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F. Hautmann

Publications and source records attributed to F. Hautmann.

At least 109 records · Page 6Linked to original sources
arXiv2001

Cancellation of Sudakov Logarithms in Radiative Decays of Quarkonia

We study infrared QCD effects in radiative quarkonia decays. We examine the endpoint region z -> 1 of the photon spectrum. We point out a cancellation mechanism for the corrections in $α_s^n \ln^{m} (1-z)$, $m \leq 2 n$, in the short-distance coefficient for the color-singlet Fock state in the quarkonium. The cancellation is due to the coherence of the color radiation, and applies even though logarithmic contributions are present in the jet distributions associated with the decay. We comment on the implications of our results for the modeling of hadronization in the endpoint region and for the role of color-octet states in the quarkonium.

hep-ph↗
arXiv2000

NLO parton showers and subtractive techniques

Motivated by asking how to combine parton showers with nonleading QCD matrix elements, we discuss a subtractive technique based on gauge-invariant Wilson-line operators and how this can be used to treat the soft region.

hep-ph↗
arXiv2000

Color transparency in deeply inelastic diffraction

We suggest a simple physical picture for the diffractive parton distributions that appear in diffractive deeply inelastic scattering. In this picture, partons impinging on the proton can have any transverse separation, but only when the separation is small can they penetrate the proton without breaking it up. By comparing the predictions from this picture with the diffractive data from HERA, we determine rough values for the small separations that dominate the diffraction process.

hep-ph↗
arXiv1999

Infrared divergences and non-lightlike eikonal lines in Sudakov processes

We propose a method to analyze infrared contributions to non-inclusive processes in QCD. We use the one-loop Sudakov form factor as a working example. Borrowing techniques from renormalization theory, we construct counterterms for the contributions from the soft and collinear regions, and we relate them to eikonal Wilson lines taken along non-lightlike directions.

hep-ph↗
arXiv1999

Diffractive parton distributions in light-cone QCD

We discuss recent theoretical results on diffractive deeply inelastic scattering, focusing on the partonic picture of diffraction in configuration space and the predictions for the beta behavior and the scaling violation.

hep-ph↗
arXiv1999

Hard scattering factorization and light cone hamiltonian approach to diffractive processes

We describe diffractive deeply inelastic scattering in terms of diffractive parton distributions. We investigate these distributions in a hamiltonian formulation that emphasizes the spacetime picture of diffraction scattering. For hadronic systems with small transverse size, diffraction occurs predominantly at short distances and the diffractive parton distributions can be studied by perturbative methods. For realistic, large-size systems we discuss the possibility that diffractive parton distributions are controlled essentially by semihard physics at a scale of nonperturbative origin of the order of a GeV. We find that this possibility accounts for two important qualitative aspects of the diffractive data from HERA: the flat behavior in beta and the delay in the fall-off with Q^2.

hep-ph↗
arXiv1998

Diffractive deeply inelastic scattering of hadronic states with small transverse size

Diffractive deeply inelastic scattering from a hadron is described in terms of diffractive quark and gluon distributions. If the transverse size of the hadronic state is sufficiently small, these distributions are calculable using perturbation theory. We present such a calculation and discuss the underlying dynamics. We comment on the relation between this dynamics and the pattern of scaling violation observed in the hard diffraction of large-size states at HERA.

hep-ph↗
arXiv1997

Virtual photon scattering at high energies as a probe of the short distance pomeron

Perturbative QCD predicts the behavior of scattering at high energies and fixed (sufficiently large) transferred momenta in terms of the BFKL pomeron (or short distance pomeron). We study the prospects for testing these predictions in two-photon processes at LEP200 and a possible future e+ e- collider. We argue that the total cross section for scattering two photons sufficiently far off shell provides a clean probe of BFKL dynamics. The photons act as color dipoles with small transverse size, so that the QCD interactions can be treated perturbatively. We analyze the properties of the QCD result and the possibility of testing them experimentally. We give an estimate of the rates expected and discuss the uncertainties of these results associated with the accuracy of the present theoretical calculations.

hep-ph↗
arXiv1997

Effective QCD coupling and power corrections to photon-photon scattering

The scattering of two off-shell photons is an infrared-safe process in QCD. For photon virtualities in the range of a few GeV, accessible at LEPII, power-behaved contributions to the total cross section may become non-negligible. Based on a dispersion relation for the running coupling, we discuss these contributions and calculate the coefficients of the leading power correction for transversely polarized and longitudinally polarized virtual photons.

hep-ph↗
arXiv1997

The photon spectrum in quarkonia decays

I discuss recent theoretical results for inclusive decays of quarkonia into a photon plus hadrons, and summarize the status of perturbative calculations.

hep-ph↗
arXiv1996

Structure Functions in Deep Inelastic Scattering at HERA

An introduction and summary is given of the main results achieved by working group 1: Structure Functions in Deep Inelastic Scattering at HERA. The prospects were discussed of future measurements of the structure functions $F_{2}, F_{L}, xG_{3}, F_{2}^{Q\overline{Q}}$ and $F_π$ at HERA. The results represent a long term programme of experimentation with high luminosity, different lepton beam charges, proton and deuteron beams, allowing for precision measurements. The theoretical investigations focussed on QED corrections, higher order QCD corrections for different observables, resummation of small $x$ contributions, and the detailed understanding of NLO QCD evolution codes, to allow for a high precision analysis of the forthcoming deep inelastic data.

hep-ph↗
arXiv1996

QCD

We discuss QCD studies that will be possible at LEP2. We examine both experimental and theoretical aspects of jets, fragmentation functions, multiplicities and particle spectra.

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arXiv1995

Resummed Predictions for the Structure Function F2 at Small x

We report the results of including resummed splitting functions in the QCD evolution equations at small x, and discuss the predictions that follow for the deep inelastic structure functions. *Contribution at XXX Rencontres de Moriond, Les Arcs, March 1995

hep-ph↗
arXiv1995

QCD Scaling Violation at Small x

We investigate the evolution of parton densities at small values of the momentum fraction, x, by including resummed anomalous dimensions in the renormalization group equations. The resummation takes into account the leading-logarithmic contributions (α_S \ln x)^k given by the BFKL equation and the next-to-leading-logarithmic corrections from quark evolution. We present numerical results for the parton densities and the deep inelastic structure function F_2.

hep-ph↗
arXiv1994

Next-to-Leading Corrections at Small X

We discuss the role of sub-leading corrections to deep inelastic processes in the small-x regime, and report recent results on the calculation of coefficient functions and quark anomalous dimensions. *To appear in the proceedings of the workshop QCD94, Montpellier, July '94.

hep-ph↗