Publications (150)475.07 Total impact
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ABSTRACT: We study the ABDK relation using maximal cuts of one and twoloop integrals with up to five external legs. We show how to find a special combination of integrals that allows the relation to exist, and how to reconstruct the terms with oneloop integrals squared. The reconstruction relies on the observation that integrals across different loop orders can have support on the same generalized unitarity cuts and can share global poles. We discuss the appearance of nonhomologous integration contours in multivariate residues. Their origin can be understood in simple terms, and their existence enables us to distinguish contributions from different integrals. Our analysis suggests that maximal and nearmaximal cuts can be used to infer the existence of integral identities more generally.Physical Review D 03/2015; 92(2). DOI:10.1103/PhysRevD.92.025015 · 4.64 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Electroweak vectorboson production, accompanied by multiple jets, is an important background to searches for physics beyond the Standard Model. A precise and quantitative understanding of this process is helpful in constraining deviations from known physics. We study four key ratios in $W + n$jet production at the LHC. We compute the ratio of cross sections for $W + n$ to $W + (n1)$jet production as a function of the minimum jet transverse momentum. We also study the ratio differentially, as a function of the $W$boson transverse momentum; as a function of the scalar sum of the jet transverse energy, $H_T^{\rm jets}$; and as a function of certain jet transverse momenta. We show how to use such ratios to extrapolate differential cross sections to $W+6$jet production at nexttoleading order, and we crosscheck the method against a direct calculation at leading order. We predict the differential distribution in $H_T^{\rm jets}$ for $W+6$ jets at nexttoleading order using such an extrapolation. We use the BlackHat software library together with SHERPA to perform the computations.Physical Review D 12/2014; 92(1). DOI:10.1103/PhysRevD.92.014008 · 4.64 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study $W$boson production accompanied by multiple jets at 7 TeV at the LHC. We study the jetproduction ratio, of total cross sections for $W$+$n$ to $W$+($n1$)jet production, and the ratio of distributions in the total transverse hadronic jet energy $H_{\rm T}^{\rm jets}$. We use the ratios to extrapolate the total cross section, and the differential distribution in $H_{\rm T}^{\rm jets}$, to $W$+6jet production. We use the BlackHat software library in conjunction with SHERPA to perform the computations.  [Show abstract] [Hide abstract]
ABSTRACT: In this contribution, we present an intermediate storage format for nexttoleading order (NLO) events and explain the advantages of presenting a NLO calculation in this format. We also present some recent applications, including the calculation of PDF uncertainties and the combination of different multiplicity samples for the prediction of gap fractions in inclusive dijet events.  [Show abstract] [Hide abstract]
ABSTRACT: We present the Flowgen tool, which generates flowcharts from annotated C++ source code. The tool generates a set of interconnected highlevel UML activity diagrams, one for each function or method in the C++ sources. It provides a simple and visual overview of complex implementations of numerical algorithms. Flowgen is complementary to the widelyused Doxygen documentation tool. The ultimate aim is to render complex C++ computer codes accessible, and to enhance collaboration between programmers and algorithm or science specialists. We describe the tool and a proofofconcept application to the VINCIA plugin for simulating collisions at CERN's Large Hadron Collider.Computer Physics Communications 05/2014; DOI:10.1016/j.cpc.2015.05.029 · 3.11 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present the Flowgen tool, which generates flowcharts from annotated C++ source code. The tool generates a set of interconnected highlevel UML activity diagrams, one for each function or method in the C++ sources. It provides a simple and visual overview of complex implementations of numerical algorithms. Flowgen is complementary to the widelyused Doxygen documentation tool. The ultimate aim is to render complex C++ computer codes accessible, and to enhance collaboration between programmers and algorithm or science specialists. We describe the tool and a proofofconcept application to the VINCIA plugin for simulating collisions at CERN's Large Hadron Collider.  [Show abstract] [Hide abstract]
ABSTRACT: We present nexttoleading order QCD predictions for cross sections and for a comprehensive set of distributions in diphoton + 2jet production at the Large Hadron Collider. We consider the contributions from loop amplitudes for two photons and four gluons, but we neglect top quarks. We use BlackHat together with SHERPA to carry out the computation. We use a Frixione cone isolation for the photons. We study standard sets of cuts on the jets and the photons, and also sets of cuts appropriate for studying backgrounds to Higgsboson production via vectorboson fusion.Physical Review D 02/2014; 90(5). DOI:10.1103/PhysRevD.90.054004 · 4.64 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present results from a recent calculation of prompt photonpair production in association with two jets to nexttoleading order (NLO) at the LHC. The virtual contribution is evaluated using the BlackHat library, a numerical implementation of onshell methods for oneloop amplitudes, in conjunction with SHERPA. We study four sets of cuts: standard jet cuts, a set of Higgsrelated cuts suggested by ATLAS, and corresponding sets which isolate the kinematic region where the process becomes the largest background to Higgs production via vectorboson fusion.  [Show abstract] [Hide abstract]
ABSTRACT: We present an eventfile format for the dissemination of nexttoleadingorder (NLO) predictions for QCD processes at hadron colliders. The files contain all information required to compute generic jetbased infraredsafe observables at fixed order (without showering or hadronization), and to recompute observables with different factorization and renormalization scales. The files also make it possible to evaluate cross sections and distributions with different parton distribution functions. This in turn makes it possible to estimate uncertainties in NLO predictions of a wide variety of observables without recomputing the shortdistance matrix elements. The event files allow a user to choose among a wide range of commonlyused jet algorithms and jetsize parameters. We provide event files for a $W$ or $Z$ boson accompanied by up to four jets, and for purejet events with up to four jets. The files are for the Large Hadron Collider with a center of mass energy of 7 or 8 TeV. A C++ library along with a Python interface for handling these files are also provided and described in this article. The library allows a user to read the event files and recompute observables transparently for different pdf sets and factorization and renormalization scales.Computer Physics Communications 10/2013; 185(5). DOI:10.1016/j.cpc.2014.01.011 · 3.11 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: This is the summary report of the energy frontier QCD working group prepared for Snowmass 2013. We review the status of tools, both theoretical and experimental, for understanding the strong interactions at colliders. We attempt to prioritize important directions that future developments should take. Most of the efforts of the QCD working group concentrate on protonproton colliders, at 14 TeV as planned for the next run of the LHC, and for 33 and 100 TeV, possible energies of the colliders that will be necessary to carry on the physics program started at 14 TeV. We also examine QCD predictions and measurements at leptonlepton and leptonhadron colliders, and in particular their ability to improve our knowledge of strong coupling constant and parton distribution functions.  [Show abstract] [Hide abstract]
ABSTRACT: We present recent nexttoleading order (NLO) results in perturbative QCD obtained using the BlackHat software library. We discuss the use of ntuples to separate the lengthy matrixelement computations from the analysis process. The use of ntuples allows many analyses to be carried out on the same phasespace samples, and also allows experimenters to conduct their own analyses using the original NLO computation.Journal of Physics Conference Series 10/2013; 523(1). DOI:10.1088/17426596/523/1/012051  [Show abstract] [Hide abstract]
ABSTRACT: We extend the maximalunitarity formalism at two loops to doublebox integrals with four massive external legs. These are relevant for higherpoint processes, as well as for heavy vector rescattering, VV > VV. In this formalism, the twoloop amplitude is expanded over a basis of integrals. We obtain formulas for the coefficients of the doublebox integrals, expressing them as products of treelevel amplitudes integrated over specific complex multidimensional contours. The contours are subject to the consistency condition that integrals over them annihilate any integrand whose integral over real Minkowski space vanishes. These include integrals over parityodd integrands and total derivatives arising from integrationbyparts (IBP) identities. We find that, unlike the zero through threemass cases, the IBP identities impose no constraints on the contours in the fourmass case. We also discuss the algebraic varieties connected with various doublebox integrals, and show how discrete symmetries of these varieties largely determine the constraints.Physical Review D 08/2013; 89(12). DOI:10.1103/PhysRevD.89.125010 · 4.64 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In these proceedings we present results from a recent calculation for the production of a W boson in conjunction with five jets at nexttoleading order in perturbative QCD. We also use results at lower multiplicities to extrapolate the cross section to the same process with six jets. 
Article: The Vincia Parton Shower
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ABSTRACT: We summarize recent developments in the VINCIA parton shower. After a brief review of the basics of the formalism, the extension of VINCIA to hadron collisions is sketched. We then turn to improvements of the efficiency of treelevel matching by making the shower history unique and by incorporating identified helicities. We conclude with an overview of matching to oneloop matrix elements.  [Show abstract] [Hide abstract]
ABSTRACT: We present nexttoleading order QCD predictions for the total cross section and for a comprehensive set of transversemomentum distributions in W + 5jet production at the Large Hadron Collider. We neglect the small contributions from subleadingcolor virtual terms, top quarks and some terms containing four quark pairs. We also present ratios of total cross sections, and use them to obtain an extrapolation formula to an even larger number of jets. We include the decay of the $W$ boson into leptons. This is the first such computation with six finalstate vector bosons or jets. We use BlackHat together with SHERPA to carry out the computation.Physical Review D 04/2013; 88(1). DOI:10.1103/PhysRevD.88.014025 · 4.64 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We discuss the extension of the maximalunitarity method to two loops, focusing on the example of the planar double box. Maximal cuts are reinterpreted as contour integrals, with the choice of contour fixed by the requirement that integrals of total derivatives vanish on it. The resulting formulae, like their oneloop counterparts, can be applied either analytically or numerically.  [Show abstract] [Hide abstract]
ABSTRACT: We study the planarflow distributions of narrow, highly boosted, massive QCD jets. Using the factorization properties of QCD in the collinear limit, we compute the planarflow jet function from the onetothree splitting function at treelevel. We derive the leadinglog behavior of the jet function analytically. We also compare our semianalytic jet function with partonshower predictions using various generators.Physical review D: Particles and fields 12/2012; 87(9). DOI:10.1103/PhysRevD.87.094013 · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present an antenna shower formalism including contributions from initialstate partons and corresponding backwards evolution. We give a set of phasespace maps and antenna functions for massless partons which define a complete shower formalism suitable for computing observables with hadronic initial states. We focus on the initialstate components: initialinitial and initialfinal antenna configurations. The formalism includes comprehensive possibilities for uncertainty estimates. We report on some preliminary results obtained with an implementation in the Vincia antennashower framework.Physics Letters B 10/2012; 718(s 4–5). DOI:10.1016/j.physletb.2012.12.003 · 6.13 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We extend the maximal unitarity method at two loops to doublebox basis integrals with up to three external massive legs. We use consistency equations based on the requirement that integrals of total derivatives vanish. We obtain unique formulae for the coefficients of the master doublebox integrals. These formulae can be used either analytically or numerically.Physical review D: Particles and fields 08/2012; 87(2). DOI:10.1103/PhysRevD.87.025030 · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We extend our investigation of backgrounds to new physics signals, following CMS's datadriven search for supersymmetry at the LHC. The aim is to use different sets of cuts in gamma + 3jet production to predict the irreducible Z + 3jet background (with the Z boson decaying to neutrinos) to searches with missing transverse energy + 3jet signal topologies. We compute ratios of Z + 3jet to gamma + 3jet production cross sections and kinematic distributions at nexttoleading order (NLO) in alpha_s. We compare these ratios with those obtained using a parton shower matched to leadingorder matrix elements (ME+PS). This study extends our previous work [arXiv:1106.1423 [hepph]] on the Z + 2jet to gamma + 2jet ratio. We find excellent agreement with the ratio determined from the earlier NLO results involving two instead of three jets, and agreement to within 10% between the NLO and ME+PS results for the ratios. We also examine the possibility of large QCD logarithms in these processes. Ratios of Z + njet to gamma + njet cross sections are plausibly less sensitive to such corrections than the cross sections themselves. Their effect on estimates of Z + 3jet to gamma + 3jet ratios can be assessed experimentally by measuring the gamma + 3jet to gamma + 2jet production ratio in search regions. We partially address the question of potentially large electroweak logarithms by computing the realemission part of the electroweak corrections to the ratio using ME+PS, and find that it is 1% or less. Our estimate of the remaining theoretical uncertainties in the Z to gamma ratio is in agreement with our earlier study.Physical Review D 06/2012; 87(3). DOI:10.1103/PhysRevD.87.034026 · 4.64 Impact Factor
Publication Stats
7k  Citations  
475.07  Total Impact Points  
Top Journals
Institutions

2012

University of California, Los Angeles
 Department of Physics and Astronomy
Los Angeles, CA, United States


2010

Weizmann Institute of Science
Israel


2007

University of Zurich
 Institut für Theoretische Physik
Zürich, Zurich, Switzerland


2004

Stanford University
Palo Alto, California, United States


1997

Campus Paris Saclay
Lutetia Parisorum, ÎledeFrance, France


1993

CERN
 Physics Department (PH)
Genève, Geneva, Switzerland


1989–1992

Fermi National Accelerator Laboratory (Fermilab)
 Theoretical Physics Department
Батавия, Illinois, United States


1991

Leiden University
Leyden, South Holland, Netherlands


1987–1989

Columbia University
 Department of Physics
New York, New York, United States


1983–1988

Harvard University
 • Department of Physics
 • Department of Mathematics
Cambridge, Massachusetts, United States
