc?meson leptonic decay rate are calculated in the framework of NRQCD factorization formalism. Two types of master integrals appearing in the calculation are obtained analytically for the first time. We get the short-distance coefficient of the leading matrix element to order?α2s?by matching the full perturbative QCD calculation results to the corresponding NRQCD ones. The result in this work helps the evaluation of the?Bc?leptonic decay constant, as well as the Cabibbo-Kobayashi-Maskawa matrix element?|Vcb|, to the full next-to-next-to-leading order degree of accuracy. |

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