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Physical Review Letters, 1995
The D collaboration reports on a search for the Standard Model top quark in p p collisions at p s = 1 : 8 T eV at the Fermilab Tevatron, with an integrated luminosity o f approximately 50 pb 1 . W e h a v e searched for t t production in the dilepton and singlelepton decay c hannels, with and without tagging of b quark jets. We observe 1 7 e v ents with an expected background of 3:8 0:6 e v ents. The probability for an upward uctuation of the background to produce the observed signal is 2 10 6 (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent with top quark decay. W e conclude that we h a v e observed the top quark and measure its mass to be 199 +19 21 (stat.) 22 (syst.) GeV/c 2 1 and its production cross section to be 6:4 2:2 pb.
Physical Review D, 2013
The Tevatron, where the top quark was discovered, and the currently functional Large Hadron Collider (LHC), with copiously produced top pairs, enable a detailed study of top-quark properties. In particular, they can be used to test the couplings of the top quark to gauge bosons. Several extensions of the standard model (SM) can give rise to anomalous couplings of the top quark to gauge bosons, in particular, the gluons. In this work we examine how top-quark polarization, which is predicted to be negligibly small in the SM, can be used to measure chromomagnetic and chromoelectric couplings of the top quark to gluons. We lay special emphasis on the use of angular distributions and asymmetries of charged leptons arising from top decay as measures of top polarization and hence of these anomalous couplings. Sensitivities that may be reached at the Tevatron and the LHC are obtained.
Physical Review Letters, 2015
A measurement of spin correlation in tt 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 tt 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 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 191 GeV are excluded at the 95% confidence level.
In this contribution we shall present the results about the physics of the top quark by CERN’s ATLAS and CMS experiments. After a brief motivation of why it is important to study the top quark at the LHC, we shall discuss the measurement of the production cross sections of top pairs and single tops. Then, we shall present an overview its properties: mass, flavour-changing neutral currents (FCNC), anomalous ETmiss, resonances and charge asymmetry. The overall agreement with the Standard Model predictions is very good.
Quantum detection of new physics in top-quark pair production at the LHC
arXiv (Cornell University), 2024
The recent observation of entanglement between top and anti-top quarks at the LHC opens the way to interpreting collider data with quantum information tools. In this work we investigate the relevance of quantum observables in searches of new physics. To this aim, we study spin correlations of tt pairs originating from various intermediate resonances, and compare the discovery reach of quantum observables compared to classical ones. We find that they provide complementary information and, in several notable cases, also the additional leverage necessary to detect new effects.
LHC Predictions from a Tevatron Anomaly in the Top Quark Forward-Backward Asymmetry
2011
We examine the implications of the recent CDF measurement of the top-quark forward-backward asymmetry, focusing on a scenario with a new color octet vector boson at 1-3 TeV. We study several models, as well as a general effective field theory, and determine the parameter space which provides the best simultaneous fit to the CDF asymmetry, the Tevatron top pair production cross section, and the exclusion regions from LHC dijet resonance and contact interaction searches. Flavor constraints on these models are more subtle and less severe than the literature indicates. We find a large region of allowed parameter space at high axigluon mass and a smaller region at low mass; we match the latter to an SU (3) 1 × SU (3) 2 /SU (3) c coset model with a heavy vector-like fermion. Our scenario produces discoverable effects at the LHC with only 1 − 2 fb −1 of luminosity at √ s = 7 − 8 TeV. Lastly, we point out that a Tevatron measurement of the b-quark forward-backward asymmetry would be very helpful in characterizing the physics underlying the top-quark asymmetry.
Top Quark Physics at the Tevatron
International Journal of Modern Physics A, 2013
The heaviest known elementary particle, the top quark, was discovered in 1995 by the CDF and D0 collaborations at the Tevatron proton–antiproton collider at Fermilab. Since its discovery, a large program was set in motion by the CDF and D0 collaborations to characterize the production and decay properties of top quarks, and investigate their potential for searches of new phenomena beyond the standard model. During the past 20 years, new methods were developed and implemented to improve the measurements and searches for new physics in the top quark sector. This paper reviews the achievements and results obtained through studies of the top quark at the Tevatron.
Enhancing the t t¯ H signal through top-quark spin polarization effects at the LHC
We compare the impact of top-quark spin polarization effects in Higgs boson production in association with top-quark pairs and in corresponding backgrounds at the LHC. Because of the spin-zero nature of the Higgs boson, one expects, in the chiral limit for the top quarks, a substantial complementarity in tt spin correlations for a Higgs decaying into fermions/gauge-bosons and tt spin correlations for the corresponding irreducible ttff /V V backgrounds. Although top mass effects in ttH production are in general dominant, and seriously spoil the chiral-limit expectations, one can find observables that capture the tt angular spin correlations and can help in separating the signal from irreducible backgrounds. In particular, we show that, for both H → bb and H → γγ, taking into account tt spin correlations in ttH production and irreducible backgrounds could appreciably improve the LHC sensitivity to the ttH channel.