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, G. and Abbott, B. and Abdallah, J. and Khalek, S. A. and Abdinov, O. and Krasznahorkay, Attila and Nagai, Yoshikazu and Pásztor, Gabriella and Tóth, József (2015) 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. PHYSICAL REVIEW LETTERS, 114 (14). ISSN 0031-9007

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Abstract

A measurement of spin correlation in t¯t 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 t¯t events by using the difference in azimuthal angle between the two charged leptons in the laboratory frame. In the helicity basis the measured degree of correlation corresponds to Ahelicity = 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.

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