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R. K. Ellis

Publications and source records attributed to R. K. Ellis.

At least 19 recordsLinked to original sources
arXiv2025

Higgs Boson Studies at Future Particle Colliders

This document aims to provide an assessment of the potential of future colliding beam facilities to perform Higgs boson studies. The analysis builds on the submissions made by the proponents of future colliders to the European Strategy Update process, and takes as its point of departure the results expected at the completion of the HL-LHC program. This report presents quantitative results on many aspects of Higgs physics for future collider projects of sufficient maturity using uniform methodologies.

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arXiv2013

Handbook of LHC Higgs Cross Sections: 3. Higgs Properties

This Report summarizes the results of the activities in 2012 and the first half of 2013 of the LHC Higgs Cross Section Working Group. The main goal of the working group was to present the state of the art of Higgs Physics at the LHC, integrating all new results that have appeared in the last few years. This report follows the first working group report Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables (CERN-2011-002) and the second working group report Handbook of LHC Higgs Cross Sections: 2. Differential Distributions (CERN-2012-002). After the discovery of a Higgs boson at the LHC in mid-2012 this report focuses on refined prediction of Standard Model (SM) Higgs phenomenology around the experimentally observed value of 125-126 GeV, refined predictions for heavy SM-like Higgs bosons as well as predictions in the Minimal Supersymmetric Standard Model and first steps to go beyond these models. The other main focus is on the extraction of the characteristics and properties of the newly discovered particle such as couplings to SM particles, spin and CP-quantum numbers etc.

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arXiv2012

Handbook of LHC Higgs Cross Sections: 2. Differential Distributions

This Report summarises the results of the second year's activities of the LHC Higgs Cross Section Working Group. The main goal of the working group was to present the state of the art of Higgs Physics at the LHC, integrating all new results that have appeared in the last few years. The first working group report Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables (CERN-2011-002) focuses on predictions (central values and errors) for total Higgs production cross sections and Higgs branching ratios in the Standard Model and its minimal supersymmetric extension, covering also related issues such as Monte Carlo generators, parton distribution functions, and pseudo-observables. This second Report represents the next natural step towards realistic predictions upon providing results on cross sections with benchmark cuts, differential distributions, details of specific decay channels, and further recent developments.

hep-ph↗
arXiv2010

QCD corrections to the hadronic production of a heavy quark pair and a W-boson including decay correlations

We perform an analytic calculation of the one-loop amplitude for the W-boson mediated process 0 \to d u-bar Q Q-bar l-bar l, retaining the mass for the quark Q. The momentum of each of the massive quarks is expressed as the sum of two massless momenta and the corresponding heavy quark spinor is expressed as a sum of two massless spinors. Using a special choice for the heavy quark spinors we obtain analytic expressions for the one-loop amplitudes which are amenable to fast numerical evaluation. The full next-to-leading order (NLO) calculation of hadron+hadron \to W(\to e nu) b b-bar with massive b-quarks is included in the program MCFM. A comparison is performed with previous published work.

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arXiv2010

MCFM for the Tevatron and the LHC

A summary is given of the current status of the next-to-leading order (NLO) parton-level integrator MCFM. Some details are given about the Higgs + 2-jet process and the production and decay of $t \bar{t}$, both of which have recently been added to the code. Using MCFM, comparisons between the Tevatron running at $\sqrt{s}=2$~TeV and the LHC running at $\sqrt{s}=7$~TeV are made for standard model process including the production of Higgs bosons. The case for running the Tevatron until 16fb$^{-1}$ are accumulated by both detectors is sketched.

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arXiv2008

Masses, fermions and generalized D-dimensional unitarity

We extend the generalized D-dimensional unitarity method for numerical evaluation of one-loop amplitudes by incorporating massive particles. The issues related to extending the spinor algebra to higher dimensions, treatment of external self-energy diagrams and mass renormalization are discussed within the context of the D-dimensional unitarity method. To validate our approach, we calculate in QCD the one-loop scattering amplitudes of a massive quark pair with up to three additional gluons for arbitrary spin states of the external quarks and gluons.

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arXiv2007

Production of a Z boson and two jets with one heavy-quark tag

We present a next-to-leading-order calculation of the production of a Z boson with two jets, one or more of which contains a heavy quark (Q=c,b). We show that the cross section with only one heavy-quark jet is larger than that with two heavy-quark jets at both the Fermilab Tevatron and the CERN LHC. These processes are the dominant irreducible backgrounds to a Higgs boson produced in association with a Z boson, followed by h->bb. Our calculation makes use of a heavy-quark distribution function, which resums collinear logarithms and makes the next-to-leading-order calculation tractable.

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arXiv2007

A Numerical Unitarity Formalism for Evaluating One-Loop Amplitudes

Recent progress in unitarity techniques for one-loop scattering amplitudes makes a numerical implementation of this method possible. We present a 4-dimensional unitarity method for calculating the cut-constructible part of amplitudes and implement the method in a numerical procedure. Our technique can be applied to any one-loop scattering amplitude and offers the possibility that one-loop calculations can be performed in an automatic fashion, as tree-level amplitudes are currently done. Instead of individual Feynman diagrams, the ingredients for our one-loop evaluation are tree-level amplitudes, which are often already known. To study the practicality of this method we evaluate the cut-constructible part of the 4, 5 and 6 gluon one-loop amplitudes numerically, using the analytically known 4, 5 and 6 gluon tree-level amplitudes. Comparisons with analytic answers are performed to ascertain the numerical accuracy of the method.

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arXiv2007

Production of a W boson and two jets with one b-quark tag

The production of a W boson and two jets, at least one of which contains a b quark, is a principal background to single-top production, Higgs production, and signals of new physics at hadron colliders. We present a next-to-leading-order (NLO) calculation of the cross section at the Fermilab Tevatron and the CERN Large Hadron Collider. The NLO cross section differs substantially from that at LO, and we provide a context in which to understand this result.

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arXiv2006

Virtual QCD corrections to Higgs boson plus four parton processes

We report on the calculation of virtual processes contributing to the production of a Higgs boson and two jets in hadron-hadron collisions. The coupling of the Higgs boson to gluons, via a virtual loop of top quarks, is treated using an effective theory, valid in the large top quark mass limit. The calculation is performed by evaluating one-loop diagrams in the effective theory. The primary method of calculation is a numerical evaluation of the virtual amplitudes as a Laurent series in $D-4$, where $D$ is the dimensionality of space-time. For the cases $H \to q\bar{q}q\bar{q}$ and $H \to q\bar{q}q'\bar{q}'$ we confirm the numerical results by an explicit analytic calculation.

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arXiv2006

Semi-Numerical Evaluation of One-Loop Corrections

We present a semi-numerical algorithm to calculate one-loop virtual corrections to scattering amplitudes. The divergences of the loop amplitudes are regulated using dimensional regularization. We treat in detail the case of amplitudes with up to five external legs and massless internal lines, although the method is more generally applicable. Tensor integrals are reduced to generalized scalar integrals, which in turn are reduced to a set of known basis integrals using recursion relations. The reduction algorithm is modified near exceptional configurations to ensure numerical stability. To test the procedure we apply these techniques to one-loop corrections to the Higgs to four quark process for which analytic results have recently become available.

hep-ph↗
arXiv2006

The one-loop amplitude for six-gluon scattering

We present results for the six-gluon scattering amplitude at one-loop. Since our method is semi-numerical, it yields the result for arbitrary momenta and helicities of the external gluons. We evaluate the colour-ordered sub-amplitudes with gluons, fermions and scalars running in the internal loop. This is more than sufficient to give a complete description of six-gluon scattering at one-loop in QCD. Combination of these results into amplitudes with ${\cal{N}}=4$ and ${\cal{N}}=1$ multiplets of supersymmetric Yang-Mills or with a complex scalar in the internal loops allows comparison with analytic results in the literature. The numerical results for most of the helicity combinations with loops of complex scalars are new.

hep-ph↗
arXiv2004

Single top production and decay at next-to-leading order

We present the results of a next-to-leading order analysis of single top production including the decay of the top quark. Radiative effects are included both in the production and decay stages, using a general subtraction method. This calculation gives a good treatment of the jet activity associated with single top production. We perform an analysis of the single top search at the Tevatron, including a consideration of the main backgrounds, many of which are also calculated at next-to-leading order.

hep-ph↗
arXiv2004

Associated Production of a Z Boson and a Single Heavy-Quark Jet

The leading-order process for the production of a Z boson and a heavy-quark jet at hadron colliders is gQ -> ZQ (Q=c,b). We calculate this cross section at next-to-leading order at the Tevatron and the LHC, and compare it with other sources of ZQ events. This process is a background to new physics, and can be used to measure the heavy-quark distribution function.

hep-ph↗
arXiv2003

Next-to-leading order QCD predictions for W+2j and Z+2j production at the CERN LHC

We present cross sections and differential distributions for QCD radiative corrections to the QCD processes pp -> W+2j and pp -> Z+2j at the CERN LHC. Calculations are performed with the Monte Carlo program MCFM. Cross section dependence on the renormalization and factorization scales is greatly reduced, except for the heavy-flavor case of Wbb~, which has new features at next-to-leading order at the LHC. We also present cross sections for Wbb~ and Z+2j in kinematic configurations relevant for Higgs boson searches.

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arXiv2003

Higgs-Boson Production in Association with a Single Bottom Quark

Higgs bosons from an extended Higgs sector, such as a two-Higgs-doublet model, can have greatly enhanced coupling to the bottom quark. Producing such a Higgs boson in association with a single high-p_T bottom quark via g b -> h b allows for the suppression of backgrounds. Previous studies have instead used g g,qbar q -> bbar b h as the production mechanism, which is valid only if both b quarks are at high p_T. We calculate g b -> h b at next-to-leading order in QCD, and find that it is an order of magnitude larger than g g,qbar q -> bbar b h at the Fermilab Tevatron and the CERN Large Hadron Collider. This production mechanism improves the prospects for the discovery of a Higgs boson with enhanced coupling to the b quark.

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