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L. Motyka

Publications and source records attributed to L. Motyka.

At least 37 records · Page 2Linked to original sources
arXiv2006

Exclusive diffractive processes at HERA within the dipole picture

We present a simultaneous analysis, within an impact parameter dependent saturated dipole model, of exclusive diffractive vector meson (J/psi, phi and rho) production, deeply virtual Compton scattering and the total gamma* p cross section data measured at HERA. Various cross sections measured as a function of the kinematic variables Q^2, W and t are well described, with little sensitivity to the details of the vector meson wave functions. We determine the properties of the gluon density in the proton in both longitudinal and transverse dimensions, including the impact parameter dependent saturation scale. The overall success of the description indicates universality of the emerging gluon distribution and proton shape.

hep-ph↗
arXiv2006

On the equivalence of Reggeon field theory in zero transverse dimensions and reaction-diffusion processes

The Reggeon field theory in zero transverse dimensions is investigated. Two versions of the theory are considered: one that allows at most triple pomeron interactions and the other that embodies an additional 2-->2 quartic Reggeon coupling. The behavior of the scattering amplitude at asymptotic rapidities is obtained in both cases. In an s-channel picture of the high energy scattering both models can be viewed as reaction-diffusion processes. We derive known results in Reggeon field theory rather easily using the reaction-diffusion formalism. We find that some results which are surprising from the Reggeon field theory point of view turn out to have a simple interpretation from the reaction-diffusion point of view.

hep-ph↗
arXiv2006

Exclusive Higgs boson production at the LHC: hard rescattering corrections

We examine, as a correction to the central exclusive Higgs boson production in $pp$ collisions at the LHC, the rescattering of gluonic ladders off the proton. As usual, at the lowest order the hard part of this process can be described as a fusion of two hard gluonic ladders. We calculate corrections to this hard amplitude which are due to rescattering of these ladders. These corrections, which contain high mass diffractive excitations of the proton, have not yet been taken into account by the usual soft survival probabilities. We find that the correction due to the exchange of a single hard rescattering is negative, large and infrared sensitive. As a first step towards a more reliable description we therefore replace the rescattering exchange by a unitarized amplitude using the BK equation which generates the saturation scale $Q_s(x)$. We also include a soft gap survival probability factor. We discuss the results and outline possible future strategies.

hep-ph↗
arXiv2004

Diffractive photoproduction of vector mesons at large momentum transfer

Diffractive photoproduction of rho, phi and J/psi was studied in the BFKL approach to hard colour singlet exchange. Differential cross sections, the energy dependence and spin density matrix elements were calculated and compared to data from HERA. The overall description of data is reasonably good, except of the single flip amplitude which has the wrong sign. Importance of chiral odd components of the photon is stressed.

hep-ph↗
arXiv2003

Vector Meson Photoproduction from the BFKL Equation I: Theory

Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation, for which a complete analytical solution is found. The scattering amplitudes for all combinations of helicity are presented.

hep-ph↗
arXiv2002

Unintegrated gluon in the photon and heavy quark production

The unintegrated gluon density in the photon is determined, using the Kimber-Martin-Ryskin prescription . In addition, a model of the unintegrated gluon is proposed, based on the saturation model extended to the large-x region. These gluon densities are applied to obtain cross sections for charm and bottom production in gamma-p and gamma-gamma collisions using the k_t factorization approach. We investigate both direct and resolved photon contributions and make comparison with the results from the collinear approach and the experimental data. An enhancement of the cross section due to inclusion of non-zero transverse momenta of the gluons is found. The charm production cross section is consistent with the data. The data exceed our conservative estimate for bottom production in gamma-p collisions, but theoretical uncertainties are too large to claim a significant inconsistency. A substantial discrepancy between theory and the experiment is found for gamma gamma -> b bbar X, not being cured by the k_t factorization approach.

hep-ph↗
arXiv2002

Diffractive vector mesons at large momentum transfer from the BFKL equation

Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation, for which an analytical solution is found for all conformal spins, giving the scattering amplitude. Results are compared to HERA data on rho production.

hep-ph↗
arXiv2002

Two-photon cross-sections from the saturation model

A saturation model for the total gamma-gamma and gamma*-gamma* cross-sections and for the real photon structure function F_2^gamma(x,Q^2) is described. The model is based on a QCD dipole picture of high energy scattering. The two-dipole cross-section is assumed to satisfy the saturation property with the saturation radius taken from the GBW analysis of the gamma*-p interaction at HERA. The model is combined with the QPM and non-pomeron reggeon contributions an it gives a very good description of the data on the gamma-gamma total cross-section, on the photon structure function F_2^gamma(x,Q^2) at low x and on the gamma*-gamma* cross-section. Production of heavy quarks in gamma-gamma collisions is also studied.

hep-ph↗
arXiv2002

Saturation model for 2-gamma physics

We introduce a saturation model for photon-photon interactions, based on a QCD dipole picture of high energy scattering. The two-dipole cross-section is assumed to satisfy the saturation property. This pomeron-like contribution is supplemented with QPM and non-pomeron reggeon contributions. The model gives a very good description of the data on the gamma-gamma total cross-section, on the photon structure function F_2^gamma(x,Q^2) at low x and on the gamma*-gamma* cross-section.

hep-ph↗
arXiv2001

The non-forward BFKL amplitude and rapidity gap physics

We discuss the BFKL approach to processes with large momentum transferred through a rapidity gap. The Mueller and Tang scheme to the BFKL non-forward parton-parton elastic scattering amplitude at large $t$, is extended to include higher conformal spins. The new contributions are found to decrease with increasing energy, as follows from the gluon reggeisation phenomenon, and to vanish for asymptotically high energies. However, at moderate energies and high $|t|$, the higher conformal spins dominate the amplitude. We illustrate the effects by studying the production of two high $E_T$ jets separated by a rapidity gap at HERA energies. In a simplified framework, we find excellent agreement with the HERA photoproduction data once we incorporate the rapidity gap survival probability against soft rescattering effects. We emphasize that measurements of the analogous process in electroproduction may probe different summations over conformal spins.

hep-ph↗
arXiv2001

Hard colour singlet exchange and gaps between jets at the Tevatron

The new kind of events with a rapidity gap between two high-E_T jets, observed in high energy ppbar collisions at the Tevatron, is found to be well described by the exchange of a colour singlet gluon system in the BFKL framework. This requires going beyond the conventional asymptotic Mueller-Tang approximation, which results in qualitatively different features of the basic parton-parton scattering amplitude. Non-leading corrections to the BFKL equation are included by incorporation of the consistency constraint and the running QCD coupling. Hadronisation and other non-perturbative QCD effects are treated through a complete Monte Carlo simulation, providing a gap survival probability that varies event-by-event, facilitating comparison with experimental results.

hep-ph↗
arXiv2001

Hard colour singlet exchange at the Tevatron from the BFKL equation

We study rapidity gaps between jets in ppbar collisions at the Tevatron by a novel solution of the nonforward BFKL equation including nonleading effects through the consistency constraint and running coupling. Results differ from earlier calculations based on the asymptotic Mueller-Tang formula, but agree with D0 data when including full event simulation using PYTHIA to model the gap survival probability.

hep-ph↗
arXiv2001

Saturation model for two-photon interactions at high energies

We formulate and analyse a saturation model for the total gamma gamma and gamma* gamma* cross-sections and for the real photon structure function F_2^gamma(x,Q^2). The model is based on a picture in which the gamma* gamma* total cross-section for arbitrary photon virtualities is driven by the interaction of colour dipoles, into which the virtual photons fluctuate. The cross-section describing this interaction is assumed to satisfy the saturation property with the saturation radius taken from the Golec-Biernat and Wusthoff analysis of the gamma* p interaction at HERA. The model is supplemented by the QPM and non-pomeron reggeon contributions. The model gives a very good description of the data on the gamma gamma total cross-section, on the photon structure function F_2^gamma(x,Q^2) at low x and on the gamma* gamma* cross-section extracted from LEP double tagged events. Production of heavy flavours in gamma gamma collisions is also studied. Predictions of the model for the very high energy range which will be probed at future linear colliders are given.

hep-ph↗
arXiv2001

Diffusion into infra-red and unitarization of the BFKL pomeron

The BFKL pomeron in perturbative QCD is plagued by the lack of unitarity and diffusion into the infra-red region of gluon virtualities. These two problems are intimately related. We perform numerical studies of the evolution equation proposed by Balitsky and Kovchegov which unitarizes the BFKL pomeron. We show how diffusion into the infra-red region is suppressed due to the emergence of a saturation scale and scaling behaviour. We study universality of this phenomenon as well as its dependence on subleading corrections to the BFKL pomeron such as the running coupling and kinematic constraint. These corrections are very important for phenomenological applications.

hep-ph↗
arXiv2001

Azimuthal decorrelation of forward and backward jets at the Tevatron

We analyse the azimuthal decorrelation of Mueller-Navelet dijets produced in the collisions at Tevatron energies using a BFKL framework which incorporates dominant subleading effects. We show that these effects significantly reduce the decorrelation yet they are still insufficient to give satisfactory description of experimental data. However a good description of the data is obtained after incorporating within formalism the effective rapidity defined by Del Duca and Schmidt.

hep-ph↗
arXiv2000

The photon structure and exclusive production of vector mesons in gamma-gamma collisions

The process of exclusive vector meson production (gamma gamma to J/psi rho^0) is studied for almost real photons. This process may be reduced to photoproduction of J/psi off the rho^0 meson. We discuss the possibility of extracting the gluon distribution of rho^0 and of the photon from such measurement. Predictions are also given for the reaction (e+e- to e+ e- J/psi rho^0) for various e+e- cms energies typical for LEP and for the future linear colliders.

hep-ph↗
arXiv2000

Theoretical description of the total gamma*gamma* cross-section and its confrontation with the LEP data on doubly tagged e+e- events

We perform a detailed analysis of the total inelastic cross-section for gamma*gamma* collisions. Different contributions coming from the quark box diagram, reggeons, the soft and hard pomeron are included. The QCD pomeron contribution contains a dominant part of subleading effects which reduces its intercept and delays the onset of the asymptotic pomeron to high energies. Estimates of the cross-section for doubly-tagged (e+e- to e+e- hadrons) events are presented and compared with the existing LEP data. Good agreement between the theoretical results and the experimental data is found. We also comment on the extraction of the BFKL pomeron intercept from the available LEP measurements.

hep-ph↗