Differential top-antitop cross-section measurements as a function of observables constructed from final-state particles using pp collisions at $\sqrt{s}=7$ TeV in the ATLAS detector
Various differential cross-sections are measured in top-quark pair ($t\bar{t}$) events produced in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 7$ TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of $4.6$ fb$^{-1}$. The differential cross-sections are presented in terms of kinematic variables, such as momentum, rapidity and invariant mass, of a top-quark proxyreferred to as the pseudo-top-quark as well as the pseudo-top-quark pair system. The dependence of the measurement on theoretical models is minimal.
The measurements are performed on $t\bar{t}$ events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a $b$-quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the $W$ boson produced by the top-quark decay in events with a single charged lepton. Differential cross-section measurements of the pseudo-top-quark variables are compared with several Monte Carlo models that implement next-to-leading order or leading-order multi-leg matrix-element calculations.
We report a measurement of the charge asymmetry $A_C$ in top quark pair production with the ATLAS experiment. The measurement focuses on dilepton channels ($ee$, $eμ$, $μμ$). The data are unfolded to parton level at full phase space using a fully Bayesian unfolding method. Inclusive and differential measurements of the charge asymmetry are performed.
We report a measurement of the charge asymmetry in top quark pair production with the ATLAS experiment at the LHC using 20.3 fb$^{-1}$ of pp collision data at $\sqrt{s}$ = 8 TeV. The data are unfolded using a fully Bayesian unfolding method. Differential measurements of the charge asymmetry are performed.
We present simulations of the production cross-section measurement of top-antitop pairs in the di-leptonic decay channel with the ATLAS detector. This study uses the Commissioning Service Challenge (CSC) data, which is the latest and centrally produced Monte-Carlo data set to validate the detector simulation before the actual data taking. The signal process was generated with MC@NLO and important background processes were studied. A cut and count method and two likelihood methods were employed to measure the cross section and important systematic effects were investigated. The expected statist…
The top quark mass has been measured using the template method in the top antitop -> lepton + jets channel based on data recorded in 2011 with the ATLAS detector at the LHC. The data were taken at a proton-proton centre-of-mass energy of sqrt(s) = 7 TeV and correspond to an integrated luminosity of 1.04/fb. The analyses in the electron + jets and muon + jets decay channels yield consistent results. The top quark mass is measured to be m_top = 174.5 +/- 0.6_stat +/- 2.3_syst GeV.
Measurements of spin correlation in top quark pair production are presented using data collected with the ATLAS detector at the LHC with proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.6 fb$^{-1}$. Events are selected in final states with two charged leptons and at least two jets and in final states with one charged lepton and at least four jets. Four different observables sensitive to different properties of the top quark pair production mechanism are used to extract the correlation between the top and antitop quark spins. Some of t…
This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4.7 fb^-1 of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at sqrt(s) = 7 TeV. Final states containing one or two isolated leptons (electrons or muons) and jets are considered. Two measurements of alpha_l P, the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a CP conserving (CPC) or a CP violating (CPV) production process. The measurements obt…
We present measurements of the top-antitop production cross section in b-tagged lepton + jets events from proton-antiproton collisions at 1.96 TeV using the CDF detector at Fermilab. B-jets are tagged with either a secondary vertex algorithm, or a soft lepton tagger that identifies muons from B hadron semileptonic decays. With Tevatron Run II data, we estimate the top-antitop signal fraction in two different ways: by estimating the various background contributions, and by fitting directly the leading jet transverse energy spectrum for the signal and background contributions. A subset of the sa…
A measurement of the top-antitop production cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV has been performed at the LHC with the CMS detector. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns and is based on the reconstruction of the final state with one isolated, high transverse-momentum electron or muon and three or more hadronic jets. The kinematic properties of the events are used to separate the top-antitop signal from W+jets and QCD multijet background events. The measured cross section is 173 + 39 - 32 (sta…
A measurement of spin correlation in $t\bar{t}$ 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 $t\bar{t}$ 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 $A_{helicity} = 0.38 \pm 0.04$, in agreement with the S…
The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of $\sqrt s =1.96$ TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is $A_{\mathrm{FB}}^{t\bar{t}} = 0.128 \pm 0.025$. The combin…
We present a measurement of the correlation between the spins of t and tbar 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 9.7 fb$^{-1}$. The measured value of the correlation coefficient in the off-diagonal basis, $O_{off} = 0.89 \pm 0.22$ (stat + syst), is in agreement with the standard model prediction, and represents evidence for a top-antitop quark spin c…
A measurement of the charge asymmetry in the production of top quark pairs in the semileptonic decay channel has been performed. A dataset corresponding to an integrated luminosity of 1.04 inverse femtobarn, obtained at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC, was used. After performing a selection of events with one isolated lepton, at least four jets and missing transverse energy, a kinematic fit was performed to reconstruct the top-antitop event topology. The charge asymmetry was determined using the differential distribution of the difference of absolute recon…
At the Tevatron, the collider experiments CDF and DO have data sets at their disposal that comprise a few thousand reconstructed top-antitop-quark pairs and allow for precision measurements of the cross section as well as production and decay properties. Besides comparing the measurements to standard model predictions, these data sets open a window to physics beyond the standard model. Dedicated analyses look for new heavy gauge bosons, fourth generation quarks, and flavor-changing neutral currents. In this mini-review the current status of these measurements is summarized.
We use 106 $\ipb$ of data collected with the Collider Detector at Fermilab to search for narrow-width, vector particles decaying to a top and an anti-top quark. Model independent upper limits on the cross section for narrow, vector resonances decaying to $\ttbar$ are presented. At the 95% confidence level, we exclude the existence of a leptophobic $\zpr$ boson in a model of topcolor-assisted technicolor with mass $M_{\zpr}$ $<$ 480 $\gev$ for natural width $Γ$ = 0.012 $M_{\zpr}$, and $M_{\zpr}$ $<$ 780 $\gev$ for $Γ$ = 0.04 $M_{\zpr}$.
We present the first results on searches for new massive resonances decaying to a top-antitop quark ($t\bar{t}$) pair with the CMS detector at the LHC in proton-proton collisions with a center of mass energy of $\sqrt{s}=13~\mathrm{TeV}$. The data set considered corresponds to an integrated luminosity of $2.6~\mathrm{fb}^{-1}$ recorded during the the first year of the LHC Run-2. Searches are performed by measuring the invariant mass distribution of the $t\bar{t}$ system in semileptonic and fully-hadronic final states. Dedicated techniques are used to identify the decay of highly-boosted top qu…
We present a direct measurement of the mass difference between top and antitop quarks (dm) in lepton+jets top-antitop final states using the "matrix element" method. The purity of the lepton+jets sample is enhanced for top-antitop events by identifying at least one of the jet as originating from a b quark. The analyzed data correspond to 3.6 fb-1 of proton-antiproton collisions at 1.96 TeV acquired by D0 in Run II of the Fermilab Tevatron Collider. The combination of the e+jets and mu+jets channels yields dm = 0.8 +/- 1.8 (stat) +/- 0.5 (syst) GeV, which is in agreement with the standard model…
A measurement of the ttbar production cross section at sqrt(s) = 1.96 TeV in the dilepton final states using a lepton+track selection and secondary vertex b-tagging is presented. One of the two leptons from the decay of the ttbar pair is allowed to be identified only as an isolated track to improve the selection efficiency. The result is combined with a measurement in the ttbar->e+mu final state. The measurements are based on 370 pb^-1 of data collected with the D0 experiment at the Tevatron collider. The preliminary cross section obtained in the combined lepton+track and e+mu channel is: sigm…
The top-quark pair production cross section in 7 TeV center-of-mass energy proton-proton collisions is measured using data collected by the CMS detector at the LHC. The measurement uses events with one jet identified as a hadronically decaying tau lepton and at least four additional energetic jets, at least one of which is identified as coming from a b quark. The analyzed data sample corresponds to an integrated luminosity of 3.9 inverse femtobarns recorded by a dedicated multijet plus hadronically decaying tau trigger. A neural network has been developed to separate the top-quark pairs from t…
We present an analysis of dilepton events originating from top-antitop production in proton-antiproton collisions at sqrt{s}=1.8 TeV at the Fermilab Tevatron Collider. The sample corresponds to an integrated luminosity of 109+-7 pb^{-1}. We observe 9 candidate events, with an estimated background of 2.4+-0.5 events. We determine the mass of the top quark to be M_top = 161+-17(stat.)+-10(syst.) GeV/c^2. In addition we measure a top-antitop production cross section of 8.2+4.4-3.4 pb (where M_top = 175 GeV/c^2 has been assumed for the acceptance estimate).
In this report a new search for a narrow-width heavy resonance decaying into top quark pairs (X -> ttbar) in ppbar collisions at sqrt(s)=1.96 TeV has been performed using data collected by the D0 detector at the Fermilab Tevatron collider. The analysis considers ttbar candidate events in the lepton+jets channel using a lifetime tag to identify b-jets and the ttbar invariant mass distribution to search for evidence of resonant production. The analyzed dataset corresponds to an integrated luminosity of approximately 370 pb^-1. Since no evidence for a ttbar resonance X is found, upper limits on s…
We present a measurement of the mass difference between t and tbar quarks observed in lepton+jets final states of ttbar events in 1 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider in ppbar collisions at sqrt(s)=1.96 TeV. The observed mass difference of 3.8+-3.7 GeV is consistent with the equality of t and tbar masses. This is the first direct measurement of a mass difference between a quark and its antiquark partner.
The top quark, discovered in 1995 by the CDF and D0 collaborations at the Tevatron proton antiproton collider at Fermilab, has undergone intense studies in the last 20 years. Currently, CDF and D0 converge on their measurements of top-antitop quark production cross sections using the full Tevatron data sample. In these proceedings, the latest results on inclusive and differential measurements of top-antitop quark production cross sections at the Tevatron are reported.
The top quark pair production cross section is measured in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data collected in 2017 by the CMS experiment at the LHC corresponding to an integrated luminosity of 304 pb$^{-1}$ are analyzed. The measurement is performed using events with one electron and one muon of opposite sign, and at least two jets. The measured cross section is found to be $σ_{\mathrm{t}\bar{\mathrm{t}}}~=~60.3~\pm5.0~\mathrm{(stat)}\pm2.8~\mathrm{(syst)}\pm0.9~\mathrm{(lumi)}$ pb. To reduce the statistical uncertainty, a combination with the result in the …
Some Beyond the Standard Model theories predict new particles that decay predominantly into top-antitop quark pairs. A search for top-antitop quark resonances that decay into the lepton plus jets final state is carried out with the ATLAS experiment at the LHC using 14 fb$^{-1}$ of $\sqrt{s}$ = 8 TeV proton-proton collisions. The search considers both cases where all of the final state jets are isolated and where some or all of the top quark decay products are merged into a single jet. Mass exclusion limits at a 95% credibility level are set for two benchmark models, one predicting leptophobic …
We report the latest results on the top-quark mass and on the top-antitop mass difference from the CDF and D0 collaborations using data collected at the Fermilab Tevatron $p\bar{p}$ collider at $\sqrt{s}=1.96$ TeV. We discuss general issues in top-quark mass measurements and present new results from direct measurements and from top-pair production cross-section. We also report new results on the top-antitop mass difference.
We perform a general parton level analysis for the search of heavy resonant states in the production of top-antitop pairs at the LHC with an integrated luminosity of 30 fb^-1. We assume the existence of resonances that only couple to quarks and propose kinematic cuts in order to increase the amount of events produced through quark-annihilation. We study the interplay between different variables and their impact on the purity of the selected sample. We make focus on the longitudinal ($β$) and transverse ($p_T$) momentum of the top-antitop pair, and the scattering angle ($θ$) in the center of ma…
Selected topics of the top-quark mass measurements in well-defined schemes are presented. The measurements have been performed using data recorded with the ATLAS and CMS detectors at the LHC at proton-proton centre-of-mass energies of 7 and 8 TeV. Precision theoretical QCD calculations for both inclusive top-antitop quark pair production and top-antitop quark pair production with an additional jet to extract the top quark mass in the pole-mass scheme have been used.
We propose a charged, electrically neutral, and flavour changing Z' model to conciliate the apparent disagreement between the important excess found in the top-antitop Tevatron forward-backward asymmetry and the null -compatible with negative- results found in the LHC charge asymmetry. We show that this model contributes positively to the forward-backward asymmetry, whereas naturally a new cancellation is turned on at the LHC, yielding a null, or even negative, charge asymmetry. We found the region in parameter space that is simultaneously allowed by the stringent Tevatron and LHC observables.…
A search for decays of the Higgs boson to invisible particles in events with a top-antitop quark pair or a vector boson in proton-proton collisions at $\sqrt{s}$ = 13 TeV
Measurement of the associated production of a top-antitop-quark pair and a Higgs boson decaying into a $b\bar{b}$ pair in $pp$ collisions at $\sqrt{s}=13$ TeV using the ATLAS detector at the LHC
本文利用ATLAS探测器140 fb$^{-1}$的13 TeV数据，在$H \rightarrow b \bar{b}$衰变道中测量了$t\bar{t}H$伴随产生，观测显著性为4.6个标准偏差，截面与标准模型预言一致，并进行了微分截面测量。
This Letter reports a search for a narrow resonant state decaying into two $W$ bosons and a bottom-antibottom quark pair where one $W$ boson decays leptonically and the other decays into a quark-antiquark pair. The search is particularly sensitive to top-antitop resonant production. We use the full data sample of proton-antiproton collisions at a center-of-mass energy of 1.96 TeV collected by the CDF II detector at the Fermilab Tevatron, corresponding to an integrated luminosity of 9.45 fb$^{-1}$. No evidence for resonant production is found and upper limits on the production cross section tim…
Top-antitop pairs will be copiously produced at the LHC, at a rate of roughly one per second at a luminosity of10^{33} cm^{-2} s^{-1}. These events have low background and produce large numbers of jets via the hadronic decay of the W's which may be used to calibrate the jet energy scale and resolution with experimental data and simulations.
Results of top-quark mass measurements in the di-lepton and the all-jets top-antitop decay channels with the ATLAS detector are presented. The measurements are obtained using proton-proton collisions at a centre-of-mass energy $\sqrt{s}$ = 8 TeV at the CERN Large Hadron Collider. The data set used corresponds to an integrated luminosity of 20.2 $fb^{-1}$. The top-quark mass in the di-lepton channel is measured to be 172.99 $\pm$ 0.41 (stat.) $\pm$ 0.74 (syst.) GeV. In the all-jets analysis, the top-quark mass is measured to be 173.72 $\pm$ 0.55 (stat.) $\pm$ 1.01 (syst.) GeV. In addition, the …
The precise measurement of top quark production and properties is one of the primary goals of the Tevatron during Run II. The total top-antitop production cross-section has been measured in a large variety of decay channels and using different selection criteria. Results from differential cross-section measurements and searches for new physics in top-antitop production and top quark decays are available. Electroweak production of single top quarks has been searched for. The results from all these analyses, using typically 200/pb of data, are presented.
Following the confirmation of the top quark discovery at the Tevatron, the next step is to begin studying its properties. Because the scale of electroweak symmetry breaking is of the same order as the measured top mass, the top quark may be very sensitive to new physics. We describe measurements of the total top-antitop cross section, the top-antitop invariant mass, the top transverse momentum distribution, and single top production from Run 1 data at D0 and CDF. All of these measurements will become more precise in Run 2.
A measurement of the top-antitop production charge asymmetry A_C is presented using data corresponding to an integrated luminosity of 1.04 fb^-1 of pp collisions at sqrt(s) = 7 TeV collected by the ATLAS detector at the LHC. Events are selected with a single lepton (electron or muon), missing transverse momentum and at least four jets of which at least one jet is identified as coming from a b-quark. A kinematic fit is used to reconstruct the ttbar event topology. After background subtraction, a Bayesian unfolding procedure is performed to correct for acceptance and detector effects. The measur…
We present a search for top-antitop events with a tau lepton in the final state. The data sample corresponds to an integrated luminosity of 194/pb collected with the CDF II detector from proton-antiproton collisions at a center of mass energy of 1.96 TeV. We observe two events with an expected signal of 1.0+/-0.2 events and a background of 1.3+/-0.3 events. We determine a 95% confidence level upper limit on r_tau, the ratio of the measured rate of top->tau nu quark to the expectation, of 5.2.
Discovered in 1995 by CDF and D0 at the Fermilab Tevatron collider, the top quark remains interesting to test the Standard Model. Having collected more than 7 fb$^{-1}$ of integrated luminosity with both experiments until today, several top quark properties have been measured with increasing precision, while other properties have been investigated for the first time. In this article recent measurements of top quark properties from CDF and D0 are presented, using between 1 fb$^{-1}$ and 4.8 fb$^{-1}$ of data. In particular, the measurement of the top quark mass, the top quark width, the top ant…
This Letter reports a search for non standard model topquark resonances, $Z'$, decaying to $t\bar{t} \rightarrow W^+b W^-\bar{b}$ %\rightarrow qq'b qq' \bar{b}$, where both $W$ decay to quarks. We examine the top-antitop quark invariant mass spectrum for the presence of narrow resonant states. The search uses a data sample of $\ppb$ collisions at a center of mass energy of 1.96 TeV collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of 2.8 fb$^{-1}$. No evidence for top-antitop quark resonant production is found. We place upper limits on the production cros…
I present the latest results on the theoretical cross section for top-antitop pair production as well as for single top production at the Tevatron and the LHC. The calculations include higher-order soft-gluon corrections which are dominant near threshold. The top quark transverse momentum distribution is also presented.
The most recent results of the top-quark mass measurements with the ATLAS detector using data collected from proton-proton collisions at the Large Hadron Collider are presented. Although several decay modes of the top-quark pairs have been used in ATLAS for top-quark mass measurements, only the latest results are presented (single lepton and dilepton channels). The top-quark pole mass from the $t\overline{t}$ cross-section measurement in the dilepton channel and the top-antitop mass difference measurement in the single-lepton channel are also shown. The systematic uncertainties associated to t…
We present a measurement of the charge asymmetry in top-antitop production using data corresponding to an integrated luminosity of $0.70 fb^{-1}$ of proton-proton collisions at $\sqrt s = 7$ TeV collected by the ATLAS detector. The top pair events decaying semileptonically (lepton+jets channel) to either an electron or muon, missing transverse energy and at least four jets are selected. The reconstruction of the $t\bar{t}$ events was performed using a kinematic likelihood approach. The difference of absolute values of top and antitop rapidities is used to define the charge asymmetry: $A_{C} = …
Preliminary results of two differential cross-section measurements in the ATLAS experiment at CERN are presented. Measurements are focused on the top-antitop quark pair production in the~lepton+jets and the~all-hadronic channels in the kinematic region with high transverse momentum top quarks. Both measurements use the full Run 2 data of 13 TeV proton-proton collisions from the Large Hadron Collider collected by the ATLAS detector in 2015-2018, corresponding to an integrated luminosity of 139 fb$^{-1}$. The measured spectra are compared with the Standard Model predictions. They are also used t…
The searches for extra-dimensions, top resonances, 4th generation quarks and leptoquark signatures are presented. The results are based on proton-proton collision data for a center-of mass energy of7 or 8 TeV, corresponding to various integrated luminosities. No signal of physics beyond the Standard Model has been observed so far.
Measurements of the branching ratios of top quark decays into leptons and jets using events with $t \overline{t}$ (top antitop) pairs are reported. Events were recorded with the ATLAS detector at the LHC in pp collisions at a center-of-mass energy of 7 TeV. The collected data sample corresponds to an integrated luminosity of 4.6 ${\mathrm{fb}}^{-1}$. The measured top quark branching ratios agree with the Standard Model predictions within the measurement uncertainties of a few percent.
The dependence of the top-quark mass measurement in top-quark production on the parton distribution functions is explored through the differential distribution of the invariant mass of the top-antitop system in top-quark pair production at hadron colliders. Several different proton-proton collider options are considered: 8 TeV, 13 TeV, 13.6 TeV, 14 TeV, and 100 TeV. The top-quark mass is obtained from a chi-squared fit to the invariant mass of the top-antitop-quark pair. The parton distribution function uncertainties are used in the chi-square evaluation. The uncertainties are reduced through …
Proceeding for LHCP2017 conference. Referencing the ATLAS publication note: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2017-005/
New measurements from ATLAS at the LHC are presented on the total cross section at $\sqrt{s}=8$ TeV from elastic scattering using the ALFA sub-detector and on the inelastic cross section at $\sqrt{s}=13$ TeV using the MBTS sub-detector.
We report a measurement of the ratio of the top-antitop to Z/gamma* production cross sections in sqrt(s) = 1.96 TeV proton-antiproton collisions using data corresponding to an integrated luminosity of up to 4.6 fb-1, collected by the CDF II detector. The top-antitop cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/gamma*->ll cross section, the extracted top-antitop cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased es…
We present a calculation of the cross section for the process p pbar -> Zt' -> t tbar, the production of a Topcolor Z' with subsequent decay to top quark pairs in proton anti-proton collisions at 1.8 TeV. Variations of the cross section with varying assumptions about the model, the resonance width, the parton distributions and the renormalization scale are presented.
We measure the top quark mass in dilepton final states of top-antitop events in proton-antiproton collisions at sqrt(s) = 1.96 TeV, using data corresponding to an integrated luminosity of 9.7 fb^-1 at the Fermilab Tevatron Collider. The analysis features a comprehensive optimization of the neutrino weighting method to minimize the statistical uncertainties. We also improve the calibration of jet energies using the calibration determined in top-antitop to lepton+jets events, which reduces the otherwise limiting systematic uncertainty from the jet energy scale. The measured top quark mass is mt …
At the Tevatron, the collider experiments CDF and DO have data sets at their disposal that compromise several hundreds of reconstructed top-antitop-quark pairs and allow for precision measurements of the cross section and production and decay properties. Besides comparing the measurements to standard model predictions, these data sets open a window to physics beyond the standard model. Dedicated analyses look for new heavy gauge bosons, fourth generation quarks, and flavor-changing neutral currents.
A measurement of the top--antitop ($t\bar{t}$) charge asymmetry is presented using 2011 LHC data collected by the ATLAS detector corresponding to an integrated luminosity of 4.6 fb$^{-1}$ at a centre-of-mass energy of 7 TeV. The analysis is performed in the dilepton channel, and two different observables are studied: $A^{\ell\ell}_{\mathrm{C}}$, based on the identified charged leptons, and $A^{t\bar{t}}_{\mathrm{C}}$, based on the reconstructed $t\bar{t}$ final state. The asymmetries, measured to be $A^{\ell\ell}_{\mathrm{C}} = 0.024 \pm 0.015 \mathrm{(stat.)} \pm 0.009 \mathrm{(syst.)}$ and $…
A measurement of spin correlation in ttbar production is reported using data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 2.1 fb^-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 0.40 +0.09 -0.08, in agreement with the next-to-leading-order Standa…
We report on the observation of the charm mesons D^\ast \pm, D^\pm and D_s ^\pm with 1.4 nb^-1 of data, and of the J/psi-->mu+mu- resonance with 78 nb-1 of data from the ATLAS detector in 7 TeV proton-proton collisions at the LHC. The resultant signals support the high performance of the ATLAS detector as predicted from simulation and prospects for future measurements in the charm and charmonium sector.
This document presents a measurement of WZ production in 1.02 fb-1 of pp collision data at CME of 7 TeV collected by the ATLAS experiment at LHC in 2011. The production cross-section is measured to be consistent with the Standard Model (SM) prediction. Limits on anomalous triple gauge boson couplings have been derived.
A summary of the most up-to-date top quark mass measurements at CDF is presented. These analyses use top-antitop candidate events detected in the CDF experiment at the Tevatron collider with an integrated luminosity of up to ~3/fb. The combination of all those measurements together with the corresponding top mass measurements from the concurrently running D0 experiment at the Tevatron yields a world average of M_t=[173.1+/-0.6(stat.)+/-1.1(syst.)] GeV/c^2.
Since the discovery of the top quark in 1995 by the CDF and D0 collaborations at the Fermilab Tevatron proton antiproton collider, precise measurements of its mass are ongoing. Using data recorded by the D0 and CDF experiment, corresponding to up to the full Tevatron data sample, top quark mass measurements performed in different final states using various extraction techniques are presented in this article. The recent Tevatron top quark mass combination yields m_t=173.20 +-0.87 GeV. Furthermore, measurements of the top antitop quark mass difference from the Tevatron are discussed.
