Standard Model HγγH \gamma \gamma discovery potential with ATLAS

This contribution summarizes the discovery potential of the Standard Model Higgs boson using the $H \gamma \gamma$ decay with the ATLAS detector. The relevant detector performance aspects of photon reconstruction, photon identification and trigger issues are discussed. The potential of inclusive $H \gamma \gamma$ as well as Higgs boson searches in association with one or two hard jets are studied. The discovery potential is finally assessed using an unbinned multivariate maximum-likelihood fit with an expected integrated luminosity of $\approx 10 fb^{-1}$.Comment: 5 pages, 4 figures, Contribution to Conference LHC0

Search for SM Higgs Decaying to Two Photons via ATLAS Detector

This dissertation reports the discovery potential of the Standard Model Higgs boson with the di-photon decay using the ATLAS detector. First, photon calibration techiques is studied and a likelihood method for photon identification and jet rejection is developed. A method to evaluate photon identification and fake photon backgrounds with data was also discussed. The potential of an inclusive SM Higgs decaying to two photons search and Higgs boson searches in association with one or two high $P_T$ jets is evaluated. Finally an extended maximum likelihood fit together with event classifications was performed to estimate the sensitivity of the search. With 30 fb$^{-1}$ data, the expected sensitivity for the channel Higgs decaying to two photons is above 5 sigma for Higgs masses between 120 and 140 GeV

LHC Search of New Higgs Boson via Resonant Di-Higgs Production with Decays into 4W

Searching for new Higgs particle beyond the observed light Higgs boson h(125GeV) will unambiguously point to new physics beyond the standard model. We study the resonant production of a CP-even heavy Higgs state $H^0$ in the di-Higgs channel via, $gg\to H^0\to h^0h^0\to WW^*WW^*$, at the LHC Run-2 and the high luminosity LHC (HL-LHC). We analyze two types of the $4W$ decay modes, one with the same-sign di-leptons ($4W\to\ell^\pm\nu\ell^\pm\nu 4q$) and the other with tri-leptons ($4W\to\ell^\pm\nu\ell^\mp\nu\ell^\pm\nu 2q$). We perform a full simulation for the signals and backgrounds, and estimate the discovery potential of the heavy Higgs state at the LHC Run-2 and the HL-LHC, in the context of generical two-Higgs-doublet models (2HDM). We determine the viable parameter space of the 2HDM as allowed by the theoretical constraints and the current experimental limits. We systematically analyze the allowed parameter space of the 2HDM which can be effectively probed by the heavy Higgs searches of the LHC, and further compare this with the viable parameter region under the current theoretical and experimental bounds.Comment: v3: JHEP published version, 34pp, 10 Figs(36 plots) and 9 Tables. Only minor typos fixed, references added. v2: JHEP version. All results and conclusions un-changed, discussions and references added. (This update is much delayed due to author's traveling and flu.

Instantaneous Symmetry Breaking to the Non-observed Dark Matter

A theory explaining the non-observation of the dark matter and the source of the dark energy is presented in this letter. By integrating the asymmetrical potential and the Higgs potential, we provide a model with instantaneous symmetrical breaking and stable symmetrical breaking, resulting in the non-observed dark matter and observed matter respectively. Two crucial parameters in this model are the frequency and strength of the symmetry breaking from the vacuum: the former helps explain the impact of the effective mass from the dark matter; the latter determines the source of the dark energy. The expected strength in a certain period varies, causing the accelerating or deccelerating expansions of the universe. Considering the expected strength correlated with the vacuum expectation value and basing on the possible variations of the measured masses of the fundamental particles such as Z boson over time, one can perhaps derive the exact stage of the current universe

The expected measurement precision of the branching ratio of the Higgs decaying to the di-photon at the CEPC

This paper presents the prospects of measuring $\sigma(e^{+}e^{-}\to ZH)\times Br(H \to \gamma\gamma)$ in 3 $Z$ decay channels $Z \to q\bar{q} / \mu^{+} \mu^{-} / \nu\bar{\nu}$ using the baseline detector with $\sqrt{s} = 240 GeV$ at the Circular Electron Positron Collider (CEPC) . The simulated Monte Carlo events are generated and scaled to an integrated luminosity of 5.6 $ab^{-1}$ to mimic the data. Extrapolated results to 20 $ab^{-1}$ are also shown. The expected statistical precision of this measurement after combining 3 channels of $Z$ boson decay is 7.7\%. With some preliminary estimation on the systematical uncertainties, the total precision is 7.9\%. The performance of CEPC electro-magnetic calorimeter (ECAL) is studied by smearing the photon energy resolution in simulated events in $e^{+}e^{-} \to ZH \to q\bar{q}\gamma\gamma$ channel. In present ECAL design, the stochastic term in resolution plays the dominant role in the precision of Higgs measurements in $H \to \gamma\gamma$ channel. The impact of the resolution on the measured precision of $\sigma(ZH)\times Br(ZH \to q\bar{q}\gamma\gamma)$ as well as the optimization of ECAL constant term and stochastic term are studied for the further detector design

Probing Higgs CPCP properties at the CEPC

In the Circular Electron Positron Collider (CEPC), a measurement of the Higgs $CP$ mixing through $e^{+} e^{-} \rightarrow Z H \rightarrow \mu^{+} \mu^{-} H(\rightarrow b \bar{b} / c \bar{c} / g g)$ process is presented, with $5.6\ \mbox{ab}^{-1}$$e^{+} e^{-}$collision data at the center-of-mass energy of$240\ \mathrm{GeV}$. In this study, the$CP$-violating parameter$\hat{\alpha}_{A \tilde{Z}}$is constrained between the region of$ -8.27\times 10^{-2}$and$8.09 \times 10^{-2}$and$\hat{\alpha}_{Z \tilde{Z}}$between$-2.15 \times 10^{-2}$and$2.02 \times 10^{-2}$at$95\%$confidence level. This study demonstrates the great potential of probing Higgs$CP$ properties at the CEPC

Application of Quantum Machine Learning in a Higgs Physics Study at the CEPC

Machine learning has blossomed in recent decades and has become essential in many fields. It significantly solved some problems in particle physics -- particle reconstruction, event classification, etc. However, it is now time to break the limitation of conventional machine learning with quantum computing. A support-vector machine algorithm with a quantum kernel estimator (QSVM-Kernel) leverages high-dimensional quantum state space to identify a signal from backgrounds. In this study, we have pioneered employing this quantum machine learning algorithm to study the $e^{+}e^{-} \rightarrow ZH$ process at the Circular Electron-Positron Collider (CEPC), a proposed Higgs factory to study electroweak symmetry breaking of particle physics. Using 6 qubits on quantum computer simulators, we optimised the QSVM-Kernel algorithm and obtained a classification performance similar to the classical support-vector machine algorithm. Furthermore, we have validated the QSVM-Kernel algorithm using 6-qubits on quantum computer hardware from both IBM and Origin Quantum: the classification performances of both are approaching noiseless quantum computer simulators. In addition, the Origin Quantum hardware results are similar to the IBM Quantum hardware within the uncertainties in our study. Our study shows that state-of-the-art quantum computing technologies could be utilised by particle physics, a branch of fundamental science that relies on big experimental data

Radiative Leptonic Decay of Heavy Quarkonia

This study examines the properties of heavy quarkonia $X$ by treating them as bound states of $Q$ and $\bar{Q}$ at the LO level within the NRQCD framework, where $Q$ represents either a charm or a bottom quark. The branching ratios for the radiative leptonic decays $X\rightarrow γl^{+} l^{-}$ are revisited and the angular and energy/momentum distributions of the final state particles are analyzed in the rest frame of $X$. Furthermore, we apply Lorentz transformations from the rest frame of $X$ to the center-of-mass frame of $l^+ l^-$ to establish the connection between the widths ${Γ_{X \rightarrow γl^{+} l^{-}}}$ and ${Γ_{X \rightarrow l^{+} l^{-}}}$. When comparing the connection with those documented in the literature (divided by $2π$) for various $X$ states, such as $J/Ψ$, $Ψ(2S)$, $Υ(1S)$, and $Υ(2S)$, relative differences typically around or below 10\% can be found, which is comparable to the NLO corrections of $O(α)$ and $O(v^4)$. However, we observe a significant disparity in the ratio between ${Γ_{Ψ(2S) \to γτ^+ τ^-}}$ and ${Γ_{Ψ(2S) \to τ^+ τ^-}}$, with our prediction being four times larger than those in the literature. The outcomes derived from this study held practical implications in describing the QED radiative processes and contribute to the investigation of QCD processes associated with the decays of heavy quarkonia and the searches for new physics.16 pages, 6 figure