arXiv subjects

E. L. Bratkovskaya

Publications and source records attributed to E. L. Bratkovskaya.

116 records · Page 7Linked to original sources

arXiv1997

Analysis of Kaon Production at SIS Energies

We analyse the production and propagation of pions and kaons in heavy-ion reactions from 0.8 -- 1.8~A$\cdot$GeV within a coupled channel transport approach including the kaon production channels $BB \to K^+YN, πB\to K^+Y, BB \to NN K \bar{K}, πB\to N K\bar{K}, K^+B\to K^+B $ and $ππ\to K \bar{K}$. Assuming the hyperon selfenergy to be 2/3 of the nucleon selfenergy we find that all inclusive experimental $K^+$ spectra at SIS energies can be reproduced reasonably well without any selfenergies for the kaons although a slightly repulsive kaon potential cannot be excluded by the present data on kaon spectra and flow.

nucl-th↗

arXiv1997

Dilepton Production from AGS to SPS Energies within a Relativistic Transport Approach

We present a nonperturbative dynamical study of $e^+e^-$ production in proton-nucleus and nucleus-nucleus collisions from AGS to SPS energies on the basis of the covariant transport approach HSD. For p + Be reactions the dilepton yield for invariant masses $M \leq 1.4$ GeV is found to be dominated by the decays of the $η, ρ, ω$ and $Φ$ mesons at all energies from 10 -- 450 GeV. For nucleus-nucleus collisions, however, the dilepton yield shows an additional large contribution from $π^+π^-$, $K^+K^-$ and $πρ$ channels. Systematic studies are presented for the 'free' meson mass scenario in comparison to a 'dropping' meson mass scenario at finite baryon density. We find that for 'dropping' meson masses the invariant dilepton mass range 0.35 GeV $\leq M \leq$ 0.65 GeV is increased in comparison to the 'free' meson mass scenario and that the data of the CERES-collaboration for nucleus-nucleus collisions can be described much better within the 'dropping' mass scheme. We study in detail the contributions from the various dilepton channels as a function of the transverse momentum and rapidity of the lepton pair as well as a function of the charged particle multiplicity. Furthermore, various direct photon channels for S + Au at 200 GeV/u are computed and found to be well below the upper bounds measured by the WA80-collaboration.

nucl-th↗

arXiv1996

Kaon versus Antikaon Production at SIS Energies

We analyse the production and propagation of kaons and antikaons in Ni + Ni reactions from 0.8--1.85 GeV/u within a coupled channel transport approach including the channels $BB \to K^+YN, πB\to K^+Y, BB \to NN K \bar{K}, πB\to N K\bar{K}, K^+B\to K^+B, \bar{K} B\to \bar{K}B, Y N\to \bar{K} NN, ππ\to K \bar{K}$ as well as $πY\to \bar{K}N$ and $\bar{K} N\to πY$ for the antikaon absorption. Whereas the experimental $K^+$ spectra can be reproduced without introducing any selfenergies for the mesons in Ni + Ni collisions from 0.8 to 1.8 GeV/u, the $K^-$ yield is underestimated by a factor of 5--7 at 1.66 and 1.85 GeV/u. However, introducing density dependent antikaon masses as proposed by Kaplan and Nelson, the antikaon spectra can be reasonably well described.

nucl-th↗

arXiv1996

Probing Hadronic Polarizations with Dilepton Anisotropies

We investigate the production of $e^+e^-$ pairs from $p + Be$ and nucleus-nucleus collisions from 2 GeV/A to 200 GeV/A within a covariant transport approach and focus on the dilepton angular anisotropies as a function of the dilepton invariant mass. Whereas the low mass regime yields information about the Dalitz decays of the $Δ, η$ and $ω$, above M $\approx $0.5 GeV the angular anisotropies provide additional information about the $π^+π^- \to ρ^0 \to e^+e^-$ channel in the medium. The anisotropy coefficient is found to change its sign for M $>$ 0.5 GeV in case of nucleus-nucleus reactions when increasing the bombarding energy from 2 GeV/A to 200 GeV/A which sheds some light on the $ππ\to ρ$ dynamics.

nucl-th↗

arXiv1996

Dilepton anisotropy from $p + Be$ and $Ca + Ca$ collisions at BEVALAC energies

A full calculation of lepton-pair angular characteristics is carried out for $e^+e^-$ pairs created in $p + Be$ and $Ca + Ca$ collisions from 1.0 to 2.1 GeV/A. It is demonstrated that the dilepton decay anisotropy depends sensitively on the different sources and may be used for their disentangling. Due to the dominance of the $η$-and $Δ$-Dalitz decays and only a small anisotropy coefficient for $π^+π^-$ annihilation, the expected anisotropy coefficients show a decrease with invariant mass of the dilepton pair and change only moderately when comparing $p + Be$ and $Ca + Ca$ reactions at the same bombarding energy.

nucl-th↗

arXiv1995

Decay Anisotropy of $e^+e^-$ Sources from $pN$ and $pd$ collisions

A full calculation of lepton-pair angular characteristics is carried out for $e^+e^-$ pairs created in $pp$, $pn$ and $pd$ collisions at intermediate energies. It is demonstrated that the proposed new observable, the dilepton decay anisotropy, quite sensitively changes for different sources and may be useful for their disentangling. The relevance of the dilepton decay anisotropy is shown in the context of a puzzling energy behavior for the ratio of the lepton yield from $pd$ to $pp$ reactions as observed at the BEVALAC.

nucl-th↗

arXiv1995

On the Four--Photon Decay of the Neutral Pion

The dominant contribution to the $π^0 \to 4γ$ branching ratio, coming from purely electromagnetic photon-splitting graph, is calculated. The result $Br(π^0 \to 4γ) \simeq (2.6 \pm 0.1) \cdot 10^{-11}$ is about three orders of magnitude below the present experimental limit.

hep-ph↗

arXiv1994

Spin-Momentum Correlation (Handedness) in the Process of Four Pions Production in the Electron-Positron Collisions

We discuss special type of polarization asymmetry (``handedness") in the process $e^+e^-\to 4π$, when one of initial particles is longitudinally polarized. The asymmetry is proportional to the degree of polarization and to the width to mass ratio of rho-meson. It can reach 4-5\% in some kinematical region. Both channels $2 π^+ 2 π^-$ and $2 π^0 π^+ π^-$ are considered in the framework of the effective chiral lagrangian with vector mesons, in the energy range $\sim 1$ GeV. The corresponding total cross sections are also calculated.

hep-ph↗