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W. -D. Nowak

Publications and source records attributed to W. -D. Nowak.

44 records · Page 3Linked to original sources
arXiv2000

Single-spin Azimuthal Asymmetries in the ``Reduced Twist-3 Approximation''

We consider the single-spin azimuthal asymmetries recently measured at the HERMES experiment for charged pions produced in semi-inclusive deep inelastic scattering of leptons off longitudinally polarized protons. Guided by the experimental results and assuming a vanishing twist-2 transverse quark spin distribution in the longitudinally polarized nucleon, denoted as ``reduced twist-3 approximation'', a self-consistent description of the observed single-spin asymmetries is obtained. In addition, predictions are given for the z dependence of the single target-spin asymmetry.

hep-ph↗
arXiv1999

The Physics Case for Polarised Proton-Nucleon Scattering at HERA

The physics case for a possible fixed target polarized nucleon-nucleon collision experiment at HERA is described. The experiment named HERA-N could be realized using an internal polarized gas target in the HERA polarized/unpolarized proton beam. A wide spectrum of nucleon spin structure problems could be investigated and the experiment would constitute a fixed target complement to the RHIC spin physics program with competitive statistical accuracy.

hep-ph↗
arXiv1997

A Possible Fixed Target Programme for the Polarized HERA Proton Ring

The physics programme for a possible fixed target polarized nucleon-nucleon collision experiment aiming at studying the nucleon spin structure at HERA is described. The experiment named HERA-N could be realized using an internal polarized gas target in the HERA polarized/unpolarized proton beam. Single spin asymmetry measurements could provide unique information on higher twist contributions. Once the HERA proton beam is polarized measurements of the polarized gluon distribution using double longitudinal spin asymmetries in both photon and J/psi production appear possible. A study of the Drell-Yan process for different relative orientation of beam and target polarization can provide information on a variety of still not or badly measured polarized structure functions. The experiment would constitute a fixed target complement to the RHIC spin physics program with competitive statistical accuracy.

hep-ph↗
arXiv1997

Double Spin Asymmetries in Charmonium Hadroproduction at HERA-$\vec N$

We discuss the double spin asymmetries in charmonium hadroproduction with nonzero transverse momenta at fixed target energies, $\sqrt{s}\simeq40$ GeV, within the framework of the factorization approach. It is shown that the color octet contribution is dominant in the asymmetries. The size of the asymmetries and the projected statistical errors in a future option of HERA with longitudinally polarized protons scattering off a polarized target (HERA-$\vec N$) should allow to distinguish between different parametrizations for the polarized gluon distribution in the proton.

hep-ph↗
arXiv1997

Summary of Physics Prospects for Polarized Nucleon-Nucleon Scattering at HERA-N

The physics scope of polarized nucleon-nucleon collisions originating from an internal polarized target in the HERA proton beam is summarized. Based on 240 pb^{-1} integrated luminosity at 40 GeV c.m. energy, statistical sensitivities are given over a wide (x_F, p_T)-range for a variety of inclusive and exclusive final states. By measuring single spin asymmetries unique information can be obtained on higher twist contributions and their p_T-dependence. From double spin asymmetries in both photon and J/psi production it appears possible to measure the polarized gluon distribution in the range 0.1 < x_{gluon} < 0.4 with a good statistical accuracy. Drell-Yan pair production asymmetries in doubly longitudinal mode, measurable in the mass range 3-10 GeV, allow discrimination between different parametrizations of the polarized light sea quark distributions. In doubly transverse mode access to the quark transversity distribution might become possible. Statistically significant results can be expected in the elastic channel.

hep-ph↗
arXiv1996

On a Possibility to Determine the Sign of the Polarized Gluon Distribution

We investigate the possibility to draw conclusions on the sign of the spin-dependent gluon distribution, $ΔG(x, Q^2)$, from existing polarized DIS data. The spin-dependent parton distributions $Δu_v, Δd_v, Δ{\bar u}, Δ{\bar d}, Δ{s}$, and $ΔG$ are constructed in the framework of a phenomenological procedure taking into account some assumptions on signs of valence and sea parton distributions motivated by 't Hooft's mechanism of quark-quark interaction induced by instantons. The axial gluon anomaly and data on integral quark contributions to the proton spin, $Δ\tilde u, Δ\tilde d$, and $Δ\tilde s$, are also taken into account. Predictions for the $x$- and $Q^2$-dependencies of the polarized proton and neutron structure functions, $g_1^p$ and $g_1^n$, are compared to experimental data. It is shown that the neutron structure function, $g_1^n$, is especially sensitive to the sign of $ΔG(x, Q^2)$. The results of our analysis supports the conclusion that this sign should be positive.

hep-ph↗
arXiv1996

On the Physics Potential of Polarized Nucleon-Nucleon Collisions at HERA

The physics of polarized nucleon--nucleon collisions originating from an internal polarized target in the HERA proton beam is investigated. Based on 240 pb^-1 integrated luminosity at 40 GeV c.m. energy, statistical sensitivities are given over a wide (x_F, p_T) range for a variety of inclusive and exclusive final states. By measuring single spin asymmetries unique information can be obtained on higher twist contributions and their p_T-dependence. From double spin asymmetries in both photon and J/psi production it appears possible to measure the polarized gluon distribution in the range 0.1<x_gluon<0.4 with a good statistical accuracy.

hep-ph↗