No Arabic abstract
The proposed Circular Electron Positron Collider (CEPC), with a center-of-mass energy $sqrt{s} = 240$ GeV, will serve as a Higgs factory. At the same time, it can offer good opportunity for searches for new physics phenomena at low energy: these are challenging in hadron colliders, but well motivated by some theory models developed to explain, e.g., the relic abundance of dark matter. This paper presents sensitivity studies of chargino pair production, considering scenarios for both a Bino-like and a Higgsino-like neutralino as lightest supersymmetric particle, using full Monte Carlo (MC) simulation. With the assumption of systematic uncertainties at the level of 5%, the CEPC has the ability to discover chargino pair production up to the kinematic limit of $sqrt{s}/2$ for both considered cases. Thanks to the conservative assumptions on the systematic uncertainties and the low dependence on the reconstruction model and detector geometry considered, the results of this study can be considered as a reference and benchmark also for similar searches in other similar electron positron colliders, such as Future Circular Collider $e^{+}e^{-}$ (FCC-ee) and the International Linear Collider (ILC).
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.
We study chargino pair production on the heavy Higgs resonances at a muon collider in the MSSM. At $sqrt{s} approx 350$ GeV cross sections up to 2 pb are reached depending on the supersymmetric scenario and the beam energy spread. The resonances of the scalar and pseudoscalar Higgs bosons may be separated for $tanbeta <8$. Our aim is to determine the ratio of the chargino couplings to the heavy scalar and pseudoscalar Higgs boson independently of the specific chargino decay characteristics. The precision of the measurement depends on the energy resolution of the muon collider and on the error in the measurement of the cross sections of the non-Higgs channels including an irreducible standard model background. With a high energy resolution the systematic error can be reduced to the order of a few percent.
We make use of recently released parton density functions (PDFs) with threshold-resummation improvement to consistently calculate theoretical predictions for neutralino and chargino pair production at next-to-leading order and next-to-leading logarithmic accuracy. The updated cross sections have been computed for experimentally relevant higgsino and gaugino search channels at the ongoing Run II of the LHC. A factorisation method is applied to exploit the smaller PDF uncertainty of the global PDF sets and to avoid complications arising in the refitting of threshold-resummation improved PDF replicas in Mellin space. The reduction of the scale uncertainty due to the resummation is, however, explicitly taken into account. As expected, the resummation contributions in the PDF fits partially compensate the cross section enhancements induced by those in the partonic matrix elements.
We present a study performed for the CLIC CDR on the measurement of chargino and neutralino production at sqrt(s) = 3 TeV. Fully hadronic final states with four jets and missing transverse energy were considered. Results obtained using full detector simulation for the masses and for the production cross sections of the changino and the lightest and next-to-lightest neutralinos are discussed.
The precise determination of the $B_c to tau u_tau$ branching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element $|V_{cb}|$ and probing new physics models. In this paper, we discuss the potential of measuring the processes of $B_c to tau u_tau$ with $tau$ decaying leptonically at the proposed Circular Electron Positron Collider (CEPC). We conclude that during the $Z$ pole operation, the channel signal can achieve five $sigma$ significance with $sim 10^9$ $Z$ decays, and the signal strength accuracies for $B_c to tau u_tau$ can reach around 1% level at the nominal CEPC $Z$ pole statistics of one trillion $Z$ decays assuming the total $B_c to tau u_tau$ yield is $3.6 times 10^6$. Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the $b to ctau u$ transition. If the total $B_c$ yield can be determined to $mathcal{O}(1%)$ level of accuracy in the future, these results also imply $|V_{cb}|$ could be measured up to $mathcal{O}(1%)$ level of accuracy.