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Register a new userA Search for leptophilic Z_(l) boson at future linear colliders
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We study the possible dynamics associated with leptonic charge in future linear colliders. Leptophilic massive vector boson, Z_(l), have been investigated through the process e^(+)e^(-) -> mu^(+)mu^(-). We have shown that ILC and CLIC will give opportunity to observe Z_(l) with masses up to the center of mass energy if the corresponding coupling constant g_(l) exceeds 10^(-3).
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This document aims to provide an assessment of the potential of future colliding beam facilities to perform Higgs boson studies. The analysis builds on the submissions made by the proponents of future colliders to the European Strategy Update process, and takes as its point of departure the results expected at the completion of the HL-LHC program. This report presents quantitative results on many aspects of Higgs physics for future collider projects of sufficient maturity using uniform methodologies. A first version of this report was prepared for the purposes of discussion at the Open Symposium in Granada (13-16/05/2019). Comments and feedback received led to the consideration of additional run scenarios as well as a refined analysis of the impact of electroweak measurements on the Higgs coupling extraction.
The leptophilic weakly interacting massive particle (WIMP) is realized in a minimal renormalizable model scenario where scalar mediators with lepton number establish the WIMP interaction with the standard model (SM) leptons. We perform a comprehensive analysis for such a WIMP scenario for two distinct cases with an SU(2) doublet or singlet mediator considering all the relevant theoretical, cosmological and experimental constraints at present. We show that the mono-photon search at near-future lepton collider experiments (ILC, FCC-ee, CEPC, etc.) can play a significant role to probe the yet unexplored parameter range allowed by the WIMP relic density constraint. This will complement the search prospect at the near-future hadron collider experiment (HL-LHC). Furthermore, we discuss the combined model scenario including both the doublet and singlet mediator. The combined model is capable of explaining the long-standing muon (g-2) anomaly which is an additional advantage. We demonstrate that the allowed region for anomalous muon (g-2) explanation, which has been updated very recently at Fermi National Accelerator Laboratory, can also be probed at the future colliders which will thus be a simultaneous authentication of the model scenario.
Doubly charged excited leptons give rise to interesting signatures for physics beyond the standard model at the present Large Hadron Collider. These exotic states are introduced in extended isospin multiplets which couple to the ordinary leptons and quarks either with gauge or contact effective interactions or a combination of both. In this paper we study the production and the corresponding signatures of doubly charged leptons at the forthcoming linear colliders and we focus on the electron-electron beam setting. In the framework of gauge interactions, the interference between the $t$ and $u$ channel is evaluated that has been neglected so far. A pure leptonic final state is considered ($e^{-} , e^{-} rightarrow e^{-} , e^{-} , u_{e} , bar{ u}_{e}$) that experimentally translates into a like-sign dilepton and missing transverse energy signature. We focus on the standard model irreducible background and we study the invariant like-sign dilepton mass distribution for both the signal and background processes. Finally, we provide the 3 and 5-sigma statistical significance exclusion curves in the model parameter space. We find that for a doubly charged lepton mass $m^*approx 2 $ TeV the expected lower bound on the compositeness scale at CLIC, $Lambda > 25$ TeV, is much stronger than the current lower bound from LHC ($Lambda > 5$ TeV) and remains highly competitive with the bounds expected from the run II of the LHC.
In this study, we investigate observability of the neutral scalar ($H$) and pseudoscalar ($A$) Higgs bosons in the framework of the Type-I 2HDM at SM-like scenario at a linear collider operating at $sqrt s=$ 500 and 1000 GeV. The signal process chain $e^- e^+ rightarrow A H rightarrow ZHHrightarrow jj bbar{b}bbar{b}$ where $jj$ is a di-jet resulting from the $Z$ boson decay and $bbar{b}$ is a $b$ quark pair, is assumed and several benchmark scenarios with different mass hypotheses are studied. The assumed signal process is mainly motivated by the possible enhancements the decay modes $Arightarrow ZH$ and $Hrightarrow bbar{b}$ may receive in the Type-I. Event generation is performed for the assumed scenarios separately and the beamstrahlung effects are taken into account. The detector response is simulated based on the SiD detector at the ILC and the simulated events are analyzed to obtain candidate mass distributions of the Higgs bosons. According to the results, the top quark pair production process has the most contribution to the total background and is, however, well-controlled. Results indicate that, in all of the considered scenarios, both of the Higgs bosons $H$ and $A$ are observable with signals exceeding $5sigma$ with possibility of mass measurement. To be specific, at $sqrt s=500$ GeV, the region of parameter space with $m_H=150$ GeV and $200leq m_A leq 250$ GeV is observable at the integrated luminosity of 500 $fb^{-1}$. Also, at $sqrt s=1000$ GeV, the region with $150leq m_H leq 250$ GeV and $200leq m_A leq 330$ GeV with a mass splitting of 50-100 GeV between the $H$ and $A$ Higgs bosons is observable at the same integrated luminosity.
New physics close to the electroweak scale is well motivated by a number of theoretical arguments. However, colliders, most notably the Large Hadron Collider (LHC), have failed to deliver evidence for physics beyond the Standard Model. One possibility for how new electroweak-scale particles could have evaded detection so far is if they carry only electroweak charge, i.e. are color neutral. Future $e^+e^-$ colliders are prime tools to study such new physics. Here, we investigate the sensitivity of $e^+e^-$ colliders to scalar partners of the charged leptons, known as sleptons in supersymmetric extensions of the Standard Model. In order to allow such scalar lepton partners to decay, we consider models with an additional neutral fermion, which in supersymmetric models corresponds to a neutralino. We demonstrate that future $e^+e^-$ colliders would be able to probe most of the kinematically accessible parameter space, i.e. where the mass of the scalar lepton partner is less than half of the colliders center-of-mass energy, with only a few days of data. Besides constraining more general models, this would allow to probe some well motivated dark matter scenarios in the Minimal Supersymmetric Standard Model, in particular the incredible bulk and stau co-annihilation scenarios.
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