Electroweak Corrections at the LHC with MCFM.
Electroweak Corrections at the LHC with MCFM.

Author:

Publisher:

Published: 2015

Total Pages:

ISBN-13:

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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.

Electroweak Corrections Using Effective Theory
Electroweak Corrections Using Effective Theory

Author: Jui-Yu Chiu

Publisher:

Published: 2009

Total Pages: 104

ISBN-13:

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We study the infrared structure of perturbative amplitudes using the effective field theory (EFT) formalism and develop a general factorization scheme, frst for electroweak dynamics and then general gauge theories. We begin by discussing the factorization structure within the framework of the Soft-Collinear-Effective Theory. For the theories with a massive gauge boson, we introduce a (new) [Delta]-regulator to regulate the collinear singularities. In this way, we avoid the confusions in distinguishing different kinds of singularities which arise when considering unbroken theories. Consequently, we propose a factorization scheme to define a soft function free of collinear singularities and a jet function free of the soft singularities. We also clarify that heavy-quark effects change only the structure of collinear singularities and not the soft ones. With our definition of the soft function, we compute the one-loop soft anomalous dimension matrix for any fixed angle, multi-particle process by weighting the soft function with the proper group theory factor without additional calculation. Next, we use EFT methods to sum the Electroweak Sudakov logarithms at high energy, of the form ([alpha]/sin2 [theta]w log^m s/M_{Z, W}^2, are summed using effective theory (EFT) methods. The exponentiation of Sudakov logarithms and factorization is discussed in the EFT formalism. Radiative corrections are computed to scattering processes in the standard model involving an arbitrary number of external particles. The computations include non-zero particle masses such as the t-quark mass, electroweak mixing effects which lead to unequal W and Z masses and a massless photon, and Higgs corrections proportional to the top quark Yukawa coupling. The structure of the radiative corrections, and which terms are summed by the EFT renormalization group is discussed in detail. The omitted terms are smaller than 1%. We give numerical results for the corrections to dijet production, dilepton production, t-bar t production, and squark pair production. The purely electroweak corrections are significant -- about 15% at 1 TeV, increasing to 30% at 5 TeV, and they change both the scattering rate and angular distribution. The QCD corrections (which are well-known) are also computed with the EFT. They are much larger -- about a factor of four at 1 TeV, increasing to a factor of thirty at 5 TeV.

Electroweak Gauginos with Highly Boosted Hadronically Decaying Bosons at the LHC
Electroweak Gauginos with Highly Boosted Hadronically Decaying Bosons at the LHC

Author: Yuta Okazaki

Publisher:

Published: 2023

Total Pages: 0

ISBN-13: 9789811965944

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Supersymmetry (SUSY) introduces superpartners of the Standard Model (SM) particles. If their masses are typically O(100 GeV) ∼ O(TeV), a lightest neutralino can be a candidate for the dark matter, and the problem is solved by canceling the correction of the Higgs boson mass. Further, SUSY can explain the experimental result of the muon magnetic moment (g-2). This book presents a search for electroweakinos-the superpartners of the SM electroweak bosons-such as charginos and neutralinos using data at the LHC collected by the ATLAS detector. Pair-produced electroweakinos decay into the light ones and SM bosons (W/Z/h), and with the large mass difference between the heavy and light electroweakinos, the SM bosons have high momenta. In a fully hadronic final state, quarks decayed from the bosons are collimated, and can consequently be reconstructed as a single large-radius jet. This search has three advantages. The first is a statistical benefit by large branching ratios of the SM bosons. The second is to use characteristic signatures-the mass and substructure-of jets to identify as the SM bosons. The last is a small dependency on the signal model by targeting all the SM bosons. Thanks to them, the sensitivity is significantly improved compared to the previous analyses. Exclusion limits at the 95% confidence level on the heavy electroweakino mass parameter are set as a function of the light electroweakino mass parameter. They are set on wino or higgsino production models with various assumptions, such as the branching ratio of their decaying and the type of lightest SUSY particle. These limits are the most stringent limits. Besides, this book provides the most stringent constraints on SUSY scenarios motivated by the dark matter, the muon g-2 anomaly, and the naturalness.