Search For Supersymmetry Research Articles

Search for supersymmetry at [Formula: see text]TeV in final states with jets and two same-sign leptons or three leptons with the ATLAS detector.

A search for strongly produced supersymmetric particles is conducted using signatures involving multiple energetic jets and either two isolated leptons (e or mu ) with the same electric charge or at least three isolated leptons. The search also utilises b-tagged jets, missing transverse momentum and other observables to extend its sensitivity. The analysis uses a data sample of proton–proton collisions at sqrt{s}= 13 TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 corresponding to a total integrated luminosity of 3.2 fb^{-1}. No significant excess over the Standard Model expectation is observed. The results are interpreted in several simplified supersymmetric models and extend the exclusion limits from previous searches. In the context of exclusive production and simplified decay modes, gluino masses are excluded at 95,% confidence level up to 1.1–1.3 TeV for light neutralinos (depending on the decay channel), and bottom squark masses are also excluded up to 540 GeV. In the former scenarios, neutralino masses are also excluded up to 550–850 GeV for gluino masses around 1 TeV.

Odd top partners at the LHC

LHC searches for fermionic top partners $T$ focus on three decay topologies: $T\to bW$, $T\to tZ$, and $T\to th$. However, top partners may carry new conserved quantum numbers that forbid these decays. The simplest possibility is a conserved parity, under which the top partner is odd and all SM states are even. In this case, decays of top partners may involve new particle-odd scalars, leading to signal topologies more commonly associated with supersymmetry, either with or without R-parity conservation. We study a simplified model in which this possibility is realized, and estimate the bounds on the top partner mass in this model implied by LHC searches for supersymmetry. We find that the bounds can be significantly weaker than in the conventional top partner decay scenario. For example, if the new parity is exact, a 500 GeV top partner is allowed as long as the lightest parity-odd scalar mass is between 325 and 500 GeV. The lower allowed top partner mass reduces the need for fine-tuning in the Higgs mass parameter, compared to the conventional decay scenario. We also present an explicit model, the Oddest Little Higgs, which exhibits this phenomenology.

Searches for supersymmetry at CMS in final states with photons

Four searches for supersymmetry at CMS in final states with photons are discussed in this article. The data analyzed corresponds to up to 19.7fb-1 and was recorded at centre-of-mass energies of 7 and 8 TeV by the CMS experiment. Searches in final states with photons are sensitive to various scenarios for physics beyond the standard model, especially gauge mediated supersymmetry breaking. To increase the sensitivity for various classes of models, four analyses with different selections and background estimation methods are performed. Wino-like neutralino mixing scenarios are probed in final states with at least one photon and jets, while final states with at least two photons are most sensitive to bino-like neutralino mixing scenarios. A higgsino-like neutralino scenario is studied by selecting two photons with an invariant mass close to the Higgs mass. While all of these analyses explore events with high missing transverse energy, a fourth analysis covers also final states with two photons and low missing transverse energy. No excess of data over the standard model expectation is observed, and upper limits on various signal cross sections are calculated.

How alive is constrained SUSY really?

Constrained supersymmetric models like the CMSSM might look less attractive nowadays because of fine tuning arguments. They also might look less probable in terms of Bayesian statistics. The question how well the model under study describes the data, however, is answered by frequentist p-values. Thus, for the first time, we calculate a p-value for a supersymmetric model by performing dedicated global toy fits. We combine constraints from low-energy and astrophysical observables, Higgs boson mass and rate measurements as well as the non-observation of new physics in searches for supersymmetry at the LHC. Using the framework Fittino, we perform global fits of the CMSSM to the toy data and find that this model is excluded at the 90% confidence level.

Searches for supersymmetry in resonance production and R-parity violating prompt signatures with the ATLAS and CMS detectors

In R-parity violating supersymmetric scenarios sparticles can be produced individually or in pairs with rates that are detectable at the LHC. Recent results from searches for resonant production and R-parity violating prompt signatures in multi-lepton and multi-jet final states in the data sample recorded by the ATLAS and CMS detectors are presented. New exclusion limits are obtained on the existence of different R-parity violating scenarios.

Search for supersymmetry with Higgs bosons in the final state

The recent observation of a Standard Model (SM) like Higgs boson offers the chance to exploit the measured properties of this particle to perform beyond-the-SM searches. A number of searches for Standard Model like Higgs bosons produced in cascade decays of supersymmetric particles are presented, including both strong and weak production mechanisms. A data sample of pp collisions at a center-of-mass energy s=8 TeV corresponding to an integrated luminosity of about 19.5 fb-1, collected by the CMS experiment [S. Chatrchyan, et al., The CMS experiment at the CERN LHC, JINST 3 (2008) S08004. 10.1088/1748-0221/3/08/S08004] at the LHC, is used. SM-like branching fractions are considered for the Higgs boson, with a mass Mh0≃125 GeV.

Inclusive Searches for Supersymmetry with the CMS detector at [formula omitted

We discuss two complementary searches for supersymmetry and their combination carried out on approximately 19 fb−1 of data collected by CMS during the s=8 TeV LHC run. Results for a variety of final state signatures, including multi-bottom, multi-top, and mixed top-plus-bottom quark topologies, are presented. The combination of results yields an improved bound on the top-squark mass. For a neutralino mass of 100 GeV, the branching fraction dependent (independent) pair production of gluinos and top squarks is excluded for gluino masses up to 1310 (1175) GeV and for top squark masses up to 730 (645) GeV.

Search for supersymmetry with extremely compressed spectra with the ATLAS and CMS detectors

Results of searches for supersymmetry via direct production of third-generation squarks and gluinos are reported. The analysis use 20.3 fb−1 of proton-proton collision data recorded by the ATLAS experiment and 19.5 fb−1 recorded by the CMS experiment at a centre-of-mass energy of s=8 TeV. Different signal regions based on monojet-like and c-tagged event selections optimize the sensitivity for direct top squark pair production with small mass differences between the hypothetical supersymmetric particles. In an complementary approach, the heavier top squark is searched for under the assumption that a Z boson is emitted in its decay to the lighter top squark. This strategy retains sensitivity for mass configurations where signals of direct production of the lighter top squark are hard to distinguish from the top quark pair production background. For the case of the gluino, a soft lepton analysis improves sensitivity for small mass differences between the gluino and the lightest neutralino. No significant excess above the Standard Model background expectation is observed in any of the analyses. The resulting limits significantly extend previous results at colliders.

The case for 100 GeV bino dark matter: a dedicated LHC tri-lepton search

Global fit studies performed in the pMSSM and the photon excess signal originating from the Galactic Center seem to suggest compressed electroweak supersymmetric spectra with a $\sim$100 GeV bino-like dark matter particle. We find that these scenarios are not probed by traditional electroweak supersymmetry searches at the LHC. We propose to extend the ATLAS and CMS electroweak supersymmetry searches with an improved strategy for bino-like dark matter, focusing on chargino plus next-to-lightest neutralino production, with a subsequent decay into a tri-lepton final state. We explore the sensitivity for pMSSM scenarios with $\Delta m = m_{\rm NLSP} - m_{\rm LSP} \sim (5 - 50)$ GeV in the $\sqrt{s} = 14$ TeV run of the LHC. Counterintuitively, we find that the requirement of low missing transverse energy increases the sensitivity compared to the current ATLAS and CMS searches. With 300 fb$^{-1}$ of data we expect the LHC experiments to be able to discover these supersymmetric spectra with mass gaps down to $\Delta m \sim 9$ GeV for DM masses between 40 and 140 GeV. We stress the importance of a dedicated search strategy that targets precisely these favored pMSSM spectra.

Role of the ‘N’ in the natural NMSSM for the LHC

In this work, we present mass limits on gluinos and stops in a natural Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a singlino as the lightest supersymmetric particle. Motivated by naturalness, we consider spectra with light higgsinos, sub-TeV third generation sparticles and gluinos well below the multi-TeV regime while the electroweak gauginos, the sleptons and the first and second generation squarks are decoupled. We check that our natural supersymmetry spectra satisfy all electroweak precision observables and flavour measurements as well as theoretical constraints. By reinterpreting the results from the 8 TeV ATLAS supersymmetry searches we present the 95% CL exclusion limits on the model. The results show that the presence of a singlino LSP can lengthen decay chains and soften the final state particle energies. Whilst this does reduce the strength of the bounds in some areas of parameter space, the LHC still displays good sensitivity to the model.

Search for the electroweak production of supersymmetric particles ins=8 TeVppcollisions with the ATLAS detector

The ATLAS experiment has performed extensive searches for the electroweak production of charginos, neutralinos, and staus. This article summarizes and extends the search for electroweak supersymmetry with new analyses targeting scenarios not covered by previously published searches. New searches use vector-boson fusion production, initial-state radiation jets, and low-momentum lepton final states, as well as multivariate analysis techniques to improve the sensitivity to scenarios with small mass splittings and low-production cross sections. Results are based on 20 fb−1 of proton-proton collision data at s=8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. The new and existing searches are combined and interpreted in terms of 95% confidence-level exclusion limits in simplified models, where a single production process and decay mode is assumed, as well as within phenomenological supersymmetric models.15 MoreReceived 23 September 2015DOI:https://doi.org/10.1103/PhysRevD.93.052002This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2016 CERN, for the ATLAS CollaborationPhysics Subject Headings (PhySH)Physical SystemsHadron collidersSuperpartnersParticles & Fields

Search for supersymmetry in electroweak production with photons and large missing transverse energy in pp collisions at s=8TeV

Results are reported from a search for supersymmetry with gauge-mediated supersymmetry breaking in electroweak production. Final states with photons and large missing transverse energy (MET) were examined. The data sample was collected in pp collisions at sqrt(s) = 8 TeV with the CMS detector at the LHC and corresponds to 7.4 inverse femtobarns. The analysis focuses on scenarios in which the lightest neutralino has bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitinos escape undetected. The data were obtained using a specially designed trigger with dedicated low thresholds, providing good sensitivity to signatures with photons, MET, and low hadronic energy. No excess of events over the standard model expectation is observed. The results are interpreted using the model of general gauge mediation. With the wino mass fixed at 10 GeV above that of the bino, wino masses below 710 GeV are excluded at 95% confidence level. Constraints are also set in the context of two simplified models, for which the analysis sets the lowest cross section limits on the electroweak production of supersymmetric particles.

Supersymmetry searches in GUT models with non-universal scalar masses

We study SO(10), SU(5) and flipped SU(5) GUT models with non-universal soft supersymmetry-breaking scalar masses, exploring how they are constrained by LHC supersymmetry searches and cold dark matter experiments, and how they can be probed and distinguished in future experiments. We find characteristic differences between the various GUT scenarios, particularly in the coannihilation region, which is very sensitive to changes of parameters. For example, the flipped SU(5) GUT predicts the possibility of ̃t1−χ coannihilation, which is absent in the regions of the SO(10) and SU(5) GUT parameter spaces that we study. We use the relic density predictions in different models to determine upper bounds for the neutralino masses, and we find large differences between different GUT models in the sparticle spectra for the same LSP mass, leading to direct connections of distinctive possible experimental measurements with the structure of the GUT group. We find that future LHC searches for generic missing ET, charginos and stops will be able to constrain the different GUT models in complementary ways, as will the Xenon 1 ton and Darwin dark matter scattering experiments and future FERMI or CTA γ-ray searches.

Folded supersymmetry with a twist

Folded supersymmetry (f-SUSY) stabilizes the weak scale against radiative corrections from the top sector via scalar partners whose gauge quantum numbers differ from their Standard Model counterparts. This non-trivial pairing of states can be realized in extra-dimensional theories with appropriate supersymmetry-breaking boundary conditions. We present a class of calculable f-SUSY models that are parametrized by a non-trivial twist in 5D boundary conditions and can accommodate the observed Higgs mass and couplings. Although the distinctive phenomenology associated with the novel folded states should provide strong evidence for this mechanism, the most stringent constraints are currently placed by conventional supersymmetry searches. These models remain minimally fine-tuned in light of LHC8 data and provide a range of both standard and exotic signatures accessible at LHC13.

Search for supersymmetry in the multijet and missing transverse momentum final state in pp collisions at 13 TeV

A search for new physics is performed based on all-hadronic events with large missing transverse momentum produced in proton-proton collisions at sqrt(s) = 13 TeV. The data sample, corresponding to an integrated luminosity of 2.3 inverse femtobarns, was collected with the CMS detector at the CERN LHC in 2015. The data are examined in search regions of jet multiplicity, tagged bottom quark jet multiplicity, missing transverse momentum, and the scalar sum of jet transverse momenta. The observed numbers of events in all search regions are found to be consistent with the expectations from standard model processes. Exclusion limits are presented for simplified supersymmetric models of gluino pair production. Depending on the assumed gluino decay mechanism, and for a massless, weakly interacting, lightest neutralino, lower limits on the gluino mass from 1440 to 1600 GeV are obtained, significantly extending previous limits.

Extracting constraints from direct detection searches of supersymmetric dark matter in the light of null results from the LHC in the squark sector

The comparison of the results of direct detection of Dark Matter, obtained with various target nuclei, requires model-dependent, or even arbitrary, assumptions. Indeed, to draw conclusions either the spin-dependent (SD) or the spin-independent (SI) interaction has to be neglected. In the light of the null results from supersymmetry searches at the LHC, the squark sector is pushed to high masses. We show that for a squark sector at the TeV scale, the framework used to extract contraints from direct detection searches can be redefined as the number of free parameters is reduced. Moreover, the correlation observed between SI and SD proton cross sections constitutes a key issue for the development of the next generation of Dark Matter detectors.

CP-violating phenomenological MSSM

We investigate the sensitivity of the next generation of flavor-based low-energy experiments to probe the supersymmetric parameter space in the context of the phenomenological MSSM (pMSSM), and examine the complementarity with direct searches for Supersymmetry at the 13 TeV LHC in a quantitative manner. To this end, we enlarge the previously studied pMSSM parameter space to include all physical non-zero CP-violating phases, namely those associated with the gaugino mass parameters, Higgsino mass parameter, and the tri-linear couplings of the top quark, bottom quark and tau lepton. We find that future electric dipole moment and flavor measurements can have a strong impact on the viability of these models even if the sparticle spectrum is out of reach of the 13 TeV LHC. In particular, the lack of positive signals in future low-energy probes would exclude values of the phases between ${\cal O}(10^{-2})$ and ${\cal O}(10^{-1})$. We also find regions of parameter space where large phases remain allowed due to cancellations. Most interestingly, in some rare processes, such as BR($B_s \to \mu^+ \mu^-$ ), we find that contributions arising from CP-violating phases can bring the potentially large SUSY contributions into better agreement with experiment and Standard Model predictions.

Killing the cMSSM softly

We investigate the constrained Minimal Supersymmetric Standard Model (cMSSM) in the light of constraining experimental and observational data from precision measurements, astrophysics, direct supersymmetry searches at the LHC and measurements of the properties of the Higgs boson, by means of a global fit using the program Fittino. As in previous studies, we find rather poor agreement of the best fit point with the global data. We also investigate the stability of the electro-weak vacuum in the preferred region of parameter space around the best fit point. We find that the vacuum is metastable, with a lifetime significantly longer than the age of the Universe. For the first time in a global fit of supersymmetry, we employ a consistent methodology to evaluate the goodness-of-fit of the cMSSM in a frequentist approach by deriving p-values from large sets of toy experiments. We analyse analytically and quantitatively the impact of the choice of the observable set on the p-value, and in particular its dilution when confronting the model with a large number of barely constraining measurements. Finally, for the preferred sets of observables, we obtain p-values for the cMSSM below 10%, i.e. we exclude the cMSSM as a model at the 90% confidence level.

Searches for Supersymmetry with the CMS Detector at the LHC

Searches for Supersymmetry with the CMS Detector at the LHC

Searches for Supersymmetry and Exotic Phenomena with the ATLAS Detector

Searches for Supersymmetry and Exotic Phenomena with the ATLAS Detector