On measuring Split-SUSY neutralino and chargino masses at the LHC

In Split-Supersymmetry models, where the only non-Standard Model states produceable at LHC-energies consist of a gluino plus neutralinos and charginos, it is conventionally accepted that only mass differences among these latter are measurable at the LHC. The present work shows that application of a simple ‘Kinematic Selection’ technique allows for full reconstruction of neutralino and chargino masses from one event, in principle. A Monte Carlo simulation demonstrates the feasibility of using this technique at the LHC.     

Test of lepton flavour violation at the LHC

We study lepton flavour violating decays of neutralinos and sleptons within the minimal supersymmetric standard model, assuming two and three generation mixings in the slepton sector. We take into account the most recent bounds on flavour violating rare lepton decays. Taking the SPS1a’ scenario as an example, we show that some of the lepton flavour violating branching ratios of neutralinos and sleptons can be sizable (∼5–10%). We study the impact of the lepton flavour violating neutralino and slepton decays on the di-lepton mass distributions measured at the LHC. We find that they can result in novel and characteristic edge structures in the distributions. In particular, double-edge structures can appear in the eτ and μτ mass spectra if is the lightest slepton. The appearance of these remarkable structures provides a powerful test of supersymmetric lepton flavour violation at the LHC.     

Signatures of gaugino mass non-universality in cascade Higgs production at the LHC

Supersymmetric cascades, involving charginos and neutralinos at various stages, contribute in a significant way to Higgs production at the LHC. We explore the nature of such cascades, completely relaxing the universality of the gaugino masses. It is found that the deviation from the scenario with universal gaugino masses would be reflected in the relative production rates for the lightest neutral Higgs and the charged Higgses.     

Search for supersymmetric particles in light gravitino scenarios and sleptons NLSP

A search for sleptons, neutralinos, charginos, sgoldstinos and heavy stable charged sleptons in the context of scenarios where the lightest supersymmetric particle is the gravitino, is presented. Data collected during 2000 with the DELPHI detector at centre-of-mass energies from 204 to 208 GeV were analysed and combined with all the data collected from 1995 to 1999 at lower energies. No evidence for the production of sleptons, neutralinos and charginos has been found, therefore new limits on the mass of these supersymmetric particles and on the model parameter space are set. The search for heavy stable charged sleptons also updates the stable sleptons mass limit. The absence of evidence for sgoldstino production allows limits to be set on its mass and on the scale of supersymmetry breaking. Received: 6 November 2002 / Published online: 14 February 2003     

CP asymmetries in the supersymmetric trilepton signal at the LHC

In the CP-violating Minimal Supersymmetric Standard Model, we study the production of a neutralino–chargino pair at the LHC. For their decays into three leptons, we analyze CP asymmetries which are sensitive to the CP phases of the neutralino and chargino sector. We present analytical formulas for the entire production and decay process, and identify the CP-violating contributions in the spin correlation terms. This allows us to define the optimal CP asymmetries. We present a detailed numerical analysis of the cross sections, branching ratios, and the CP observables. For light neutralinos, charginos, and squarks, the asymmetries can reach several 10%. We estimate the discovery potential for the LHC to observe CP violation in the trilepton channel.     

Perspectives of SM Higgs measurements at the LHC

The latest unsuccessful Higgs searches at LEP have pushed its mass well into the domain where significant signals can be expected from the LHC experiments. The most sensitive LHC Higgs signatures are reviewed and the discovery year is estimated as a function of the Higgs mass. Finally, we give some ideas about: ‘What might be known about the production and decays of a SM Higgs boson’ after 10 years of LHC?     

ALPs effective field theory and collider signatures

We study the leading effective interactions between the Standard Model fields and a generic singlet CP-odd (pseudo-) Goldstone boson. Two possible frameworks for electroweak symmetry breaking are considered: linear and non-linear. For the latter case, the basis of leading effective operators is determined and compared with that for the linear expansion. Associated phenomenological signals at colliders are explored for both scenarios, deriving new bounds and analyzing future prospects, including LHC and High Luminosity LHC sensitivities. Mono-Z, mono-W, W-photon plus missing energy and on-shell top final states are most promising signals expected in both frameworks. In addition, non-standard Higgs decays and mono-Higgs signatures are especially prominent and expected to be dominant in non-linear realisations.     

Search for supersymmetry at LHC

One of the main motivations for the experiments at the Large Hadron Collider (LHC), scheduled to start around 2006, is to search for supersymmetric particles. The region of the parameter space of the minimal supersymmetric standard model, where supersymmetry can be discovered, is investigated. We show that if supersymmetry exists at the electroweak scale, it would be easy to find signals for it at the LHC. If the LHC does find supersymmetry, this would be one of the greatest achievements in the history of theoretical physics.     

Search for supersymmetric particles in scenarios with a gravitino LSP and stau NLSP

Sleptons, neutralinos and charginos were searched for in the context of scenarios where the lightest supersymmetric particle is the gravitino. It was assumed that the stau is the next-to-lightest supersymmetric particle. Data collected with the DELPHI detector at a centre-of-mass energy near 189 GeV were analysed combining the methods developed in previous searches at lower energies. No evidence for the production of these supersymmetric particles was found. Hence, limits were derived at 95% confidence level. Received: 3 February 2000 / Revised version: 3 March 2000 / Published online: 8 May 2000     

Production and decay of neutralinos in the Next-to-Minimal Supersymmetric Standard Model

Within the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) we study neutralino production (i,j=1, …, 5) at center-of-mass energies between 100 and 600 GeV and the decays of the heavier neutralinos into the LSP plus a fermion pair, a photon or a Higgs boson. For representative gaugino/higgsino mixing scenarios, where the light neutralinos have significant singlet components, we find some striking differences between the NMSSM and the minimal supersymmetric model. Since in the NMSSM neutralino and Higgs sector are strongly correlated, the decay of the second lightest neutralino into a Higgs boson and the LSP often is kinematically possible and even dominant in a large parameter region of typical NMSSM scenarios. Also, the decay rates into final states with a photon may be enhanced.     

Light Higgs bosons in phenomenological NMSSM

We consider scenarios in the next-to-minimal supersymmetric model (NMSSM) where the CP-odd and charged Higgs bosons are very light. As we demonstrate, these can be obtained as simple deformations of existing phenomenological MSSM benchmarks scenarios with parameters defined at the weak scale. This offers a direct and meaningful comparison to the MSSM case. Applying a wide set of up-to-date constraints from both high-energy collider and flavor physics, the Higgs boson masses and couplings are studied in viable parts of parameter space. The LHC phenomenology of the light Higgs scenario for neutral and charged Higgs boson searches is discussed.     

Phenomenological aspects of heterotic orbifold models at one loop

We provide a detailed study of the phenomenology of orbifold compactifications of the heterotic string within the context of supergravity effective theories. Our investigation focuses on those models where the soft Lagrangian is dominated by loop contributions to the various soft supersymmetry breaking parameters. Such models typically predict non-universal soft masses and are thus significantly different from minimal supergravity and other universal models. We consider the pattern of masses that are governed by these soft terms and investigate the implications of certain indirect constraints on supersymmetric models, such as flavor-changing neutral currents, the anomalous magnetic moment of the muon and the density of thermal relic neutralinos. We also comment on the possible discovery of these models at the LHC. These string-motivated models show a novel behavior that interpolates between the phenomenology of unified supergravity models and models dominated by the superconformal anomaly. PACS 11.25.Wx, 12.60.Jv, 04.65.+e     

A new window at the LHC: BSM signals using tagged protons

The signature at the LHC of many Beyond the Standard Model (BSM) scenarios is events with large missing energy. If the forward outgoing protons are measured, we show that the production and decay of BSM particles in the central rapidity interval, with gaps in rapidity either side, offer certain advantages over inclusive production, to search for signals (a) with missing longitudinal 4-momentum (typical of invisible Higgs production), and (b) for new light pseudoscalar bosons.     

Dark matter constraints on gaugino/Higgsino masses in split supersymmetry and their implications at colliders

In split supersymmetry, gauginos and Higgsinos are the only supersymmetric particles that are potentially accessible at soon-to-be-completed colliders. While direct experimental research, such as the LEP and Tevatron experiments, have given robust lower bounds on the masses of these particles, cosmic dark matter can give some upper bounds and thus have important implications for research at future colliders. In this work we scrutinize such dark matter constraints and show the allowed mass range for charginos and neutralinos (the mass eigenstates of gauginos and Higgsinos). We find that the lightest chargino must be lighter than about 1 TeV under the popular assumption M₁=M₂/2 and about 2 or 3 TeV in other cases. The corresponding production rates of the lightest chargino at the CERN large hadron collider (LHC) and the International Linear Collider (ILC) are also given. While in some parts of the allowed region the chargino pair production rate can be larger than 1 pb at the LHC and 100 fb at the ILC, other parts of the region correspond to very small production rates, and thus there is no guarantee of finding the charginos of split supersymmetry at future colliders. PACS 14.80.Ly, 95.35.+d     

Chargino and neutralino decays revisited

We perform a comprehensive analysis of the decays of charginos and neutralinos in the minimal supersymmetric standard model where the neutralino is assumed to be the lightest supersymmetric particle. We focus, in particular, on the three-body decays of the next-to-lightest neutralino and the lightest chargino into the lightest neutralino and fermion–antifermion pairs and include vector boson, Higgs boson and sfermion exchange diagrams, where in the latter contribution the full mixing in the third generation is included. The radiative corrections to the heavy fermion and SUSY particle masses will also be taken into account. We present complete analytical formulae for the Dalitz densities and the integrated partial decay widths in the massless fermion case, as well as the expressions of the differential decay widths including the masses of the final fermions and the polarization of the decaying charginos and neutralinos. We then discuss these decay modes, in particular in scenarios where the parameter is large and in models without universal gaugino masses at the grand unification scale, where some new decay channels, such as decays into gluinos and pairs, open up. Received: 12 April 2001 / Published online: 8 June 2001     

MSSM Higgs boson searches at the Tevatron and the LHC: Impact of different benchmark scenarios

The Higgs boson search has shifted from LEP2 to the Tevatron and will subsequently move to the LHC. The current limits from the Tevatron and the prospective sensitivities at the LHC are often interpreted in specific MSSM scenarios. For heavy Higgs boson production and subsequent decay into or τ⁺τ^–, the present Tevatron data allow one to set limits in the M_A–tan β plane for small M_A and large tan β values. Similar channels have been explored for the LHC, where the discovery reach extends to higher values of M_A and smaller tan β. Searches for MSSM charged Higgs bosons, produced in top decays or in association with top quarks, have also been investigated at the Tevatron and the LHC. We analyze the current Tevatron limits and prospective LHC sensitivities. We discuss how robust they are with respect to variations of the other MSSM parameters and possible improvements of the theoretical predictions for Higgs boson production and decay. It is shown that the inclusion of supersymmetric radiative corrections to the production cross sections and decay widths leads to important modifications of the present limits on the MSSM parameter space. The impact on the region where only the lightest MSSM Higgs boson can be detected at the LHC is also analyzed. We propose to extend the existing benchmark scenarios by including additional values of the higgsino mass parameter μ. This affects only slightly the search channels for a SM-like Higgs boson, while having a major impact on the searches for non-standard MSSM Higgs bosons.     

Implications of the pseudo-scalar Higgs boson in determining the neutralino dark matter

In the framework of the constrained minimal supersymmetric standard model (CMSSM) we discuss the impact of the pseudo-scalar Higgs boson in delineating regions of the parameters which are consistent with cosmological data and E821 data on the anomalous magnetic moment of the muon. For the large values of the parameter , cosmologically allowed corridors of large are opened, due to the s-channel pseudo-scalar exchange in the pair annihilation of the lightest of the neutralinos to or , which dominates in this region. However, no such corridors are found for values . Combining cosmological and E821 data puts severe upper limits on the sparticle masses. We find that at LHC, but even at a linear collider with center of mass energy GeV, such as TESLA, supersymmetry can be discovered, if it is based on the CMSSM. Received: 22 July 2001 / Revised version: 13 November 2001 / Published online: 18 January 2002     

Identification of the origin of monojet signatures at the LHC

Several new physics scenarios can lead to monojet signatures at the LHC. If such events are observed above the Standard Model background it will be important to identify their origin. In this Letter we compare and contrast these signatures as produced in two very different pictures: vector or scalar unparticle production in the scale-invariant/conformal regime and graviton emission in the Arkani-Hamed, Dimopoulos and Dvali extra-dimensional model. We demonstrate that these two scenarios can be distinguished at the LHC for a reasonable range of model parameters through the shape of their respective monojet and/or missing E_T distributions.     

Direct chargino–neutralino production at the LHC: interpreting the exclusion limits in the complex MSSM

We re-assess the exclusion limits on the parameters describing the supersymmetric (SUSY) electroweak sector of the MSSM obtained from the search for direct chargino–neutralino production at the LHC. We start from the published limits obtained for simplified models, where for the case of heavy sleptons the relevant branching ratio, $\mathrm {BR}(\tilde{\chi}^{0}_{2} \to \tilde{\chi}^{0}_{1} Z)$ , is set to one. We show how the decay mode $\tilde{\chi}^{0}_{2} \to \tilde{\chi}^{0}_{1} h$ , which cannot be neglected in any realistic model once kinematically allowed, substantially reduces the excluded parameter region. We analyze the dependence of the excluded regions on the phase of the gaugino soft SUSY-breaking mass parameter, M ₁, on the mass of the light scalar tau, $m_{{\tilde{\tau}_{1}}}$ , on tanβ as well as on the squark and slepton mass scales. Large reductions in the ranges of parameters excluded can be observed in all scenarios. The branching ratios of charginos and neutralinos are evaluated using a full NLO calculation for the complex MSSM. The size of the effects of the NLO calculation on the exclusion bounds is investigated. We furthermore assess the potential reach of the experimental analyses after collecting 100 fb^?1 at the LHC running at 13 TeV.     

Searches for Dark Matter via Mono-W Production in Inert Doublet Model at the LHC

The Inert Doublet Model(IDM) is one of the many beyond Standard Model scenarios with an extended scalar sector, which provide a suitable dark matter particle candidate. Dark matter associated visible particle production at high energy colliders provides a unique way to determine the microscopic properties of the dark matter particle. In this paper, we investigate that the mono-W + missing transverse energy production at the Large Hadron Collider(LHC),where W boson decay to a lepton and a neutrino. We perform the analysis for the signal of mono-W production in the IDM and the Standard Model(SM) backgrounds, and the optimized criteria employing suitable cuts are chosen in kinematic variables to maximize signal significance. We also investigate the discovery potential in several benchmark scenarios at the 14 TeV LHC. When the light Z_2 odd scalar higgs of mass is about 65 GeV, charged Higgs is in the mass range from 120 GeV to 250 GeV, it provides the best possibility with a signal significance of about 3σ at an integrated luminosity of about 3000 fb~(-1).