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Book A Study of Weak Corrections to Drell Yan Top quark Pair and Di jet Production at High Energies with MCFM

Download or read book A Study of Weak Corrections to Drell Yan Top quark Pair and Di jet Production at High Energies with MCFM written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Electroweak (EW) corrections can be enhanced at high energies due to the soft or collinear radiation of virtual and real $W$ and $Z$ bosons that result in Sudakov-like corrections of the form $\alpha_W^l\log^n(Q^2/M_{W, Z}^2)$, where $\alpha_W =\alpha/(4\pi\sin^2\theta_W)$ and $n\le 2l-1$. The inclusion of EW corrections in predictions for hadron colliders is therefore especially important when searching for signals of possible new physics in distributions probing the kinematic regime $Q^2 \gg M_V^2$. Next-to-leading order (NLO) EW corrections should also be taken into account when their size ($\mathcal{O}(\alpha)$) is comparable to that of QCD corrections at next-to-next-to-leading order (NNLO) ($\mathcal{O}(\alpha_s^2)$). To this end we have implemented the NLO weak corrections to the Neutral-Current Drell-Yan process, top-quark pair production and di-jet production in the parton-level Monte-Carlo program MCFM. This enables a combined study with the corresponding QCD corrections at NLO and NNLO. We provide both the full NLO weak corrections and their Sudakov approximation since the latter is often used for a fast evaluation of weak effects at high energies and can be extended to higher orders. With both the exact and approximate results at hand, the validity of the Sudakov approximation can be readily quantified.

Book Electroweak Corrections at the LHC with MCFM

Download or read book Electroweak Corrections at the LHC with MCFM written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Electroweak (EW) corrections at the LHC can be enhanced at high energies due to soft/collinear radiation of W and Z bosons, being dominated by Sudakov-like corrections in the form of $\alpha_W^l\log^n(Q^2/M_W^2)$ $(n \le 2l, \alpha_W = \alpha/(4\pi\sin\theta_W^2))$ when the energy scale $Q$ enters the TeV regime. Thus, the inclusion of EW corrections in LHC predictions is important for the search of possible signals of new physics in tails of kinematic distributions. EW corrections should also be taken into account in virtue of their comparable size ($\mathcal{O}(\alpha)$) to that of higher order QCD corrections ($\mathcal{O}(\alpha_s^2)$). We calculated the next-to-leading-order (NLO) weak corrections to the neutral-current (NC) Drell-Yan process, top-quark pair production and di-jet producion, and implemented them in the Monte-Carlo program MCFM. This enables a combined study with the corresponding NLO QCD corrections. We provide both the full NLO weak corrections and their weak Sudakov approximation valid at high energies. The latter is often used for a fast evaluation of weak effects, and having the exact result available as well allows to quantify the validity of the Sudakov approximation.

Book Higher Order QCD Corrections to Single Top Quark Production

Download or read book Higher Order QCD Corrections to Single Top Quark Production written by Mohammad Assadsolimani and published by disserta Verlag. This book was released on 2014-08 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is known that the LHC has a considerable discovery potential because of its large centre-of-mass energy (vs =14 TeV) and the high design luminosity. In addition, the two experiments ATLAS and CMS perform precision measurements for numerous models in physics. The increasing experimental precision demands an even higher level of accuracy on the theoretical side. For a more precise prediction of outcomes, one has to consider the corrections obtained typically from Quantum Chromodynamics (QCD). The calculation of these corrections in the high energy regime is described by perturbation theory. In the present study, multi-loop calculations in QCD, including in particular two-loop corrections for single top quark production, are considered. There are several phenomenological motivations to study single top quark production: Firstly, the process is sensitive to the electroweak Wtb-vertex; moreover, non-standard couplings can hint at physics beyond the Standard Model. Secondly, the t-channel cross section measurement provides information on the b-quark Parton Distribution Functions (PDF). Finally, single top quark production enables us to directly measure the Cabibbo-Kobayashi-Maskawa(CKM) matrix element Vtb. The next-to-next-to-leading-order (NNLO) calculation of the single top quark production has many building blocks. In this study, two blocks will be presented: one-loop corrections squared and two-loop corrections interfered with Born. Initially, the one-loop squared contribution at NNLO for single top quark production will be calculated. Before we begin with the calculation of the two-loop corrections to single top quark production, we calculate the QCD form factors of heavy quarks at NNLO, along with the axial vector coupling as a first independent check. A comparison with the relevant literature suggests that this approach is in line with generally accepted procedure. This consistency check provides a proof of the validity of our setup. In the next step, the two-loop corrections to single top quark production will be calculated. After reducing all occurring tensor integrals to scalar integrals, we apply the integration by parts method (IBP) to find the master integrals. This step is a major challenge compared to all similar calculations because of the number of variables in the problem (two Mandelstam variables s and t, the dimension d and the mass of the top quark mt as well as the mass of the W boson mw). Finally, the calculation of the three kinds of topologies – vertex corrections, double boxes and non-planar double boxes – in the two-loop contribution at NNLO calculation will be presented.

Book One Loop QCD Correction for Inclusive Jet Production and Drell Yan Process in Composite Models

Download or read book One Loop QCD Correction for Inclusive Jet Production and Drell Yan Process in Composite Models written by and published by . This book was released on 1996 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: We calculate the one-loop QCD correction for inclusive jet cross section and Drell-Yan process in a general low-energy effective Lagrangian for composite quarks and leptons.

Book Next to Leading Order Corrections to Weak Boson Production with a Massive Quark Jet Pair at Hadron Colliders

Download or read book Next to Leading Order Corrections to Weak Boson Production with a Massive Quark Jet Pair at Hadron Colliders written by Fernando Febres Cordero and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: We present the calculation of Next-to-Leading-Order Quantum Chromo Dynamics corrections for the production of W or Z weak bosons associated with a bottom anti-bottom quark pair at hadron colliders (ppbar, pp to W/Z bbbar), including the effects of a non-zero bottom-quark mass. We find a considerable reduction of the renormalization and factorization scale dependence of our results with respect to Leading-Order calculations. In particular, we study the impact of the corrections on the total cross section and invariant mass distributions of the bottom anti-bottom quark pair at the Fermilab Tevatron ppbar collider. We perform a detailed comparison with a calculation that considers massless bottom quarks and find significant deviations in regions of phase space with small invariant mass of the bottom anti-bottom quark pair. Our results will be relevant to ongoing and future searches at hadron colliders, as the W/Z bbbar production mode is the main background to important signals, such as light Standard Model Higgs boson production or single top-quark production.

Book Top quark Loop Corrections in Z jet and Z 2 Jet Production

Download or read book Top quark Loop Corrections in Z jet and Z 2 Jet Production written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The sophistication of current predictions for $Z+$jet production at hadron colliders necessitates a re-evaluation of any approximations inherent in the theoretical calculations. In this paper we address one such issue, the inclusion of mass effects in top-quark loops. We ameliorate an existing calculation of $Z+1$~jet and $Z+2$~jet production by presenting exact analytic formulae for amplitudes containing top-quark loops that enter at next-to-leading order in QCD. Although approximations based on an expansion in powers of $1/m_t^2$ can lead to poor high-energy behavior, an exact treatment of top-quark loops demonstrates that their effect is small and has limited phenomenological interest.

Book Mixed QCD and Weak Corrections to Top Quark Pair Production at Hadron Colliders

Download or read book Mixed QCD and Weak Corrections to Top Quark Pair Production at Hadron Colliders written by Werner Bernreuther and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Fully Differential QCD Corrections to Single Top Quark Final States

Download or read book Fully Differential QCD Corrections to Single Top Quark Final States written by and published by . This book was released on 2000 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors have performed a fully differential calculation of QCD corrections to electroweak production of single top quarks. The method used allows for jet definitions and experimental cuts. The corresponding computer code passes the necessary check of reproducing the previously known total rate. First examination of the rapidity and transverse momentum of the top quark shows the corrections to be flat relative to leading order. Additional phenomenological studies are in order. Further work is in progress on the corrections to t-b-jet final states which will give a comprehensive set of tools for studying single-top-quark production at future hadron-hadron colliders.

Book Resummation of Threshold Corrections in QCD to Power Accuracy

Download or read book Resummation of Threshold Corrections in QCD to Power Accuracy written by and published by . This book was released on 1996 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resummation of large infrared logarithms in perturbation theory can, in certain circumstances, enhance the sensitivity to small gluon momenta and introduce spurious nonperturbative contributions. In particular, different procedures--equivalent in perturbation theory--to organize this resummation can differ by 1/Q power corrections. The question arises whether one can formulate resummation procedures that are explicitly consistent with the infrared behavior of finite-order Feynman diagrams. They explain how this problem can be treated and resolved in Drell-Yan (lepton pair) production and briefly discuss more complicated cases, such as top quark production and event shape variables in the ee− annihilation.

Book Electroweak Production of the Top Quark in the Run II of the D0 Experiment

Download or read book Electroweak Production of the Top Quark in the Run II of the D0 Experiment written by Benoit Clement and published by . This book was released on 2006 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work exposed in this thesis deals with the search for electroweak production of top quark (single top) in proton-antiproton collisions at {radical}s = 1.96 TeV. This production mode has not been observed yet. Analyzed data have been collected during the Run II of the D0 experiment at the Fermilab Tevatron collider. These data correspond to an integrated luminosity of 370 pb{sup -1}. In the Standard Model, the decay of a top quark always produce a high momentum bottom quark. Therefore bottom quark jets identification plays a major role in this analysis. The large lifetime of b hadrons and the subsequent large impact parameters relative to the interaction vertex of charged particle tracks are used to tag bottom quark jets. Impact parameters of tracks attached to a jet are converted into the probability for the jet to originate from the primary vertex. This algorithm has a 45% tagging efficiency for a 0.5% mistag rate. Two processes (s and t channels) dominate single top production with slightly different final states. The searched signature consists in 2 to 4 jets with at least one bottom quark jet, one charged lepton (electron or muon) and missing energy accounting for a neutrino. This final state is background dominated and multivariate techniques are needed to separate the signal from the two main backgrounds: associated production of a W boson and jets and top quarks pair production. The achieved sensitivity is not enough to reach observation and we computed upper limits at the 95% confidence level at 5 pb (s-channel) and 4.3 pb (t-channel) on single top production cross-sections.

Book Quark Model and High Energy Collisions

Download or read book Quark Model and High Energy Collisions written by Vladimir Vladislavovich Anisovich and published by World Scientific. This book was released on 2004 with total page 547 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is an updated version of the book published in 1985. QCD-motivated, it gives a detailed description of hadron structure and soft interactions in the additive quark model, where hadrons are regarded as composite systems of dressed quarks. In the past decade it has become clear that nonperturbative QCD, responsible for soft hadronic processes, may differ rather drastically from perturbative QCD. The understanding of nonperturbative QCD requires a detailed investigation of the experiments and the theoretical approaches. Bearing this in mind, the book has been rewritten paying special attention to the interplay of soft hadronic collisions and the quark model. It is at the crossroads of these domains that peculiar features of strong QCD reveal themselves. The book discusses constituent quarks, diquarks, the massive effective gluons and the problem of scalar isoscalar mesons. The quark-gluonium classification of meson states is also given. Experimentally observed properties of hadrons are presented together with the corresponding theoretical interpretation in the framework of the composite hadron structure. The text includes a large theoretical part, which shows how to treat composite systems (including relativistic ones) with a technique based on spectral integration. This technique provides the possibility of handling hadrons as weakly bound systems of quarks and, at the same time, takes into account confinement. Attention is focused on the composite structure revealing itself in high energy hadron collisions. Fields of applicability of the additive quark model are discussed, as is colour screening in hadronic collisions at high and superhigh energies. Along with a detailed presentation of hadronOCohadron collisions, a description of hadronOConucleus collisions is given. Sample Chapter(s). Chapter 1: Introduction (1,047 KB). Contents: High Energy Hadron Interactions; Composite Systems; High Energy Interactions of Composite Systems; Hadron Zoology and Static Features of Hadrons; Binary Processes in the Quark Model; Multiparticle Production in the Quark Model: Hadron Collisions at Moderately High Energies; HadronOCoNucleus Collisions. Readership: Graduate students and researchers in particle and nuclear physics."

Book Observation of Electroweak Single Top Quark Production with the CDF II Experiment

Download or read book Observation of Electroweak Single Top Quark Production with the CDF II Experiment written by and published by . This book was released on 2009 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: The standard model of elementary particle physics (SM) predicts, besides the top-quark pair production via the strong interaction, also the electroweak production of single top-quarks [19]. Up to now, the Fermilab Tevatron proton-antiproton-collider is the only place to produce and study top quarks emerging from hadron-hadron-collisions. Top quarks were directly observed in 1995 during the Tevatron Run I at a center-of-mass energy of √s = 1.8 TeV simultaneously by the CDF and D0 Collaborations via the strong production of top-quark pairs. Run II of the Tevatron data taking period started 2001 at √s = 1.96 TeV after a five year upgrade of the Tevatron accelerator complex and of both experiments. One main component of its physics program is the determination of the properties of the top quark including its electroweak production. Even though Run II is still ongoing, the study of the top quark is already a successful endeavor, confirmed by dozens of publications from both Tevatron experiments. A comprehensive review of top-quark physics can be found in reference. The reasons for searching for single top-quark production are compelling. As the electroweak top-quark production proceeds via a Wtb vertex, it provides the unique opportunity of the direct measurement of the CKM matrix element.

Book Studies of Top Quark Production at

Download or read book Studies of Top Quark Production at written by and published by . This book was released on 2011 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: I present recent results on top quark production in pp collisions at a center of mass energy of 1.96 TeV. The studies were performed by the D0 collaboration using approximately 5 fb−1 of data taken during Run II at the Fermilab Tevatron accelerator. The top quark is the heaviest known elementary particle and completes the quark sector of the three-generation structure of the standard model (SM). It differs from the other quarks not only by its much larger mass, but also by its lifetime which is too short to build hadronic bound states. The SM predicts that top quarks are created via two independent production mechanisms at hadron colliders. The primary mode, in which a t{bar t} pair is produced from a gtt vertex via the strong interaction, was used by the D0 and CDF collaborations to establish the existence of the top quark in 1995. The second production mode of top quarks at hadron colliders is the electroweak production of a single top quark from a Wtb vertex. The predicted cross section for single top quark production is about half that of t{bar t} pairs but the signal-to-background ratio is much worse; observation of single top quark production has therefore until recently been impeded by its low rate and difficult background environment compared to the top pair production. In the following sections I will present results for the measurement of the t{bar t} pair and the single top quark production cross section using respectively 5.3 fb−1 and 5.4 fb−1 of data taken by the D0 experiment.