Measurement Of Top Quark Antiquark Pair Production In Association With A Z Boson With A Trilepton Final State In Pp Collisions At 8 Tev Center Of Mass Energy
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Measurement Of Top Quark Antiquark Pair Production In Association With A Z Boson With A Trilepton Final State In Pp Collisions At 8 Tev Center Of Mass Energy
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Author : Ian Christopher MacNeill
language : en
Publisher:
Release Date : 2015
Measurement Of Top Quark Antiquark Pair Production In Association With A Z Boson With A Trilepton Final State In Pp Collisions At 8 Tev Center Of Mass Energy written by Ian Christopher MacNeill and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
A search for Z boson production with associated top-antitop pairs is performed with a final state which contains trileptons and b-tagged jets. The measurement is performed on the complete dataset of pp collisions at a center-of-mass energy of 8 TeV collected at the CMS detector, for a total instantaneous luminosity of 19.5 fb−1. A cross section is calculated for this final state and compared to the standard model prediction. The cross section for tt̄Z production is measured to be sigma=194+105/−89 fb. The measured cross section to theoretical cross section ratio is 0.94+0̇̇̇·51/−43. The process is measured with a significance of 2.33. This measurement is then combined with an outside 4 lepton channel measurement for an equivalent cross section measurement of sigma=200+90/−76 fb and a significance of 3.1.
Measurement Of Top Quark Antiquark Pair Production In Association With A W Or Z Boson In Pp Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2014
Measurement Of Top Quark Antiquark Pair Production In Association With A W Or Z Boson In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.
A measurement of the cross section for the production of top quark-antiquark pairs (${\mathrm {t}}\overline{{\mathrm {t}}}$) in association with a vector boson V (W or Z) in proton-proton collisions at $\sqrt{s} = 8$ $\, \text {TeV}$ is presented. The results are based on a dataset corresponding to an integrated luminosity of 19.5 fb$^{-1}$ recorded with the CMS detector at the LHC. The measurement is performed in three leptonic (e and $\mu$) channels: a same-sign dilepton analysis targeting ${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W} $ events, and trilepton and four-lepton analyses designed for ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}} $ events. In the same-sign dilepton channel, the ${\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W} $ cross section is measured as $\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} \mathrm {W}} = 170 ^{+90-80}\, \text {(stat)} \pm 70\, \text {(syst)} \, \text {fb} $, corresponding to a significance of 1.6 standard deviations over the background-only hypothesis. Combining the trilepton and four-lepton channels, a direct measurement of the ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}} $ cross section, $\sigma _{{\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {Z}}} = 200 ^{+80-70}\, \text {(stat)} ^{+40-30}\, \text {(syst)} \mathrm{fb}^{-1} $, is obtained with a significance of 3.1 standard deviations. The measured cross sections are compatible with standard model predictions within their experimental uncertainties. The inclusive ${\mathrm {t}}\overline{{\mathrm {t}}} {\mathrm {V}} $ process is observed with a significance of 3.7 standard deviations from the combination of all three leptonic channels.
Measurement Of The Top Pair Production Cross Section In 8 Tev Proton Proton Collisions Using Kinematic Information In The Lepton Plus Jets Final State With Atlas
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Author :
language : en
Publisher:
Release Date : 2015
Measurement Of The Top Pair Production Cross Section In 8 Tev Proton Proton Collisions Using Kinematic Information In The Lepton Plus Jets Final State With Atlas written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
Measurement Of The Top Pair Production Cross Section In 8 Tev Proton Proton Collisions Using Kinematic Information In The Lepton Jets Final State With Atlas
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Author :
language : en
Publisher:
Release Date : 2015
Measurement Of The Top Pair Production Cross Section In 8 Tev Proton Proton Collisions Using Kinematic Information In The Lepton Jets Final State With Atlas written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
Measurement Of The Charge Asymmetry In Top Quark Pair Production In Pp Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2015
Measurement Of The Charge Asymmetry In Top Quark Pair Production In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
The charge asymmetry in the production of top quark and antiquark pairs is measured in proton-proton collisions at a center-of-mass energy of 8 TeV. The data, corresponding to an integrated luminosity of 19.6 fb -1 were collected by the CMS experiment at the LHC. Events with a single isolated electron or muon, and four or more jets, at least one of which is likely to have originated from hadronization of a bottom quark, are selected. A template technique is used to measure the asymmetry in the distribution of differences in the top quark and antiquark absolute rapidities. The measured asymmetry is Ayc= [0.33_0.26 (stat)_0.33 (syst)]%, which is the most precise result to date. The results are compared to calculations based on the standard model and on several beyond-the-standard-model scenarios.
Measurement Of Spin Correlation In Top Antitop Quark Events And Search For Top Squark Pair Production In Pp Collisions At S
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Author :
language : en
Publisher:
Release Date : 2015
Measurement Of Spin Correlation In Top Antitop Quark Events And Search For Top Squark Pair Production In Pp Collisions At S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
We present a measurement of spin correlation in t¯t production 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¯t 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 Ahelicity = 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. Lastly, top squarks with masses between the top quark mass and 191 GeV are excluded at the 95% confidence level.
Measurement Of The Mass Difference Between Top Quark And Antiquark In Pp Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2016
Measurement Of The Mass Difference Between Top Quark And Antiquark In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
The invariance of the standard model (SM) under the CPT transformation predicts equality of particle and antiparticle masses. This prediction is tested by measuring the mass difference between the top quark and antiquark (Delta m[t] = m[t] - m[t-bar]) that are produced in pp collisions at a center-of-mass energy of 8 TeV, using events with a muon or an electron and at least four jets in the final state. The analysis is based on data corresponding to an integrated luminosity of 19.6 inverse-femtobarns collected by the CMS experiment at the LHC, and yields a value of Delta m[t] = -0.15 +/- 0.19 (stat) +/- 0.09 (syst) GeV, which is consistent with the SM expectation. This result is significantly more precise than previously reported measurements.
Measurement Of The Top Quark Pair Production Cross Section In P Anti P Collisions At S 1 2
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Author : Gustavo J. Otero y Garzon
language : en
Publisher:
Release Date : 2006
Measurement Of The Top Quark Pair Production Cross Section In P Anti P Collisions At S 1 2 written by Gustavo J. Otero y Garzon and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
The subject of this thesis is the measurement of the rate at which a top-antitop quark pair is produced in pp collisions at a center of mass energy of ps = 1:96 TeV. The data are collected with the D detector, a multi-purpose detector operating at the Fermilab Tevatron collider during Run II. A measurement of the top quark pair (t$\bar{t}$) production cross section ( [sigma]t$\bar{t}$) in p$\bar{p}$ collisions at a center of mass energy of 1.96 TeV is presented. The measurement is based on data recorded by the D0 Detector at the Fermilab Tevatron Collider, and preselected in the e+jets (366 pb-1) and [mu]+jets (363 pb-1) channels. The cross section is extracted by applying a lifetime-tagging technique to the data, and yields [sigma]t$\bar{t}$ = 6.96$+1.07\atop{-0.98}$(stat + syst) ± 0.45(lumi) pb; for a top quark mass mt =175 GeV, in good agreement with the Standard Model prediction.
Measurement Of The Top Quark Pair Production Cross Section In Proton Antiproton Collisions At A Center Of Mass Energy Of 1 96 Tev Hadronic Top Decays With The D0 Detector
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Author :
language : en
Publisher:
Release Date : 2009
Measurement Of The Top Quark Pair Production Cross Section In Proton Antiproton Collisions At A Center Of Mass Energy Of 1 96 Tev Hadronic Top Decays With The D0 Detector written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
Of the six quarks in the standard model the top quark is by far the heaviest: 35 times more massive than its partner the bottom quark and more than 130 times heavier than the average of the other five quarks. Its correspondingly small decay width means it tends to decay before forming a bound state. Of all quarks, therefore, the top is the least affected by quark confinement, behaving almost as a free quark. Its large mass also makes the top quark a key player in the realm of the postulated Higgs boson, whose coupling strengths to particles are proportional to their masses. Precision measurements of particle masses for e.g. the top quark and the W boson can hereby provide indirect constraints on the Higgs boson mass. Since in the standard model top quarks couple almost exclusively to bottom quarks (t 2!Wb), top quark decays provide a window on the standard model through the direct measurement of the Cabibbo-Kobayashi-Maskawa quark mixing matrix element V{sub tb}. In the same way any lack of top quark decays into W bosons could imply the existence of decay channels beyond the standard model, for example charged Higgs bosons as expected in two-doublet Higgs models: t 2!Hb. Within the standard model top quark decays can be classified by the (lepton or quark) W boson decay products. Depending on the decay of each of the W bosons, t{bar t} pair decays can involve either no leptons at all, or one or two isolated leptons from direct W 2!e{bar {nu}}{sub e} and W 2![mu]{bar {nu}}{sub {mu}} decays. Cascade decays like b 2!Wc 2!e{bar {nu}}{sub e}c can lead to additional non-isolated leptons. The fully hadronic decay channel, in which both Ws decay into a quark-antiquark pair, has the largest branching fraction of all t{bar t} decay channels and is the only kinematically complete (i.e. neutrino-less) channel. It lacks, however, the clear isolated lepton signature and is therefore hard to distinguish from the multi-jet QCD background. It is important to measure the cross section (or branching fraction) in each channel independently to fully verify the standard model. Top quark pair production proceeds through the strong interaction, placing the scene for top quark physics at hadron colliders. This adds an additional challenge: the huge background from multi-jet QCD processes. At the Tevatron, for example, t{bar t} production is completely hidden in light q{bar q} pair production. The light (i.e. not bottom or top) quark pair production cross section is six orders of magnitude larger than that for t{bar t} production. Even including the full signature of hadronic t{bar t} decays, two b-jets and four additional jets, the QCD cross section for processes with similar signature is more than five times larger than for t{bar t} production. The presence of isolated leptons in the (semi)leptonic t{bar t} decay channels provides a clear characteristic to distinguish the t{bar t} signal from QCD background but introduces a multitude of W- and Z-related backgrounds.
First Measurement Of The Top Quark Pair Production Cross Section In Proton Proton Collisions At The Center Of Mass Energy Of 7 Tev
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Author : Puneeth D. Kalavase
language : en
Publisher:
Release Date : 2011
First Measurement Of The Top Quark Pair Production Cross Section In Proton Proton Collisions At The Center Of Mass Energy Of 7 Tev written by Puneeth D. Kalavase and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
The first measurement of the cross section for top-quark pair production in proton-proton collisions at the Large Hadron Collider at center-of-mass energy of 7 TeV has been performed using a data sample corresponding to an integrated luminosity of 3 pb-1 recorded by the CMS detector. This result utilizes the final state with two isolated, highly energetic charged leptons, large missing transverse energy, and two or more jets. Backgrounds from Drell-Yan and non-W/Z boson production are estimated from data. Eleven events are observed in the data with 2.1+/-1.0 events expected from background. The measured cross section is 194+/-72 (statistical) +/-24 (systematic) +/-21 (luminosity) pb. The result is consistent with next-to-leading order theoretical predictions.