Abstract
A measurement of spin correlation in tt[over ¯] 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 8TeV, corresponding to an integrated luminosity of 20.3 fb^{-1}. The correlation between the top and antitop quark spins is extracted from dilepton tt[over ¯] 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 191GeV are excluded at the 95% confidence level.
Highlights
Detailed studies of the correlation of the spin of top and antitop quarks in tt events produced at hadron colliders are of great interest; they provide important precision tests of the predictions of the standard model (SM) and are sensitive to many new physics scenarios [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
An observable very sensitive to tt spin correlation is the azimuthal angle Δφ between the charged leptons [34], which is well measured by the ATLAS detector
Monte Carlo (MC) simulation samples are used to evaluate the contributions, and shapes of distributions of week ending 10 APRIL 2015 kinematic variables, for signal tt events and for background processes not evaluated from complementary data samples
Summary
Detailed studies of the correlation of the spin of top and antitop quarks in tt events produced at hadron colliders are of great interest; they provide important precision tests of the predictions of the standard model (SM) and are sensitive to many new physics scenarios [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. The orientations of the top and antitop quark spins are transferred to the decay products and can be measured directly via their angular distributions [3,17,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36]. Because the polarization-analyzing power of the angular distributions of charged leptons from top and antitop quark decays is effectively 100% [44,45], dilepton final states of ee, μμ, and eμ are analyzed.
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