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Register a new userSearching for Colorons at the Large Hadron Collider
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Joshua Sayre
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We investigate the prospects for the discovery of massive color-octet vector bosons at the CERN Large Hadron Collider with $sqrt{s} = 14$ TeV. A phenomenological Lagrangian is adopted to evaluate the cross section of a pair of colored vector bosons (colorons, $tilde{rho}$) decaying into four colored scalar resonances (hyper-pions, $tilde{pi}$), which then decay into eight gluons. We include the dominant physics background from the production of $8g,7g1q, 6g2q$, and $5g3q$, and determine the masses of $tilde{pi}$ and $tilde{rho}$ where discovery is possible. For example, we find that a 5$sigma$ signal can be established for $M_{tilde{pi}} alt 495$ GeV ($M_{tilde{rho}} alt 1650$ GeV). More generally we give the reach of this process for a selection of possible cuts and integrated luminosities.
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Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, t-bar t production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such particles. We present a detailed study of the discovery potential of the CERN Large Hadron Collider for Kaluza-Klein (KK) excitations of the gluon in bulk Randall-Sundrum (RS) models in the t-bar t -> ell^+/- nu b-bar bq-bar q (ell=e, mu) final state. We utilize final states with one or two tagged b-quarks, and two, three or four jets (including b-jets). Our calculations take into account the finite resolution of detectors, the energy loss due to b-quark decays, the expected reduced b-tagging efficiency at large t-bar t invariant masses, and include the background originating from Wb-bar b+jets, (Wb+W-bar b)+jets, W+jets, and single top + jets production. We derive semi-realistic 5 sigma discovery limits for nine different KK gluon scenarios, and compare them with those for KK gravitons, and a Z_H boson in the Littlest Higgs model. We also analyze the capabilities of the LHC experiments to differentiate between individual KK gluon models and measure the couplings of KK gluons to quarks. We find that, for the parameters and models chosen, KK gluons with masses up to about 4 TeV can be discovered at the LHC. The ability of the LHC to discriminate between different bulk RS models, and to measure the couplings of the KK gluons is found to be highly model dependent.
Weak singlet charged scalar exists in many new physics models beyond the Standard Model. In this work we show that a light singlet charged scalar with mass above 65~GeV is still allowed by the LEP and LHC data. The interactions of the singlet charged scalar with the Standard Model particles are described by operators up to dimension-5. Dominant decay modes of the singlet charged scalar are obtained, and a subtlety involving field redefinition and gauge fixing due to a dimension-5 operator is also clarified. We demonstrate that it is promising to observe the singlet charged scalar at the LHC.
A spectrum of massive graviton states is present in several recent theoretical models that include extra space dimensions. In some such models the graviton states are well separated in mass, and can be detected as resonances in collider experiments. The ability of the ATLAS detector at the Large Hadron Collider to identify such states and measure their properties is considered, in the case that the resonances are narrow compared to the experimental resolution. The discovery limits for the detection of the decay mode G->e+e- are derived. The angular distribution of the lepton pair is used to determine the spin of the intermediate state. In one specific model, the resonance can be detected up to a graviton resonance mass of 2080 GeV, while the angular distribution favours a spin-2 hypothesis over a spin-1 hypothesis at 90% confidence for resonance masses up to 1720 GeV.
Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments --- as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER --- to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the High-Luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity dark showers, highlighting opportunities for expanding the LHC reach for these signals.
We investigate new physics scenarios where systems comprised of a single top quark accompanied by missing transverse energy, dubbed monotops, can be produced at the LHC. Following a simplified model approach, we describe all possible monotop production modes via an effective theory and estimate the sensitivity of the LHC, assuming 20 fb$^{-1}$ of collisions at a center-of-mass energy of 8 TeV, to the observation of a monotop state. Considering both leptonic and hadronic top quark decays, we show that large fractions of the parameter space are reachable and that new physics particles with masses ranging up to 1.5 TeV can leave hints within the 2012 LHC dataset, assuming moderate new physics coupling strengths.
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