Davison E. Soper

Transverse momentum distribution in Drell-Yan pair and W and Z boson production

Abstract We exhibit and discuss the QCD prediction for the transverse momentum distribution of W bosons, Z bosons and high-mass virtual photons produced in high-energy hadron-hadron collisions. Recent work has shown that this prediction is consistent with the structure of leading twist initial state interactions. The expression we present is expected to give results correct up to order αsN(Q) for anyQT when the boson mass Q is very large (> 108 GeV!), given only input from perturbative calculations at order αsN+2 and deeply inelastic scattering structure functions. We specify the required N = 0 coefficients, employing the order αs2 results of Kodaira and Trentadue and of Davies and Stirling. We then show how the expression should be modified to deal with current energy scales. We also discuss the connection between low-QT and high-QT formulae.

Back-to-back jets in QCD☆

Abstract We give a procedure for calculating in QCD (in terms of quark decay functions d A a (z) ) the cross section for the semi-inclusive process e+ + e− → A + B + X. The procedure is useful at high energy in the back-to-back region 0 ⩽ θ ⪡ 1, where θ is the angle between P A and − P B .

Factorization of Hard Processes in QCD

We summarize the standard factorization theorems for hard processes in QCD, and describe their proofs.

Improved parton distributions from global analysis of recent deep inelastic scattering and inclusive jet data

The impact of recent precision measurements of DIS structure functions and inclusive jet production at the Fermilab Tevatron on the global QCD analysis of parton distribution functions is studied in detail. Particular emphasis is placed on exploring the range of variation of the gluon distribution G(x,Q) allowed by these new data. The strong coupling of G(x,Q) with {alpha}{sub s} is fully taken into account. A new generation of CTEQ parton distributions, CTEQ4, is presented. It consists of the three standard sets [modified minimal subtraction ({ovr MS}), deep inelastic scattering (DIS), and leading order (LO)], a series that gives a range of parton distributions with corresponding {alpha}{sub s}`s, and a set with a low starting value of Q. Previously obtained gluon distributions that are consistent with the high E{sub t} jet cross section are also discussed in the context of this new global analysis. {copyright} {ital 1997} {ital The American Physical Society}

Parton Distribution and Decay Functions

We define parton distribution and decay functions in QCD and prove some of their basic properties. These include renormalization, light-cone expansions and sum rules.

Factorization for short distance hadron-hadron scattering

Abstract We show that factorization holds at leading twist in the Drell-Yan cross section dσ/dQ2dy and related inclusive hadron-hadron cross sections. We review the heuristic arguments for factorization, as well as the difficulties which must be overcome in a proof. We go on to give detailed arguments for the all order cancellation of soft gluons, and to show how this leads to factorization.

Jet Substructure at the Tevatron and LHC: New results, new tools, new benchmarks

In this paper, we review recent theoretical progress and the latest experimental results in jet substructure from the Tevatron and the LHC. We review the status of and outlook for calculation and simulation tools for studying jet substructure. Following up on the report of the Boost 2010 workshop, we present a new set of benchmark comparisons of substructure techniques, focusing on the set of variables and grooming methods that are collectively known as ‘top taggers’. To facilitate further exploration, we have attempted to collect, harmonize and publish software implementations of these techniques.

Back-to-back jets: Fourier transform from b to kT☆

In an earlier paper, we derived an algorithm for calculating the cross section for e+ +e− → A + B + X, with hadrons A and B nearly back to back. The result was given in transverse position (b) space for the Fourier transform of the small angle part of the cross section. Here we discuss the structure of this result, particularly at large b, where purely perturbative calculations are not useful. We then describe how to return from b space to transverse momentum space.

Soft gluons and factorization

We clarify the role of soft gluons in hard inclusive hadron-hadron cross sections, emphasizing the mechanisms by which they decouple from the incoming hadrons and cancel.

Numerical integration of one-loop Feynman diagrams for N -photon amplitudes

In the calculation of cross sections for infrared-safe observables in high energy collisions at nextto-leading order, one approach is to perform all of the integrations, including the virtual loop integration, numerically. One would use a subtraction scheme that removes infrared and collinear divergences from the integrand in a style similar to that used for real emission graphs. Then one would perform the loop integration by Monte Carlo integration along with the integrations over final state momenta. In this paper, we explore how one can perform the numerical integration. We study the N-photon scattering amplitude with a massless electron loop in order to have a case with a singular integrand that is not, however, so singular as to require the subtractions. We report results for N = 4, N = 5 with left-handed couplings, and N = 6.