Oscillating Color Transparency in $\pi A\to \pi p (A-1)$ and $\gamma A\to \pi N (A-1)$

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 present a relativistic and cross-section factorized framework for computing nuclear transparencies extracted from A(\gamma,\pi N) reactions at intermediate energies. The proposed quantummechanical model adopts a relativistic extension to the multiple-scattering Glauber approximation to account for the final state interactions of the ejected nucleon and pion. The theoretical predictions are compared against the experimental ^4He(\gamma,p \pi^-) data from Jefferson Lab. For ...

We argue that the observation of the color transparency effect in the semiexclusive $A(\pi^-,l^+ l^-)$ process is important for determining whether it is possible to extract the generalized parton distributions of the nucleon from the elementary reaction $\pi^- p \to l^+ l^- n$ at $p_{\rm lab}=15-20$ GeV/c at small $|t|$ and large invariant mass of the dilepton pair $l^+ l^-$. Assuming that the transverse size of the pionic $q \bar q$ pair in the hard interaction point is sim...

We review the theoretical formalism for hard exclusive processes in a nuclear medium. Theory suggests that these processes will show the very interesting phenomena of color transparency and nuclear filtering. The survival probability in nuclear media has also been predicted to show a scaling behavior at large momentum and large nuclear number. We show that all of these effects may have already been seen experimentally.

We calculate quasi-exclusive scattering of a virtual photon and a proton or pion in nuclear targets. This is the first complete calculation of ``color transparency" and "nuclear filtering " in perturbative QCD. The calculation includes full integrations over hard interaction kernels and distribution amplitudes in Feynman -x fractions and transverse spatial separation space $b$. Sudakov effects depending on $b$ and the momentum transfer $Q^2$ are included. Attenuation of the h...

We consider exclusive two-pion production in antiproton-deuteron interactions at the beam momenta around 10 GeV/c in the kinematics with large momentum transfer in the underlying hard process $\bar p n \to \pi^- \pi^0$. The calculations are performed taking into account the antiproton and pion soft rescattering on the spectator proton in the framework of the generalized eikonal approximation. We focus on the color transparency effect that is modeled by introducing the depende...

We have measured the nuclear transparency of the A(e,e' pi^+) process in ^{2}H,^{12}C, ^{27}Al, ^{63}Cu and ^{197}Au targets. These measurements were performed at the Jefferson Laboratory over a four momentum transfer squared range Q^2 = 1.1 - 4.7 (GeV/c)^2. The nuclear transparency was extracted as the super-ratio of $(\sigma_A/\sigma_H)$ from data to a model of pion-electroproduction from nuclei without pi-N final state interactions. The Q^2 and atomic number dependence of ...

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.

Quantum filtering of the ejectile wave packet from hard $ep$ scattering on bound nucleons puts stringent constraints on the onset of color transparency in $(e,e'p)$ reactions in nuclei at moderate energies. Based on multiple-scattering theory, we derive a novel formula for nuclear transparency and discuss its energy dependence in terms of a color transparency sum rule.

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.