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Abstract:The results of a search for pair production of supersymmetric partners of the Standard Model third-generation quarks are reported. This search uses 20.1 fb −1 of pp collisions at √ s = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. The lightest bottom and top squarks (b 1 andt 1 respectively) are searched for in a final state with large missing transverse momentum and two jets identified as originating from b-quarks. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the visible cross section for processes beyond the Standard Model. Exclusion limits at the 95% confidence level on the masses of the third-generation squarks are derived in phenomenological supersymmetric R-parityconserving models in which either the bottom or the top squark is the lightest squark. Thẽ b 1 is assumed to decay viab 1 → bχ 0 1 and thet 1 viat 1 → bχ ± 1 , with undetectable products of the subsequent decay of theχ ± 1 due to the small mass splitting between theχ ± 1 and theχ 0 1 . Keywords: Hadron-Hadron Scattering, SupersymmetryOpen Access, Copyright CERN, for the benefit of the ATLAS collaboration The ATLAS collaboration 24 IntroductionSupersymmetry (SUSY) [1][2][3][4][5][6][7][8][9] provides an extension of the Standard Model (SM) that solves the hierarchy problem [10][11][12][13] by introducing supersymmetric partners of the known bosons and fermions. In the framework of the R-parity-conserving minimal supersymmetric extension of the SM (MSSM) [14][15][16][17][18], SUSY particles are produced in pairs and the lightest supersymmetric particle (LSP) is stable, providing a possible candidate for dark matter. In a large variety of models, the LSP is the lightest neutralino (χ 0 1 ). The coloured superpartners of quarks and gluons, the squarks (q) and the gluinos (g), if not too heavy, would be produced in strong interaction processes at the Large Hadron Collider (LHC) [19] and decay via cascades ending with the LSP. The undetected LSP would result in missing transverse momentum while the rest of the cascade would yield final states with multiple jets and possibly leptons.A study of the expected SUSY particle spectrum derived from naturalness considerations [20, 21] suggests that the supersymmetric partners of the third-generation SM quarks are the lightest coloured supersymmetric particles. This may lead to the lightest bottom squark (sbottom,b 1 ) and top squark (stop,t 1 ) mass eigenstates being significantly lighter than the other squarks and the gluinos. As a consequence,b 1 andt 1 could be pair-produced with relatively large cross sections at the LHC.-1 - JHEP10(2013)189Two possible sets of SUSY mass spectra are considered in this paper. In the first set of scenarios, the lightest sbottom is the only coloured sparticle contributing to the production processes and it only decays viab 1 → bχ 0 1 . In the second set, the lightest stop is the only coloured sparticle allowed in the production processes and it decays exclusively...

A search is presented for direct top-squark pair production in final states with two leptons (electrons or muons) of opposite charge using 20.3 fb −1 of pp collision data at √ s = 8 TeV, collected by the ATLAS experiment at the Large Hadron Collider in 2012. No excess over the Standard Model expectation is found. The results are interpreted under the separate assumptions (i) that the top squark decays to a b-quark in addition to an on-shell chargino whose decay occurs via a real or virtual W boson, or (ii) that the top squark decays to a t-quark and the lightest neutralino. A top squark with a mass between 150 GeV and 445 GeV decaying to a b-quark and an on-shell chargino is excluded at 95% confidence level for a top squark mass equal to the chargino mass plus 10 GeV, in the case of a 1 GeV lightest neutralino. Top squarks with masses between 215 (90) GeV and 530 (170) GeV decaying to an on-shell (off-shell) t-quark and a neutralino are excluded at 95% confidence level for a 1 GeV neutralino. A Generator-level object and event selection 44 Keywords: Hadron-Hadron ScatteringThe ATLAS collaboration 50 IntroductionSupersymmetry (SUSY) [1][2][3][4][5][6][7][8][9] is an extension to the Standard Model (SM) which introduces supersymmetric partners of the known fermions and bosons. For each known boson or fermion, SUSY introduces a particle with identical quantum numbers except for a difference of half a unit of spin (S). The introduction of gauge-invariant and renormalisable interactions into SUSY models can violate the conservation of baryon number (B) and lepton number (L), resulting in a proton lifetime shorter than current experimental limits [10]. This is usually solved by assuming that the multiplicative quantum number R-parity (R),-1 - JHEP06(2014)124defined as R = (−1) 3(B−L)+2S , is conserved. In the framework of a generic R-parityconserving minimal supersymmetric extension of the SM (MSSM) [11][12][13][14][15], SUSY particles are produced in pairs where the lightest supersymmetric particle (LSP) is stable, and is a candidate for dark matter. In a large variety of models, the LSP is the lightest neutralino (χ 0 1 ). The scalar partners of right-handed and left-handed quarks (squarks),q R andq L , mix to form two mass eigenstates,q 1 andq 2 , withq 1 defined to be the lighter one. In the case of the supersymmetric partner of the top quark (top squark,t), large mixing effects can lead to one top-squark mass eigenstate,t 1 , that is significantly lighter than the other squarks. Consideration of naturalness and its impact on the SUSY particle spectrum, suggests that top squarks cannot be too heavy, to keep the Higgs boson mass close to the electroweak scale [16,17]. Thust 1 could be pair-produced with relatively large cross-sections at the Large Hadron Collider (LHC).The top squark can decay into a variety of final states, depending, amongst other factors, on the hierarchy of the mass eigenstates formed from the linear superposition of the SUSY partners of the Higgs boson and electroweak gauge bosons. I...

With the growing popularity of short-form video sharing platforms such as Instagram and Vine, there has been an increasing need for techniques that automatically extract highlights from video. Whereas prior works have approached this problem with heuristic rules or supervised learning, we present an unsupervised learning approach that takes advantage of the abundance of user-edited videos on social media websites such as YouTube. Based on the idea that the most significant sub-events within a video class are commonly present among edited videos while less interesting ones appear less frequently, we identify the significant sub-events via a robust recurrent auto-encoder trained on a collection of user-edited videos queried for each particular class of interest. The auto-encoder is trained using a proposed shrinking exponential loss function that makes it robust to noise in the web-crawled training data, and is configured with bidirectional long short term memory (LSTM) [5] cells to better model the temporal structure of highlight segments. Different from supervised techniques, our method can infer highlights using only a set of downloaded edited videos, without also needing their pre-edited counterparts which are rarely available online. Extensive experiments indicate the promise of our proposed solution in this challenging unsupervised setting.

Research on screen content images (SCIs) becomes important as they are increasingly used in multi-device communication applications. In this paper, we present a study on perceptual quality assessment of distorted SCIs subjectively and objectively. We construct a large-scale screen image quality assessment database (SIQAD) consisting of 20 source and 980 distorted SCIs. In order to get the subjective quality scores and investigate, which part (text or picture) contributes more to the overall visual quality, the single stimulus methodology with 11 point numerical scale is employed to obtain three kinds of subjective scores corresponding to the entire, textual, and pictorial regions, respectively. According to the analysis of subjective data, we propose a weighting strategy to account for the correlation among these three kinds of subjective scores. Furthermore, we design an objective metric to measure the visual quality of distorted SCIs by considering the visual difference of textual and pictorial regions. The experimental results demonstrate that the proposed SCI perceptual quality assessment scheme, consisting of the objective metric and the weighting strategy, can achieve better performance than 11 state-of-the-art IQA methods. To the best of our knowledge, the SIQAD is the first large-scale database published for quality evaluation of SCIs, and this research is the first attempt to explore the perceptual quality assessment of distorted SCIs.