Measurement of the Forward-backward Asymmetry in Top Quark-antiquark Production in Ppbar Collisions Using the Lepton+jets Channel
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Published: 2014
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Spin Correlations in tt Events from pp Collisions
Author: Boris Lemmer
Publisher: Springer
Published: 2015-06-24
Total Pages: 246
ISBN-13: 3319189328
DOWNLOAD EBOOKThis thesis introduces readers to the Standard Model, the top quark and its properties, before explaining the concept of spin correlation measurement. The first measurement of top quark spin correlations at the LHC in the lepton+jets decay channel is presented. As the heaviest elementary particle, the top quark plays an essential role in the Standard Model of elementary particle physics. In the case of top quarks being produced in pairs at hadron colliders, the Standard Model predicts their spins to be correlated. The degree of correlation depends on both the production mechanism and properties of the top quark. Any deviation from the Standard Model prediction can be an indicator for new physics phenomena. The thesis employs an advanced top quark reconstruction algorithm including dedicated identification of the up- and down-type quarks from the W boson decay.
Measurement of the Forward-backward Asymmetry in Top-antitop Quark Events in the Lepton+jets Channel at DØ
Author: Douglas A. Orbaker
Publisher:
Published: 2012
Total Pages: 298
ISBN-13:
DOWNLOAD EBOOK"We present a measurement of forward-backward asymmetries in top-antitop quark pairs produced in proton-antiproton collisions decaying via the lepton+jets channel. Using data recorded by the DØ experiment at the Fermilab Tevatron collider and corresponding to an integrated luminosity of 5.4 fb -1, we measure the forward-backward asymmetry in top-antitop quark events to be (9.2 ± 3.7)%, after background processes have been subtracted. After correcting for the effects of acceptance and detector reconstruction, we measure an asymmetry of (19.6 ± 6.5)%. In addition, we measure an acceptance-corrected asymmetry based on the lepton from top-antitop quark decay of (15.2 ± 4.0)%. We compare these results to predictions from the mc@nlo next-to-leading-order QCD simulation"--Leaf v.
The Black Book of Quantum Chromodynamics — A Primer for the LHC Era
Author: John Campbell
Publisher: Oxford University Press
Published: 2018-01-19
Total Pages: 761
ISBN-13: 0191014990
DOWNLOAD EBOOKThe Black Book of Quantum Chromodynamics is an in-depth introduction to the particle physics of current and future experiments at particle accelerators. The book offers the reader an overview of practically all aspects of the strong interaction necessary to understand and appreciate modern particle phenomenology at the energy frontier. It assumes a working knowledge of quantum field theory at the level of introductory textbooks used for advanced undergraduate or in standard postgraduate lectures. The book expands this knowledge with an intuitive understanding of relevant physical concepts, an introduction to modern techniques, and their application to the phenomenology of the strong interaction at the highest energies. Aimed at graduate students and researchers, it also serves as a comprehensive reference for LHC experimenters and theorists. This book offers an exhaustive presentation of the technologies developed and used by practitioners in the field of fixed-order perturbation theory and an overview of results relevant for the ongoing research programme at the LHC. It includes an in-depth description of various analytic resummation techniques, which form the basis for our understanding of the QCD radiation pattern and how strong production processes manifest themselves in data, and a concise discussion of numerical resummation through parton showers, which form the basis of event generators for the simulation of LHC physics, and their matching and merging with fixed-order matrix elements. It also gives a detailed presentation of the physics behind the parton distribution functions, which are a necessary ingredient for every calculation relevant for physics at hadron colliders such as the LHC, and an introduction to non-perturbative aspects of the strong interaction, including inclusive observables such as total and elastic cross sections, and non-trivial effects such as multiple parton interactions and hadronization. The book concludes with a useful overview contextualising data from previous experiments such as the Tevatron and the Run I of the LHC which have shaped our understanding of QCD at hadron colliders.
Measurement of the Forward-Backward Asymmetry in Top-Antitop Quark Events in the Lepton+Jets Channel at
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Publisher:
Published: 2012
Total Pages: 168
ISBN-13:
DOWNLOAD EBOOKWe present a measurement of forward-backward asymmetries in top-antitop quark pairs produced in proton-antiproton collisions decaying via the lepton+jets channel. Using data recorded by the D0 experiment at the Fermilab Tevatron collider and corresponding to an integrated luminosity of 5.4 fb-1, we measure the forward-backward asymmetry in top-antitop quark events to be $\left(9.2 \pm 3.7\right)\%$, after background processes have been subtracted. After correcting for the effects of acceptance and detector reconstruction, we measure an asymmetry of $\left(19.6 \pm 6.5\right)\%$. In addition, we measure an acceptance-corrected asymmetry based on the lepton from top-antitop quark decay of $\left(15.2 \pm 4.0\right)\%$. We compare these results to predictions from the MC@NLO next-to-leading-order QCD simulation.
Forward-backward Asymmetry in Top Quark-antiquark Production
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Publisher:
Published: 2011
Total Pages:
ISBN-13:
DOWNLOAD EBOOKWe present a measurement of forward-backward asymmetry in top quark-antiquark production in proton-antiproton collisions in the final state containing a lepton and at least four jets. Using a dataset corresponding to an integrated luminosity of 5.4 fb−1, collected by the D0 experiment at the Fermilab Tevatron Collider, we measure the t{bar t} forward-backward asymmetry to be (9.2 ± 3.7)% at the reconstruction level. When corrected for detector acceptance and resolution, the asymmetry is found to be (19.6 ± 6.5)%. We also measure a corrected asymmetry based on the lepton from a top quark decay, found to be (15.2 ± 4.0)%. The results are compared to predictions based on the next-to-leading-order QCD generator mc@nlo. The sensitivity of the measured and predicted asymmetries to the modeling of gluon radiation is discussed.
Forward-Backward Asymmetry in Top Quark Production in Ppbar Collisions at Sqrt{s}
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Publisher:
Published: 2008
Total Pages: 8
ISBN-13:
DOWNLOAD EBOOKReconstructable final state kinematics and charge assignment in the reaction p{bar p} --> t{bar t} allows tests of discrete strong interaction symmetries at high energy. We define frame dependent forward-backward asymmetries for the outgoing top quark in both the p{bar p} and t{bar t} rest frames, correct for experimental distortions, and derive values at the parton-level. Using 1.9 fb−1 of p{bar p} collisions at (square root)s = 1.96 TeV recorded with the CDF II detector at the Fermilab Tevatron, we measure forward-backward top quark production asymmetries in the p{bar p} and t{bar t} rest frames of A{sub FB}{sup p{bar p}} = 0.17 ± 0.08 and A{sub FB}{sup t{bar t}} = 0.24 ± 0.14.
Forward-Backward Asymmetry of Top Quark Pair Productionn at the Fermilab Tevatron
Author:
Publisher:
Published: 2015
Total Pages: 297
ISBN-13:
DOWNLOAD EBOOKThis dissertation presents the final measurements of the forward-backward asymmetry (AFB) of top quark-antiquark pair events (t t- ) at the Collider Detector at Fermilab (CDF) experiment. The t t- events are produced in proton{anti-proton collisions with a center of mass energy of 1:96 TeV during the Run II of the Fermilab Tevatron. The measurements are performed with the full CDF Run II data (9.1 fb-1) in the final state that contain two charged leptons (electrons or muons, the dilepton final state), and are designed to con rm or deny the evidence-level excess in the AFB measurements in the final state with a single lepton and hadronic jets (lepton+jets final state) as well as the excess in the preliminary measurements in the dilepton final state with the first half of the CDF Run II data. New measurements include the leptonic AFB (AlFB), the lepton-pair AFB (All FB) and the reconstructed top AFB (At t FB). Each are combined with the previous results from the lepton+jets final state measured at the CDF experiment. The inclusive Al FB, All FB, and At t FB measured in the dilepton final state are 0.072 ± 0.060, 0.076 ± 0.081, and 0.12 ± 0.13, to be compared with the Standard Model (SM) predictions of 0.038 ± 0.003, 0.048 ± 0.004, and 0.010 ± 0.006, respectively. The CDF combination of AlFB and At t FB are 0.090+0:028 -0.026, and 0.160 ± 0.045, respectively. The overall results are consistent with the SM predictions.
Measurement of the Front Back Asymmetry in Top-antitop Quark Pairs Produced in Proton-antiproton Collisions at Center of Mass Energy
Author: Thomas A. Schwarz
Publisher:
Published: 2006
Total Pages: 110
ISBN-13:
DOWNLOAD EBOOKQuarks, along with leptons and force carrying particles, are predicted by the Standard Model to be the fundamental constituents of nature. In distinction from the leptons, the quarks interact strongly through the chromodynamic force and are bound together within the hadrons. The familiar proton and neutron are bound states of the light ''up'' and ''down'' quarks. The most massive quark by far, the ''top'' quark, was discovered by the CDF and D0 experiments in March, 1995. The new quark was observed in p{bar p} collisions at 1.8 TeV at the Fermilab Tevatron. The mass of the top quark was measured to be 176 {+-} 13 GeV/c{sup 2} and the cross section 6.8{sub -2.4}{sup +3.6} pb. It is the Q = 2/3, T{sub 3} = +1/2 member of the third generation weak-isospin doublet along with the bottom quark. The top quark is the final Standard Model quark to be discovered. Along with whatever is responsible for electroweak symmetry breaking, top quark physics is considered one of the least understood sectors of the Standard Model and represents a front line of our understanding of particle physics. Currently, the only direct measurements of top quark properties come from the CDF and D0 experiments observing p{bar p} collisions at the Tevatron. Top quark production at the Tevatron is almost exclusively by quark-antiquark annihilation, q{bar q} {yields} t{bar t} (85%), and gluon fusion, gg {yields} t{bar t} (15%), mediated by the strong force. The theoretical cross-section for this process is {sigma}{sub t{bar t}} = 6.7 {+-} 0.8 pb for m{sub t} = 175 GeV/c{sup 2}. Top quarks can also be produced at the Tevatron via q{bar b}{prime} {yields} tb and qg {yields} q{prime}tb through the weak interaction. The cross section for these processes is lower (3pb) and the signal is much more difficult to isolate as backgrounds are much higher. The top quark is predicted to decay almost exclusively into a W-boson and a bottom quark (t {yields} Wb). The total decay width t {yields} Wb is {Lambda} = 1.50 GeV. This corresponds to an incredibly short lifetime of 0.5 x 10{sup -24} seconds. This happens so quickly that hadronization and bound states do not take place, which leads to the interesting consequence that the top quark spin information is passed to the decay products.
Measurements of the Top Quark Pair Production Cross Section in Lepton + Jets Final States Using a Topological Multivariate Technique as Well as Lifetime B-Tagging InProton - Anti-proton Collisions at S**(1/2)
Author: Tobias F. Golling
Publisher:
Published: 2005
Total Pages: 299
ISBN-13:
DOWNLOAD EBOOKTwo alternative measurements of the t{bar t} production cross section at {radical}s = 1.96 TeV in proton-antiproton collisions in the lepton+jets channel are presented. The t{bar t} production cross section is extracted by combining the kinematic event information in a multivariate discriminant. The measurement yields {sigma}{sub p{bar p} {yields} t{bar t} + x} = 5.13{sub -1.57}{sup +1.76}(stat){sub -1.10}{sup +0.96}(syst) {+-} 0.33 (lumi) pb in the muon+jets channel, using 229.1 pb{sup -1}, and in the combination with the electron+jets channel 226.3 pb{sup -1} {sigma}{sub p{bar p} {yields} t{bar t} + x} = 6.60{sub -1.28}{sup +1.37}(stat){sub -1.11}{sup +1.25}(syst) {+-} 0.43 (lumi) pb. The second measurement presented reconstructs explicitly secondary vertices to d lifetime b-tagging. The measurement combines the muon+jets and the electron+jets channel, using 158.4 pb{sup -1} and 168.8 pb{sup -1}, respectively: {sigma}{sub p{bar p} {yields} t{bar t} + x} = 8.24{sub -1.25}{sup +1.34}(stat){sub -1.63}{sup +1.89}(syst) {+-} 0.54 (lumi) pb.
