Nuclear Transparency with the gamma + n -> pi- + p Process in 4He

Color transparency (CT) is an effect of suppression of nuclear shadowing of hard reactions, closely related to the color screening. A brief review of theoretical development and experimental search for CT, failed and successful, are presented. A special emphasis is made on a quantum-mechanical nature of CT, as opposed to a wide spread erroneousclassical treatment of this phenomenon. The typical predictions of the classical approach, all contradicting quantum mechanics are: ...

The physics observables dedicated to the study of color transparency are diverse. After a brief pedagogical introduction, we emphasize the complementarity of the nuclear filtering and color transparency concepts. The importance of quantum interferences leads to suspect pictures based on the preparation of a squeezed state of small transverse size leading to a rapid transverse expansion. The different roles of heavy and light nuclei are emphasized. The possibility of color tra...

The process $\pi + A$ leading to a pair of mini-jets at high relative transverse momentum ($k_t \gsim 2$ GeV) while leaving the nucleus in its ground state was selected as a definitive test of the existence of color transparency by Frankfurt, Miller and Strikman in 1993. The preliminary results of Fermilab experiment E791, led by Ashery and Weiss-Babai, show a strong A-dependence, consistent with the notion of color transparency.

40 years after its introduction, the phenomenon of color transparency remains a domain of controversial interpretations of experimental data. We review present evidence for or against its manifestation in various exclusive hard scattering reactions. The nuclear transparency experiments reveal whether short distance processes dominate a scattering amplitude at some given kinematical point. We plead for a new round of nuclear transparency measurements in a variety of experiment...

We summarize basic theoretical ideas which let to the observation of the short-range correlations (SRC) in nuclei using hard probes and outline directions for probing quark-gluon structure of SRCs. Implications of the observations of color transparency for processes involving pions are reviewed. Open questions and directions for further studies of color transparency phenomena using hadronic projectiles are presented using as an example the PANDA detector at FAIR.

Nuclear transparency in pion-induced nuclear reactions has been investigated based on Glauber multiple scattering theory considering a two-step process within the framework of vector meson dominance (VMD). In the present context, the application of the quantum diffusion model (QDM) to the Glauber theory plays a role in explaining the dependence of the transparency on the four-momentum transfer squared $Q^2$. The short-range correlation (SRC) considered further gives the contr...

We argue that the experimentally measured color transparency ratio is directly related to the interacting hadron wave function at small transverse separation, $b^2<1/Q^2$. We show that the present experimental data is consistent with pure scaling behavior of the hadron-hadron and lepton-hadron scattering inside the nuclear medium.

The nuclear transparency of the charged hadron produced in the inclusive $(e,e^\prime)$ reaction on the nucleus has been calculated using Glauber model for the nuclear reaction. The color transparency (CT) of the produced hadron and the short-range correlation (SRC) of the nucleons in the nucleus have been incorporated in the Glauber model to investigate their effects on the nuclear transparency of the hadron. The calculated nuclear transparencies for the proton and pion are ...

We study the electroproduction of rho mesons in nuclei at intermediate energies, deriving a treatment of the energy lost by the rho in each step of multiple-scattering. This enables a close match between calculations and the experimental kinematic conditions. A standard Glauber calculation is presented, and then the effects of color-transparency are included. The influence of poor experimental resolution on the extracted transparency is assessed. The effects of $\rho$ meson d...

We introduce a data analysis procedure for color transparency experiments which is considerably less model dependent than the transparency ratio method. The new method is based on fitting the shape of the A dependence of the nuclear cross section at fixed momentum transfer to determine the effective attenuation cross section for hadrons propagating through the nucleus. The procedure does not require assumptions about the hard scattering rate inside the nuclear medium. Instead...