Publications (120)
A perturbative approach to decays into two mesons
M. Dahm, R. Jakob, P. Kroll
The modified perturbative approach in which transverse degrees of freedom as well as Sudakov suppressions are taken into account, is applied to decays into two mesons. The…
Linking Parton Distributions to Form Factors and Compton Scattering
M. Diehl, T. Feldmann, R. Jakob +1
We relate ordinary and skewed parton distributions to soft overlap contributions to elastic form factors and large angle Compton scattering, using light-cone wave functions in a Fo…
Workshop on High-Intensity Photon Sources (HIPS2017) Mini-Proceedings
S. Ali, L. Allison, M. Amaryan +39
This workshop aimed at producing an optimized photon source concept with potential increase of scientific output at Jefferson Lab, and at refining the science for hadron physics ex…
Generalized parton distributions at large momentum transfer
P. Kroll
The role of generalized parton distributions in wide-angle exclusive reactions will be discussed. In contrast to deep virtual exclusive reactions the wide angle processes offer the…
GSC 4232.2830, an Eclipsing Binary with Elliptical Orbit
V. P. Goranskij, S. Yu. Shugarov, P. Kroll +1
The discovery of an Algol type eclipsing variable star having highly elliptical orbit with the period of 11.628 day is reported.
Generalized parton distributions from nucleon form factor data
M. Diehl, Th. Feldmann, R. Jakob +1
We present a simple empirical parameterization of the x- and t-dependence of generalized parton distributions at zero skewness, using forward parton distributions as input. A fit t…
Gamma-Gamma Physics at LEP2
P. Aurenche, G. A. Schuler, A. Bawa +41
This report is an overview of the gamma-gamma physics capabilities of LEP2, and covers the following topics: structure functions, equivalent photon approximation, tagging condition…
Nucleon and nuclear structure through dilepton production
I. V. Anikin, N. Batzell, M. Boer +29
Transverse momentum distributions and generalized parton distributions provide a comprehensive framework for the three-dimensional imaging of the nucleon and the nucleus experiment…
The transition of virtual photons into pseudoscalar mesons
P. Kroll
The possibility to constrain the meson distribution amplitude from the transitions of virtual photons to pseudoscalar mesons is investigated. It is shown that for a large range in…
Gluons and the quark sea at high energies: distributions, polarization, tomography
D. Boer, M. Diehl, R. Milner +186
This report is based on a ten-week program on "Gluons and the quark sea at high-energies", which took place at the Institute for Nuclear Theory in Seattle in Fall 2010. The princip…
High spectral and time resolution observations of the eclipsing polar RX J0719.2+6557
G. H. Tovmassian, P. Szkody, J. Greiner +7
We present phase-resolved spectral and multicolor CCD-photometric observations of the eclipsing polar RX J0719.2+6557 obtained with relatively high time (~600 sec/15 sec) and spect…
The handbag mechanism in wide-angle exclusive reactions
P. Kroll
The handbag mechanism for wide-angle exclusive scattering reactions is discussed and compared with other theoretical approaches. Its application to Compton scattering, meson photop…
within a Handbag Picture -- Cross Section and Spin Observables
A. T. Goritschnig, P. Kroll, W. Schweiger
We study the process within the generalized parton picture. Our starting point is the double handbag diagram which factorizes into soft generalized par…
Status of DVMP, DVCS and GPDs
P. Kroll
The analysis of exclusive meson leptoproduction (DVMP) within the handbag approach is reviewed and the parametrization of the generalized parton distributions (GPDs) is discussed i…
The process p + pbar --> gamma + pi^0 within the handbag approch
P. Kroll, A. Schafer
We analyse the exclusive channel $p\pb\toγÏ^0$, assuming handbag dominance. The soft parts are parametrized in terms of CGLN amplitudes for the $q\qb\toγÏ^0$ transition and for…
Spin effects in hard exclusive electroproduction of mesons
P. Kroll
In this talk various spin effects in hard exclusive electroproduction of mesons are briefly reviewed. The data are discussed in the light of recent theoretical calculations within…
Large momentum transfer electroproduction of mesons
H. W. Huang, P. Kroll
Assuming the proton's light-cone wave function to be dominated by small parton virtualities and small intrinsic transverse momenta, we show that the electroproduction amplitudes at…
The annihilation of virtual photons into pseudoscalar mesons
M. Diehl, P. Kroll, C. Vogt
We investigate the possibility to constrain the pion distribution amplitude from the gamma* gamma* -> pi transition. For a surprisingly large range in the two photon virtualities w…
Generalized parton distributions from meson leptoproduction
P. Kroll
Generalized parton distributions (GPDs) extracted from exclusive meson leptoproduction within the handbag approach are briefly reviewed. Only the GPD E is discussed in some detail.…
A study of photometric errors on two different photographic plate scans
M. Spasovic, C. Dersch, A. Schrimpf +1
A considerable number of photographic plate archives exist world wide and digitization is in progress or already has been finished. Not only different type of scanners were used bu…
Spin density matrix elements in vector meson leptoproduction
S. V. Goloskokov, P. Kroll
It is reported on an analysis of vector meson leptoproduction at small Bjorken- and large photon virtuality within an approach that bases on generalized parton distributions (GP…
A New Cataclysmic Variable RX J0757.0+6306: Candidate for the Shortest Period Intermediate Polar
G. H. Tovmassian, J. Greiner, P. Kroll +8
A new cataclysmic variable is identified as the optical counterpart of the faint and hard X-ray source RX J0757.0+6306 discovered during the ROSAT all-sky survey. Strong double-pea…
Mixing and Decay Constants of Pseudoscalar Mesons
T. Feldmann, P. Kroll, B. Stech
We propose a new eta-eta' mixing scheme where we start from the quark flavor basis and assume that the decay constants in that basis follow the pattern of particle state mixing. On…
Large Exclusive Processes:RECENT Developments
P. Kroll
Recent improvements of the hard scattering picture for exclusive reactions, namely the inclusion of both Sudakov corrections and the intrinsic transverse momentum dependence of the…
Transversity in exclusive electroproduction of pseudoscalar mesons
P. Kroll
In this talk it is reported on an analysis of hard exclusive electroproduction of pseudoscalar mesons within the handbag approach. It is argued that recent measurements of pion ele…
A modern view of wide-angle exclusive scattering
P. Kroll
The basic theoretical ideas of the handbag mechanism for wide-angle exclusive scattering reactions are discussed and, with regard to the present experimental program carried out at…
Probing moments of baryon-antibaryon generalized parton distributions at BELLE and FAIR
P. Kroll, A. Schaefer
We analyze the time-like processes gamma gamma -> B Bbar and p p-bar -> gamma M at large Mandelstam variables within the handbag approach for which the process amplitudes factorize…
Diquark model predictions for photon induced exclusive reactions
P. Kroll
The present status of the diquark model for exclusive reactions at moderately large momentum transfer is reviewed. That model is a variant of the Brodsky-Lepage approach in which d…
Mixing of pseudoscalar mesons and isospin symmetry breaking
P. Kroll
Mixing of the pseudoscalar mesons is discussed in the quark-flavor basis with the hypothesis that the basis decay constants follow the pattern of particle state mixing. The diverge…
Spin effects in hard exclusive reactions
P. Kroll
The present status of applications of perturbative QCD to large momentum transfer exclusive reactions is discussed. It is argued that in the region of momentum transfer accessible…
RX J0719.2+6557: A new eclipsing polar
G. H. Tovmassian, J. Greiner, F. -J. Zickgraf +5
A new magnetic cataclysmic variable is identified as the counterpart of the X-ray source RX J0719.2+6557. The emission lines show radial velocity variations with a period of 98.2 m…
Deeply Virtual Meson Production on the nucleon
L. Favart, M. Guidal, T. Horn +1
We review the status of the data and phenomenology in the Generalized Parton Distribution approach of Deep Virtual Meson Production.
Twist-3 contributions to wide-angle photoproduction of pions
P. Kroll, K. Passek-Kumericki
We investigate wide-angle pi^0 photoproduction within the handbag approach to twist-3 accuracy. In contrast to earlier work both the 2-particle as well as the 3-particle twist-3 co…
Generalized parton distributions and wide-angle exclusive scattering
P. Kroll
The handbag mechanism for wide-angle exlusive scattering reactions is discussed and compared with other theoretical approaches. Its application to Compton scattering, meson photopr…
Virtual Compton Scattering Off Protons at Moderately Large Momentum Transfer
P. Kroll, M. Schürmann, P. A. M. Guichon
The amplitudes for virtual Compton scattering off protons are calculated within the framework of the diquark model in which protons are viewed as being built up by quarks and diqua…
Implications of light-quark admixtures on charmonium decays into meson pairs
Th. Feldmann, P. Kroll
We argue that charmonium decays into meson pairs fall into two distinct classes: one that is under control of perturbative QCD and another one that is governed by a soft mechanism.…
The form factors for the photon to pseudoscalar meson transitions - an update
P. Kroll
The form factors for the transitions pi-photon, eta-photon, eta'-photon and etac-photon are analyzed within the modified perturbative approach in which quark transverse degrees of…
Form factors and other measures of strangeness in the nucleon
M. Diehl, Th. Feldmann, P. Kroll
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 parti…
GPDs, form factors and Compton scattering
P. Kroll
The basic theoretical ideas of the handbag factorization and its application to wide-angle scattering reactions are reviewed. With regard to the present experimental program carrie…
Skewed parton distributions for B->pi transitions
Th. Feldmann, P. Kroll
We investigate the b-u skewed parton distributions (SPDs) for B->pi transitions and determine the contributions from several sources (overlaps of soft light-cone wave functions, qu…
Exclusive pion electroproduction and transversity
P. Kroll
In this talk it is reported on an analysis of hard exclusive pion electroproduction within the handbag approach. Particular emphasis is laid on single-spin asymmetries. It is argue…
Heavy Baryon Transitions in a Relativistic Three-Quark Model
M. A. Ivanov, J. G. Korner, P. Kroll +1
Exclusive semileptonic decays of bottom and charm baryons are considered within a relativistic three-quark model with a Gaussian shape for the baryon-three-quark vertex and standar…
Colour Octet Contribution in Exclusive Charmonium Decay into Baryon-Antibaryon
P. Kroll, S. M. H. Wong
It is argued that colour octet contribution in exclusive charmonium decays is very important even though the same infrared divergence found in P-wave colour singlet inclusive decay…
Meson-Photon Transition Form Factors
R. Jakob, P. Kroll, M. Raulfs
We report results on the - transition form factor obtained within the hard scattering approach including transverse momentum effects and Sudakov corrections. The results cl…
Hard exclusive processes involving kaons
P. Kroll
Hard exclusive electroproduction of kaons as well as the kaon-induced exclusive Drell-Yan process are investigated within the handbag approach which is based on factorization in ha…
Spin effects in high-energy proton-proton scattering within a diquark model
S. V. Goloskokov, P. Kroll
We study scattering at high energies and moderately large momentum transfer, using a model in which the proton is viewed as being composed of a quark and a diquark. We show th…
Wide-angle pion-Delta(1232) photoproduction
P. Kroll
High-energy wide-angle photoproduction of pion-Delta final states is investigated within the handbag mechanism to twist-3 accuracy. In this approach the process amplitudes factoriz…
The role of the quark and gluon GPDs in hard vector-meson electroproduction
S. V. Goloskokov, P. Kroll
Electroproduction of light vector mesons is analyzed on the basis of handbag factorization. The required generalized parton distributions are constructed from the CTEQ6 parton dist…
Octet-Baryon Form Factors in the Diquark Model
R. Jakob, P. Kroll, M. Schuermann +1
We present an alternative parameterization of the quark-diquark model of baryons which particularly takes care of the most recent proton electric form-factor data from the E136 exp…
An attempt to understand exclusive pi+ electroproduction
S. V. Goloskokov, P. Kroll
Hard exclusive pi+ electroproduction is investigated within the handbag approach. The prominent role of the pion-pole contribution is demonstrated. It is also shown that the experi…
The Overlap Representation of Skewed Quark and Gluon Distributions
M. Diehl, Th. Feldmann, R. Jakob +1
Within the framework of light-cone quantisation we derive the complete and exact overlap representation of skewed parton distributions for unpolarised and polarised quarks and gluo…
Transversity in exclusive vector-meson leptoproduction
S. V. Goloskokov, P. Kroll
The role of transversity or helicity-flip generalized parton distributions (GPDs) in leptoproduction of vector mesons is investigated within the framework of the handbag approach.…
The gluon contents of the eta and eta' mesons
P. Kroll
It is reported on a leading-twist analysis of the eta - photon and eta' - photon transition form factors. The analysis allows for an estimate of the lowest Gegenbauer coefficients…
Historical light curve of the black hole binary V4641 Sgr based on the Moscow and Sonneberg plate archives
E. A. Barsukova, V. P. Goranskij, P. Kroll
We performed digital processing of a large set of photographic plates for X-ray binary system V4641 Sgr containing a black hole. A total of 277 plates were found in archives dated…
Deeply virtual vector meson electroproduction at small Bjorken-x
P. Kroll
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 calculatin…
RX J0719.2+6557: A New Eclipsing Polar
G. Tovmassian, J. Greiner, F. -J. Zickgraf +4
A new magnetic, eclipsing cataclysmic variable is identified as the counterpart of the X-ray source RX J0719.2+6557 detected during the ROSAT all-sky survey. The relative phasing o…
Isospin symmetry breaking through pi^0 - eta -eta' mixing
P. Kroll
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 assu…
Extraction of beam-spin asymmetries from the hard exclusive channel off protons in a wide range of kinematics
S. Diehl, K. Joo, A. Kim +135
We have measured beam-spin asymmetries to extract the moment from the hard exclusive reaction above the resonance region,…
The pion pole in hard exclusive vector-meson leptoproduction
S. V. Goloskokov, P. Kroll
Exploiting a set of generalized parton distributions (GPDs) derived from analyses of hard exclusive leptoproduction of rho0, phi and pi+ mesons, we investigate the omega spin densi…
GPDs, the structure of the proton and wide-angle Compton scattering
P. Kroll
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 parameteri…
Leptoproduction of Vector Mesons at Small $\xbj$ and Generalized Parton Distributions
S. V. Goloskokov, P. Kroll, B. Postler
Deep virtual vector meson leptoproduction at small $\xbj$ is analyzed in the framework of generalized parton distributions. It is shown that the inclusion of transverse degrees of…
The longitudinal cross section of vector meson electroproduction
S. V. Goloskokov, P. Kroll
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 distributi…
Ratios of helicity amplitudes for exclusive electroproduction on transversely polarized protons
The HERMES Collaboration, A. Airapetian, N. Akopov +74
Exclusive -meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarize…
The pion form factor: Sudakov suppressions and intrinsic transverse momentum
R. Jakob, P. Kroll
It is demonstrated that any attempt to calculate the perturbative QCD contribution to the pion form factor requires the inclusion of intrinsic transverse momentum besides Sudakov f…
Phi meson electroproduction at small Bjorken-x
P. Kroll
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 pa…
Generalized perton distributions: analysis and applications
P. Kroll
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 parameter…
The perturbative limit of the two-pion distribution amplitude
M. Diehl, Th. Feldmann, P. Kroll +1
We consider pion pair production in two-photon collisions, gamma* gamma -> pi+ pi-, at large photon virtuality Q^2 and center-of-mass energy \sqrt{s} in the hard-scattering picture…
Colour-octet contributions to exclusive charmonium decays
J. Bolz, P. Kroll, G. A. Schuler
We investigate the theoretical uncertainties of -wave charmonium decays into two pions, , . Constraining the pion distribution-amplitude…
Skewed Parton Distributions in Real and Virtual Compton Scattering
M. Diehl, T. Feldmann, R. Jakob +1
The handbag contribution to Compton scattering at moderately large momentum transfer factorises into parton-photon subprocess amplitudes and new form factors representing 1/x-momen…
Transversity in hard exclusive electroproduction of pseudoscalar mesons
S. V. Goloskokov, P. Kroll
Estimates for electroproduction of pseudoscalar mesons at small values of skewness are presented. Cross sections and asymmetries for these processes are calculated within the handb…
Exclusive Photoproduction of Large Momentum-Transfer K and K* Mesons
P. Kroll, M. Schuermann, K. Passek +1
The reactions gamma p -> K+ Lambda and gamma p -> K* Lambda are analyzed within perturbative QCD, allowing for diquarks as quasi-elementary constituents of baryons. The diquark-mod…
A set of generalized parton distributions
P. Kroll
The information about generalized parton distributions (GPDs) extracted from exclusive meson leptoproduction within the handbag approach is summarized. Details are only discussed f…
within the generalized parton picture - first results
A. T. Goritschnig, P. Kroll, W. Schweiger
We study proton-antiproton annihilation into pairs within the generalized parton picture. Our starting point is the double handbag diagram which is shown to factori…
The progenitor and remnant of the helium nova V445 Puppis
V. P. Goranskij, S. Yu. Shugarov, A. V. Zharova +2
V445 Pup was a peculiar nova with no hydrogen spectral lines during the outburst. The spectrum contained strong emission lines of carbon, oxygen, calcium, sodium, and iron. We have…
Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction
I. G. Aznauryan, A. Bashir, V. Braun +24
Studies of the structure of excited baryons are key to the N* program at Jefferson Lab. Within the first year of data taking with the Hall B CLAS12 detector following the 12 GeV up…
What did we learn about GPDs from hard exclusive electroproduction of mesons?
P. Kroll
It is reported on an analysis of electroproduction of light mesons at small Bjorken-x within the handbag approach. The partonic subprocesses, meson electroproduction off quarks or…
Perturbative and non-perturbative QCD corrections to wide-angle Compton scattering
H. W. Huang, P. Kroll, T. Morii
We investigate corrections to the handbag approach for wide-angle Compton scattering off protons at moderately large momentum transfer: the photon-parton subprocess is calculated t…
Lepton-pair production in hard exclusive hadron-hadron collisions
S. V. Goloskokov, P. Kroll, O. Teryaev
We investigate lepton-pair production in hard exclusive hadron-hadron collisions. We consider a double handbag (DH) mechanism in which the process amplitude factorizes in hard subp…
Mixing of Pseudoscalar Mesons
Th. Feldmann, P. Kroll
Eta-eta' mixing is discussed in the quark-flavor basis with the hypothesis that the decay constants follow the pattern of particle state mixing. On exploiting the divergences of th…
Intrinsic Transverse Size Effect
J. Bolz, R. Jakob, P. Kroll +2
Two recently proposed concepts to improve the perturbative calculation of exclusive amplitudes, gluonic radiative corrections (Sudakov factor) and confinement size effects (intrins…
The target asymmetry in hard vector-meson electroproduction and parton angular momenta
S. V. Goloskokov, P. Kroll
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…
The path to Z And-type outbursts: The case of V426 Sagittae (HBHA 1704-05)
A. Skopal, S. Yu. Shugarov, U. Munari +16
The star V426 Sge (HBHA~1704-05), originally classified as an emission-line object and a semi-regular variable, brightened at the beginning of August 2018, showing signatures of a…
The transition form factor and the pion wave function
P. Kroll, M. Raulfs
The pion wave function is discussed in the light of the recent CLEO data on the pion gamma transition form factor. It turns out that the wave function is close to the asymptotic fo…
S 10943 Vulpeculae: A New ROSAT Selected Dwarf Nova, probably of SU Ursae Majoris Subclass
G. A. Richter, J. Greiner, P. Kroll
We have identified the ROSAT all-sky survey source RX J1953.1+2115 with a newly discovered dwarf novae (named S 10943 Vulpeculae) with a recurrence time of 83.6 days. With the expe…
Some comments on the handbag approach to wide-angle exclusive scattering
P. Kroll
The handbag mechanism for wide-angle exclusive scattering reactions is discussed and compared to other theoretical approaches. The role of power laws in observables is critically e…
Transversity in exclusive meson electroproduction
P. Kroll
In this talk various spin effects in hard exclusive electroproduction of mesons are briefly reviewed and the data discussed in the light of recent theoretical calculations within t…
Modelling the nucleon wave function from soft and hard processes
J. Bolz, P. Kroll
Current light-cone wave functions for the nucleon are unsatisfactory since they are in conflict with the data of the nucleon's Dirac form factor at large momentum transfer. Therefo…
Infinite Momentum Frame Calculation of Semileptonic Heavy Î_b\toÎ_c Transitions Including HQET Improvements
B. König, J. G. Körner, M. Krämer +1
We calculate the transition form factors that occur in heavy -type baryon semileptonic decays as e.g. in . We use Bauer-Stech-Wirbe…
The GPD H-tilde and spin correlations in wide-angle Compton scattering
P. Kroll
Wide-angle Compton scattering (WACS) is discussed within the handbag approach in which the amplitudes are given by products of hard subprocess amplitudes and form factors, specific…
Hard exclusive scattering at Jlab
P. Kroll
The various factorization schemes for hard exclusive processes and the status of their applications is briefly reviewed.
Comment on the paper: ``The perturbative proton form factor reexamined'' by Kundu et al
J. Bolz, R. Jakob, P. Kroll +1
We point out some serious problems in the investigation of Kundu et al. which claims agreement with the existing data of the proton form factor, calculated without taking into acco…
Spin and hard processes
P. Kroll
It is argued that spin is a fundamental aspect of gauge theories at short distances. As a consequence there are characteristic helicity asymmetries in hard inclusive and exclusive…
Discovery of The New WZ Sge Star, SDSS J080434.20+510349.2
E. Pavlenko, S. Yu. Shugarov, N. A. Katysheva +13
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 peculiari…
THE LARGE MOMENTUM TRANSFER BEHAVIOUR OF MESON-PHOTON TRANSITION FORM FACTORS
P. Kroll
It is reported on predictions for the - transition form factor obtained within a perturbative approach which includes transverse momentum effects and Sudakov corrections. T…
Generalized parton distributions from nucleon form factors
P. Kroll
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 parameteri…
The near-synchronous polar V1432 Aql (RX J1940.1-1025): Accretion geometry and synchronization time scale
R. Staubert, S. Friedrich, K. Pottschmidt +5
The magnetic Cataclysmic Variable (mCV) V1432 Aql (RX 1940.1-1025) belongs to the four-member subclass of near-synchronous polars with a slight non-synchronism (<2 %) between the s…
The handbag contribution to gamma gamma to pi pi and K K
M. Diehl, P. Kroll, C. Vogt
We investigate the soft handbag contribution to two-photon annihilation into pion or kaon pairs at large energy and momentum transfer. The amplitude is expressed as a hard gamma ga…
A Critical Analysis of the Proton Form Factor with Sudakov Suppression and Intrinsic Transverse Momentum
J. Bolz, R. Jakob, P. Kroll +2
The behavior of the proton magnetic form factor is studied within the modified hard scattering picture, which takes into account gluonic radiative corrections in terms of transvers…
The exclusive limit of the pion-induced Drell-Yan process
S. V. Goloskokov, P. Kroll
Based on previous studies of hard exclusive leptoproduction of pions in which the essential role of the pion pole and the transversity generalized parton distributions has been poi…
Electron Scattering with Polarized Targets at TESLA
N Study Group, M. Anselmino, E. C. Aschenauer +39
Measurements of polarized electron-nucleon scattering can be realized at the TESLA linear collider facility with projected luminosities that are about two orders of magnitude highe…