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Wojciech Broniowski

Publications and source records attributed to Wojciech Broniowski.

At least 199 records · Page 11Linked to original sources
arXiv2001

Thermal analysis of particle ratios and p_T spectra at RHIC

The thermal model of particle production is used to analyze the particle ratios and the p_T spectra measured recently at RHIC. Our fit of the particle ratios yields the temperature at the chemical freeze-out T_chem = 165 +- 7 MeV with the corresponding baryon chemical potential mu^B_chem = 41 +- 5 MeV. The quality of the fit shows that the model works well for RHIC. The p_T spectra are evaluated in an approach which takes into account the modifications of the initial thermal distributions by the secondary decays of resonances. All two- and three-body decays are included. This leads to an effective ``cooling'' of the spectra in the data region by about 35-40 MeV. We find that the pion spectrum is characterized by the inverse slope which agrees well with the value inferred from the RHIC data.

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arXiv2001

Solitons in nonlocal chiral quark models

Properties of hedgehog solitons in a chiral quark model with nonlocal regulators are described. We discuss the formation of the hedgehog soliton, the quantization of the baryon number, the energetic stability, the gauging and construction of Noether currents with help of path-ordered P-exponents, and the evaluation of observables. The issue of nonlocality is thoroughly discussed, with a focus on contributions to observables related to the Noether currents. It is shown that with typical model parameters the solitons are not far from the weak nonlocality limit. The methods developed are applicable to solitons in models with separable nonlocal four-fermion interactions.

hep-ph↗
arXiv2001

pi^0 -> gamma gamma*, omega -> pi^0 gamma*, and rho -> pi gamma* decays in nuclear medium

We calculate the medium modification of the pi-omega-rho vertex and analyze its significance for the pi^0 -> gamma gamma*, omega -> pi^0 gamma*, and rho -> pi gamma* decays in nuclear matter. We use a relativistic hadronic approach at zero temperature and in the leading-density limit, and consider decays of particles at rest with respect to the medium. It is shown that for the pi^0 -> gamma gamma* the effects of the Delta isobar cancel almost exactly the effects of the nucleon ph excitations, such that the net medium effect is small. On the contrary, for the decays omega -> pi^0 gamma* and rho -> pi gamma* we find a sizeable increase of the partial widths at virtualities of the photon in the range 0.3-0.6 GeV. The effect has direct significance for the calculation of dilepton yields from the Dalitz decays in relativistic heavy-ion collisions.

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arXiv2001

Scaling of hadron masses and widths in thermal models for ultra-relativistic heavy-ion collisions

By means of a simple rescaling, modifications of hadron masses and widths are incorporated into the thermal analysis of particle ratios in ultra-relativistic heavy-ion collisions. We find that moderate, up to 20%, changes of hadron masses do not spoil the quality of the fits, which remain as good as those obtained without modifications. The fits with the modified masses yield, however, modified values of the optimal temperature and baryon chemical potential. In particular, with decreasing masses of all hadrons (except for pseudo-Goldstone bosons) the fitted values of the temperature and the baryon chemical potential are lowered, with the change approximately proportional to the scaling of masses. In addition, we find that the broadening of the hadron widths by less than a factor of two practically does not affect the fits.

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arXiv2001

rho -> pi pi decay in nuclear medium

We calculate the medium modifications of the rho pi pi vertex in a relativistic hadronic framework, incorporating nucleons and Delta(1232) isobars. We find a substantial increase of the rho pi pi coupling, dominated by processes where the Delta is excited. The coupling depends significantly on the virtuality of the rho, which is related to analytic properties of the vertex function. We analyze the general case of a non-zero three-momentum of the rho with respect to the nuclear medium, and evaluate the resulting widths and spectral strength in the transverse and longitudinal channels for the rho -> pi pi decay. These widths are used to obtain the dilepton yields from rho decays in relativistic heavy-ion collisions.

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arXiv2000

Distinct Hagedorn temperatures from particle spectra: a higher one for mesons, a lower one for baryons

We analyze experimental particle spectra and show that the Hagedorn temperature is significantly larger for mesons than for baryons. The effect can be explained within dual string models: excitations of three strings in the baryon produce ``faster'' combinatorics than a single string in the meson, hence lead to a more rapid growth of baryons than mesons. Predictions of other approaches for the gross features of particle spectra are also discussed.

hep-ph↗
arXiv2000

Different Hagedorn temperatures for mesons and baryons from experimental mass spectra, compound hadrons, and combinatorial saturation

We analyze the light-flavor particle mass spectra and show that in the region up to ~1.8GeV the Hagedorn temperature for baryons is about 30% smaller than for mesons, reflecting the fact that the number of baryon states grows more rapidly with the mass. We also show that the spectra are well reproduced in a model where hadrons are compound objects of quanta, whose available number increases with mass. The rapid growth of number of hadronic states is a combinatorial effect. We also point out that an upper limit on the excitation energy of these quanta results in a maximum number of hadron states that can be formed. According to this combinatorial saturation, no more light-flavor hadron resonances exist above a certain mass.

hep-ph↗
arXiv2000

Non-uniform chiral phase in effective chiral quark models

We analyze the phase diagram in effective chiral quark models (the Nambu-Jona-Lasinio model, the sigma-model with quarks) and show that at the mean-field level a phase with a periodically-modulated chiral fields separates the usual phases with broken and restored chiral symmetry. A possible signal of such a phase is the production of multipion jets travelling in opposite directions, with individual pions having momenta of the order of several hundred MeV. This signal can be interpreted in terms of disoriented chiral condensates.

hep-ph↗
arXiv1999

Mesons in non-local chiral quark models

Vector meson correlators are studied in effective chiral quark models with both local and non-local regulators. A set of sum rules based on dispersion relations is derived, which allows for a comparison of model predictions to data. We show that the two Weinberg sum rules for vector correlators hold in the non-local model.

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arXiv1999

Gauging non-local quark models

Gauging of effective chiral quark models with non-local regulators is discussed in the context of solitons. In particular, we show that with the P-exponent method the current algebra is satisfied and the charges are properly quantized.

hep-ph↗
arXiv1999

Matter-induced omega -> pi pi decay

We calculate the width for the omega -> pi pi decay in nuclear matter in a hadronic model including mesons, nucleons and Delta isobars. We find a substantial width of the longitudinally polarized omega modes, reaching ~100MeV for mesons moving suitably fast with respect to the nuclear medium.

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arXiv1998

Collective modes and current-algebraic sum rules in nuclear medium

In-medium sum rules following from the chiral charge algebra of QCD are reviewed, and new sum rules are derived. The new sum rules relate the I^G(J^{PC})=1^-(0^{++}) excitations (quantum numbers of a_0(980)) to the scalar and isovector densities, and are nontrivial for the isospin-asymmetric medium. We present an extensive illustration of the sum rules with help of quark matter in the Nambu-Jona--Lasinio model. Collective excitations different from the usual meson branches (spin-isospin sound modes) are shown to contribute significantly to the sum rules and to play a crucial role in the limit of vanishing current quark masses.

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arXiv1998

Solitons in a chiral quark model with non-local interactions

Hedgehog solitons are found in a chiral quark model with non-local interactions. The solitons are stable without the chiral-circle constraint for the meson fields, as was assumed in previous Nambu-Jona--Lasinio model with local interactions.

hep-ph↗
arXiv1998

Tensor susceptibilities of the vacuum from constituent quarks

We show that the constituent quark model leads to simple expressions for the isoscalar and isovector tensor susceptibilities of the vacuum. The found values are negative and of magnitude compatible with QCD-sum-rule parameterizations of spectral densities in appropriate L=1-meson channels.

hep-ph↗
arXiv1998

rho-omega mixing in relativistic heavy-ion collisions

We show that even moderate excess of neutrons over protons in nuclear matter, such as in ${}^{208} Pb$, can lead to large $ρ$-$ω$ mixing at densities of the order of twice the nuclear saturation density and higher. The typical mixing angle is of the order of $10^o$. The mixing may result in noticeable shifts of the positions and widths of resonances. We also analyze temperature effects and find that temperatures up to 50 MeV have practically no effect on the mixing.

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arXiv1997

Fixed-Velocity Chiral Sum Rules for Nuclear Matter

Infinite sets of sum rules involving the excitations of infinite nuclear matter are derived using only completeness, the current algebra implicit in QCD, and relativistic covariance. The sum rules can be used for isospin-asymmetric nuclear matter, including neutron matter. They relate the chiral condensate and the isospin density to weighted sums over states with fixed velocity relative to the nuclear matter ground state.

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