Observation of spin correlation in tt̄ events from pp collisions at √s=7TeV Using the ATLAS detector

G Aad; B Abbott; J Abdallah; S Abdel Khalek; AA Abdelalim; A Abdesselam; O Abdinov; B Abi; M Abolins; OS Abouzeid; H Abramowicz; H Abreu; E Acerbi; BS Acharya; L Adamczyk; DL Adams; TN Addy; J Adelman; M Aderholz; S Adomeit; P Adragna; T Adye; S Aefsky; JA Aguilar-Saavedra; M Aharrouche; SP Ahlen; F Ahles; A Ahmad; M Ahsan; G Aielli; T Akdogan; TPA Åkesson; G Akimoto; AV Akimov; A Akiyama; MS Alam; MA Alam; J Albert; S Albrand; M Aleksa; IN Aleksandrov; F Alessandria; C Alexa; G Alexander; G Alexandre; T Alexopoulos; M Alhroob; M Aliev; G Alimonti; J Alison; M Aliyev; BMM Allbrooke; PP Allport; SE Allwood-Spiers; J Almond; A Aloisio; R Alon; A Alonso; B Alvarez Gonzalez; MG Alviggi; K Amako; P Amaral; C Amelung; VV Ammosov; A Amorim; G Amorós; N Amram; C Anastopoulos; LS Ancu; N Andari; T Andeen; CF Anders; G Anders; KJ Anderson; A Andreazza; V Andrei; ML Andrieux; XS Anduaga; A Angerami; F Anghinolfi; A Anisenkov; N Anjos; A Annovi; A Antonaki; M Antonelli; A Antonov; J Antos; F Anulli; S Aoun; L Aperio Bella; R Apolle; G Arabidze; I Aracena; Y Arai; ATH Arce; S Arfaoui; JF Arguin; E Arik; M Arik; AJ Armbruster

Journal article

Observation of spin correlation in tt̄ events from pp collisions at √s=7TeV Using the ATLAS detector

G Aad, B Abbott, J Abdallah, S Abdel Khalek, AA Abdelalim, A Abdesselam, O Abdinov, B Abi, M Abolins, OS Abouzeid, H Abramowicz, H Abreu, E Acerbi, BS Acharya, L Adamczyk, DL Adams, TN Addy, J Adelman, M Aderholz, S Adomeit Show all

Physical Review Letters | Published : 2012

DOI: 10.1103/PhysRevLett.108.212001

Open access

Abstract

A measurement of spin correlation in tt production is reported using data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 2.1fb-1. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. The difference in azimuthal angle between the two charged leptons in the laboratory frame is used to extract the correlation between the top and antitop quark spins. In the helicity basis the measured degree of correlation corresponds to Ahelicity=0.40 min 0.08 plus 0.09, in agreement with the next-to-leading-order standard model prediction. The hypothesis of zero spin correlation is excluded at 5.1 standard..

View full abstract

University of Melbourne Researchers

Anna Phan Author

Martin Sevior Author

Elisabetta Barberio Author

Matteo Volpi Author

Grants

Awarded by European Commission

Funding Acknowledgements

We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC, and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST, and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR, and VSC CR, Czech Republic; DNRF, DNSRC, and Lundbeck Foundation, Denmark; EPLANET and ERC, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS, Georgia; BMBF, DFG, HGF, MPG, and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP, and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, The Netherlands; RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MVZT, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular, from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (U.K.) and BNL (U.S.) and in the Tier-2 facilities worldwide.