Measurement of spin correlation between top and antitop quarks produced in pp¯ collisions at s=1.96 TeV

V M Abazov ,A Khanov,E Nagy,H.S Lee,S Bhatia,J Clutter,V Shary,S Söldner-Rembold,R Beuselinck,M Strauss,A Bean,B Penning,J Martínez-Ortega,N Khalatyan,M Cooke,D Smirnov,T Yasuda,W.M Lee,M Wobisch,T Scanlon,P Slattery,M Eads,H Schellman,V Buescher,J Lellouch,G Davies,O Karacheban,P Lebrun,H Liu,S Kermiche,J Qian,B Tuchming,L Han,J Orduna,J Joshi,J Sekaric,H Hegab,A Dominguez,S Greder,S Snyder,M Fortner,M Merkin,H Yin,Y Aushev,B Hoeneisen,I Heredia-De La Cruz,A Lobodenko,V Aushev,L Li,M Savitskyi,N Varelas,S Malik,S Yang,A Pal,W Ye,M Borysova,W Geng,L Sonnenschein,S Uvarov,M Diesburg,A Jonckheere,P Pétroff,C Schwanenberger,J Meyer,J Hays,J Linnemann,U Heintz,R Illingworth,C Royon,M Vesterinen,S Burdin,S Uzunyan,Y Xie,A Duperrin,V Bunichev,E Camacho-Pérez,M Hohlfeld,G Bernardi,D Edmunds,G Borissov,D Vilanova,T Head,F Badaud,V Parihar,R Madar,G Sajot,L Bellantoni,B Quinn,M Prewitt,X Lei,F Filthaut,F Rizatdinova,G Grenier,S Desai,R Partridge,I Ripp-Baudot,J Haley,G Alkhazov,H Severini,N Osman,R Jesik,U Bassler,R Nayyar,T Adams,E Shabalina,J Weichert,J Franc,S Cihangir,A Grohsjean,J Ellison,K Devaughan,L Uvarov,D Boline,P Rubinov,Y Enari,K Bloom,F Miconi,S Lammers,Ph Gris,G Petrillo,M Kaur,A Melnitchouk,Q.Z Li,T Hebbeker,S Atkins,A Bross,M Rominsky,R Lipton,R Van Kooten,M Titov,A Evdokimov,D Denisov,C Hensel,A Harel,T Guillemin,P Skubic,R Hirosky,Y Scheglov,M Mulhearn,I Razumov,K Harder,I Katsanos,M Buehler,B Baldin,M Corcoran,R Yamada,D Hedin,V Gavrilov,D Brown,F Couderc,M Narain,A Chandra,H Fox,J Snow,M Schott,C Deterre,L Bagby,R Kehoe,B Zhou,Z Ye,J Osta,P Baringer,S Grünendahl,A Sánchez-Hernández,M Verzocchi,L Sawyer,Y Peters,T Ferbel,F Déliot,R Magaña-Villalba,D Tsybychev,A Patwa,S Fuess,B Abbott,R Bernhard,D Price,A Brandt,A Ross,E Kajfasz,K Petridis,A Jayasinghe,O Brandt,T Hoang,G Savage,L Suter,K Augsten,Y Ilchenko,N Parua,S.W Lee,S Caughron,D Li,I Iashvili,N Parashar,N Stefaniuk,D Menezes,V Hynek,H Greenlee,M Wayne,Y Gershtein,C Tully,M Begalli,A Quadt,T Nunnemann,Y Liu,S Chakrabarti,J Zennamo,E De La Cruz-Burelo,K Yip,G Watts,A Alton,L Welty-Rieger,R Schwienhorst,A Boehnlein,J Warchol,H Li,G Golovanov,J.-F Grivaz,S Banerjee,S.K Park,R Brock,J Zhu,K Herner,O Gogota,P Svoisky,F Fiedler,T Kurča,G Chen,P Neustroev,D Karmanov,E Johnson,S Blessing,S Jabeen,A Dubey,M Jaffré,S.W Cho,I Howley,J Stark,V Bhatnagar,S Dutt,R Ruchti,M Besançon,G Ginther,D Lincoln,N Prokopenko,G Blazey,E Barberis,I Kiselevich,M Perfilov,A Askew,A Kharchilava,A A Shchukin ,A García-Bellido ,A Juste Rozas ,A Kupčo ,A L Lyon ,A P Heinson ,A S Ito ,A V Kozelov ,A Y Verkheev ,Alexandre Fauré ,Andreas Bernhard Meyer ,Arindam Das ,Ashok Kumar ,B C.k Casey ,C E Gerber ,C L Mcgivern ,C P Buszello ,C Ávila ,D A Stoyanova ,D R Claes ,D V Bandurin ,D Wood ,D Ziemińska ,D Ćutts ,E Boos ,E W Varnes ,Feng Liu ,G D Alexeev ,G Gutiérrez ,G R Snow ,G W Wilson ,H A Neal ,H Castilla‐Valdez ,H D Wahl ,H E Fisk ,H M Evans ,H Nguyen ,H T Diehl ,I A Bertram ,I A Vasilyev ,J A García-González ,J Cúth ,J F Bartlett ,J Hobbs ,J K Kraus ,J L Holzbauer ,J M Hauptman ,J M Hogan ,J P Agnew ,J Yu ,Jun Kyu Lim ,K A Johns ,K M Chan ,K Soustružnı́k ,L Dudko ,L S Vertogradov ,M A Pleier ,M C Cousinou ,M Grünewald ,M Hildreth ,M Lokajı́ček ,M M Meijer ,M R Adams ,M S Jeong ,M Zieliński ,Mark D Johnson ,Mark Richard James Williams ,Michael Wang ,P C Bhat ,P D Grannis ,P F Ding ,P Gutiérrez ,P H Garbincius ,P Jönsson ,P N Ratoff ,P Vokáč ,Peng Jiang ,R D Schamberger ,R Démina ,R L Mccarthy ,R Lopes De ,R Luna-García ,S M Shaw ,S P Denisov ,S W Youn ,Sijbrand J De Jong ,Sung Wook Choi ,T R Wyatt ,T Zhao ,V A Kuzmin ,V D Elvira ,V E Bazterra ,V L Malyshev ,V M Podstavkov ,V V Lipaev ,V V Tokmenin ,V Šimák ,W C Fisher ,W E Cooper ,W M Van Leeuwen ,X B Bu ,Y A Yatsunenko ,Y N Kharzheev ,Y T Tsai ,Z Hubáček ,É Chapon ,А В Попов ,В Н Евдокимов ,P G Mercadante ,B S Acharya ,N K Mondal ,J P Negret ,J M Kohli ,S B Beri ,B C Choudhary ,J D Mansour ,G G Hesketh ,M P Sanders ,A K.a Maciel ,A S Santos ,A W Jung ,L Živković

doi:10.1016/j.physletb.2016.03.053

Abstract

We present a measurement of the correlation between the spins of t and t¯ quarks produced in proton–antiproton collisions at the Tevatron Collider at a center-of-mass energy of 1.96 TeV. We apply a matrix element technique to dilepton and single-lepton+jets final states in data accumulated with the D0 detector that correspond to an integrated luminosity of 9.7fb−1. The measured value of the correlation coefficient in the off-diagonal basis, Ooff=0.89±0.22(stat+syst), is in agreement with the standard model prediction, and represents evidence for a top–antitop quark spin correlation difference from zero at a level of 4.2 standard deviations.

Highlights

The top quark is the heaviest elementary particle in the standard model (SM) [1,2,3,4]
Despite the fact that the top quark decays weakly, its large mass leads to a very short lifetime of ≈ 5 · 10−25 s [5,6,7]. It decays to a W boson and a b quark before hadronizing, a process that has a characteristic time of 1/ QCD ≈ (200 MeV)−1 equivalent to τhad ≈ 3.3 · 10−24 s, where QCD is the fundamental scale of quantum chromodynamics (QCD)
The difficulty arises from the fact that the cross sections for the gq → ttq and gq → ttqprocesses at leading order (LO), as well as g g and qqproduction at next-to-leading order (NLO), contain a singularity when the final state quark is collinear with the quark in the initial state

Summary

Introduction

The top quark is the heaviest elementary particle in the standard model (SM) [1,2,3,4]. Antiquark annihilation versus like-helicity g g fusion), and their different collision energies, make the measurements of the strength of the spin correlation at both the Tevatron and LHC interesting and complementary. The expected and observed number of events are consistent when the systematic uncertainties, partially correlated between the +jets and channels, are taken into account. These uncertainties are of the order of 10%. The most important contributions are the integrated luminosity, b-quark jet modeling, uncertainties on the ttmodeling and uncertainty in the heavy flavor NLO K -factors of the W +jets background in the +jets channel

Measurement technique and results

Background contribution

Systematic uncertainties

Spin correlation and the ttproduction mechanism

Summary