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Register a new userGluino reach and mass extraction at the LHC in radiatively-driven natural SUSY
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Radiatively-driven natural SUSY (RNS) models enjoy electroweak naturalness at the $10%$ level while respecting LHC sparticle and Higgs mass constraints. Gluino and top squark masses can range up to several TeV (with other squarks even heavier) but a set of light Higgsinos are required with mass not too far above $m_hsim 125$ GeV. Within the RNS framework, gluinos dominantly decay via ${tilde g} to t{tilde t}_1^{*}, bar{t}{tilde t}_1 to tbar{t}{widetilde Z}_{1,2}$ or $tbar{b}{widetilde W}_1^-+c.c.$, where the decay products of the higgsino-like ${widetilde W}_1$ and ${widetilde Z}_2$ are very soft. Gluino pair production is, therefore, signalled by events with up to four hard $b$-jets and large ${ ot!!{E_T}}$. We devise a set of cuts to isolate a relatively pure gluino sample at the (high luminosity) LHC and show that in the RNS model with very heavy squarks, the gluino signal will be accessible for $m_{{tilde g}} < 2400 (2800)$ GeV for an integrated luminosity of 300 (3000) fb$^{-1}$. We also show that the measurement of the rate of gluino events in the clean sample mentioned above allows for a determination of $m_{{tilde g}}$ with a statistical precision of $2.5-5%$ (depending on the integrated luminosity and the gluino mass) over the range of gluino masses where a $5sigma$ discovery is possible at the LHC.
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Radiatively-driven natural supersymmetry (RNS) potentially reconciles the Z and Higgs boson masses close to 100 GeV with gluinos and squarks lying beyond the TeV scale. Requiring no large cancellations at the electroweak scale in constructing M_Z=91.2 GeV while maintaining a light Higgs scalar with m_h 125 GeV implies a sparticle mass spectrum including light higgsinos with mass 100-300 GeV, electroweak gauginos in the 300-1200 GeV range, gluinos at 1-4 TeV and top/bottom squarks in the 1-4 TeV range (probably beyond LHC reach), while first/second generation matter scalars can exist in the 5-30 TeV range (far beyond LHC reach). We investigate several characteristic signals for RNS at LHC14. Gluino pair production yields a reach up to m_{tg} 1.7 TeV for 300 fb^{-1}. Wino pair production -- pptotw_2tz_4 and tw_2tw_2 -- leads to a unique same-sign diboson (SSdB) signature accompanied by modest jet activity from daughter higgsino decays; this signature provides the best reach up to m_{tg} 2.1 TeV within this framework. Wino pair production also leads to final states with (WZto 3ell)+eslt as well as 4ell+eslt which give confirmatory signals up to m_{tg} 1.4 TeV. Directly produced light higgsinos yield a clean, soft trilepton signature (due to very low visible energy release) which can be visible, but only for a not-too-small a tz_2-tz_1 mass gap. The clean SSdB signal -- as well as the distinctive mass shape of the dilepton mass distribution from tz_{2,3}totz_1ellell decays if this is accessible -- will mark the presence of light higgsinos which are necessary for natural SUSY. While an e^+e^- collider operating with sqrt{s} 600 GeV should unequivocally reveal the predicted light higgsinos, the RNS model with m_{1/2}> 1 TeV may elude all LHC14 search strategies even while maintaining a high degree of electroweak naturalness.
We derive the latest constraints on various simplified models of natural SUSY with light higgsinos, stops and gluinos, using a detailed and comprehensive reinterpretation of the most recent 13 TeV ATLAS and CMS searches with $sim 15$ fb$^{-1}$ of data. We discuss the implications of these constraints for fine-tuning of the electroweak scale. While the most vanilla version of SUSY (the MSSM with $R$-parity and flavor-degenerate sfermions) with 10% fine-tuning is ruled out by the current constraints, models with decoupled valence squarks or reduced missing energy can still be fully natural. However, in all of these models, the mediation scale must be extremely low ($<100$ TeV). We conclude by considering the prospects for the high-luminosity LHC era, where we expect the current limits on particle masses to improve by up to $sim 1$ TeV, and discuss further model-building directions for natural SUSY that are motivated by this work.
We generalize the scalar triplet neutrino mass model, the type II seesaw. Requiring fine-tuning and arbitrarily small parameters to be absent leads to dynamical lepton number breaking at the electroweak scale and a rich LHC phenomenology. A smoking gun signature at the LHC that allows to distinguish our model from the usual type II seesaw scenario is identified. Besides, we discuss other interesting phenomenological aspects of the model such as the presence of a massless Goldstone boson and deviations of standard model Higgs couplings
We study the effects of squark generation mixing on squark and gluino production and decays at LHC in the Minimal Supersymmetric Standard Model (MSSM) with focus on the mixing between second and third generation squarks. Taking into account the constraints from B-physics experiments we show that various regions in parameter space exist where decays of squarks and/or gluinos into quark flavour violating (QFV) final states can have large branching ratios. Here we consider both fermionic and bosonic decays of squarks. Rates of the corresponding QFV signals, e.g. pp -> t t bar{c} bar{c} missing-E_T X, can be significant at LHC(14 TeV). We find that the inclusion of flavour mixing effects can be important for the search of squarks and gluinos and the determination of the underlying model parameters of the MSSM at LHC.
We propose a new mass reconstruction technique for SUSY processes at the LHC. The idea is to completely solve the kinematics of the SUSY cascade decay by using the assumption that the selected events satisfy the same mass shell conditions of the sparticles involved in the cascade decay. Using this technique, we study the measurement of the mass of the bottom squarks in the cascade decay of the gluino. Based on the final state including two high p_T leptons and two b-jets, we investigate different possible approaches to the mass reconstruction of the gluino and the two bottom squarks. In particular we evaluate the performance of different algorithms in discriminating two bottom squark states with a mass difference as low as 5%.
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