Medium effects in the production and decay of vector mesons in pion-nucleus reactions

The $\omega$-, $\rho$- and $\phi$-resonance production and their dileptonic decay in $\pi^- A$ reactions at 1.1 - 1.7 GeV/c are calculated within the intranuclear cascade (INC) approach. The invariant mass distribution of the dilepton pair for each resonance can be decomposed in two components which correspond to their decay 'inside' the target nucleus and in the vacuum, respectively. The first components are strongly distorted by the nuclear medium due to resonance-nucleon scattering and a possible mass shift at finite baryon density. These medium modifications are compared to background sources in the dilepton spectrum from $\pi N$ bremsstrahlung as well as the Dalitz decays of $\omega$ and $\eta$ mesons produced in the reaction. Detailed predictions for $\pi^- Pb$ reactions at 1.3 and 1.7 GeV/c are made within several momentum bins for the lepton pair.Comment: 29 pages, LaTeX, including 12 postscript figures, UGI-97-07, Nucl. Phys. A., in pres

Probing the interactions of charmed mesons with nuclei in pˉ\bar p induced reactions

We study the perspectives of resonant and nonresonant charmed meson production in $\bar{p} + A$ reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances $\Psi(3770), \Psi(4040)$ and $\Psi(4160)$ on various nuclei, their propagation and decay to $D, \bar{D}, D^*, \bar{D}^*, D_s, \bar{D}_s$ in the medium and vacuum, respectively. The modifications of the open charm vector mesons in the nuclear medium are found to be rather moderate or even small such that dilepton spectroscopy will require an invariant mass resolution of a few MeV. Furthermore, the elastic and inelastic interactions of the open charm mesons in the medium are taken into account, which can be related to $(u,d)$-, $s$- or $c$-quark exchange with nucleons. It is found that by studying the $D/\bar{D}$ ratio for low momenta in the laboratory ($\leq 2-2.2$ GeV/c) as a function of target mass $A$ stringent constraints on the $c$-quark exchange cross section can be obtained. On the other hand, the ratios $D^-_s/D^+_s$ as well as $D/D^-_s$ and $D/D^+_s$ at low momenta as a function of $A$ will permit to fix independently the strength of the $s$-quark exchange reaction in $D^-_s N$ scattering.Comment: 9 pages, LaTeX, including 9 postscript figures, submitted to Eur. Phys. J.

Nuclear transparency in quasielastic A(e,e'p): intranuclear cascade versus eikonal approximation

The problem of nuclear propagation through the nuclear medium in quasielastic A(e,e'p) reactions is discussed in the kinematic range 1<Q^2<7 (GeV/c)^2. The coefficient of nuclear transparency is calculated for each Q^2 in the framework of the intranuclear cascade model (INC) and of the eikonal approximation (EA). The predictions of both models are in good agreement with each other and with experimental data recently obtained at SLAC, BATES and TJNAF. The EA gives an explanation of the Q^2 behaviour of the transparency coefficient as a kinematic effect related to the superposition of contributions from each target shell.Comment: RevTeX, 23 pages, 11 figures separately, submitted to Phys. Rev.

Density dependence of resonance broadening and shadowing effects in nuclear photoabsorption

Medium effects as a function of the mass number $A$ are studied in the total photonuclear cross section from the $\Delta$-resonance region up to the region where shadowing effects are known to exist. A consistent picture is obtained by simply assuming a density dependence of the different mechanisms of resonance broadening and shadowing. The $\Delta$-mass shift is found to increase with $A$.Comment: 7 pages, LaTeX, 2 figures available from the author

Interactions of charmed mesons with nucleons in the pˉd\bar p d reaction

We study the possibility to measure the elastic $\Phi N$ ($\Phi \equiv J/\psi, \psi(2S), \psi(3770),\chi_{2c}$) scattering cross section in the reaction $\bar p{+}d{\to}\Phi{+}n_{sp}$ and the elastic $D(\bar D) N$ scattering cross section in the reaction $\bar p{+}d \to D^- D^0 p_{sp}$. Our studies indicate that the elastic scattering cross sections can be determined for $\Phi$ momenta about 4-6 GeV/c and $D/ \bar D$ momenta 2 -- 5 GeV/c by selecting events with $p_t \geq 0.4$ GeV/c for $\Phi$'s and $p_t(p_{sp})\geq$ 0.5 GeV/c for $D/\bar D$-meson production.Comment: 7 pages, including 9 postscript figure

Studying the ωN\omega N elastic and inelastic cross section with nucleons

We explore the possibility to measure the elastic and inelastic $\omega N$ cross section in $p{+}d{\to}d{+}\omega{+}p_{sp}$ and $p{+}A$ reactions. Our studies indicate that the elastic scattering cross sections can be determined for $\omega$ momenta above 1 GeV/c in $p{+}d$ reactions by gating on high proton spectator momenta whereas the $\omega N$ absorption cross section down to low relative $\omega$ momenta is most effectively studied in $p{+}A$ reactions at beam energies 2.0--2.7 GeVComment: 7 pages, svjour-style, including 9 ps-figure

Medium effects in the production and pi0 gamma decay of omega-mesons in pA collisions in the GeV region

The omega-resonance production and its pi0 gamma decay in p-A reactions close to threshold is considered within the Intranuclear Cascade (INC) Model. The pi0 gamma invariant mass distribution shows two components which correspond to the omega decay 'inside' and 'outside' the nucleus, respectively. The 'inside' component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the omega-meson and its decaying pion. The relative contribution of the 'inside' component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the pi0 and gamma momenta allows to separate events related to the 'inside' omega decay from different sources of background when uncorrelated pi0's and gamma's are produced.Comment: 24 pages, 11 figure