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Chapter 9
Nuclear Transparency
The issue of nucleon propagation through the nuclear medium has received much
attention during the last few decades. For large enough energies, perturbative QCD
predicts the so-called phenomenom of color transparency. The possible occurence
of this effect was predicted by Brodsky and Mueller in the early 1980s [107, 108].
In the context of exclusive A(e, e ′ p) reactions this phenomenon causes the struck
nucleon to undergo minimal interactions with the surrounding nuclear environment,
thereby making the nucleus more “transparent” for the emission of the proton.
In Sec. 9.1 we outline the theoretical assumptions which underly the color transparency
(CT) phenomenon. These assumptions are actually predictions by different
non-perturbative QCD-models which in theirselves await experimental verification.
The onset of CT in (e, e ′ p) processes can only be observed provided that realistic
models for proton transparency can determine the baseline for standard final-state
interactions. In Secs. 9.2 and 9.3, we present a brief overview of experimental results
so far. As we will see, there remain a lot of unsolved or not so-well understood facets
of this phenomenon. In Sec. 9.3 we present our calculations for the nuclear transparency
in the 12 C(e, e ′ p) reaction. These calculations cover quasielastic kinematics
in a wide kinematic range [0.1 (GeV/c) 2 ≤ Q 2 ≤ 20 (GeV/c) 2 ]. In comparison
with other nuclear transparency calculations which are available in literature, our
calculations are unfactorized and account for relativistic effects. In the Q 2 ≤ 2 − 3
(GeV/c) 2 regime, we will compare calculated transparencies obtained within the
optical potential model (OMEA) and the Glauber (RMSGA) approach.
9.1 Theoretical Background
For color transparency to occur in semi-exclusive (e, e ′ p) reactions, basically three
requirements have to be fulfilled [2, 3, 4]
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