Measurement of Spin Correlation in Top-Antitop Quark Events and Search for Top Squark Pair Production in pp Collisions at s√=8 TeV Using the ATLAS Detector
Aad, Georges; Abbott, Brad; Abdallah, Jalal; Abdel Khalek, Samah; Abdinov, Ovsat Bahram oglu; Aben, Rosemarie; Abi, Babak; Abolins, Maris; AbouZeid, Hass; Abramowicz, Halina; Buanes, Trygve; Dale, Ørjan; Eigen, Gerald; Kastanas, Alex; Liebig, Wolfgang; Lipniacka, Anna; Martin dit Latour, Bertrand; Rosendahl, Peter Lundgaard; Sandaker, Heidi; Sjursen, Therese B.; Smestad, Lillian; Stugu, Bjarne; Ugland, Maren; Bugge, Lars; Bugge, Magnar Kopangen; Cameron, David Gordon; Catmore, James Richard; Czyczula, Zofia; Franconi, Laura; Gjelsten, Børge Kile; Gramstad, Eirik; Morisbak, Vanja; Ould-Saada, Farid; Pajchel, Katarina; Pedersen, Maiken; Read, Alexander Lincoln; Røhne, Ole Myren; Stapnes, Steinar; Strandlie, Are; Abreu, Henso; Abreu, Rômulo F.; Abulaiti, Yiming; Acharya, Bobby S.; Adamczyk, Leszek; Adams, David; Adelman, Jareed; Adomeit, Stefanie; Adye, Tim; Agatonovic-Jovin, Tatjana; Aguilar Saavedra, Juan Antonio; ATLAS, Collaboration
Peer reviewed, Journal article
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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 =0.38±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.