Measurement of Spin Correlation in Top-Antitop Quark Events and Search for Top Squark Pair Production inppCollisions ats=8  TeVUsing the ATLAS Detect

Abstract

A measurement of spin correlation in tt production is presented using data collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb −1 . The correlation between the top and antitop quark spins is extracted from dilepton tt events by using the difference in the azimuthal angle between the two charged leptons in the laboratory frame. In the helicity basis the measured degree of correlation corresponds to A helicity ¼ 0.38 AE 0.04, in agreement with the standard model prediction. A search is performed for pair production of top squarks with masses close to the top quark mass decaying to predominantly right-handed top quarks and a light neutralino, the lightest supersymmetric particle. Top squarks with masses between the top quark mass and 191 GeV are excluded at the 95% confidence level.

Third generation SUSY searches in CMS

“…This note presents results of several searches for third generation squark pair production using a dataset corresponding to an integrated luminosity of 2.3 fb −1 of proton-proton (pp) collisions collected at a center-of-mass energy of 13 TeV with the CMS detector [1] at LHC in 2015. The results of similar searches were previously reported by the ATLAS and CMS collaborations using datasets of 7 and 8 TeV pp collisions [2,3,4,5,6,7,8,9,10,11]and earlier by CDF and D0 collaborations at the Tevatron. No excess above the SM expectations was observed and the results of those searches were used to place lower limits on the mass of the squarks for different decay scenarios.…”

Beyond Standard Model Collider Phenomenology of Higgs Physics and Supersymmetry

“…Both plots are similar, however the ATLAS exclusion limits are more stringent in the low stop mass region of interest. Both are reproduced in Figure 5.2 [155][156][157][158][159][160][161][162][163].…”

Probing light stops with stoponium

“…It is also worthwhile to note that the "stealth" stop region -the phase spacesuppressed part of region I near m t 1 ∼ m t , m χ 0 0 -is also potentially amenable to stoponium searches (within the red-shaded region in the bottom part of figure 9) This region is challenging to probe with direct stop searches, and several dedicated observables such as spin correlations [64,65], top pair production rates [66,67] and special kinematic variables [68][69][70][71] have been studied. However, they primarily rely on precision measurements and calculations, which are often subject to subtle uncertainties.…”