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Register a new userConstraining the Compressed Top Squark and Chargino along the W Corridor
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Studying superpartner production together with a hard initial state radiation (ISR) jet has been a useful strategy for searches of supersymmetry with a compressed spectrum at the Large Hadron Collider (LHC). In the case of the top squark (stop), the ratio of the missing transverse momentum from the lightest neutralinos and the ISR momentum, defined as $bar{R}_M$, turns out to be an effective variable to distinguish the signal from the backgrounds. It has helped to exclude the stop mass below 590 GeV along the top corridor where $m_{tilde{t}} - m_{tilde{chi}_1^0} approx m_t$. On the other hand, the current experimental limit is still rather weak in the $W$ corridor where $m_{tilde{t}} - m_{tilde{chi}_1^0} approx m_W +m_b$. In this work we extend this strategy to the parameter region around the $W$ corridor by considering the one lepton final state. In this case the kinematic constraints are insufficient to completely determine the neutrino momentum which is required to calculate $bar{R}_M$. However, the minimum value of $bar{R}_M$ consistent with the kinematic constraints still provides a useful discriminating variable, allowing the exclusion reach of the stop mass to be extended to $sim 550$ GeV based on the current 36 fb$^{-1}$ LHC data. The same method can also be applied to the chargino search with $m_{tilde{chi}_1^pm} -m_{tilde{chi}_1^0} approx m_W$ because the analysis does not rely on $b$ jets. If no excess is present in the current data, a chargino mass of 300 GeV along the $W$ corridor can be excluded, beyond the limit obtained from the multilepton search.
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In supersymmetric models with radiatively-driven naturalness and light higgsinos, the top squarks may lie in the 0.5- 3TeV range and thus only a fraction of natural parameter space is accessible to LHC searches. We outline the range of top squark and lightest SUSY particle masses preferred by electroweak naturalness in the standard parameter space plane. We note that the branching fraction for b-> sgamma decay favors top squarks much heavier than 500 GeV. Such a range of top-squark mass values is in contrast to previous expectations where m(stop)<500 GeV had been considered natural. In radiative natural SUSY, top squarks decay roughly equally via t1-> bW1 and Z_{1,2} where W1 and Z_{1,2} are higgsino-like electroweak-inos. Thus, top squark pair production should yield all of tbar{t}+eslt, tbar{b}+eslt, bbar{t}+eslt and bbar{b}+eslt signatures at comparable rates. We propose that future LHC top squark searches take place within a semi-simplified model which corresponds more closely to expectations from theory.
Within the Minimal Supersymmetric Standard Model we study the three body decay of the lighter top squark into a b-quark, a W-boson and the lightest neutralino and compare this decay with the flavour changing two body decay of the lighter top squark into a c-quark and the lightest neutralino. We do this for scenarios where two body decays at tree level are forbidden for the light top squark. We give the complete analysis for the three body and compare it with the mentioned two body decay. We discuss our numerical results in view of the upgraded Tevatron, the LHC and a 500~GeV $e^+ e^-$ Linear Collider.
The scalar partner of the top quark is relatively light in many models of supersymmetry breaking. We study the production of top squarks (stops) at the Tevatron collider and their subsequent decay through baryon-number violating couplings such that the final state contains no leptons. Performing a detector-level analysis, we demonstrate that, even in the absence of leptons or missing energy, stop masses upto 210 gev/c^2 can be accessible at the Tevatron.
We investigate possible scenarios of light-squark production at the LHC as a new mechanism to produce Higgs bosons in association with jets. The study is motivated by the SUSY search for H+jets events, performed by the CMS collaboration on 8 and 13 TeV data using the razor variables. Two simplified models are proposed to interpret the observations in this search. The constraint from Run I and the implications for Run II and beyond are discussed.
We present predictions of the total cross sections for pair production of squarks and gluinos at the LHC, including the stop-antistop production process. Our calculation supplements full fixed-order NLO predictions with resummation of threshold logarithms and Coulomb singularities at next-to-leading logarithmic (NLL) accuracy, including bound-state effects. The numerical effect of higher-order Coulomb terms can be as big or larger than that of soft-gluon corrections. For a selection of benchmark points accessible with data from the 2010-2012 LHC runs, resummation leads to an enhancement of the total inclusive squark and gluino production cross section in the 15-30 % range. For individual production processes of gluinos, the corrections can be much larger. The theoretical uncertainty in the prediction of the hard-scattering cross sections is typically reduced to the 10 % level.
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