Gluino Mass Research Articles

Naturalness of the non-universal MSSM in the light of the recent Higgs results

We analyse the naturalness of the Minimal Supersymmetric Standard Model (MSSM) in the light of recent LHC results from the ATLAS and CMS experiments. We study non-universal boundary conditions for the scalar and the gaugino sector, with fixed relations between some of the soft breaking parameters, and find a significant reduction of fine-tuning for non-universal gaugino masses. For a Higgs mass of about 125 GeV, as observed recently, we find parameter regions with a fine-tuning of O(10), taking into account experimental and theoretical uncertainties. These regions also survive after comparison with simplified model searches in ATLAS and CMS. For a fine-tuning less than 20 the lightest neutralino is expected to be lighter than about 400 GeV and the lighter stop can be as heavy as 3.5 TeV. On the other hand, the gluino mass is required to be above 1.5 TeV. For non-universal gaugino masses, we discuss which fixed GUT scale ratios can lead to a reduced fine-tuning and find that the recent Higgs results have a strong impact on which ratio is favoured. We also discuss the naturalness of GUT scale Yukawa relations, comparing the non-universal MSSM with the CMSSM.

Search for SUSY in final states with photons at CMS

ResumeThe Compact Muon Solenoid (CMS) collaboration has developed a complete program of searches beyond the Standard Model (SM) covering a wide range of final states. This document focuses on searches in final states with photons and missing transverse energy E T miss organised in three analyses. The first two include comparison of the E T miss distribution (isolation sideband method) in events with either at least two photons plus at least one hadronic jet, or at least one photon plus at least two hadronic jets. The third analysis corresponds to a new approach, the Jet-Gamma Balance (JGB) method, for events with at least one photon plus at least three hadronic jets.We observe no significant deviations from the SM expectation and thus derive upper limits on the signal cross section at the 95% confidence level (CL) for a range of squark, gluino and neutralino mass points in the Gauge Mediated Supersymmetry Breaking scenario.

Natural Gauge Mediation with a Bino Next-to-Lightest Supersymmetric Particle at the LHC

Natural models of supersymmetry with a gravitino lightest supersymmetric particle provide distinctive signatures at the LHC. For a neutralino next-to-lightest supersymmetric particle, sparticles can decay to two high energy photons plus missing energy. We use the ATLAS diphoton search with 4.8 b(-1) of data to place limits in both the top-squark-gluino and neutralino-chargino mass planes for this scenario. If the neutralino is heavier than 50 GeV, the lightest top squark must be heavier than 580 GeV, the gluino must be heavier than 1100 GeV, and charginos must be heavier than approximately 300-470 GeV. This provides the first nontrivial constraints in natural gauge mediation models with a neutralino next-to-lightest supersymmetric particle decaying to photons and implies a fine-tuning of at least a few percent in such models.

Search for pair production of massive particles decaying into three quarks with the ATLAS detector in $ \sqrt{s}=7\;\mathrm{TeV} $ pp collisions at the LHC

AbstractA search is conducted for hadronic three-body decays of a new massive coloured particle in$ \sqrt{s}=7\;\mathrm{TeV} $ppcollisions at the LHC using an integrated luminosity of 4.6 fb−1collected by the ATLAS detector. Supersymmetric gluino pair production in the context of a model withR-parity violation is used as a benchmark scenario. The analysis is divided into two search channels, each optimised separately for their sensitivity to high-mass and low-mass gluino production. The first search channel uses a stringent selection on the transverse momentum of the six leading jets and is performed as a counting experiment. The second search channel focuses on low-mass gluinos produced with a large boost. Large-radius jets are selected and the invariant mass of each of the two leading jets is used as a discriminant between the signal and the background. The results are found to be consistent with Standard Model expectations and limits are set on the allowed gluino mass.

Natural supersymmetry and kaon mixing in view of recent results from lattice QCD

Lattice results are available for $\ensuremath{\Delta}S=2$ matrix elements for the first time in full QCD, which improve considerably the status of hadronic uncertainties in $K\mathrm{\text{\ensuremath{-}}}\overline{K}$ mixing with respect to earlier phenomenological studies. Using an average of the ETMC and RBC-UKQCD results, we analyze ${ϵ}_{K}$ in natural supersymmetry (SUSY). This scenario arises as a consistent BSM framework after the latest results from the LHC. The analysis is improved with respect to previous studies including next-to-leading order matching conditions of order ${\ensuremath{\alpha}}_{s}^{3}$. We derive new bounds for SUSY mass insertions in the scenario with a light third generation and study the implications for squark and gluino masses, compared with direct searches at the LHC. Assuming natural values for the flavor-violating SUSY couplings of both chiralities, we find that the sbottom must be heavier than 3 TeV for a gluino mass up to 10 TeV. In this scenario no natural values for squark and gluino masses can satisfy the flavor bounds.

Constrained exceptional supersymmetric standard model with a Higgs signal near 125 GeV

We study the parameter space of the constrained exceptional supersymmetric standard model (${\mathrm{cE}}_{6}\mathrm{SSM}$) consistent with a Higgs signal near 125 GeV and the LHC searches for squarks, gluinos and ${Z}^{\ensuremath{'}}$. The ${\mathrm{cE}}_{6}\mathrm{SSM}$ parameter space, consistent with correct electroweak symmetry breaking, is represented by scans in the $({m}_{0},{M}_{1/2})$ plane for fixed ${Z}^{\ensuremath{'}}$ mass and $\mathrm{tan}\ensuremath{\beta}$, with squark, gluino and Higgs masses plotted as contours in this plane. We find that a 125 GeV Higgs mass only arises for a sufficiently large ${Z}^{\ensuremath{'}}$ mass, mostly above current limits, and for particular regions of squark and gluino masses corresponding to multi-TeV squark masses, but with lighter gluinos typically within reach of the LHC 8 TeV or forthcoming 14 TeV runs. Successful dark matter relic abundance may be achieved over all the parameter space, assuming a binolike lightest supersymmetric particle with a nearby heavier inert Higgsino doublet and decoupled inert singlinos, resulting in conventional gluino decay signatures. A set of typical benchmark points with a Higgs near 125 GeV is provided which exemplifies these features.

Constrained SUSY seesaws with a 125 GeV Higgs

Abstract Motivated by the ATLAS and CMS discovery of a Higgs-like boson with a mass around 125 GeV, and by the need of explaining neutrino masses, we analyse the three canonical SUSY versions of the seesaw mechanism (type I, II and III) with CMSSM boundary conditions. In type II and III cases, SUSY particles are lighter than in the CMSSM (or the constrained type I seesaw), for the same set of input parameters at the universality scale. Thus, to explain $ {m_{{{h^0}}}}\simeq 125 $ GeV at low energies, one is forced into regions of parameter space with very large values of m 0, M 1/2 or A 0. We compare the squark and gluino masses allowed by the ATLAS and CMS ranges for $ {m_{{{h^{{^0}}}}}} $ (extracted from the 2011-2012 data), and discuss the possibility of distinguishing seesaw models in view of future results on SUSY searches. In particular, we briefly comment on the discovery potential of LHC upgrades, for squark/gluino mass ranges required by present Higgs mass constraints. A discrimination between different seesaw models cannot rely on the Higgs mass data alone, therefore we also take into account the MEG upper limit on BR(μ → eγ) and show that, in some cases, this may help to restrict the SUSY parameter space, as well as to set complementary limits on the seesaw scale.

Search for New Physics in the Multijet and Missing Transverse Momentum Final State in Proton-Proton Collisions ats=7 TeV

A search for physics beyond the standard model is performed in events with at least three jets and large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of √s=7 TeV. No significant excess of events above the expected backgrounds is observed in 4.98 fb(-1) of data collected with the CMS detector at the Large Hadron Collider. The results are presented in the context of the constrained minimal supersymmetric extension of the standard model and more generically for simplified models. For the simplified models of gluino-gluino and squark-squark production, gluino masses below 1.0 TeV and squark masses below 0.76 TeV are excluded in case the lightest supersymmetric particle mass is below 200 GeV. These results significantly extend previous searches.

Search for three-jet resonances in pp collisions at [formula omitted

Results are reported from a search for the production of three-jet resonances in pp collisions at a center-of-mass energy s=7 TeV. The study uses the data sample collected by the CMS experiment at the LHC in 2011, corresponding to an integrated luminosity of 5.0 fb−1. Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed for the presence of resonances in the three-jet invariant mass spectrum. No evidence for a narrow resonance is found in the data, and limits are set on the cross section for gluino pair production in an R-parity-violating supersymmetry model, for gluino masses greater than 280 GeV. Assuming a branching fraction for gluino decay into three jets of 100%, gluino masses below 460 GeV are excluded at 95% confidence level. These results significantly extend the range of previous limits.

Probing supersymmetry using event shape variables at the 8 TeV LHC

We have revisited the prospects of supersymmetry searches at the LHC with 7 TeV energy along with the prediction of the discovery potential at 8 TeV energy assuming an integrated luminosity $5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ and $20\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ with minimal supergravity/minimal supersymmetric standard model as a model framework. We discuss further optimization of our selection strategy, which is based on the hadronic event shape variables. Evaluating the standard model backgrounds and signal rates in detail, we predict the discovery reach in the ${m}_{0}\ensuremath{-}{m}_{1/2}$ plane for 7 TeV with $5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ luminosity. We also present the discovery reach for 8 TeV energy with an integrated luminosity $5\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ and $20\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. A comparison is made between our results and the exclusion plots obtained by CMS and ATLAS. Finally, discovery reach in the gluino and squark mass plane at the 7 TeV and 8 TeV energy is also presented.

Search for top and bottom squarks from gluino pair production in final states with missing transverse energy and at least three b-jets with the ATLAS detector

This letter reports the results of a search for top and bottom squarks from gluino pair production in 4.7 fb^-1 of pp collisions at sqrt(s) = 7 TeV using the ATLAS detector at the LHC. The search is performed in events with large missing transverse momentum and at least three jets identified as originating from a b-quark. Exclusion limits are presented for a variety of gluino-mediated models with gluino masses up to 1 TeV excluded.

Search for supersymmetry in hadronic final states using M T2 in pp collisions at $ \sqrt{s}=7 $ TeV

Abstract A search for supersymmetry or other new physics resulting in similar final states is presented using a data sample of 4.73 fb−1 of pp collisions collected at $ \sqrt{s}=7 $ TeV with the CMS detector at the LHC. Fully hadronic final states are selected based on the variable M T2, an extension of the transverse mass in events with two invisible particles. Two complementary studies are performed. The first targets the region of parameter space with medium to high squark and gluino masses, in which the signal can be separated from the standard model backgrounds by a tight requirement on M T2. The second is optimized to be sensitive to events with a light gluino and heavy squarks. In this case, the M T2 requirement is relaxed, but a higher jet multiplicity and at least one b-tagged jet are required. No significant excess of events over the standard model expectations is observed. Exclusion limits are derived for the parameter space of the constrained minimal supersymmetric extension of the standard model, as well as on a variety of simplified model spectra.

Light gravitino production in association with gluinos at the LHC

We study the jets plus missing energy signature at the LHC in a scenario where the gravitino is very light and the gluino is the next-to-lightest supersymmetric particle and promptly decays into a gluon and a gravitino. We consider both associated gravitino production with a gluino and gluino pair production. By merging matrix elements with parton showers, we generate inclusive signal and background samples and show how information on the gluino and gravitino masses can be obtained by simple final state observables.

Yukawa unification and the superpartner mass scale

Naturalness in supersymmetry (SUSY) is under siege by increasingly stringent LHC constraints, but natural electroweak symmetry breaking still remains the most powerful motivation for superpartner masses within experimental reach. If naturalness is the wrong criterion then what determines the mass scale of the superpartners? We motivate supersymmetry by (1) gauge coupling unification, (2) dark matter, and (3) precision b-tau Yukawa unification. We show that for an LSP that is a bino-Higgsino admixture, these three requirements lead to an upper-bound on the stop and sbottom masses in the several TeV regime because the threshold correction to the bottom mass at the superpartner scale is required to have a particular size. For tan beta about 50, which is needed for t-b-tau unification, the stops must be lighter than 2.8 TeV when A_t has the opposite sign of the gluino mass, as is favored by renormalization group scaling. For lower values of tan beta, the top and bottom squarks must be even lighter. Yukawa unification plus dark matter implies that superpartners are likely in reach of the LHC, after the upgrade to 14 (or 13) TeV, independent of any considerations of naturalness. We present a model-independent, bottom-up analysis of the SUSY parameter space that is simultaneously consistent with Yukawa unification and the hint for m_h = 125 GeV. We study the flavor and dark matter phenomenology that accompanies this Yukawa unification. A large portion of the parameter space predicts that the branching fraction for B_s to mu^+ mu^- will be observed to be significantly lower than the SM value.

Constraining compressed supersymmetry using leptonic signatures

Abstract 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 $ E_T^{\mathrm{miss}} $ . On the other hand, lepton searches do have much lower thresholds for $ E_T^{\mathrm{miss}} $ 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−1 at $ \sqrt{s}=7\,\mathrm{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 $ E_T^{\mathrm{miss}} $ 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.

Implications of gauge kinetic mixing onZ′and slepton production at the LHC

We consider a supersymmetric version of the standard model extended by an additional $U(1{)}_{B\ensuremath{-}L}$. This model can be embedded in an mSUGRA-inspired model where the mass parameters of the scalars and gauginos unify at the scale of grand unification. In this class of models the renormalization group equation evolution of gauge couplings as well as of the soft SUSY-breaking parameters require the proper treatment of gauge kinetic mixing. We first show that this has a profound impact on the phenomenolgy of the ${Z}^{\ensuremath{'}}$ and as a consequence the current LHC bounds on its mass are reduced significantly from about 1970 GeV to 1790 GeV. They are even further reduced if the ${Z}^{\ensuremath{'}}$ can decay into supersymmetric particles. Secondly, we show that in this way sleptons can be produced at the LHC in the 14 TeV phase with masses of several hundred GeV. In the case of squark and gluino masses in the multi-TeV range, this might become an important discovery channel for sleptons up to 800 GeV (900 GeV) for an integrated luminosity of $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ ($300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$).

How constrained is the constrained MSSM?

We study the allowed parameter space of the constrained minimal supersymmetric Standard Model (cMSSM) in the light of direct searches, constraints from $B$-physics (including the recent measurement of the branching ratio for $B_s \to \mu^+\mu^-$) and the dark matter relic density. For low or moderate values of $\tan\beta$, the strongest constraints are those imposed by direct searches, and therefore, large areas of the parameter space are still allowed. In the large $\tan \beta$ limit, however, the $B$-physics constraints are more restrictive, effectively forcing the squark and gluino masses to lie close to or above a TeV. A light Higgs boson could dramatically change the allowed parameter space, but we need to know its mass precisely for this to be effective. We emphasize that it is still too early to write off the cMSSM, even in the large $\tan\beta$ limit. Finally we explore strategies to extend the LHC search for cMSSM signals beyond the present reach of the ATLAS and CMS Collaborations.

The gluino-glue particle and finite size effects in supersymmetric Yang-Mills theory

Abstract The spectrum of particles in supersymmetric Yang-Mills theory is expected to contain a spin 1/2 bound state of gluons and gluinos, the gluino-glue particle. We study the mass of this particle in softly broken supersymmetric Yang-Mills theory on a lattice by means of numerical simulations. The main focus is the estimation of finite size effects. We extrapolate the mass first to the infinite volume and then to the limit of a vanishing gluino mass. The results indicate that finite size effects are tolerable on lattices of moderate size, and that remaining deviations from supersymmetry are probably due to finite lattice spacing effects.

Yukawa coupling unification inSO(10)with positiveμand a heavier gluino

The $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unification with positive Higgs mass parameter $\ensuremath{\mu}$ in the minimal supersymmetric standard model prefers ``just so'' Higgs splitting and a light gluino $\ensuremath{\lesssim}500\text{ }\text{ }\mathrm{GeV}$ which appears to be ruled out by the recent LHC searches. We reanalyze constraints on soft supersymmetry breaking parameters in this scenario, allowing independent splittings among squarks and Higgs doublets at the grand unification scale, and show that it is possible to obtain $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unification and satisfy experimental constraints on gluino mass without raising supersymmetry breaking scale to very high value $\ensuremath{\sim}20\text{ }\text{ }\mathrm{TeV}$. We discuss the origin of independent squark and Higgs splittings in realistic $SO(10)$ models. Just so Higgs splitting can be induced without significantly affecting the $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unification in $SO(10)$ models containing Higgs fields transforming as $10+\overline{126}+126+210$. This splitting arises in the presence of nonuniversal boundary conditions from mixing between 10 and other Higgs fields. Similarly, if additional matter fields are introduced then their mixing with the matter multiplet 16 is shown to generate the squark splitting required to raise the gluino mass within the $t\mathrm{\text{\ensuremath{-}}}b\mathrm{\text{\ensuremath{-}}}\ensuremath{\tau}$ unified models with positive $\ensuremath{\mu}$.

QCD correction to gluino decay to in the MSSM

We calculate the complete next-to-leading order QCD corrections to the three-body decay of gluino into top pair associated with a lightest neutralino in the minimal supersymmetric standard model. We obtain that the LO and NLO QCD-corrected decay widths of at the SPS6 benchmark point are 0.1490 and 0.1069 GeV respectively, and the relative correction is −28.2%. We investigate the dependence of the QCD correction to on tan β and the masses of gluino, scalar top quarks and the lightest neutralino around the SPS6 benchmark point, separately. We find that the NLO QCD corrections suppress the LO decay width, and the absolute relative correction can exceed 30% in some parameter space. Therefore, the QCD corrections to the three-body decay should be taken into account for the precise experimental measurement at future colliders. Moreover, we study the distributions of the top-pair invariant mass () and the missing energy (Emiss) and find that the line shapes of the LO distributions of and Emiss are not obviously distorted by the NLO QCD corrections.