Search

With the increasing usage of machine-learning in high-energy physics analyses, the publication of the trained models in a reusable form has become a crucial question for analysis preservation and reuse. The complexity of these models creates practical issues for both reporting them accurately and for ensuring the stability of their behaviours in different environments and over extended timescales. In this note we discuss the current state of affairs, highlighting specific practical issues and focusing on the most promising technical and strategic approaches to ensure trustworthy analysis-preservation. This material originated from discussions in the LHC Reinterpretation Forum and the 2023 PhysTeV workshop at Les Houches., Comment: 12 pages; v2: added funding acknowledgement

We revisit LHC searches for heavy invisible particles by exploiting QCD initial state radiation. We recast a dijet signal region in a general multijet plus MET search by ATLAS. We find that non-trivial mass limit can be obtained for various models of the electroweakino sector with the present data in hadronic channels. The winos are bound to be heavier than $m_{\tilde W} \gtrsim {160}$ GeV and higgsinos $m_{\tilde h} \gtrsim {100}$ GeV, depending on the chargino-neutralino mass splitting. The expected exclusion limits at the LHC Run 3 with $\mathcal{L} = 300$ fb$^{-1}$ increase to $m_{\tilde W} \gtrsim {200}$ GeV and $m_{\tilde h} \gtrsim {130}$ GeV for winos and higgsino, respectively. This is the first LHC limit for promptly decaying nearly mass-degenerate winos., Comment: 8 pages, 5 figures; updated references, expectations for LHC Run 3 added; to appear in PRD

We study the monojet and dijet channels at the LHC as a tool for searching for squarks and gluinos. We consider two separate R-parity conserving supersymmetric scenarios. In the first scenario we postulate a large mass hierarchy between squarks ($\tilde q$) and winos ($\widetilde W$), and wino-like neutralino is assumed to be the lightest supersymmetric particle (LSP). The associated squark-wino production, $pp \to \tilde q \widetilde W$, then leads to a monojet-like signature, where the high $p_T$ jet is originated from the squark decay, $\tilde q \to q + \widetilde W$. We demonstrate that this associated production, as well as the $pp \to \widetilde W \widetilde W + {\rm jets}$ production, have a significant impact on the exclusion limit in the squark-neutralino mass plane. The second scenario postulates that the lighter of the squark and gluino is only a few GeV heavier than the LSP neutralino. The associated squark-gluino production, $pp \to \tilde q \tilde g$, then leads to a distinctive monojet signature, where the high $p_T$ jet is produced from the decay of the heavier coloured particle into the lighter one ($\tilde q \to q + \tilde g$ for $m_{\tilde q} > m_{\tilde g}$ and $\tilde g \to q + \tilde q$ for $m_{\tilde g} > m_{\tilde q}$). The lighter coloured particle is effectively regarded as an invisible particle since the decay products are soft due to the approximate mass degeneracy. We recast existing monojet and dijet analyses and find a non-trivial exclusion limit in the squark-gluino mass plane in this scenario., Comment: 20 pages, 10 figures. Version published in JHEP

We present updated LHC limits on the minimal universal extra dimensions (MUED) model from the Run 2 searches. We scan the parameter space against a number of searches implemented in the public code \textsc{CheckMATE} and derive up-to-date limits on the MUED parameter space from 13 TeV searches. The strongest constraints come from a search dedicated to squarks and gluinos with one isolated lepton, jets and missing transverse energy. In the procedure we take into account initial state radiation and stress its importance in the MUED searches, which is not always appreciated., Comment: 9 pages, 6 figures

Long-lived particles have become a new frontier in the exploration of physics beyond the Standard Model. In this paper, we present the implementation of four types of long-lived particle searches, viz. displaced leptons, disappearing track, displaced vertex (together with muons or with missing energy), and heavy charged tracks. These four categories cover the signatures of a large range of physics models. We illustrate their potential for exclusion and discuss their mutual overlaps in mass-lifetime space for two simple phenomenological models involving either a U(1)-charged or a coloured scalar., Comment: 28 pages, 7 figures; minor typesetting changes and references added

Using the latest LHC data, we analyse and compare the lower limits on the masses of gluinos and the lightest stop in two natural supersymmetric motivated scenarios: one with a neutralino being the lightest supersymmetric particle (LSP) and the other one with gravitino as the LSP and neutralino as the next-to-lightest supersymmetric particle. In the second case our analysis applies to neutralinos promptly decaying to very light gravitinos, which are of cosmological interest, and are generic for low, of order O(100) TeV, messenger scale in gauge mediation models. We find that the lower bounds on the gluino and the lightest stop masses are stronger for the gravitino LSP scenarios due to the extra handle from the decay products of neutralinos. Generally, in contrast to the neutralino LSP case the limits now extend to a region of compressed spectrum. In bino scenarios the highest excluded stop mass increases from 1000 GeV to almost 1400 GeV. Additionally, in the higgsino-like NLSP scenario the higgsinos below 650 GeV are universally excluded and the stop mass limit is $m_{\tilde{t}} > 1150$ GeV, whereas there is no limit on stops in the higgsino LSP model for $m_{\tilde{h}} = 650$ GeV. Nevertheless, we find that the low messenger scale still ameliorates the fine tuning in the electroweak potential., Comment: 22 pages, 5 figures, minor changes, to appear in JHEP

An analytical formalism, including RG running at two loop order, is used to link the supersymmetric and GUT spectra in any GUT model in which the three gauge couplings unify. In each specific GUT model, one can then fully explore the interplay between the pattern of supersymmetry breaking and the prediction for the proton lifetime. With this formalism at hand, we study three concrete GUT models: (i) Minimal SU(5) SUSY GUT, (ii) Missing Partner SU(5) SUSY GUT, and (iii) an orbifold SU(5) SUSY GUT. In each case we derive interesting conclusions about the possible patterns of the supersymmetric spectrum once the present limits on the proton lifetime are imposed, and vice versa, we obtain the predictions for the proton lifetime for specific viable choices of the SUSY spectrum., Comment: 23 pages, 4 figures, version published in JHEP

We present a deep learning solution to the prediction of particle production cross sections over a complicated, high-dimensional parameter space. We demonstrate the applicability by providing state-of-the-art predictions for the production of charginos and neutralinos at the Large Hadron Collider (LHC) at the next-to-leading order in the phenomenological MSSM-19 and explicitly demonstrate the performance for $pp\to\tilde{\chi}^+_1\tilde{\chi}^-_1,$ $\tilde{\chi}^0_2\tilde{\chi}^0_2$ and $\tilde{\chi}^0_2\tilde{\chi}^\pm_1$ as a proof of concept which will be extended to all SUSY electroweak pairs. We obtain errors that are lower than the uncertainty from scale and parton distribution functions with mean absolute percentage errors of well below $0.5\,\%$ allowing a safe inference at the next-to-leading order with inference times that improve the Monte Carlo integration procedures that have been available so far by a factor of $\mathcal{O}(10^7)$ from $\mathcal{O}(\rm{min})$ to $\mathcal{O}(\mu\rm{s})$ per evaluation., Comment: 7 pages, 3 figures

We show that gauge coupling unification in SUSY models can make a non-trivial interconnection between collider and proton decay experiments. Under the assumption of precise gauge coupling unification in the MSSM, the low energy SUSY spectrum and the unification scale are intertwined, and the lower bound on the proton lifetime can be translated into upper bounds on SUSY masses. We found that the current limit on $\tau(p \to \pi^0 e^+)$ already excludes gluinos and winos heavier than $\sim 120$ and 40 TeV, respectively, if their mass ratio is $M_3/M_2 \sim 3$. Next generation nucleon decay experiments are expected to bring these upper bounds down to $\sim 10$ and 3 TeV., Comment: 5 pages, 3 figures

We present the latest developments to the CheckMATE program that allows models of new physics to be easily tested against the recent LHC data. To achieve this goal, the core of CheckMATE now contains over 60 LHC analyses of which 12 are from the 13 TeV run. The main new feature is that CheckMATE 2 now integrates the Monte Carlo event generation via Madgraph and Pythia 8. This allows users to go directly from a SLHA file or UFO model to the result of whether a model is allowed or not. In addition, the integration of the event generation leads to a significant increase in the speed of the program. Many other improvements have also been made, including the possibility to now combine signal regions to give a total likelihood for a model., Comment: 53 pages, 6 figures; references updated, instructions slightly changed

The elucidation of the nature of new phenomena requires a multi-pronged approach to understand the essential physics that underlies it. As an example, we study the simplified model containing a new scalar singlet accompanied by vector-like quarks, as motivated by the recent diphoton excess at the LHC. To be specific, we investigate three models with $SU(2)_L$-doublet, vector-like quarks with Yukawa couplings to a new scalar singlet and which also couple off-diagonally to corresponding Standard Model fermions of the first or third generation through the usual Higgs boson. We demonstrate that three classes of searches can play important and complementary roles in constraining this model. In particular, we find that missing energy searches designed for superparticle production, supply superior sensitivity for vector-like quarks than the dedicated new quark searches themselves., Comment: References added; small bug found in model and analysis implementation, numerical results slightly modified, conclusions unchanged

As we anticipate the first results of the 2016 run, we assess the discovery potential of the LHC to `natural supersymmetry'. To begin with, we explore the region of the model parameter space that can be excluded with various centre-of-mass energies (13 TeV and 14 TeV) and different luminosities (20 fb$^{-1}$, 100 fb$^{-1}$, 300 fb$^{-1}$ and 3000 fb$^{-1}$). We find that the bounds at 95% CL on stops vary from $m_{\tilde{t}_1}\gtrsim 900$ GeV expected this summer to $m_{\tilde{t}_1}\gtrsim 1500$ GeV at the end of the high luminosity run, while gluino bounds are expected to range from $m_{\tilde{g}}\gtrsim 1700$ GeV to $m_{\tilde{g}}\gtrsim 2500$ GeV over the same time period. However, more pessimistically we find that if no signal begins to appear this summer, only a very small region of parameter space can be discovered with 5-$\sigma$ significance. For this conclusion to change, we find that both theoretical and systematic uncertainties will need to be significantly reduced., Comment: 19 pages, 13 figures, minor changes, Phys.Rev.D version

A key research question at the Large Hadron Collider (LHC) is the test of models of new physics. Testing if a particular parameter set of such a model is excluded by LHC data is a challenge: It requires the time consuming generation of scattering events, the simulation of the detector response, the event reconstruction, cross section calculations and analysis code to test against several hundred signal regions defined by the ATLAS and CMS experiment. In the BSM-AI project we attack this challenge with a new approach. Machine learning tools are thought to predict within a fraction of a millisecond if a model is excluded or not directly from the model parameters. A first example is SUSY-AI, trained on the phenomenological supersymmetric standard model (pMSSM). About 300,000 pMSSM model sets - each tested with 200 signal regions by ATLAS - have been used to train and validate SUSY-AI. The code is currently able to reproduce the ATLAS exclusion regions in 19 dimensions with an accuracy of at least 93 percent. It has been validated further within the constrained MSSM and a minimal natural supersymmetric model, again showing high accuracy. SUSY-AI and its future BSM derivatives will help to solve the problem of recasting LHC results for any model of new physics. SUSY-AI can be downloaded at http://susyai.hepforge.org/. An on-line interface to the program for quick testing purposes can be found at http://www.susy-ai.org/.

A diphoton excess with an invariant mass of about 750 GeV has been recently reported by both ATLAS and CMS experiments at LHC. While the simplest interpretation requires the resonant production of a 750 GeV (pseudo)scalar, here we consider an alternative setup, with an additional heavy parent particle which decays into a pair of 750 GeV resonances. This configuration improves the agreement between the 8 TeV and 13 TeV data. Moreover, we include a dark matter candidate in the form of a Majorana fermion which interacts through the 750 GeV portal. The invisible decays of the light resonance help to suppress additional decay channels into Standard Model particles in association with the diphoton signal. We realise our hierarchical framework in the context of an effective theory, and we analyse the diphoton signal as well as the consistency with other LHC searches. We finally address the interplay of the LHC results with the dark matter phenomenology, namely the compatibility with the relic density abundance and the indirect detection bounds., Comment: 11 figures, 2 tables, 29 pages

Despite their appealing features, models with gauge-mediated supersymmetry breaking (GMSB) typically present a high degree of fine-tuning, due to the initial absence of the top trilinear scalar couplings, $A_t=0$. In this paper, we carefully evaluate such a tuning, showing that is worse than per mil in the minimal model. Then, we examine some existing proposals to generate $A_t\neq 0$ term in this context. We find that, although the stops can be made lighter, usually the tuning does not improve (it may be even worse), with some exceptions, which involve the generation of $A_t$ at one loop or tree level. We examine both possibilities and propose a conceptually simplified version of the latter; which is arguably the optimum GMSB setup (with minimal matter content), concerning the fine-tuning issue. The resulting fine-tuning is better than one per mil, still severe but similar to other minimal supersymmetric standard model constructions. We also explore the so-called "little $A_t^2/m^2$ problem", i.e. the fact that a large $A_t$-term is normally accompanied by a similar or larger sfermion mass, which typically implies an increase in the fine-tuning. Finally, we find the version of GMSB for which this ratio is optimized, which, nevertheless, does not minimize the fine-tuning., Comment: 16 pages, 11 figures, 1 appendix. Discussion extended, matches EPJC published version

Motivated by the recent diphoton excess reported by both the ATLAS and CMS collaborations, we provide a model-independent combination of diphoton results obtained at $\sqrt{s}=8$ and 13 TeV at the LHC. We consider resonant s-channel production of a spin-0 and spin-2 particle with a mass of 750 GeV that subsequently decays to two photons. The size of the excess reported by ATLAS appears to be in slight tension with other measurements under the spin-2 particle hypothesis., Comment: 14 pages, 6 figures, improved text, validation information added; to appear in EPJC

We point out that there is a parameter region in supersymmetry with heavy scalars and higgsinos, in which the heavier of bino and wino becomes long-lived as a consequence of the heavy higgsinos. In this region these electroweak gaugino sectors are secluded from each other with very small mixings that are inversely proportional to the higgsino mass. We revisit the bino and bino decays and provide simple formulae for the partial decay rates and the lifetimes in the limit of heavy higgsinos. We discuss the collider signatures of the long-lived binos and winos in this scenario., Comment: 23 pages, 9 figures, text clarified, additional formulas, comparison with SDecay; to appear in JHEP

If light supersymmetric top (stop) quarks are produced at the LHC and decay via on- or off-shell $W$-bosons they can be expected to contribute to a precision $W^+W^-$ cross section measurement. Using the latest results of the CMS experiment, we revisit constraints on the stop quark production and find that this measurement can exclude portions of the parameter space not probed by dedicated searches. In particular we can exclude light top squarks up to 230~GeV along the line separating three- and four-body decays, $\tilde{t}_1 \to \tilde{\chi}_1^0 W^{(*)} b$. We also study the exclusion limits in the case when the branching ratio for these decays is reduced and we show significant improvement over previously existing limits., Comment: 5 pages, 2 figures; references updated, minor changes; to appear in Phys. Lett. B

We explore the scenarios where the only accessible new states at the electroweak scale consist of a pair of color-singlet electroweak particles, whose masses are degenerate at the tree level and split only by electroweak symmetry breaking at the loop level. For the sake of illustration, we consider a supersymmetric model and study the following three representative cases with the lower-lying states as (a) two spin-1/2 Higgsino SU(2)$_L$ doublets, (b) a spin-1/2 wino SU(2)$_L$ triplet and (c) a spin-0 left-handed slepton SU(2)$_L$ doublet. Due to the mass-degeneracy, those lower-lying electroweak states are difficult to observe at the LHC and rather challenging to detect at the $e^+ e^-$ collider as well. We exploit the pair production in association with a hard photon radiation in high energy $e^+ e^-$ collisions. If kinematically accessible, such single-photon processes at $e^+e^-$ colliders with polarized beams enable us to characterize each scenario by measuring the energy and scattering angle of the associated hard photon, and to determine the spin of the nearly invisible particles unambiguously through the threshold behavior in the photon energy distribution., Comment: 15 pages, 6 figures

Checkmate is a framework that allows the user to conveniently test simulated BSM physics events against current LHC data in order to derive exclusion limits. For this purpose, the data runs through a detector simulation and is then processed by a user chosen number of experimental analyses. These analyses are all defined by signal regions that can be compared to the experimental data with a multitude of statistical tools. Due to the large and continuously growing number of experimental analyses available, users may quickly find themselves in the situation that the study they are particularly interested in has not (yet) been implemented officially into the Checkmate framework. However, the code includes a rather simple framework to allow users to add new analyses on their own. This document serves as a guide to this. In addition, Checkmate serves as a powerful tool for testing and implementing new search strategies. To aid this process, many tools are included to allow a rapid prototyping of new analyses., Comment: 32 pages; V3: Fixed typos, additional comments, updated references, version submitted to CPC

The idea of "Natural SUSY", understood as a supersymmetric scenario where the fine-tuning is as mild as possible, is a reasonable guide to explore supersymmetric phenomenology. In this paper, we re-examine this issue in the context of the MSSM including several improvements, such as the mixing of the fine-tuning conditions for different soft terms and the presence of potential extra fine-tunings that must be combined with the electroweak one. We give tables and plots that allow to easily evaluate the fine-tuning and the corresponding naturalness bounds for any theoretical model defined at any high-energy (HE) scale. Then, we analyze in detail the complete fine-tuning bounds for the unconstrained MSSM, defined at any HE scale. We show that Natural SUSY does not demand light stops. Actually, an average stop mass below 800 GeV is disfavored, though one of the stops might be very light. Regarding phenomenology, the most stringent upper bound from naturalness is the one on the gluino mass, which typically sets the present level of fine-tuning at ${\cal O}(1\%)$. However, this result presents a strong dependence on the HE scale. E.g. if the latter is $10^7$ GeV the level of fine-tuning is $\sim$ four times less severe. Finally, the most robust result of Natural SUSY is by far that Higgsinos should be rather light, certainly below 700 GeV for a fine-tuning of ${\cal O}(1\%)$ or milder. Incidentally, this upper bound is not far from $\simeq1$ TeV, which is the value required if dark matter is made of Higgsinos., Comment: 41 pages, 8 figures, 9 tables. References added, matches JHEP published version

It is one of the most challenging tasks at the Large Hadron Collider and at a future Linear Collider not only to observe physics beyond the Standard Model, but to clearly identify the underlying new physics model. In this paper we concentrate on the distinction between two different supersymmetric models, the MSSM and the NMSSM, as they can lead to similar low energy spectra. The NMSSM adds a singlet superfield to the MSSM particle spectrum and simplifies embedding a SM-like Higgs candidate with the measured mass of about 125.5 GeV. In parts of the parameter space the Higgs sector itself does not provide sufficient indications for the underlying model. We show that exploring the gaugino/higgsino sectors could provide a meaningful way to distinguish the two models. Assuming that only the lightest chargino and neutralino masses and polarized cross sections $e^+e^-\to \tilde{\chi}^0_i\tilde{\chi}^0_j$, $\tilde{\chi}^+_i\tilde{\chi}^-_j$ are accessible at the linear collider, we reconstruct the fundamental MSSM parameters $M_1$, $M_2$, $\mu$, $\tan\beta$ and study whether a unique model distinction is possible based on this restricted information. Depending on the singlino admixture in the lightest neutralino states, as well as their higgsino or gaugino nature, we define several classes of scenarios and study the prospects of experimental differentiation., Comment: 20 pages, 11 figures

A number of LHC searches now display intriguing excesses. Most prominently, the measurement of the $W^+W^-$ cross-section has been consistently $\sim 20\%$ higher than the theoretical prediction across both ATLAS and CMS for both 7 and 8 TeV runs. More recently, supersymmetric searches for final states containing two or three leptons have also seen more events than predicted in certain signal regions. We show that a supersymmetric model containing a light stop, winos and binos can consistently match the data. We perform a fit to all measurements and searches that may be sensitive to our model and find a reduction in the log-likelihood of 15.4 compared to the Standard Model which corresponds to 3.5-$\sigma$ once the extra degrees of freedom in the fit are considered., Comment: 19 pages, 5 Figures. v3: minor corrections, to appear at JHEP

One of the challenging tasks at future experiments is the clear identification of the underlying new physics model. In this study we concentrate on the distinction between different supersymmetric models, the MSSM and the NMSSM, exploring the gaugino/higgsino sector as an alternative to the Higgs sector. Under the assumption that only the light chargino and neutralino masses and polarized cross sections $e^+e^-\to \tilde{\chi}^0_i\tilde{\chi}^0_j$, $\tilde{\chi}^+_i\tilde{\chi}^-_j$ have been measured, we perform a fit of the fundamental MSSM parameters $M_1$, $M_2$, $\mu$ and $\tan\beta$ and study whether a model distinction is possible. We focus here on the challenging cases of scenarios with a relatively heavy singlino and address two classes of neutralino mixing, $\tilde{\chi}^0_1\sim$higgsino-like versus $\tilde{\chi}^0_1\sim$gaugino-like., Comment: 9 pages, 10 figures. Talk presented at the International Workshop on Future Linear Colliders (LCWS13), Tokyo, Japan, 11-15 November 2013

In supersymmetric extensions of the Standard Model, higgsino-like charginos and neutralinos are preferred to have masses of the order of the electroweak scale by naturalness arguments. Such light $\widetilde{\chi}^0_1$, $\widetilde{\chi}^0_2$ and $\widetilde{\chi}^{\pm}_1$ states can be almost mass degenerate, and their decays are then difficult to observe at colliders. In addition to the generic naturalness argument, light higgsinos are well motivated from a top-down perspective. For instance, they arise naturally in certain models of hybrid gauge-gravity mediation. In the present analysis, we study two benchmark points which have been derived in the framework of such a model, which exhibit mass differences of O(GeV) in the higgsino sector. For chargino pair and neutralino associated production with initial-state photon radiation, we simulate the detector response and determine how accurately the small mass differences, the absolute masses and the cross sections can be measured at the International Linear Collider. Assuming that 500/fb has been collected at each of two beam-polarisations $P(e^+,e^-)=(\pm 30\%,\mp 80\%)$, we find that the mass differences can be measured to 40-300 MeV, the cross sections to 2-5%, and the absolute masses to 1.5-3.3 GeV, where the range of values correspond to the different scenarios and channels. Based on these observables we perform a parameter fit in the MSSM, from which we infer that the higgsino mass parameter $\mu$ can be measured to a precision of about $\Delta\mu=$2--7 GeV. For the electroweak gaugino mass parameters $M_1$, $M_2$, which are chosen in the multi-TeV range, a narrow region is compatible with the measurements. For both parameters independently, we can determine a lower bound., Comment: 29 pages, 12 figures; minor changes, discussion of negative M_1 added; to appear in EPJC

A rather high Higgs mass, m_h = 126 GeV, suggests that at least a part of the supersymmetric spectrum of the MSSM may live beyond O(1TeV) and hence inaccessible to the LHC. However, there are theoretical and phenomenological reasons supporting a possibility that charginos and neutralinos remain much closer to the electroweak scale. In this paper, we explore such a scenario in the light of recent Higgs measurements, mainly its di-photon decay rate, where the data might indicate a slight excess over the SM prediction. That excess could be fitted by the contribution of light charginos provided tan(beta) is low to moderate, a possibility that is receiving much attention for other theoretical reasons. We investigate the implications of this scenario for other observables, such as dark matter constraints, electroweak observables and experimental signals at the LHC, like di-lepton, tri-lepton and same-sign dilepton. An important part of the models survive all the constraints and are able to give positive signals at LHC-14TeV and/or XENON1T., Comment: 21 pages, 10 figures

Recent ATLAS and CMS measurements show a slight excess in the WW cross section measurement. While still consistent with the Standard Model within 1-2 sigma, the excess could be also a first hint of physics beyond the Standard Model. We argue that this effect could be attributed to the production of scalar top quarks within supersymmetric models. The stops of mstop_1 ~ 200 GeV has the right pair-production cross section and under some assumptions can significantly contribute to the final state of two leptons and missing energy. We scan this region of parameter space to identify stop mass range preferred by the WW cross section measurements. Taking one sample benchmark point we show that it can be consistent with low energy observables and Higgs sector measurements and propose a method to distinguish supersymmetric signal from the Standard Model contribution., Comment: 16 pages, 5 figures, minor revision, discussion of asymmetry expanded, to appear in JHEP

At a future linear collider, very precise measurements, typically with errors of <1%, are expected to be achievable. Such an accuracy yields sensitivity to quantum corrections, which therefore must be incorporated into theoretical calculations in order to determine the underlying new physics parameters from linear collider measurements. In the context of the chargino--neutralino sector of the minimal supersymmetric standard model, this involves fitting one-loop predictions to prospective measurements of cross sections, forward-backward asymmetries and the accessible chargino and neutralino masses. Taking recent results from LHC SUSY and Higgs searches into account, we consider three phenomenological scenarios, each displaying characteristic features. Our analysis demonstrates how an accurate determination of the desired parameters is possible, and could additionally provide access to the stop masses and mixing angle., Comment: 23 pages, 4 figures, v2: typos corrected, minor clarifications, version submitted to journal

Current experimental constraints on a large parameter space in supersymmetric models rely on the large missing energy signature. This is usually provided by the lightest neutralino which stability is ensured by the R-parity. However, if the R-parity is violated, the lightest neutralino decays into the standard model particles and the missing energy cut is not efficient anymore. In particular, the UDD type R-parity violation induces the neutralino decay to three quarks which potentially leads to the most difficult signal to be searched at hadron colliders. In this paper, we study the constraints on the R-parity violating supersymmetric model using a same-sign dilepton and a multijet signatures. We show that the gluino and squarks lighter than a TeV are already excluded in constrained minimal supersymmetric standard model with R-parity violation if their masses are approximately equal. We also analyze constraints in a simplified model with R-parity violation. We compare how R-parity violation changes some of the observables typically used to distinguish a supersymmetric signal from standard model backgrounds., Comment: 14 pages, 4 figures

Very precise measurements of masses and cross sections, with errors of <1%, are expected to be achievable with a future linear collider. Such an accuracy gives sensitivity at the level of quantum corrections, which therefore must be incorporated in order to make meaningful predictions for the underlying new physics parameters. For the chargino-neutralino sector, this involves fitting one-loop predictions to expected measurements of the cross sections and forward-backward asymmetries and of the accessible chargino and neutralino masses. Our analysis shows how an accurate determination of the desired parameters is possible, providing in addition access to the mass of the lighter stop., Comment: 8 pages, 2 figures, talk given at the 3rd Linear Collider Forum, DESY, Hamburg, Germany, Feb 7-9, 2012

We study the impact of the multi-lepton searches at the LHC on supersymmetric models with compressed mass spectra. For such models the acceptances of the usual search strategies are significantly reduced due to requirement of large effective mass and missing E_T. On the other hand, lepton searches do have much lower thresholds for missing E_T and p_T of the final state objects. Therefore, if a model with a compressed mass spectrum allows for multi-lepton final states, one could derive constraints using multi-lepton searches. For a class of simplified models we study the exclusion limits using ATLAS multi-lepton search analyses for the final states containing 2-4 electrons or muons with a total integrated luminosity of 1-2/fb at \sqrt{s}=7 TeV. We also modify those analyses by imposing additional cuts, so that their sensitivity to compressed supersymmetric models increase. Using the original and modified analyses, we show that the exclusion limits can be competitive with jet plus missing E_T searches, providing exclusion limits up to gluino masses of 1 TeV. We also analyse the efficiencies for several classes of events coming from different intermediate state particles. This allows us to assess exclusion limits in similar class of models with different cross sections and branching ratios without requiring a Monte Carlo simulation., Comment: 18 pages, 5 figures

Supersymmetric models provide many new complex phases which lead to CP violating effects in collider experiments. As an example, CP-sensitive triple product asymmetries in neutralino production and subsequent leptonic two-body decays are studied within the Minimal Supersymmetric Standard Model. A full ILD detector simulation has been performed at a center of mass energy of 500GeV, including the relevant Standard Model background processes, a realistic beam energy spectrum, beam backgrounds and a beam polarization of 80% and -60% for the electron and positron beams, respectively. Assuming an integrated luminosity of 500fb-1 collected by the experiment and the performance of the current ILD detector, a relative measurement accuracy of 10% for the CP-sensitive asymmetry can be achieved in the chosen scenario.

If signals of new physics are discovered at the LHC it will be crucial to determine the spin structure of the new model. We discuss a method that can help to address this question with a low integrated luminosity, L=1 fb^-1, at sqrt{s}=14 TeV. Based on the differences in angular distributions of primarily produced particles we show that a significant difference can be observed in the final state jet-pairs rapidity distance. An additional advantage of the method is that it does not rely on any particular structure of the couplings in the decay chain. We simulate samples for models with supersymmetric and UED-like spin structure and show that a distinction can be made early on., Comment: 7 pages, 5 figures, discussion of new scenarios added, to appear in Phys. Lett. B

We study the potential to observe CP-violating effects in SUSY cascade decay chains at the LHC. Asymmetries composed by triple products of momenta of the final state particles are sensitive to CP-violating effects. Due to large boosts that dilute the asymmetries, these can be difficult to observe. Extending the methods of momentum reconstruction we show that the original size of these asymmetries may be measurable. A study is done at the hadronic level with backgrounds to estimate the expected sensitivity at the LHC., Comment: 4 pages, 5 figures; to appear in the proceedings of Physics at the LHC 2010 (PLHC 2010), Hamburg, Germany, 7-12 June 2010

We study the potential to observe CP-violating effects in SUSY stop cascade decay chains at the LHC. Asymmetries composed by triple products of momenta of the final state particles are sensitive to CP-violating effects. Due to large boosts that dilute the asymmetries, these can be difficult to observe. If all particle masses in a cascade decay are known, it may be possible to reconstruct all momenta in the decay chains on an event-by-event basis even when we have missing momentum due to a stable LSP. After the reconstruction, the non-diluted CP-violating signal can be recovered and gets significantly enhanced so that an observation may become feasible. A fully hadronic study has been completed to define the areas of the mSUGRA parameter space that may yield a 3-sigma observation with 500 fb^(-1) at the LHC., Comment: Version published in Phys.Rev. D83 (2011) 115012

In models with gravitino as the lightest supersymmetric particle(LSP), the next to lightest supersymmetric particle (NLSP) can have a long lifetime and appear stable in collider experiments. We study the leptonic signatures of such a scenario with tau-sneutrino as the NLSP, which is realized in the non-universal Higgs masses scenario. We focus on an interesting trilepton signature with two like-sign taus and an electron or a muon of opposite sign. The neutralinos and charginos are quite heavy in the model considered, and the trilepton signal comes mostly from the slepton-sneutrino production. We identify the relevant backgrounds, taking into account tau decays, and devise a set of cuts to optimize this trilepton signal. We simulate signal and backgrounds at the LHC with 14 TeV center-of-mass energy. Although the sleptons in this model are relatively light, O(100 GeV), discovery is more demanding compared to typical neutralino LSP scenarios. The trilepton signal requires large amount of accumulated data, at least ~80 fb^-1, at the CM energy of 14 TeV., Comment: 25 pages, 6 figures, minor changes to match the version published in Phys.Rev.D

We address the question of how to determine the stop mixing angle and its CP-violating phase at the LHC. As an observable we discuss ratios of branching ratios for different decay modes of the light stop ~t_1 to charginos and neutralinos. These observables can have a very strong dependence on the parameters of the stop sector. We discuss in detail the origin of these effects. Using various combinations of the ratios of branching ratios we argue that, depending on the scenario, the observable may be promising in exposing the light stop mass, the mixing angle and the CP phase. This will, however, require a good knowledge of the supersymmetric spectrum, which is likely to be achievable only in combination with results from a linear collider., Comment: 30 pages, 11 figures, version to appear in EPJC

The CP-violating effects in the neutralino sector of the MSSM can be observed in event-counting type experiments, i.e. without the need of exploiting variables sensitive to beam or neutralino polarization. On the other hand, such CP-odd effects in the chargino sector can be generated only at the loop level. We contrast the two sectors and present results of full one-loop analysis of the CP-odd asymmetry in the non-diagonal chargino pair production in e+e- collisions., Comment: 8 pages, 3 figures, presented at the Epiphany Conference on LHC Physics, 4 - 6 January 2008, Cracow, Poland

We present the analysis of CP-violating effects in non-diagonal chargino pair production in e+e- collisions. These effects appear only at the one-loop level. We show that CP-odd asymmetries in chargino production are sensitive to the phases of mu and A_t parameters and can be of the order of a few %., Comment: 5 pages, 3 figures, presented at the XXXI Conference of Theoretical Physics "Matter to the Deepest", Ustron, Poland, September 5-11, 2007

We calculate full one-loop corrections to the genuine three-body decays of the light chargino \chi_1^\pm to \chi^0_1 l^\pm \nu in the Minimal Supersymmetric Standard Model. We find that the corrections to the decay width can be of the order of a few percent. We show also how radiative corrections affect energy and angular distributions of the final lepton., Comment: 4 pages, 6 figures, reference added, Submitted for the SUSY07 proceedings

We discuss CP violation in the process e^+e^- \to \tilde\chi^+_i\tilde\chi^-_j with unpolarized beams. When the scalars are heavy, the box-diagram results constitute a major part of the full result. However, there are situations when the vertex and self-energy corrections dominate over the box diagrams. We also comment on CP violation in the final chargino decay., Comment: 4 pages, Latex, 3 eps-figures included, Talk given at 2007 International Linear Collider Workshop (LCWS07 and ILC07), Hamburg, Germany, 30 May - 3 Jun 2007