Searcharxiv⌕ Search

arXiv subjects

P. Kroll

Publications and source records attributed to P. Kroll.

At least 55 records · Page 3Linked to original sources
arXiv2008

The target asymmetry in hard vector-meson electroproduction and parton angular momenta

The target asymmetry for electroproduction of vector mesons is investigated within the handbag approach. While the generalized parton distribution (GPD) H is taken from a previous analysis of the elctroproduction cross section, we here construct the GPD E from double distributions and constrain it by the Pauli form factors of the nucleon, positivity bounds and sum rules. Predictions for the target asymmetry are given for various vector mesons and discussed how experimental data on the asymmetry will further constrain E and what we may learn about the angular momenta the partons carry.

hep-ph↗
arXiv2008

Hard electroproduction of vector mesons

It is reported on a global analysis of hard vector-meson electroproduction which is based on the handbag factorization. The generalized parton distributions are constructed from their forward limits with the help of double distributions and the partonic subprocesses are calculated within the modified perturbative approach.

hep-ph↗
arXiv2008

Form factors and other measures of strangeness in the nucleon

We discuss the phenomenology of strange-quark dynamics in the nucleon, based on experimental and theoretical results for electroweak form factors and for parton densities. In particular, we construct a model for the generalized parton distribution that relates the asymmetry s(x)-sbar(x) between the longitudinal momentum distributions of strange quarks and antiquarks with the form factor F1^s(t), which describes the distribution of strangeness in transverse position space.

hep-ph↗
arXiv2007

Discovery of The New WZ Sge Star, SDSS J080434.20+510349.2

We present the results of photometric observations of SDSS J080434.20+510349.2 in its low state and during an outburst and spectroscopy during the outburst. We found such peculiarities as a long-term outburst with amplitude probably not less than 6m, rarity of the outbursts, eleven rebrightenings, and a short (0.059713(7) d) superhump period. We conclude that this star belongs to the WZ Sge-type subclass of cataclysmic variables. The spectrum shows both emission and absorption lines of H and He superimposed on the blue continuum. We also found 8 -- 9 min. brightness variations during the end of the super-outburst plateau that could be related to pulsations of the white dwarf in the binary.

astro-ph↗
arXiv2007

The role of the quark and gluon GPDs in hard vector-meson electroproduction

Electroproduction of light vector mesons is analyzed on the basis of handbag factorization. The required generalized parton distributions are constructed from the CTEQ6 parton distributions with the help of double distributions. The partonic subprocesses are calculated within the modified perturbative approach. The present work extends our previous analysis of the longitudinal cross section to the transverse one and other observables related to both the corresponding amplitudes. Our results are compared to recent experimental findings in detail.

hep-ph↗
arXiv2007

Electroproduction of longitudinally polarized vector mesons

It is reported on an analysis of electroproduction of light vector mesons at small Bjorken-x within the handbag approach. The partonic subprocesses, meson electroproduction off quarks or gluons, are calculated within the modified perturbative approach in which quark transverse momenta are retained. The soft hadronic matrix elements, generalized parton distributions, are constructed from the CTEQ6 parton distribution functions by means of double distributions. The cross sections for longitudinal polarized virtual photons evaluated from this approach, are in very good agreement with experiment in a wide range of kinematics. Talk presented at the DIS2007 conference, Munich (2007)

hep-ph↗
arXiv2006

GPDs, the structure of the proton and wide-angle Compton scattering

Results from a recent analysis of the zero-skewness generalized parton distributions (GPDs) for valence quarks are reviewed. The analysis bases on a physically motivated parameterization of the GPDs with a few free parameters adjusted to the nucleon form factor data. Results for the GPDs are presented and a number of applications such as moments, Ji's sum rule or their impact parameter representation are discussed. The 1/x moments, in particular, form the soft physics input to Compton scattering off protons within the handbag approach. The Compton cross section evaluated from this information is found to be in good agreement with experiment.

hep-ph↗
arXiv2006

The longitudinal cross section of vector meson electroproduction

We analyze electroproduction of light vector mesons (V=rho, phi and omega) at small Bjorken-x in the handbag approach in which the process factorizes into general parton distributions and partonic subprocesses. The latter are calculated in the modified perturbative approach where the transverse momenta of the quark and antiquark forming the vector meson are retained and Sudakov suppressions are taken into account. Modeling the generalized parton distributions through double distributions and using simple Gaussian wavefunctions for the vector mesons, we compute the longitudinal cross sections at large photon virtualities. The results are in fair agreement with the findings of recent experiments performed at HERA and HERMES.

hep-ph↗
arXiv2005

Generalized parton distributions from nucleon form factors

Results from a recent analysis of the zero-skewness generalized parton distributions (GPDs) for valence quarks are reviewed. The analysis bases on a physically motivated parameterization of the GPDs with a few free parameters adjusted to the nucleon form factor data. The Fourier transforms of the GPDs representing quark densities in the impact parameter plane, as well as moments of the GPDs are also discussed. The 1/x moments in particular form the soft physics input to Compton scattering off protons within the handbag approach. The Compton cross section evaluated from this information is found to be in good agreement with experiment.

hep-ph↗
arXiv2005

Phi meson electroproduction at small Bjorken-x

It is reported on an analysis of Phi-meson electroproduction at small Bjorken-x within the handbag approach. The amplitudes factorize into generalized parton distributions and a partonic subprocess, electroproduction off gluons. Cross sections and spin density matrix elements are evaluated for Phi-meson electroproduction and found to be in fair agreement with recent HERA data.

hep-ph↗
arXiv2005

Isospin symmetry breaking through pi^0 - eta -eta' mixing

Mixing of the pseudoscalar mesons is discussed in the quark-flavor basis. The divergences of the axial vector currents which embody the axial vector anomaly, combined with the assumption that the decay constants follow the pattern of particle state mixing in that basis, determine the mixing parameters for given masses of the physical mesons. These mixing parameters are compared in some detail with results from other work. Phenomenological applications of the quark-flavor mixing scheme are presented with particular interest focussed on isospin symmetry breaking which is generated by means of eta and eta' admixtures to the pion. Consequences of a possible difference in the basis decay constants f_u and f_d for the strength of isospin symmetry breaking are also examined.

hep-ph↗
arXiv2005

Heavy Quarkonium Physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

hep-ph↗
arXiv2005

Deeply virtual vector meson electroproduction at small Bjorken-x

It is reported on an analysis of vector meson electroproduction at small Bjorken-x within the handbag approach. Using a model for the generalized parton distribution and calculating the partonic subprocess, electroproduction off gluons, within the modified perturbative approach, cross sections and spin density matrix elements are evaluated. The numerical results agree fairly well with recent HERA data.

hep-ph↗
arXiv2005

Vector meson electroproduction at small Bjorken-x and generalized parton distributions

We analyze electroproduction of light vector mesons at small Bjorken-x in an approach that includes the gluonic generalized parton distributions and a partonic subprocess, gamma g --> (q q-bar) g, q q-bar --> V. The subprocess is calculated to lowest order of perturbative QCD taking into account the transverse momenta of the quark and antiquark as well as Sudakov suppressions. Our approach allows to investigate the transition amplitudes for all kind of polarized virtual photons and polarized vector mesons. Modelling the generalized parton distributions through double distributions and using simple Gaussian wavefunctions for the vector mesons, we compute the longitudinal and transverse cross sections at large photon virtualities as well as the spin density matrix elements for the vector mesons. Our results are in fair agreement with the findings of recent experiments performed at HERA.

hep-ph↗
arXiv2005

The process p + pbar --> gamma + pi^0 within the handbag approch

We analyse the exclusive channel $p\pb\toγπ^0$, assuming handbag dominance. The soft parts are parametrized in terms of CGLN amplitudes for the $q\qb\toγπ^0$ transition and form factors for the $p\pb\to q\qb$ ones, the latter represent moments of Generalized Distribution Amplitudes. We present a combined fit to Fermilab data from E760 taking simultaneously into account information from other exclusive reactions, especially from $p\pb\to γγ$ data. Overall a nicely consistent picture emerges, such that one can hope, that our theoretical analysis will be reliable also for the kinematics of GSI/FAIR, which hopefully will provide much more precise and complete data. Consequently, data from this facility should improve our knowledge both on the proton-antiproton distribution amplitudes and the pion production mechanism.

hep-ph↗
arXiv2004

Generalized perton distributions: analysis and applications

Results from a recent analysis of the zero-skewness generalized parton distributions (GPDs) for valence quarks are discussed. The analysis bases on a physically motivated parameterization of the GPDs with a few free parameters adjusted to the available nucleon form factor data. Various moments of the GPDs as well as their Fourier transfroms, the quark densities in the impact parameter plane, are also presented. The 1/x moments of the zero-skewness GPDs are form factors specific to Compton scattering off protons within the handbag approach. The results of the GPD analysis enables one to predict Compton scattering.

hep-ph↗