Measurements of top-quark pair spin correlations in the eμ channel at s√=13 TeV using pp collisions in the ATLAS detector
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Aaboud, M., Aad, G., Abbott, B. et al. Measurements of top-quark pair spin correlations in the eμ channel at s√=13 TeV using pp collisions in the ATLAS detector. Eur. Phys. J. C 80, 754 (2020). [https://doi.org/10.1140/epjc/s10052-020-8181-6]
SponsorshipANPCyT; YerPhI, Armenia; Australian Research Council; BMWFW, Austria; Austrian Science Fund (FWF); Azerbaijan National Academy of Sciences (ANAS); SSTC, Belarus; National Council for Scientific and Technological Development (CNPq); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Natural Sciences and Engineering Research Council of Canada; NRC, Canada; Canada Foundation for Innovation; CERN; Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT); Chinese Academy of Sciences; Ministry of Science and Technology, China; National Natural Science Foundation of China (NSFC); Departamento Administrativo de Ciencia, Tecnologia e Innovacion Colciencias; Ministry of Education, Youth & Sports - Czech Republic Czech Republic Government; DNRF, Denmark; Danish Natural Science Research Council; Centre National de la Recherche Scientifique (CNRS); CEA-DRF/IRFU, France; SRNSFG, Georgia; Federal Ministry of Education & Research (BMBF); HGF, Germany; Max Planck Society; Greek Ministry of Development-GSRT; RGC, China; Hong Kong SAR, China; Israel Science Foundation; Benoziyo Center, Israel; Istituto Nazionale di Fisica Nucleare (INFN); Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science; CNRST, Morocco; Netherlands Organization for Scientific Research (NWO) Netherlands Government; RCN, Norway; Ministry of Science and Higher Education, Poland; NCN, Poland; Portuguese Foundation for Science and Technology; MNE/IFA, Romania; MES of Russia, Russia Federation; NRC KI, Russia Federation; JINR; MESTD, Serbia; MSSR, Slovakia; Slovenian Research Agency - Slovenia; MIZS, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC, Sweden; Wallenberg Foundation, Sweden; SERI, Switzerland; Swiss National Science Foundation (SNSF); Canton of Bern, Switzerland; Canton of Geneva, Switzerland; Ministry of Science and Technology, Taiwan; Ministry of Energy & Natural Resources - Turkey; Science & Technology Facilities Council (STFC); United States Department of Energy (DOE); National Science Foundation (NSF); BCKDF, Canada; CANARIE, Canada; Compute Canada, Canada; CRC, Canada; European Union (EU) European Research Council (ERC); Horizon 2020, European Union; COST, European Union; French National Research Agency (ANR); German Research Foundation (DFG); Alexander von Humboldt Foundation; Herakleitos programme; Thales programme; Aristeia programme; European Union (EU); Greek NSRF, Greece; BSF-NSF, Israel; German-Israeli Foundation for Scientific Research and Development; CERCA Programme Generalitat de Catalunya, Spain; PROMETEO Programme GeneralitatValenciana, Spain; GoranGustafssons Stiftelse, Sweden; Royal Society of London; Leverhulme Trust
A measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb−1 of pp collision data at s√=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the tt¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.