Narrow Results

The article reviews the status of the Compact Linear Collider (CLIC) study towards feasibility demonstration of a novel and challenging technology which has been specially developed to extend Linear Colliders energy reach into the multi-TeV range in order to be complementary to LHC (Large Hadron Collider). A Conceptual Design Report is being published summarizing the performance of a High Energy facility based on such a technology as well as the results of the R&D performed to address its feasibility.

The single production of fourth family sneutrino via R-parity violating interactions in electron–positron collisions has been investigated. We study the decays of into different flavor dilepton e^±μ^∓ via R-parity violation. It is shown that R-parity violating couplings (λ₄₁₁, λ₄₁₂) down to 0.001 will be reachable at future linear colliders which would provide better accuracy comparing to the indirect measurements as complementary to the LHC results.

In this paper, we will give a brief review of some important beam physics in circular and linear electron–positron collider designs, covering beam–beam tune limits, longitudinal and transverse single bunch collective effects, electron cloud and space charge effects, dynamic aperture estimations, etc. The main feature of this review is that the corresponding beam physics treatments are coming from author's previous research works which are scattered in different scientific publications both for circular and linear colliders. With the progresses of future linear colliders, such as ILC, and future circular electron–positron colliders, such as CEPC, it is high time to review the key beam physics issues in the optimization designs of these two kinds of machines.

The charged Higgs production associated with a W^± boson has a smooth cross-section as a function of the charged Higgs mass at muon colliders. The cross-section in minimal supersymmetric standard model (MSSM) is about 25 fb in the range 200 GeV < m_H^± <400 GeV with tan β = 50. This is much larger than the corresponding cross-section at an e⁺e^- collider which reaches a fraction of femtobarn. The observability of this charged Higgs production at a muon collider has been recently studied in an earlier work leading to the result that with 1 ab^-1, a 5σ signal can be observed throughout the aforementioned mass range. In this paper, results of a study based on a general two Higgs doublet model (types II and III) are presented and the cross-section of the charged Higgs production in the most sensitive parameter space is evaluated. It is concluded that the cross-section increases with increasing neutral Higgs boson masses involved in the s-channel diagram and can be as large as several picobarn with tan β = 50. The region of "physical Higgs boson mass" parameter space which could lead to a 5σ signal at 50 fb^-1 is specified.

We study the pair production of new heavy leptons within a new U(1)′ symmetry extension of the Standard Model. Because of the new symmetry, the production and decay modes of the new heavy leptons would be different from those of three families of the standard model. The pair production cross-sections depending on the mixing parameter and the mass of heavy leptons have been calculated for the center-of-mass energies of 0.5 TeV, 1 TeV and 3 TeV. The accessible ranges of the parameters have been obtained for different luminosity projections at linear colliders. The search can be performed within the range of mixing parameter -1<x<-0.35 and 0.05<x<1, given that the heavy lepton mass M_l′ = 400 GeV at and L_int = 100 fb^-1. We find the sensitivity to the range of mixing parameter -1<x<1 for the mass range M_l′<800 GeV at and L_int = 100 fb^-1.

In this paper the charged Higgs signal through triple or double Higgs production in a two Higgs doublet model (2HDM) type II is studied. The main production process is e⁺e^- →H⁺H^-H⁰ followed by the charged Higgs decay to a pair of τν and the neutral Higgs decay to . The alternative process H⁺W^-H⁰ is also included as a source of charged Higgs signal in the analysis. The focus is on a future e⁺e^- linear collider operating at . The final state under consideration is suitable for electroweak background rejection using the b-tagging tools. It is shown that although the signal cross-section is small, with a reasonable background suppression, high signal significance values are achievable at an integrated luminosity 500 fb^-1 depending on the charged Higgs mass, tan β and the CP-odd neutral Higgs mass. Finally results are quoted in terms of the signal significance for charged Higgs in the mass range 160 < m_H^± < 400 GeV.

The singly and doubly charged Higgs bosons (H^± and H^±±) are the typical particles predicted in the Higgs Triplet Model and the observation of these particles can be regarded as the direct evidence of new physics. In this paper, we focus on the study of the singly and doubly charged Higgs bosons associated production process: e⁺e^- → H⁺H^--W⁺. We present the production cross sections and the distributions of the transverse momenta and the rapidity distributions for outgoing particles. The numerical results show that the production rates can reach the level of several fb with reasonable parameter values. So, one can expect that enough signals could be produced in the future high-energy e⁺e^- collider experiments. The relevant SM backgrounds are also discussed in the case that the vacuum expectation value of the triplet is around 1 GeV.

The purpose of this article is to introduce some of the basic physical principles underlying the operation of electron linear accelerators (electron linacs). Electron linacs have applications ranging from linacs with an energy of a few MeV, such that the electrons are approximately relativistic, to future electron–positron linear colliders having a collision energy in the several-TeV energy range. For the most part, only the main accelerating linac is treated in this article.

In this article the potential application of advanced accelerator concepts to future high energy colliders is discussed. The emphasis is on lepton colliders, since the advanced technologies appear to be most applicable in this field.

The purpose of this article is to introduce some of the basic physical principles underlying the operation of electron linear accelerators (electron linacs). Electron linacs have applications ranging from linacs with an energy of a few MeV, such that the electrons are approximately relativistic, to future electron–positron linear colliders having a collision energy in the several-TeV energy range. For the most part, only the main accelerating linac is treated in this article.

In this article the potential application of advanced accelerator concepts to future high energy colliders is discussed. The emphasis is on lepton colliders, since the advanced technologies appear to be most applicable in this field.