Sven-Olaf Moch

Parton Distribution Functions and Benchmark Cross Sections at NNLO

We present a determination of parton distribution function s (ABM11) and the strong coupling constantαs at next-to-leading order and next-to-next-to-leading ord er (NNLO) in QCD based on world data for deep-inelastic scattering and fixed-target d ata for the Drell-Yan process. The analysis is performed in the fixed-flavor number scheme for n f = 3, 4, 5 and uses the MS -scheme for αs and the heavy-quark masses. At NNLO we obtain the valueαs(MZ) = 0.1134± 0.0011. The fit results are used to compute benchmark cross sections at hadron colliders to NNLO accuracy and to compare to data from the LHC.

The third-order QCD corrections to deep-inelastic scattering by photon exchange

We compute the full three-loop coefficient functions for the structure functions F2 and FL in massless perturbative QCD. The results for FL complete the next-to-next-to-leading order description of unpolarized electromagnetic deep-inelastic scattering. The third-order coefficient functions for F2 form, at not too small values of the Bjorken variable x, the dominant part of the next-to-next-to-next-to-leading order corrections, thus facilitating improved determinations of the strong coupling αs from scaling violations. The three-loop corrections to FL are larger than those for F2. Especially for the latter quantity the expansion in powers of αs is very stable, for photon virtualities Q2≫1GeV2, over the full x-range accessible to fixed-target and collider measurements.

3-, 4-, and 5-flavor next-to-next-to-leading order parton distribution functions from deep-inelastic-scattering data and at hadron colliders

We determine the parton distribution functions (PDFs) in a n ext-to-next-to-leading order (NNLO) QCDanalysis of the inclusive neutral-current deep-inelastic cattering (DIS) world data combined with the neutrino-nucleon DIS di-muon data and the fixed-target Drell-Yan d ta. The PDF-evolution is performed in the Nf = 3 fixed-flavor scheme and supplementary sets of PDFs in the 4a nd 5-flavor schemes are derived from the results in the 3-flavor scheme using matching condit ions. The charm-quark DIS contribution is calculated in a general-mass variable-flavor-number (GM VFN) scheme interpolating between the zeromass 4-flavor scheme at asymptotically large values of momen tum transferQ2 and the 3-flavor scheme at the value ofQ2 = mc in a prescription of Buza-Matiounine-Smith-van Neerven (B MSN). The results in the GMVFN scheme are compared with those of the fixed-flavor scheme and other prescriptions used in global fits of PDFs. The strong coupling constant is measur ed at an accuracy of ≈ 1.5%. We obtain at NNLO αs(M Z) = 0.1135± 0.0014 in the fixed-flavor scheme and αs(M 2 Z) = 0.1129± 0.0014 applying the BMSN prescription. The implications for important stan d rd candle and hard scattering processes at hadron colliders are illustrated. Predictions for cross se ctions ofW±andZ-boson, the top-quark pairand Higgs-boson production at the Tevatron and the LHC based on t he 5-flavor PDFs of the present analysis are provided. 1e-mail: sergey.alekhin@ihep.ru 2e-mail: johannes.bluemlein@desy.de 3e-mail: sebastian.klein@desy.de 4e-mail: sven-olaf.moch@desy.de

The ABM parton distributions tuned to LHC data

We present a global fit of parton distributions at next-to-ne xt-to-leading order (NNLO) in QCD. The fit is based on the world data for deep-inelastic scatteri ng, fixed-target data for the Drell-Yan process and includes, for the first time, data from the Large H adron Collider (LHC) for the DrellYan process and the hadro-production of top-quark pairs. The analysis applies the fixed-flavor number scheme for n f = 3, 4, 5, uses the MS scheme for the strong couplingαs and the heavyquark masses and keeps full account of the correlations among all non-perturbative parameters. At NNLO this returns the values ofαs(MZ) = 0.1132± 0.0011 and mt(pole) = 171.2± 2.4 GeV for the top-quark pole mass. The fit results are used to comput e benchmark cross sections for Higgs production at the LHC to NNLO accuracy. We compare our results to those obtained by other groups and show that differences can be linked to different theoretical descriptions of the underlying physical processes.

Higgs Boson Production via Vector-Boson Fusion at Next-to-Next-to-Leading Order in QCD

We present the total cross sections at next-to-next-to-leading order (NNLO) in the strong coupling for single and double charged Higgs production via weak boson fusion. Results are obtained via the structure function approach, which builds upon the approximate, though very accurate, factorization of the QCD corrections between the two quark lines. The theoretical uncertainty on the total cross sections at the LHC from higher order corrections and the parton distribution uncertainties are estimated at the 2% level each for a wide range of Higgs boson masses.

Deep inelastic structure functions at two loops

Abstract We present the analytic calculation of the Mellin moments of the structure functions F 2 , F 3 and F L in perturbative QCD up to second-order corrections and in leading twist approximation. We calculate the two-loop contributions to the anomalous dimensions of the singlet and non-singlet operator matrix elements and the two-loop coefficient functions of F 2 , F 3 and F L . We perform the inverse Mellin transformation analytically and find our results in agreement with earlier calculations in the literature by Zijlstra and van Neerven.

The quark form factor at higher orders

We study the electromagnetic on-shell form factor of quarks in massless perturbative QCD. We derive the complete pole part in dimensional regularization at three loops, and extend the resummation of the form factor to the next-to-next-to-leading contributions. These results are employed to evaluate the infrared finite absolute ratio of the time-like and space-like form factors up to the fourth order in the strong coupling constant. Besides for the pole structure of higher-loop QCD amplitudes, our new contributions to the form factor are also relevant for the high-energy limit of massive gauge theories like QED. The highest-transcendentality component of our results confirms a result recently obtained in = 4 Super-Yang-Mills theory.

The Singular behavior of massive QCD amplitudes

We discuss the structure of infrared singularities in on-shell QCD amplitudes with massive partons and present a general factorization formula in the limit of small parton masses. The factorization formula gives rise to an all-order exponentiation of both, the soft poles in dimensional regularization and the large collinear logarithms of the parton masses. Moreover, it provides a universal relation between any on-shell amplitude with massive external partons and its corresponding massless amplitude. For the form factor of a heavy quark we present explicit results including the fixed-order expansion up to three loops in the small mass limit. For general scattering processes we show how our constructive method applies to the computation of all singularities as well as the constant (mass-independent) terms of a generic massive n-parton QCD amplitude up to the next-to-next-to-leading order corrections.

Vector boson fusion at next-to-next-to-leading order in QCD: Standard model Higgs boson and beyond

Weak vector boson fusion provides a unique channel to direct ly probe the mechanism of electroweak symmetry breaking at hadron colliders. We present a method that allows to calculate total cross sections to next-to-next-to-leading order (NN LO) in QCD for an arbitraryV∗V∗→ X process, the so-called structure function approach. By dis cussing the case of Higgs production in detail, we estimate several classes of previously neglecte d contributions and we argue that such method is accurate at a precision level well above the typica l residual scale and PDF uncertainties at NNLO. Predictions for cross sections at the Tevatron and t he LHC are presented for a variety of cases: the Standard Model Higgs (including anomalous cou plings), neutral and charged scalars in extended Higgs sectors and (fermiophobic) vector resona nce production. Further results can be easily obtained through the public use of the VBF@NNLO code.

Soft gluon resummation for heavy quark electroproduction

We present the threshold resummation for the cross section for electroproduction of heavy quarks. We work to next-to-leading logarithmic accuracy, and in single-particle inclusive kinematics. We provide next-to-leading and next-to-next-to-leading order expansions of our resummed formula, and examine numerically the quality of these finite order approximations. For the case of charm we study their impact on the structure function F2 and its differential distribution with respect to the charm transverse momentum.