Measurements of decay branching fractions of H→b■/c■/gg in associated (e~+e~-/μ~+μ~-)H production at the CEPC

The high-precision measurement of Higgs boson properties is one of the primary goals of the Circular Electron Positron Collider(CEPC).The measurements ofH→b■/c■/gg decay branching fraction in the CEPC experiment is presented,considering a scenario of analysing 5000 fb-1 e~+e~-collision data with the center-of-mass energy of 250 Ge V.In this study the Higgs bosons are produced in association with a pair of leptons,dominantly mediated by the ZH production process.The statistical uncertainty of the signal cross section is estimated to be about 1%in theH→b■ final state,and approximately 5%-10%in theH→c■/gg final states.In addition,the main sources of the systematic uncertainties and their impacts to the measurements of branching fractions are discussed.This study demonstrates the potential of precise measurement of the hadronic final states of the Higgs boson decay at the CEPC,and will provide key information to understand the Yukawa couplings between the Higgs boson and quarks,which are predicted to be the origin of quarks’masses in the standard model.     

Measurement of H→μ~+μ~- production in association with a Z boson at the CEPC

The Circular Electron-Positron Collider(CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. It is planned to operate at a center-of-mass energy of 240–250 Ge V and is expected to accumulate an integrated luminosity of 5 ab~(-1) over ten years of operation. At the CEPC, Higgs bosons will be dominantly produced from the ZH associated process. The vast number of Higgs events collected will enable precise studies of its properties, including Yukawa couplings to massive particles. With GEANT4-based simulation of detector effects, we study the feasibility of measuring the Higgs boson decaying into a pair of muons at the CEPC.The results with and without information from the Z boson decay products are provided, showing that a signal significance of over 10 standard deviations can be achieved and the H-μ-μ coupling can be measured within 10%accuracy.     

Cross section and Higgs mass measurement with Higgsstrahlung at the CEPC

The Circular Electron Positron Collider(CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. It will operate at a center-of-mass energy of 240–250 Ge V. The CEPC will accumulate an integrated luminosity of 5 ab-1over ten years of operation, producing one million Higgs bosons via the Higgsstrahlung and vector boson fusion processes. This sample allows a percent or even sub-percent level determination of the Higgs boson couplings. With GEANT4-based full simulation and a dedicated fast simulation tool, we have evaluated the statistical precisions of the Higgstrahlung cross section σZH and the Higgs mass m H measurement at the CEPC in the Z →μ~+μ~-channel. The statistical precision of σZH(m_H) measurement could reach 0.97%(6.9 MeV) in the model-independent analysis which uses only the information from Z boson decays. For the standard model Higgs boson, the m H precision could be improved to 5.4 Me V by including the information from Higgs decays. The impact of the TPC size on these measurements is investigated. In addition, we studied the prospect of measuring the Higgs boson decaying into invisible final states at the CEPC. With the Standard Model ZH production rate, the upper limit of B(H → inv.) could reach 1.2% at 95% confidence level.     

Precision study of W~-W~+H production including parton shower effects at CERN Large Hadron Collider

The precision study of W~-W~+H production with subsequent W~±→l~±_v_l~((-)) and H→bb decays at the Large Hadron Collider(LHC) aids in the investigation of Higgs gauge couplings and the search for new physics beyond the standard model.In this study,we calculate the shower-matched next-to-leading order QCD and electroweak(EW)corrections from the qq annihilation and photon-induced channels to the W~-W~+H production at the 14 TeV LHC.We deal with the subsequent decays of Higgs and W~± bosons by adopting the MADSPIN method.Both the integrated cross section and some kinematic distributions of W~±,H,and their decay products are provided.We find that the QCD correction significantly enhances the leading-order differential cross section,while the EW correction from the qq annihilation channel obviously suppresses it,especially in the high energy phase-space region,due to the Sudakov effect.The qy-and yy-induced relative corrections are positive and insensitive to the transverse momenta of W~±,H,and their decay products.These photon-induced corrections compensate the negative qq-initiated EW correction,and become the dominant EW contribution as the increment of the pp colliding energy.The parton shower(PS) effects on kinematic distributions are not negligible.The relative PS correction to the b-jet transverse momentum distribution can exceed 100% in the high p_(T,b) region.Moreover,we investigate the scale and PDF uncertainties,and find that the theoretical error of the QCD+EW+qγ+γγ-corrected integrated cross section mainly originates from the renormalization scale dependence of the QCD correction.     

Azimuthal Dependence of Intrinsic Top in Photon-Quark Scattering and Higgs Production in Boson-Gluon Fusion DIS

In this paper, we study the top content of nucleon by analyzing azimuthal asymmetries in lepton-nucleon deep inelastic scattering(DIS), also we search for the Higgs boson associated production channel, tˉt H, at the large hadron-electron collider(LHe C) caused by boson-gluon fusion(BGF) contribution. We use azimuthal asymmetries inγ*Q cross sections in terms of helicity contributions to semi-inclusive deep inelastic scattering to investigate numerical properties of the cos 2? distribution. We conclude that measuring azimuthal distributions caused by intrinsic heavy quark production can directly probe heavy quarks inside nucleon. Moreover, in order to estimate the probability of producing the Higgs boson, we suggest another approach in the framework of calculating tˉt cross section in boson-gluon fusion mechanism. Finally, we can confirm that this observed massive particle is referred to Higgs boson produced by fermion loop.     

LHT model and Higgs boson production in association with a weak gauge boson at the LHC

Considering the process pp → VH+X(V = W or Z) is a significant channel for searching for a light Higgs boson,we calculate the contributions of the littlest Higgs model with T-parity(called LHT model) to its production cross section.We find that,in most of the parameter space,the value of the relative correction parameter R is very small.However,with reasonable values of the free parameters,its value can be significantly larger.     

Charged Higgs Pair Production in a General Two Higgs Doublet Model at e^＋e^- and μ^＋μ^- Linear Colliders

In this paper, charged Higgs pair production through l^＋l^- → H^＋ H^-, where l = e or μ, is studied within the framework of a general Two Higgs Doublet Model （2HDM）. The analysis is relevant to a future e^＋e^- or μ^＋ μ^- collider operating at center of mass energy of √s = 500 GeV. Two different scenarios of small and large a values are studied. Here a is the parameter, which diagonMizes the neutral CP-even Higgs boson mass matrix. Within the Minimal Supersymmetric Standard Model （MSSM）, cross section of this process is almost the same at e＋ e- and #＋#- colliders. It is shown that at e^＋e^- eolliders within a general 2HDM, cross section is not sensitive to the mass of neutral Higgs bosons, however, it can acquire large values up to several picobarn at μ^＋μ^- colliders with the presence of heavy neutral Higgs bosons. A scan over Higgs boson mass parameter space is performed to analyze the effect of large masses of neutral Higgs bosons involved in the s-channel propagator and thus in the total cross section of this process.     

O(α_sv~2) correction to J/ψ plus η_c production in e~+e~- annihilation at s~(1/2)=10.6 GeV

Based on the nonrelativistic QCD factorization approach, O(αsv2) corrections to J/ψ plus ηc production in e+e-annihilation at √ s=10.6 GeV are calculated in this work. The numerical results show that the correction at αsv2order is only about a few percent of the total theoretical result. This indicates that the perturbative expansions become convergent and that a higher order correction will be smaller. The uncertainties from the long-distance matrix elements, renormalization scale and the measurement in the experiment are also discussed. Our result is in agreement with the previous result by Jia.     

具有T宇称的最小Higgs模型与LHC上Higgs波色子与弱规范波色子的联合产生

Considering the process pp→VH ＋X（V = W or Z） is a significant channel for searching for a light Higgs boson, we calculate the contributions of the littlest Higgs model with T-parity （called LHT model） to its production cross section. We find that, in most of the parameter space, the value of the relative correction parameter R is very small. However, with reasonable values of the free parameters, its value can be significantly larger.     

The Higgs signatures at the CEPC CDR baseline

As a Higgs factory, the CEPC(Circular Electron-Positron Collider) project aims at precision measurements of the Higgs boson properties. A baseline detector concept, APODIS(A PFA Oriented Detector for the HIggS factory), has been proposed for the CEPC CDR(Conceptual Design Report) study. We explore the Higgs signatures for this baseline design with ■ Higgs events. The detector performance for reconstructing charged particles, photons and jets is quantified with H→μμ, γγ and jet final states, respectively. The resolutions of reconstructed Higgs boson mass are comparable for the different decay modes with jets in the final states. We also analyze the H→WW~* and ZZ* decay modes, where a clear separation between different decay cascades is observed.     

The Effect of Slepton Flavor Mixing on the Mass of SM-like Higgs Boson in the MSSM

We investigate the one-loop contributions to the mass of the SM-like Higgs boson in the MSSM considering the effect of slepton flavor mixing, which is parametrized by the dimensionless parameter δXY(X, Y = L, R) in the slepton mass matrices. For the surviving samples under the experimental constraints, we calculate the corrections to the mass of the SM-like Higgs boson in terms of δXY. We find that the mass correction ?mhcan even be larger than 10 GeV for large δRLor δLR. Moreover, ?mhhas strong sensitivity to δRLor δLR, while the weak sensitivity to δLLor δRR, sinceδRLor δLRenters directly into the coupling of Higgs boson with sleptons in the calculations of Higgs boson self-energies.     

Categorization of two-loop Feynman diagrams in the O(α~2) correction to e~+e~-→ ZH

The e~+e~-→ZH process is the dominant process for the Higgs boson production at the future Higgs factory.In order to match the analysis on the Higgs properties with highly precise experiment data,it will be crucial to include the theoretical prediction to the full next-to-next-to-leading order electroweak effect in the production rateσ(e~+e~-→ZH).In this inspiring work,we categorize the two-loop Feynman diagrams of the O(α~2) correction to e~+e~-ZH into 6 categories according to relevant topological structures.Although 25377 diagrams contribute to the O(a~2) correction in total,the number of the most challenging diagrams with seven denominators is 2250,which contain only 3 12 non-planar diagrams with 155 independent types.This categorization could be a valuable reference for the complete calculation in future.     

Exotic decays of the 125 GeV Higgs boson at future e~+e~- colliders

The discovery of unexpected properties of the Higgs boson would offer an intriguing opportunity to shed light on some of the most profound puzzles in particle physics. Beyond Standard Model(BSM) decays of the Higgs boson could reveal new physics in a direct manner. Future electron-positron lepton colliders operating as Higgs factories, including CEPC, FCC-ee and ILC, with the advantages of a clean collider environment and large statistics,could greatly enhance sensitivity in searching for these BSM decays. In this work, we perform a general study of Higgs exotic decays at future e~+e~-lepton colliders, focusing on the Higgs decays with hadronic final states and/or missing energy, which are very challenging for the High-Luminosity program of the Large Hadron Collider(HL-LHC).We show that with simple selection cuts,O(10~(-3)-10~(-5)) limits on the Higgs exotic decay branching fractions can be achieved using the leptonic decaying spectator Z boson in the associated production mode e~+e~-→ZH. We further discuss the interplay between detector performance and Higgs exotic decays, and other possibilities of exotic decays.Our work is a first step in a comprehensive study of Higgs exotic decays at future lepton colliders, which is a key area of Higgs physics that deserves further investigation.     

Cross Section of Heavy Ion Reaction （14.5 MeV/u） ^132Xe ＋ Bi

We investigate the cross section of the heavy ion reaction （14.5 MeV/u） ^132Xe ＋ Bi by using a CR-39 plastic track detector. The target-detector assembly is exposed at UNILAC beam facility of GSI, Germany. After etching under appropriate etching conditions, the detector is scanned for multipronged events produced as a result of interactions of projectile ions with target atoms. The elastic events are separated from binary events and used for the determination of the quarter-point angle. The quarter-point angle obtained is used to determine the total reaction cross section. The total experimental reaction cross section is determined by using statistics of inelastic events of two-pronged and higher multiplicity events. The experimental reaction cross sections determined by using elastic and inelastic data observed in the reaction under study are found to be in good agreement with the theoretically calculated value of reaction cross section using a sharp cutoff model.     

Can a Higgs boson be produced at the LHC?

A simple model is designed to simulate, by using the mean free path method, the probability of Higgs boson production at the Large Hadron Collider (LHC). The probability that the colliding particles could get close to a given distance with different colliding energies is discussed in this model. Calculated results imply that the probability of producing a Higgs boson is near zero according to the existing theoretical mechanism for Higgs boson production.     

Probing the TC2 model via Production of Top Quark Pairs at Tevatron and LHC

The topcolour-assisted technicolour （TC2） model is an interesting dynamical theory among the various new physics models. We cMculate the total tt cross section and the relative correction of the TC2 model to the cross section at Tevatron Run Ⅱ and LHC. At the Tevatron Run Ⅱ, the cross section predicted by the standard model （SM） is consistent with the experimental data, and in most parameter spaces of the TC2 model, the relative correction of the TC2 model to the cross section is too small to be detectable. We find that the tt cross section is more sensitive to the parameters of the TC2 model at the LHC and the relative correction of the TC2 model to the cross section is over 10% in general. Such a value of the relative correction should be large enough to be detectable at the LHC. Therefore, it is promising to find the clue of the TC2 model via the tt production at the LHC.     

Analytic forms for cross sections of di-lepton production from e~+e~- collisions around the J/ψ resonance

A detailed theoretical derivation of the cross sections of e~+e~-→e~+e~-and e~+e~-→μ+μ-around the J/ψ resonance is reported. The resonance and interference parts of the cross sections, related to J/ψ resonance parameters, are calculated. Higher-order corrections for vacuum polarization and initial-state radiation are considered. An arbitrary upper limit of radiative correction integration is involved. Full and simplified versions of analytic formulae are given with precision at the level of 0.1% and 0.2%, respectively. Moreover, the results obtained in the paper can be applied to the case of the ψ(3686) resonance.     

Study of the process e+e-→π+π-π0π0 at energies √s< 1 GeV

In an experiment with the Spherical Neutral Detector at VEPP-2M collider the cross section of the process e+e-→π+π-π0π0 was measured. At energies √s < 920 MeV this cross section was measured for the first time. The energy dependence of the cross section is well discribed by the vector dominance model with contributions from ρ, ρ' ρ", mesons. The decay probability ρ→π+π-π0π0was found to be Bρ = (1.60±0.74±0.18)×10-5. The upper limit for the decay ω→π+π-π0π0 was improved by two orders of magnitude compared to the previous measurements and is Bω < 2 × 10-4 at 90% confidence level.     

NLO Corrections of HTC∏^0 and ∏＋∏- Pair Production at ILC in TC2 Model

As well known, if the Higgs boson were not observed at LHC, the technicolor model would be the most favorable candidate responsible for the symmetry breaking. To overcome some defects in the previous model, some extended versions have been proposed. In the TC2 model typical signature is existence of heavy HTC and technipion ∏. A direct proof of validity of the model is to produce them at accelerator. Thus we study the production rates of e＋e^- → HTC∏^0 and e＋e^- → ∏＋∏- at ILC in the topcolor-assisted technicolor （TC2） model. In fact, there is a flood of models belonging to new physics, which can result in products with characteristics similar to HTC ＋ ∏ of the TC2 model. Therefore to distinguish this model from others one may need to investigate some details by calculating the cross section to NLO. We indeed find that the NLO corrections are significant, namely the ratio δ ≡（ σNLO - σLO）/σLO in e＋e- →HTC∏^0 exceeds 100% within a plausible parameter space.     

Monte Carlo simulation of exposure factor

In this paper, we simulate the exposure factor by a simple model of a free-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to parameters of the chamber model. The reason for the variation in exposure factor with incident ray energy is also analysed in terms of reaction cross section for different types of reactions. The obtained results indicate that our simulation is accurate in the calculation of the exposure factor and can serve as a reference in designing air ionization chambers.