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Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one long-lived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. This analysis uses a data sample of proton-proton collisions at ffiffi ffi s p ¼ 8 TeV corresponding to an integrated luminosity of 20.3 fb −1 collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving R-parity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual long-lived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios.

A search for long-lived, massive particles predicted by many theories beyond the Standard Model is presented. The search targets final states with large missing transverse momentum and at least one highmass displaced vertex with five or more tracks, and uses 32.8 fb −1 of ffiffi ffi s p ¼ 13 TeV pp collision data collected by the ATLAS detector at the LHC. The observed yield is consistent with the expected background. The results are used to extract 95% C.L. exclusion limits on the production of long-lived gluinos with masses up to 2.37 TeV and lifetimes of Oð10 −2 Þ − Oð10Þ ns in a simplified model inspired by split supersymmetry.

High-energy lepton colliders with a centre-of-mass energy in the multi-TeV range are currently considered among the most challenging and far-reaching future accelerator projects. Studies performed so far have mostly focused on the reach for new phenomena in lepton-antilepton annihilation channels. In this work we observe that starting from collider energies of a few TeV, electroweak (EW) vector boson fusion/scattering (VBF) at lepton colliders becomes the dominant production mode for all Standard Model processes relevant to studying the EW sector. In many cases we find that this also holds for new physics. We quantify the size and the growth of VBF cross sections with collider energy for a number of SM and new physics processes. By considering luminosity scenarios achievable at a muon collider, we conclude that such a machine would effectively be a “high-luminosity weak boson collider,” and subsequently offer a wide range of opportunities to precisely measure EW and Higgs couplings as well as discover new particles.

This paper presents a search for direct electroweak gaugino or gluino pair production with a chargino nearly mass-degenerate with a stable neutralino. It is based on an integrated luminosity of 36.1 fb −1 of pp collisions at √ s = 13 TeV collected by the ATLAS experiment at the LHC. The final state of interest is a disappearing track accompanied by at least one jet with high transverse momentum from initial-state radiation or by four jets from the gluino decay chain. The use of short track segments reconstructed from the innermost tracking layers significantly improves the sensitivity to short chargino lifetimes. The results are found to be consistent with Standard Model predictions. Exclusion limits are set at 95% confidence level on the mass of charginos and gluinos for different chargino lifetimes. For a pure wino with a lifetime of about 0.2 ns, chargino masses up to 460 GeV are excluded. For the strong production channel, gluino masses up to 1.65 TeV are excluded assuming a chargino mass of 460 GeV and lifetime of 0.2 ns. Keywords: Hadron-Hadron scattering (experiments)ArXiv ePrint: 1712.02118Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP 3 .https://doi.org/10.1007/JHEP06 (2018) [7], SUSY particles are produced in pairs and decay such that their final products consist only of SM particles and the stable lightest supersymmetric particle (LSP). In many supersymmetric models, the supersymmetric partners of the SM W boson fields, the wino fermions, are the lightest gaugino states. In this case, the lightest of the charged mass eigenstates, a chargino, and the lightest of the neutral mass eigenstates, a neutralino, are both almost pure wino and nearly mass-degenerate. As a result, the lightest chargino can have a lifetime long enough that it can reach the AT-LAS detector before decaying. For example, anomaly-mediated supersymmetry breaking (AMSB) scenarios [8,9] naturally predict a pure wino LSP, which is a dark-matter candidate. The mass-splitting between the charged and neutral wino (∆mχ 1 ) in such models is suppressed at tree level by the approximate custodial symmetry; it has been calculated at the two-loop level to be around 160 MeV [10], corresponding to a chargino lifetime of about 0.2 ns [11]. This prediction for the value of the lifetime is actually a general feature of models with a wino LSP: within the generated models of the ATLAS phenomenological Minimal Supersymmetric Standard Model (pMSSM) scan [12] that have a wino-like LSP, about 70% have a charged-wino lifetime between 0.15 ns and 0.25 ns. Most of the models in the other 30% have a larger mass-splitting (and therefore the charged wino has a shorter lifetime) due to a non-decoupled higgsino mass. The search presented here is sensitive to a wide range of lifetimes, from 10 ps to 10 ns, and reaches maximum sensitivity for lifetimes around 1 ns.The decay products of SUSY particles that are strongly mass-degenerate with the lightest neutralino leave little visible energy in the detector. T...