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.     

Precision Higgs physics at the CEPC

The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics.The Higgs boson will be the subject of extensive studies of the ongoing LHC program.At the same time,lepton collider based Higgs factories have been proposed as a possible next step beyond the LHC,with its main goal to precisely measure the properties of the Higgs boson and probe potential new physics associated with the Higgs boson.The Circular Electron Positron Collider(CEPC)is one of such proposed Higgs factories.The CEPC is an e~+e~- circular collider proposed by and to be hosted in China.Located in a tunnel of approximately 100 km in circumference,it will operate at a center-of-mass energy of 240 GeV as the Higgs factory.In this paper,we present the first estimates on the precision of the Higgs boson property measurements achievable at the CEPC and discuss implications of these measurements.     

Study of beamstrahlung effects at CEPC

The discovery of a 125 GeV Higgs boson at the LHC marked a breakthrough in particle physics. The relative lightness of the new particle has inspired consideration of a high-luminosity Circular Electron Positron Collider(CEPC) as a Higgs Factory to study the particle's properties in an extremely clean environment. Given the high luminosity and high energy of the CEPC, beamstrahlung is one of the most important sources of beaminduced background that might degrade the detector performance. It can introduce even more background to the detector through the consequent electron-positron pair production and hadronic event generation. In this paper,beamstrahlung-induced backgrounds are estimated with both analytical methods and Monte Carlo simulation. Hit density due to detector backgrounds at the first vertex detector layer is found to be~0.2 hits/cm~2 per bunch crossing, resulting in a low detector occupancy below 0.5%. Non-ionizing energy loss(NIEL) and total ionizing dose(TID), representing the radiation damage effects, are estimated to be~10~(11)1 Me V neq/cm~2/yr and~300 k Rad/yr,respectively.     

Study of CEPC performance with different collision energies and geometric layouts

The Circular Electron-Positron Collider(CEPC) is one of the largest projects planned for high energy physics in China.It would serve first as a Higgs factory and then upgrade to a hadron collider.In this paper we give the 50 km and 100 km design for both single ring and double ring schemes,including Z boson,W boson and Higgs boson,by using an optimized method.Also,we give the potential of CEPC running at the Z and W poles.We analyse the relationship of luminosity with circumference and filling factor,which gives a way to evaluate the choice of geometry,and compare the nominal performances of CEPC-SPPC,LHC and FCC.     

New physics searches with Higgs-photon associated production at the Higgs factory

A future Higgs factory is being designed for precise measurement of Higgs characteristics and to search for new physics. In this paper we propose that the Higgs-photon associated production process, e+e-→γh could be a useful channel for new physics. We express new physics model-independently in the effective Lagrangian approach,and find that the new physics effects of γh have only two degrees of freedom, much fewer than the Higgsstrahlung process. This point could be used to reduce the degeneracies of Wilson coefficients. We also calculate for the first time the 95% confidence level(CL) bounds of γh at the Higgs factory, and prove that γh is more sensitive to some dimension-6 operators than the current experimental data. In the optimistic scenario new physics effects may be observed at the CEPC or FCC-ee after the first couple of years of their run.     

Classify the Higgs decays with the PFN and ParticleNet at electron–positron colliders

Various Higgs factories are proposed to study the Higgs boson precisely and systematically in a model- independent way. In this study, the Particle Flow Network and ParticleNet techniques are used to classify the Higgs decays into multicategories, and the ultimate goal is to realize an "end-to-end" analysis. A Monte Carlo simulation study is performed to demonstrate the feasibility, and the performance looks rather promising. This result could be the basis of a "one-stop" analysis to measure all the branching fractions of the Higgs decays simultaneously.     

Physics cross sections and event generation of e~+e~- annihilations at the CEPC

The cross sections of the Higgs production and the corresponding backgrounds of e~+e~- annihilations at the CEPC(Circular Electron and Positron Collider) are calculated by a Monte-Carlo method, and the beamstrahlung effect at the CEPC is carefully investigated. The numerical results and the expected number of events for the CEPC are provided.     

Two-photon physics at future electron-positron colliders

Two photon collisions offer a variety of physics phenomena that can be studied at future electron-positron colliders. Using the planned CEPC parameters as a benchmark, we consider several topics within two-photon collisions. With the full integrated luminosity, Higgs boson photoproduction can be reliably observed, and large statistics on various quarkonium states can be collected. The LEP results for the photon structure function and tau lepton anomalous magnetic moment can be improved by 1-2 orders of magnitude.     

Interference effects on Higgs mass measurement in e~+e~-→H(γγ)Z at CEPC

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

Search for Higgs boson in beyond standard model scenarios at large hadron collider

The principal physics motivation of the LHC experiments is to search for the Higgs boson and to probe the physics of TeV energy scale. Potential of discovery for Higgs bosons in various scenarios beyond standard model have been estimated for both CMS and ATLAS experiments through detailed detector simulations. Main results from the recently published studies of CMS collaboration are only included in this write-up. on behalf of the ATLAS and CMS Collaborations     

Physical design study of the CEPC booster

A physical design study of the Circular Electron-Positron Collider(CEPC) booster is reported. The booster provides 120 GeV electron and positron beams for the CEPC collider with top-up injection. The booster is mounted above the collider in the same tunnel. To save cost, the energy of the linac injector for the booster is chosen as 6 GeV, corresponding to a magnetic field of 30.7 Gs. In this paper, the booster lattice is described and optimization of the cell length is discussed. A novel scheme of bypass near the detector of the collider is designed.The extremely low magnetic field caused by low injection energy is studied, and a new ideal of wiggling bands is proposed to mitigate the low-field problem. Beam transfer and injection from the linac to the booster are considered.     

HZ associated production with decay in the Alternative Left-Right Model at CEPC and future linear colliders

In this study, Higgs and Z boson associated production with subsequent decay is attempted in the framework of alternative left-right model, which is motivated by superstring-inspired E_6 model at CEPC and future linear colliders. We systematically analyze each decay channel of Higgs with theoretical constraints and latest experimental methods. Due to the mixing of scalars in the Higgs sector, charged Higgs bosons can play an essential role in the phenomenological analysis of this process. Even though the predictions of this model for the signal strengths of this process are close to the standard model expectations, it can be distinct under high luminosity.     

Large hadron collider physics program: Compact muon solenoid experiment

The LHC physics program at CERN addresses some of the fundamental issues in particle physics and CMS experiment would concentrate on them. The CMS detector is designed for the search of Standard Model Higgs boson in the whole possible mass range. Also it will be sensitive to Higgs bosons in the minimal supersymmetric model and well adapted to searches for SUSY particles, new massive vector bosons, CP-violation in B-system, search for subtructure of quarks and leptons, etc. In the LHC heavy ion collisions the energy density would be well above the threshold for the possible formation of quark-gluon plasma.     

CMS: Hadronic calorimetry,jets, and $\rlap{\,/}E_T$ performance

The European Physical Journal C - The CMS experiment&;nbsp;[1] uses a general purpose detector designed for detecting the diverse signatures associated with Higgs production and new physics...     

Physics design of collimators to reduce lost particle background at the CEPC

At the CEPC (Circular Electron Positron Collider), which is proposed by the Chinese high energy physics community, the dominant background comes from radiative Bhabha scattering and the beamstrahlung effect according to preliminary research. Therefore, it is necessary to incorporate a collimator system to intercept particles that may be lost near the interaction region (IR). In this paper, we introduce some limitations in choosing the position and width of the collimators. A certain parameter range is determined which is confined by the β function and the width of the collimators. A suitable choice of the half width is made by exploring this parameter range. A simulation of the particle loss rate in the IR and the hit density in the vertex detector with and without the collimators shows that the set of parameters of the collimators we designed is appropriate and effective.     

Discovery potential of Higgs boson pair production through 4■+■ final states at a 100 TeV collider

We explore the discovery potential of Higgs pair production at a 100 Te V collider via full leptonic mode.The same mode can be explored at the LHC when Higgs pair production is enhanced by new physics. We examine two types of fully leptonic final states and propose a partial reconstruction method, which can reconstruct some useful kinematic observables. It is found that the m T2 variable determined by this reconstruction method and the reconstructed visible Higgs mass are crucial to discriminate the signal and background events. It is also noticed that a new variable, denoted as ?m, which is defined as the mass difference of two possible combinations, is very useful as a discriminant. To examine the detector effects, we consider seven detector setups for a 100 Te V collider and investigate the changes in the sensitivity, and we find that lepton isolation and the minimal lepton P t cut are crucial in order to reduce the integrated luminosity.     

Performance of GLD detector

Most of the important physics processes to be studied in the international linear collider (ILC) experiment have multi-jets in the final state. In order to achieve better jet energy resolution, the so-called particle flow algorithm (PFA) will be employed and there is a general consensus that PFA derives overall ILC detector design. Four detector concepts for the ILC experiment have been proposed so far in the world; the GLD detector that has a large inner calorimeter radius, which is considered to have an advantage for a PFA, is one of them. In this paper, general scheme and performance of the GLD-PFA will be presented.      

What can we learn from the total width of the Higgs boson?

As one of the key properties of the Higgs boson, the Higgs total width is sensitive to the global profile of the Higgs boson couplings, and thus new physics would modify the Higgs width. We investigate the total width in various new physics models, including various scalar extensions, composite Higgs models, and the fraternal twin Higgs model. Typically, the Higgs width is smaller than the standard model value due to mixture with other scalars if the Higgs is elementary, or curved Higgs field space for the composite Higgs. On the other hand, except for the possible invisible decay mode, the enhanced Yukawa coupling in the two Higgs doublet model or the exotic fermion embeddings in the composite Higgs could enhance the Higgs width greatly. The precision measurement of the Higgs total width at the high-luminosity LHC can be used to discriminate certain new physics models.     

Prospects for chargino pair production at the CEPC

The proposed Circular Electron Positron Collider(CEPC)with a center-of-mass energy√s=240GeV will primarily serve as a Higgs factory.Additionally,it will offer good opportunities to search for new physics phenomena at low energies,which can be challenging with hadron colliders;however,these discoveries are highly motivated by theoretical models developed to explain,e.g.,the relic abundance of dark matter.This paper presents sensitivity studies for chargino pair production by considering scenarios for both a Bino-like and a Higgsino-like neutralino as the lightest supersymmetric particle and using a full Monte Carlo(MC)simulation.By assuming systematic uncertainties at the level of 5%,the CEPC has the ability to discover chargino pair production up to the kinematic limit of for√s/2 both scenarios.The results have a minor dependence on the reconstruction model and detector geometry.These results can also be considered as a reference and benchmark for similar searches at other proposed electron-positron colliders,such as the Future Circular Collider ee(FCC-ee)or the International Linear Collider(ILC),given the similar nature of the facilities,detectors,center-of-mass energies,and target luminosities.     

Higgs type excitations in cold atom systems

Higgs type excitations are the excitations which give mass to particles. The Higgs type excitations has a critical role both in particle physics and condensed matter physics. In particle physics, the suspected Higgs boson has been found by the Large Hadron Collider (LHC) in 2012. In condensed matter physics, the Higgs type excitations relate to order phase of the system. In this review, we present an overview of recent studies on the Higgs type excitations both in non-interacting and interacting cold atom systems. First, in non-interacting cold atom system, by synthesizing artificial non-Abelian gauge potential, we demonstrate that when a non-Abelian gauge potential is reduced to Abelian potential, the Abelian part constructs spin-orbit coupling, and the non-Abelian part emerges Higgs excitations. Secondly, the Higgs excitations which are the reputed Higgs amplitude mode in interacting cold atom system are discussed. We review the theoretical model and the experimental detection of Higgs amplitude mode in two dimensional superfluid. The observation of both Higgs type excitations in real experiments are also discussed.