Measurement Of Spin Correlation Between Top And Antitop Quarks Produced In P Bar P Collisions At Sqrt S
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Measurement Of Spin Correlation Between Top And Antitop Quarks Produced In P Bar P Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2015
Measurement Of Spin Correlation Between Top And Antitop Quarks Produced In P Bar P 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.
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 correlation difference from zero at a level of 4.2 standard deviations.
Measurement Of Spin Correlations In Top Anti Top Events From Pp Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2014
Measurement Of Spin Correlations In Top Anti Top Events From 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.
The top quark decays before it hadronises. Before its spin state can be changed in a process of strong interaction, it is directly transferred to the top quark decay products. The top quark spin can be deduced by studying angular distributions of the decay products. The Standard Model predicts the top/anti-top quark (tt) pairs to have correlated spins. The degree is sensitive to the spin and the production mechanisms of the top quark. Measuring the spin correlation allows to test the predictions. New physics e ects can be reflected in deviations from the prediction. In this thesis the spin ...
Spin Correlations In Tt Events From Pp Collisions
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Author : Boris Lemmer
language : en
Publisher:
Release Date : 2015
Spin Correlations In Tt Events From Pp Collisions written by Boris Lemmer 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.
This 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 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 Front Back Asymmetry In Top Antitop Quark Pairs Produced In Proton Antiproton Collisions At Center Of Mass Energy
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Author : Thomas A. Schwarz
language : en
Publisher:
Release Date : 2006
Measurement Of The Front Back Asymmetry In Top Antitop Quark Pairs Produced In Proton Antiproton Collisions At Center Of Mass Energy written by Thomas A. Schwarz 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.
Quarks, 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.
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 Inclusive T Bar T Production Cross Section In P Bar P Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2016
Measurement Of The Inclusive T Bar T Production Cross Section In P Bar P 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 inclusive cross section of top quark-antiquark pairs produced in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV is measured in the lepton+jets and dilepton decay channels. The data sample corresponds to 9.7 fb-1 of integrated luminosity recorded with the D0 detector during Run II of the Fermilab Tevatron Collider. Employing multivariate analysis techniques we measure the cross section in the two decay channels and we perform a combined cross section measurement. For a top quark mass of 172.5 GeV, we measure a combined inclusive top quark-antiquark pair production cross section of [sigma]$t\bar{t}$=7.26±0.13(stat)$+0.57\atop{-0.50}$(syst) pb which is consistent with standard model predictions. We also perform a likelihood fit to the measured and predicted top quark mass dependence of the inclusive cross section, which yields a measurement of the pole mass of the top quark. The extracted value is mt=172.8±1.1(theo)$+3.3\atop{-3.1}$(exp) GeV.
Measurement Of The Mass Difference Between Top And Anti Top Quarksin Top Pair Events From Pp Collisions At S
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Author : Vikash Chavda
language : en
Publisher:
Release Date : 2013
Measurement Of The Mass Difference Between Top And Anti Top Quarksin Top Pair Events From Pp Collisions At S written by Vikash Chavda and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with categories.
A measurement of the mass difference between top and anti-top quarks produced in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector at the LHC is presented. The analysis uses the full 2011 data sample, corresponding to an integrated luminosity of 4.7 fb$ {-1}$. An event-by-event mass difference is calculated for every event consistentwith $\ttbar$ production and decay in the semi-leptonic channel. A likelihood fit to the full double $b$-tagged data set yields a measured valueof $\Delta(m) = m_{t}-m_{\bar{t}} = 0.67 \pm{0.61}~(\mathrm{stat.}) \pm{0.19}~(\mathrm{syst.})~\mathrm{GeV}$, consistent with the Standard Model, and more generally, the CPT Theorem, prediction of no mass difference.
Search For Scalar Top Quark Production In P Bar P Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2012
Search For Scalar Top Quark Production In P Bar P 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 2012 with categories.
We report on a search for the supersymmetric partner of the top quark (scalar top) decaying into a charm quark and a neutralino in p{bar p} collisions at √s = 1.96 TeV. The data sample, collected by the CDF II detector at the Fermilab Tevatron, corresponds to an integrated luminosity of 2.6 fb−1. Candidate events are selected by requiring two or more jets and a large imbalance in the transverse momentum. To enhance the analysis sensitivity, at least one of the jets is required to be identified as originating from a charm quark using an algorithm specifically designed for this analysis. The selected events are in good agreement with standard model predictions. In the case of large mass splitting between the scalar top quark and the neutralino we exclude a scalar top quark mass below 180 GeV/c2 at 95% confidence level.
Measurements Of Spin Correlation In Top Antitop Quark Events From Proton Proton Collisions At S
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Author :
language : en
Publisher:
Release Date : 2014
Measurements Of Spin Correlation In Top Antitop Quark Events From Proton Proton 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 2014 with categories.
We present measurements of spin correlation in top quark pair production 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 these observables are measured for the first time. The measurements are in good agreement with the Standard Model prediction at next-to-leading-order accuracy.