QCD Resummation Research Articles

QCD prediction for heavy boson transverse momentum distributions.

We investigate the predictive power of the Collins, Soper, and Sterman b-space QCD resummation formalism for transverse momentum ( Q(T)) distributions of heavy boson production in hadronic collisions. We show that the predictive power has a strong dependence on the collision energy sqrt[S] in addition to its well known Q2 dependence, and the sqrt[S] dependence improves the predictive power at collider energies. We demonstrate that, at the Fermilab Tevatron and the CERN LHC energies, the Q(T) distributions derived from b-space resummation are not sensitive to the nonperturbative input at large b, and give good descriptions of the Q(T) distributions of heavy boson production at all transverse momenta Q(T)< or =Q.

Achieving renormalization-scale- and scheme-independence in Padé-related resummation in QCD

Previously developed Padé-related method of resummation for QCD observables, which achieves exact renormalization-scale-invariance, is extended so that the scheme-invariance is obtained as well. The dependence on the leading scheme parameter c 2 is eliminated by a variant of the method of the principle of minimal sensitivity. The subleading parameter c 3 in the approximant is then fixed in such a way that the correct known location of the leading infrared renormalon pole is reproduced. Thus, β-functions which go beyond the last perturbatively calculated order in the observable are used. The β-functions in the approximant are quasianalytically continued by Padé approximants. Two aspects of nonperturbative physics are accounted for in the presented resummation: a mechanism of quasianalytic continuation from the weak- into the strong-coupling regime, and the (approximant-specific) contribution of the leading infrared renormalon. The case of the Bjorken polarized sum rule is considered as a specific example of how the method works.

QCD corrections to scalar production via heavy quark fusion at hadron colliders

We recently proposed that, due to the top-quark-mass enhanced Yukawa coupling, the s-channel production of a charged scalar or pseudo-scalar from heavy quark fusion can be an important new mechanism for discovering non-standard spin-0 particles. In this work, we present the complete O(alpha_s) QCD corrections to this s-channel production process at hadron colliders, including the results of QCD resummation over multiple soft-gluon emission. The systematic QCD-improved production and decay rates at the FermiLab Tevatron and the CERN LHC are given for the charged top-pions in the topcolor models and for the charged Higgs bosons in the generic two Higgs doublet model. The direct extension to the production of the neutral (pseudo-)scalars via bb\bar fusion is studied in the minimal supersymmetric standard model (MSSM) with large tan(beta), and in the topcolor model with large bottom Yukawa coupling.

Measurement of the Shape of the Transverse Momentum Distribution ofWBosons Produced inpp¯Collisions at√s=1.8TeV

The shape of the transverse momentum distribution of W bosons (p_T(W)) produced in pbarp collisions at sqrt(s)= 1.8 TeV is measured with the DO detector at Fermilab. The result is compared to QCD perturbative and resummation calculations over the p_T(W) range from 0-200 GeV/c. The shape of the distribution is consistent with the theoretical prediction.

Effects of QCD resummation on W+h and production at the Tevatron

The resummation of multiple soft gluon emission affects the production rate and kinematic distributions of $W^+h$ (where h is a Higgs boson) and $t \bar b$ pairs at the Tevatron with $\sqrt{s}=2$ TeV. Using the Collins-Soper-Sterman resummation formalism, the production rate is enhanced over the next-to-leading-order (NLO) prediction by 2-3% for the $W^+h$ process, for Higgs boson masses between 80-120 GeV, and over 3% for the $t\bar b$ process for $m_t=175$ GeV. After resummation, the $t\bar b$ rate changes by 12-13% when $m_t$ is varied by $\pm 5$ GeV. Various kinematic distributions are presented for the individual final state particles and for the pair. The explicit radiation of hard gluons in NLO QCD is included also for the $t\bar b$ final state.

Effects of QCD resummation on distributions of top-quark–top-antiquark pairs produced at the Fermilab Tevatron

We study the kinematic distributions of top--antitop quark pairs produced at the Tevatron, including the effects of initial state and final state multiple soft gluon emission, using the Collins--Soper--Sterman resummation formalism. The resummed results are compared with those predicted by the showering event generator PYTHIA for various distributions involving the top--antitop quark pair and the individual top quark or antiquark. The comparison between the experimental and predicted distributions will be a strong test of our understanding and application of perturbative QCD. Our results indicate that the showering event generators do not produce enough radiation. We reweight the PYTHIA distributions to agree with our resummed calculation, then use the reweighted events to better estimate the true hadronic activity in top--antitop quark pair production at hadron colliders.

Effects of QCD resummation on distributions of leptons from the decay of electroweak vector bosons

We study the distributions of leptons from the decay of electroweak vector bosons produced in hadron collisions. The effects of the initial state multiple soft-gluon emission, using the Collins-Soper resummation formalism, are included. The resummed results are compared with the next-to-leading-order results for the distributions of the transverse momentum, rapidity asymmetry, and azimuthal angle of the decay leptons.

Nonperturbative regime in QCD resummation for gauge boson production at hadron colliders.

We study the nonperturbative functions in the Collins--Soper--Sterman resummation formalism by examing Drell--Yan data in both fixed target and collider experiments and then predict the transverse momentum distributions of the $W^\pm$ and $Z^0$ bosons at the Tevatron. Our results differ from that in the literature and agree better with published CDF data. Using statistical arguments, we find a $1\,$fb${}^{-1}$ luminosity at the Fermilab Tevatron should be able to provide useful constraints on the nonperturbative functions.

Can perturbative QCD predict a substantial part of diffractive LHC/SSC physics?

We examine a model of hadronic diffractive scattering which interpolates between perturbative QCD and non-perturbative fits. We restrict the perturbative QCD resummation to the large transverse momentum region, and use a simple Regge-pole parametrization in the infrared region. This picture allows us to account for existing data, and to estimate the size of the perturbative contribution to future diffractive measurements. At LHC and SSC energies, we find that a cut-off BFKL equation can lead to a measurable perturbative component in traditionally soft processes. In particular, we show that the total pp cross section could become as large as 228 mb (160 mb) and the ϱ parameter as large as 0.23 (0.24) at the SSC (LHC).

An analysis of intermediate transverse momentum pion and photon production inpp collisions through a QCD resummation mechanism

We propose a resummation of QCD radiative corrections in large transverse momentum hadronic processes, based on the introduction of an infrared cut-off, linked to the confinement radius. An analysis of the inclusive reactionspp → π0X andpp → γX and of γ/π0 ratio is presented.

Intermediate p⊥ distribution through a QCD resummation mechanism

We argue that it is possible to use an alternative resummation technique of QCD perturbative expansion, introducing a physically sensible infrared parameter. The application of this procedure to large p ⊥ distribution for the process pp→π 0X is studied.