W.L. van Neerven

NNLO corrections to the total cross section for Higgs boson production in hadron–hadron collisions

Abstract We present the next-to-next-to-leading order (NNLO) corrections to the total cross section for (pseudo-) scalar Higgs boson production using an alternative method than those used in previous calculations. All QCD partonic subprocesses have been included and the computation is carried out in the effective Lagrangian approach which emerges from the standard model by taking the limit mt→∞ where mt denotes the mass of the top quark. Our results agree with those published earlier in the literature. We estimate the theoretical uncertainties by comparing the K-factors and the variation with respect to the mass factorization/renormalization scales with the results obtained by lower order calculations. We also investigate the dependence of the cross section on several parton density sets provided by different groups.

A complete calculation of the order αs2 correction to the Drell-Yan K-factor

In this paper we present the complete calculation of the order αs2 correction in the MS scheme to the Drell-Yan K-factor. All channels represented by the qq, qg, gg and qq subprocesses have been included now. One of our conclusions is that the O(αs2) part of the K-factor is dominated by the qq as well as the qg reaction. The latter leads to a negative contribution over the whole energy range under investigation (0.5 TeV < S < 50 TeV). It even overwhelms the positive qq contribution at large collider energies characteristic for LHC and SSC. It turns out that the order αs2 corrected K-factor is quite insensitive to variations of the factorization scale M over the region 10 GeV < M < 1000 GeV. We also compare our results with the data obtained by UA1, UA2 and CDF.

QCD corrections to heavy quark production in hadron-hadron collisions

We investigate the QCD corrections to the cross section and single-particle inclusive differential distributions for p + p → Q(Q) + X where Q and Q are heavy quarks. We calculate the order α S corrections to the parton reaction q + q → Q + Q which involves the computation of the virtual gluon contributions and the soft and hard contributions from the reaction q + q → Q + Q + g. The contributions from the channels g + q(q) → Q + Q + q(q) are also calculated. Including the order α S corrections to g + g → Q + Q from our previous paper, we give exact results for the order α 3 S cross sections and single-particle inclusive differential distributions for the production of t and b quarks in pp collisions at energies presently available at the CERN SppS and the Fermilab tevatron. Results for future pp colliders are also presented. Finally we compare the results of the simple approximations to the order α S corrections with the exact results.

Higher Order Radiative Corrections at LEP Energies

Abstract A complete two-loop O( α 2 ) initial state radiative correction to the Z-resonance shape is presented. The correction is compared with those expressions where only the soft-photon effects are resummed in all orders of perturbation theory. Our result shows that the soft-photon part constitutes the bulk of the radiative correction near the top of the Z-peak. The effect of non-photonic QED processes on the Z-resonance is found to be very small. The above results have been obtained by means of a standard Feynman diagram calculation. In addition we have also computed the cross sections by using the renormalization group method, where besides the leading logs ln( s / m 2 ), the next-to-leading ones also have been taken into account.

Complete O(αS) corrections to heavy-flavour structure functions in electroproduction

The complete O(αS) QCD corrections to the virtual-photon cross sections for heavy-flavour production in deep-elastic electron-proton scattering are presented. These results are then used to calculate the O(αS) corrections to the heavy-flavour contributions to the structure functions F2(x, Q2, m2) and FL(x, Q2, m2). We examine these corrections in the x and Q2 range appropriate for c- and b-quark production at HERA. Our results are also compared with the O(αS) plus O(αS2) corrections for massless quarks.

Order-αs2 QCD corrections to the deep inelastic proton structure functions F2 and FL

We present the calculation of the order-αs2 correction to the deep inelastic coefficient functions Ci(x, Q2) (i=2, L). Its effect on the behaviour of the proton structure functions Fi(x, Q2) for fixed target and HERA energies is studied. We investigate the dependence of the O(αs2) QCD corrected structure functions on the mass factorization scale and the specific parametrization chosen for the parton densities. Also discussed are the implications of the higher-order QCD corrections for the extraction of the parton densities, in particular the gluon distribution function, from the data. Our analysis reveals that the O(αs2) contributions to F2(x, Q2) are appreciable and can amount from +10% (large-x region) to −20% (small-x region), depending on the chosen value for Q2 and the parton density set. In the case of FL(x, Q2) the corrections in the small-x region can be even larger (about 45%). The large corrections in the region 0.5<x<1, which can be attributed to soft-gluon radiation, may explain the difference observed between the combined SLAC-BCDMS data and the fit based on the next-to-leading-log (NLL) approximation for the proton structure function F2(x, Q2).

The calculation of the second order soft and virtual contributions to the Drell-Yan cross section

Abstract We present an order α s 2 calculation of the K -factor in the Drell-Yan process. Only contributions due to soft and virtual gluons have been taken into account. Our findings are that the abelian ( C F ) part of the K -factor exponentiates, at least in the numerical sense. The deviation of the exponentiation for the total K -factor is wholly due to the non-abelian part ( C A C F ). It appears that the order α s 2 correction is noticeable in particular for low di-lepton pair masses ( Q 2 ∼ 100 GeV 2 ). Its implication for massive muon pair production at fixed target experiments and electro-weak vector boson production in collider experiments are discussed.

Order α2S contributions to the deep inelastic Wilson coefficient

Abstract We present the result of the full order α 2 S correction to the singlet (quark) as well as the non-singlet part of the Wilson coefficient appearing in deep inelastic lepton-hadron scattering. Its implication for the extraction of the parton distribution functions from the lepton-hadron data will be analyzed.

Charm electroproduction viewed in the variable-flavour number scheme versus fixed-order perturbation theory

Starting from fixed-order perturbation theory (FOPT) we derive expressions for the heavy-flavour components of the deep-inelastic structure functions (Fi,H (x, Q2, mH2),i = 2, L; H = c, b, t) in the variable-flavour number scheme (VFNS). These expressions are valid in all orders of perturbation theory. This derivation establishes a relation between the parton densities parametrized atnf andnf + 1 light flavours. One of the results is that the heavy quark parton density does not vanish when the factorization scale becomes equal tomH contrary to what is assumed in the literature. Further we observe that in charm electroproduction the exact and asymptotic expressions for the heavy-quark coefficient functions yield identical results forF2,c(ξ, Q2, mc2) whenx < 0.01 andQ2 > 20 (GeV/c)2. From this observation an analysis of the size of the higher order corrections we conclude that in this region the VFNS description and ofF2,c is better than the one given by FOPT. On the other hand in the charm threshold region i.e.x > 0.01 andQ2 < 20 (GeV/c)2 it turns out that the reverse is true.

Next-to-leading order QCD corrections to differential distributions of Higgs boson production in hadron-hadron collisions

We present the full next-to-leading order corrected differential distributions d 2 σ/dpT /dy, dσ/dpT and dσ/dy for the semi-inclusive process p + p → H + ′ X ′ . Here X denotes the inclusive hadronic state and pT and y are the transverse momentum and rapidity of the Higgs-boson H respectively. All QCD partonic subprocesses have been included. The computation is carried out in the limit that the top-quark mass mt → ∞ which is a very good approximation as long as mH, pT < 200 GeV. Our calculations reveal √