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Wojciech Broniowski

Publications and source records attributed to Wojciech Broniowski.

At least 163 records · Page 9Linked to original sources

Confined Chiral Solitons in the Spectral Quark Model

Chiral solitons with baryon number one are investigated in the Spectral Quark Model. In this model the quark propagator is a superposition of complex-mass propagators weighted with a suitable spectral function. This technique is a method of regularizing the effective quark theory in a way preserving many desired features crucial in analysis of solitons. We review the model in the vacuum sector, stressing the feature of the absence of poles in the quark propagator. We also investigate in detail the analytic structure of meson two-point functions. We provide an appropriate prescription for constructing valence states in the spectral approach. The valence state in the baryonic soliton is identified with a saddle point of the Dirac eigenvalue treated as a function of the spectral mass. Due to this feature the valence quarks never become unbound nor dive into the negative spectrum, hence providing stable solitons as absolute minima of the action. This is a manifestation of the absence of poles in the quark propagator. Self-consistent mean field hedgehog solutions are found numerically and some of their properties are determined and compared to previous chiral soliton models. Our analysis constitutes an involved example of a treatment of a relativistic complex-mass system.

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Pion-photon Transition Distribution Amplitudes in the Spectral Quark Model

The vector and axial pion-photon transition distribution amplitudes are analyzed in the Spectral Quark Model. We proceed by the evaluation of double distributions through the use of a manifestly covariant calculation based on the alpha representation of propagators. As a result polynomiality is incorporated and calculations become rather simple. Explicit formulas, holding at the low-energy quark-model scale, are obtained. The corresponding form factors for the anomalous decay pi0 -> gamma gamma* and the radiative pion decays are also evaluated and confronted with the data.

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pT-fluctuations and multiparticle clusters in heavy-ion collisions

We investigate the centrality dependence of the pT-correlations in the event-by-event analysis of relativistic heavy-ion collisions at RHIC made recently by the PHENIX and STAR Collaborations. We notice that sigma^2 dynamical scales to a very good accuracy with the inverse number of the produced particles, n. This scaling can be naturally explained by formation of clusters. We discuss the nature of clusters and provide numerical estimates of correlations coming from resonance decays, which are tiny, and a model where particle are emitted from local thermalized sources moving at the same collective velocity. This "lumped cluster" model can explain the data when on the average 6-15 particles are contained in a cluster. We also point out simple relations of the popular correlation measures to the covariance, which arise under the assumptions (well holding at RHIC) that the distributions are sharply peaked in n and that the dynamical compared to statistical fluctuations are small.

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Rapidity-dependent spectra from a single-freeze-out model of relativistic heavy-ion collisions

An extension of the single-freeze-out model with thermal and geometric parameters dependent on the spatial rapidity, $α_\parallel$, is used to describe the rapidity and transverse-momentum spectra of pions, kaons, protons, and antiprotons measured at RHIC at $\sqrt{s_{NN}}=200 {\rm GeV}$ by the BRAHMS collaboration. {\tt THERMINATOR} is used to perform the necessary simulation, which includes all resonance decays. The result of the fit to the rapidity spectra in the range of the BRAHMS data is the expected growth of the baryon and strange chemical potentials with the magnitude of $α_\parallel$, while the freeze-out temperature is kept fixed. The value of the baryon chemical potential at $α_\parallel \sim 3$, which is the relevant region for particles detected at the BRAHMS forward rapidity $y \sim 3$, is about $200 {\rm GeV}$, {\em i.e.} lies in the range of the values obtained for the highest SPS energy. The chosen geometry of the fireball has a decreasing transverse size as the magnitude of $α_\parallel$ is increased, which also corresponds to decreasing transverse flow. This feature is verified by reproducing the transverse momentum spectra of pions and kaons at various rapidities. The strange chemical potential obtained from the fit to the $K^+/K^-$ ratio is such that the local strangeness density in the fireball is compatible with zero. The resulting rapidity spectra of net protons are described qualitatively in the model. As a result of the study, the knowledge of the ``topography'' of the fireball is achieved, making other calculations possible. As an example, we give predictions for the rapidity spectra of hyperons.

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Dimension-2 condensates, zeta-regularization and large-Nc Regge Models

Dimension-2 and -4 gluon condensates are re-analyzed in large-Nc Regge models with the zeta-function regularization which preserves the spectrum in any q qbar channel separately. We demonstrate that the signs and magnitudes of both condensates can be properly described within the framework.

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Pion transition form factor and distribution amplitudes in large-Nc Regge models

We analyze the pi -> gamma* gamma* amplitude in the framework of radial Regge models in the large-Nc limit. With the assumption of similarity of the asymptotic Regge rho and omega meson spectra we find that the pion distribution amplitude is constant in the large-$N_c$ limit at the scale Q0 where the QCD radiative corrections are absent -- a result found earlier in a class of chiral quark models. We discuss the constraints on the couplings from the anomaly and from the limit of large photon virtualities, and find that the coupling of the pion to excited rho and omega mesons must be asymptotically constant. We also discuss the effects of the QCD evolution on the pion electromagnetic transition form factor. Finally, we use the Regge model to evaluate the slope of the form factor at zero momentum and compare the value to the experiment, finding very reasonable agreement.

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Dimension-two gluon condensate from large-Nc Regge models

It is shown that in the large-N_c limit radial Regge trajectories give rise in a natural way to the presence of the dimension-2 gluon condensate, , in meson correlators. We match these models to QCD and provide estimates for in terms of other physical quantities. In particular, in the simplest strictly linear radial Regge model with equal residues is proportional to the pion decay constant squared. However, the linear model fails a consistency condition based on matching the short- and long-distance string tensions, nor reproduces the phenomenological values of the gluon condensates. On the contrary, in Regge models departing from strict linearity one may reproduce both the consistency condition and the signs of condensates. We demonstrate this in a simple explicit model.

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Femtoscopy in hydro-inspired models with resonances

Effects of the choice of the freeze-out hypersurface and resonance decays on the HBT interferometry in relativistic heavy-ion collisions are studied in detail within a class of models with single freeze-out. The Monte-Carlo method, as implemented in THERMINATOR, is used to generate hadronic events describing production of particles from a thermalized and expanding source. All well-established hadronic resonances are included in the analysis as their role is crucial at large freeze-out temperatures. We use the two-particle method to extract the correlation functions, which allows us to study the Coulomb effects. We find that the pion HBT data from RHIC are fully compatible with the single freeze-out scenario, pointing at the shape of the freeze-out hypersurface where the transverse radius is decreasing with time. Results for the single-particle spectra for this situation are also presented. Finally, we present predictions for the kaon femtoscopy.

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Therminator: Thermal heavy-Ion generator

THERMINATOR is a Monte Carlo event generator designed for studying of particle production in relativistic heavy-ion collisions performed at such experimental facilities as the SPS, RHIC, or LHC. The program implements thermal models of particle production with single freeze-out. It performs the following tasks: 1) generation of stable particles and unstable resonances at the chosen freeze-out hypersurface with the local phase-space density of particles given by the statistical distribution factors, 2) subsequent space-time evolution and decays of hadronic resonances in cascades, 3) calculation of the transverse-momentum spectra and numerous other observables related to the space-time evolution. The geometry of the freeze-out hypersurface and the collective velocity of expansion may be chosen from two successful models, the Cracow single-freeze-out model and the Blast-Wave model. All particles from the Particle Data Tables are used. Experimental cuts may be introduced in a very straightforward manner. The code is written in the object-oriented c++ language and complies to the standards of the ROOT environment.

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Landau-gauge condensates from the quark propagator on the lattice

We compute the dimension-2 condensate, , and the dimension-4 mixed condensate, <\bar q A q>, from the recent quenched lattice results for the quark propagator in the Landau gauge. We fit the lattice data to the Operator Product Expansion in the "fiducial" region 1.2 GeV < Q < 3 GeV. Our result for the dynamical gluon mass at the scale of 10 GeV^2 is m_A=600-650 MeV, in agreement with independent determinations. For the mixed Landau gauge condensate of dimension-4 we get alpha_s <\bar q g A q> = (-0.11 +/- 0.03) GeV^4. This value is an order of magnitude larger than the gluon condensate.

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Hydro-inspired parameterizations of freeze-out in relativistic heavy-ion collisions

Popular parameterizations of the freeze-out conditions in relativistic heavy-ion collisions are discussed. Similarities and differences between the blast-wave model and the single-freeze-out model, both used recently to interpret the RHIC data, are outlined. A non-boost-invariant extension of the single-freeze-out model is proposed and applied to describe the recent BRAHMS data.

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Application of chiral quark models to high-energy processes

We discuss the predictions of chiral quark models for basic pion properties entering high-energy processes: generalized parton distributions (GPD's) and unintegrated parton distributions (UPD's). We stress the role of the QCD evolution, necessary to compare the predictions to data.

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Kwiecinski evolution of unintegrated parton distributions

The Kwiecinski evolution of unintegrated parton distributions (UPDs) in the transverse-coordinate space is analyzed with the help of the Mellin transform. Numerical results are presented for the unintegrated pion distributions with a simple valence-like initial condition at the low scale, which follows from chiral large-Nc quark models. The effect of spreading of UPDs in the transverse momentum with the increasing scale is confirmed, with growing asymptotically as Q^2 alpha(Q^2). Formal aspects of the equations, such as the limits of UPDs at x -> 0, x -> 1, and at low and large b, are straightforward to obtain with our method.

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Update of the Hagedorn mass spectrum

We present an update of the Hagedorn hypothesis of the exponential growth of the number of hadronic resonances with mass. We use the newest available experimental data for the non-strange mesons and baryons, as well as fill in some missing states according to the observation that the high-lying states form chiral multiplets. The results show, especially for the case of the mesons, that the Hagedorn growth continues with the increasing mass, with the new states lining up along the exponential growth.

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SHARE: Statistical Hadronization with Resonances

SHARE is a collection of programs designed for the statistical analysis of particle production in relativistic heavy-ion collisions. With the physical input of intensive statistical parameters, it generates the ratios of particle abundances. The program includes cascade decays of all confirmed resonances from the Particle Data Tables. The complete treatment of these resonances has been known to be a crucial factor behind the success of the statistical approach. An optional feature implemented is a Breit--Wigner type distribution for strong resonances. An interface for fitting the parameters of the model to the experimental data is provided.

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Solution of the Kwiecinski evolution equations for unintegrated parton distributions using the Mellin transform

The Kwiecinski equations for the QCD evolution of the unintegrated parton distributions in the transverse-coordinate space (b) are analyzed with the help of the Mellin-transform method. The equations are solved numerically in the general case, as well as in a small-b expansion which converges fast for b Lambda_QCD sufficiently small. We also discuss the asymptotic limit of large bQ and show that the distributions generated by the evolution decrease with b according to a power law. Numerical results are presented for the pion distributions with a simple valence-like initial condition at the low scale, following from chiral large-N_c quark models. We use two models: the Spectral Quark Model and the Nambu--Jona-Lasinio model. Formal aspects of the equations, such as the analytic form of the b-dependent anomalous dimensions, their analytic structure, as well as the limits of unintegrated parton densities at x -> 0, x -> 1, and at large b, are discussed in detail. The effect of spreading of the transverse momentum with the increasing scale is confirmed, with growing asymptotically as Q^2 alpha(Q^2). Approximate formulas for for each parton species is given, which may be used in practical applications.

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Production of resonances in a thermal model

We discuss the pi+ pi- invariant-mass correlations and the resonance production in a thermal model with single freeze-out. The predictions are confronted with the data from the STAR Collaboration.

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Resonance production in a thermal model

We discuss the pi+ pi- invariant-mass correlations and the resonance production in a thermal model with single freeze-out. The predictions are confronted with the recent data from the STAR Collaboration.

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