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H. Holtmann

Publications and source records attributed to H. Holtmann.

6 recordsLinked to original sources
arXiv1996

How to measure the pion structure function at HERA

We suggest a method of determination of the pion structure function down to x \simeq 10^{-4} based on semi-exclusive deep inelastic scattering off protons. The idea is to exploit the nonperturbative πN$ and πΔFock components of the nucleon, which contribute significantly to deep inelastic scattering and dominate the fragmentation of protons into fast neutrons and deltas. The intrinsic factorization properties of the semi-exclusive cross section give a good test for the validity of this approach.

hep-ph↗
arXiv1996

Testing the meson cloud in the nucleon in Drell-Yan processes

We discuss the present status of the \bar u-\bar d asymmetry in the nucleon and analize the quantities which are best suited to verify the asymmetry. We find that the Drell-Yan asymmetry is the quantity insensitive to the valence quark distributions and very sensitive to the flavour asymmetry of the sea. We compare the prediction of the meson cloud model with different experimental data including the Fermilab E772 data and recent data of the NA51 Collaboration at CERN and make predictions for the planned Drell-Yan experiments.

hep-ph↗
arXiv1996

Flavour and Spin of the Proton and the Meson Cloud

We present a complete set of formulas for longitudinal momentum distribution functions (splitting functions) of mesons in the nucleon. It can be applied in the framework of convolution formalism to the deep-inelastic structure functions (quark distributions) of the nucleon viewed as a system composed of virtual 'mesons' and 'baryons'. Pseudoscalar and vector mesons as well as octet and decuplet baryons are included. In contrast to many approaches in the literature the present approach ensures charge and momentum conservation by the construction. We present not only spin averaged splitting functions but also helicity dependent ones, which can be used to study the spin content of the nucleon. The cut-off parameters of the underlying form factors for different vertices are determined from high-energy particle production data. This information allows one to calculate the flavour and spin content of the nucleon. The value of the Gottfried Sum Rule obtained from our model (S_G = 0.224) nicely agrees with that obtained by the NMC. In addition, we calculate the x-dependence of the \bar d - \bar u asymmetry and get an impressive agreement with a recent fit of Martin-Stirling-Roberts. The calculated axial coupling constants for semileptonic decays of the octet baryons agree with the experimental data already with SU(6) wave function for the bare nucleon. Although we get improvements for the Ellis-Jaffe Sum Rules for the proton and neutron in comparison to the naive quark model, the MCM is not sufficient to reproduce the experimental data.

hep-ph↗
arXiv1995

Mesonic Corrections to the Shape of Quark Distributions

We compute the full x - dependence of the proton and neutron spin structure functions in the MIT bag model, including the effect of gluon exchange and the meson cloud. Impressive agreement is found for x larger than 0.1, where polarised gluons are not expected to play a significant role.

hep-ph↗
arXiv1995

On the determination of double diffraction dissociation cross section at HERA

The excitation of the proton into undetected multiparticle states (double diffraction dissociation) is an important background to single diffractive deep-inelastic processes $ep \rightarrow e'p'ρ^{0}, ~e'p'J/Ψ, ~e'p'X$ at HERA. We present estimates of the admixture of the double diffraction dissociation events in all diffractive events. We find that in the $J/Ψ$ photoproduction, electroproduction of the $ρ^0$ at large $Q^2$ and diffraction dissociation of real and virtual photons into high mass states $X$ the contamination of the double diffraction dissociation can be as large as $\sim 30\%$, thus affecting substantially the experimental tests of the pomeron exchange in deep inelastic scattering at HERA. We discuss a possibility of tagging the double diffraction dissociation by neutrons observed in the forward neutron calorimeter. We present evaluations of the spectra of neutrons and efficiency of neutron tagging based on the experimental data for diffractive processes in the proton-proton collisions.

hep-ph↗