Soft Gluon Resummation Effects Research Articles

QCD Resummation for Single Spin Asymmetries

We study the transverse momentum dependent factorization for single spin asymmetries in Drell-Yan and semi-inclusive deep inelastic scattering processes at one-loop order. The next-to-leading order hard factors are calculated in the Ji-Ma-Yuan factorization scheme. We further derive the QCD resummation formalisms for these observables following the Collins-Soper-Sterman method. The results are expressed in terms of the collinear correlation functions from initial and/or final state hadrons coupled with the Sudakov form factor containing all order soft-gluon resummation effects. The scheme-independent coefficients are calculated up to one-loop order.

Soft gluon resummation of Drell–Yan rapidity distributions: Theory and phenomenology

We examine critically the theoretical underpinnings and phenomenological implications of soft gluon (threshold) resummation of rapidity distributions at a hadron collider, taking Drell–Yan production at the Tevatron and the LHC as a reference test case. First, we show that in perturbative QCD soft gluon resummation is necessary whenever the partonic (rather the hadronic) center-of-mass energy is close enough to threshold, and we provide tools to assess when resummation is relevant for a given process. Then, we compare different prescriptions for handling the divergent nature of the series of resummed perturbative corrections, specifically the minimal and Borel prescriptions. We assess the intrinsic ambiguities of resummed results, both due to the asymptotic nature of their perturbative expansion, and to the treatment of subleading terms. Turning to phenomenology, we introduce a fast and accurate method for the implementation of resummation with the minimal and Borel prescriptions using an expansion on a basis of Chebyshev polynomials. We then present results for W and Z production as well as both high- and low-mass dilepton pairs at the LHC, and show that soft gluon resummation effects are generally comparable in size to NNLO corrections, but sometimes affected by substantial ambiguities.

Revisiting the QCD Corrections to the R-Parity Violating Processes pp̄/pp → eμ + X

We present the theoretical predictions up to QCD next-to-leading order for the cross section of high-mass electron-muon pair production at the Tevatron and at the Large Hadron Collider (LHC), considering only the dominant contributions from the third-generation sneutrino. The dependence of the renormalization and factorization scales on the total cross section, and the effects on the K-factor due to the uncertainty of parton distribution function are carefully investigated. By considering soft-gluon resummation effects to all orders in αs of leading logarithm, we present the transverse momentum distributions of the final eμ pair.

Resummation effects in the search of standard model Higgs boson at hadron colliders

We examine the soft-gluon resummation effects, including the exact spin correlations among the final state particles, in the search of the standard model Higgs boson, via the process $gg\ensuremath{\rightarrow}H\ensuremath{\rightarrow}WW/ZZ\ensuremath{\rightarrow}4$ leptons, at the Tevatron and the LHC. A comparison between the resummation and the next-to-leading order (NLO) calculation is performed after imposing various kinematics cuts suggested in the literature for the Higgs boson search. For the $H\ensuremath{\rightarrow}ZZ$ mode, the resummation effects increase the acceptance of the signal events by about 25%, as compared to the NLO prediction, and dramatically alter various kinematics distributions of the final state leptons. For the $H\ensuremath{\rightarrow}WW$ mode, the acceptance rates of the signal events predicted by the resummation and NLO calculations are almost the same, but some of the predicted kinematical distributions are quite different. Thus, to precisely determine the properties of the Higgs boson at hadron colliders, the soft-gluon resummation effects have to be taken into account.

Soft gluon resummation effects in single graviton production at the CERN Large Hadron Collider in the Randall-Sundrum model

We study QCD effects in single graviton production at the CERN Large Hadron Collider (LHC) in the Randall-Sundrum (RS) model. We present in detail the complete next-to-leading order (NLO) QCD corrections to the inclusive total cross sections. The NLO QCD corrections enhance significantly the total cross sections and decrease efficiently the dependence of the total cross sections on the factorization and renormalization scales. We also examine the uncertainty of the total cross sections due to the parton distribution function (PDF) uncertainties. For the differential cross sections on the transverse momentum (q{sub T}) of the graviton, within the CSS resummation formalism, we resum the logarithmically-enhanced terms at small q{sub T} to all orders up to NLO logatithmic accuracy. Combined with the fixed-order calculations, we give consistent predictions for both small q{sub T} and large q{sub T}.

Soft gluon resummation effects in single slepton production at hadron colliders

We investigate QCD effects in the production of a single slepton at hadron colliders in the minimal supersymmetric standard model without $R$ parity. We calculate the total cross sections and the transverse momentum distributions at next-to-leading order in QCD. The next-to-leading-order corrections enhance the total cross sections and decrease the dependence of the total cross sections on the factorization and renormalization scales. For the differential cross sections, we resum all-order soft gluon effects to give reliable predictions for the transverse momentum distributions. We also compare two approaches to the nonperturbative parametrization and found that the results are slightly different at the Tevatron and are in good agreement at the Large Hadron Collider. Our results can be useful to the simulation of the events and to the future collider experiments.

Soft-gluon resummation effects on parton distributions

We gauge the impact of soft-gluon resummation on quark distributions by performing a simple fit of Deep Inelastic Scattering structure function data using next-to-leading order (NLO) and next-to-leading-logarithmic (NLL)-resummed coefficient functions. We make use of NuTeV charged-current data, as well as New Muon Collaboration (NMC) and Bologna-CERN-Dubna-Munich-Saclay (BCDMS) neutral-current results, which probe large values of x. Our results suggest that the inclusion of resummation effects in global fits of parton distributions is both feasible and desirable, in order to achieve at large x the accuracy goals of the LHC physics program.

Resummation effects in the Higgs boson transverse momentum distribution within the framework of unintegrated parton distributions

The cross sections describing the transverse momentum distributions of Higgs bosons are discussed within the framework of unintegrated parton distributions obtained from the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) equations in the single-loop approximation. It is shown how the approximate treatment of the CCFM equations generates the standard expressions describing the soft gluon resummation effects in the corresponding cross sections. Possible differences between exact and approximate solutions of the CCFM equations are discussed on the example of the $g\stackrel{\ensuremath{\rightarrow}}{g}H$ fusion mechanism, which gives the dominant contribution to Higgs boson production.

Soft gluon effects in the extraction of higher twists at large Bjorken x

Existing data on the (unpolarised) transverse structure function of the proton are analyzed for large values of the Bjorken variable x. The leading-twist and a phenomenological higher-twist contributions are simultaneously determined from a power correction analysis of the Nachtmann moments for values of the squared four-momentum transfer between ∼1 and 20 (GeV/ c) 2. The results obtained adopting the next-to-leading-order approximation and those including the effects of soft gluon resummation are compared. The sensitivity of the extraction of large- x higher twists to high-order radiative corrections as well as to the value of α s ( M Z 2) is illustrated.

Sudakov resummation effects in prompt-photon hadroproduction

We compute the effects of soft-gluon resummation, at the next-to-leading-logarithmic level, in the fixed-target hadroproduction cross section for prompt photons. We find in general that the corrections to the fixed next-to-leading-order results are large for large renormalization scales, and small for small scales. This leads to a significant reduction of the scale dependence of the results for most experimental configurations of interest. We compare our results to the recent measurements by the E706 and UA6 collaborations.

The resummation of soft gluons in hadronic collisions

We compute the effects of soft-gluon resummation for the production of high mass systems in hadronic collisions. We carefully analyse the growth of the perturbative expansion coefficients of the resummation formula. We propose an expression consistent with the known leading and next-to-leading resummation results, in which the coefficients grow much less than factorially. We apply our formula to Drell-Yan pair production, heavy flavour production, and the production of high invariant mass jet pairs in hadronic collisions. We find that, with our formula, resummation effects become important only fairly close to the threshold region. In the case of heavy flavour production we find that resummation effects are small in the experimental configurations of practical interest.