l - th / 0 30 60 44 v 3 2 3 Ju l 2 00 3 Transparent Nuclei and Deuteron - Gold Collisions at RHIC ∗

The current normalization of the cross section of inclusive high-p T particle production in deuteron-gold collisions measured at RHIC relies on Glauber model calculations for the inelastic dAu cross section. These calculations should be corrected for diffrac-tion. Moreover, they miss the Gribov's inelastic shadowing which makes nuclei more transparent (color transparency) and reduce the inelastic cross section. The magnitude of this effect rises with energy and one may anticipate it to affect dramatically the normalization of the RHIC data. We evaluate the inelastic shadowing corrections employing the light-cone dipole formalism which effectively sums up multiple interactions in all orders. We found a rather modest correction factor for the current normalization of the dAu data. The results of experiments insensitive to diffraction (PHENIX, PHOBOS) should be renormalized by about 20% down, while those which include diffraction (STAR), by only 10%. In spite of smallness of the correction it completely eliminates the Cronin enhancement in the PHENIX data for pions. The largest theoretical uncertainty comes from the part of the inelastic shadowing which is related to diffractive gluon radiation, or gluon shadowing. Our estimate is adjusted to data for the triple-Pomeron coupling and is small, however, other models do not have such a restrictions and predict much stronger gluon shadowing. Treating all models on the same footing one arrives at quite diverse predictions for the correction factor which may be even as small as K = 0.65. Thus, one should admit that the current data for high-p T hadron production in dAu collisions at RHIC cannot exclude in a model independent way the possibility if initial state suppression proposed by Kharzeev-Levin-McLerran. Probably the only way to settle this uncertainty is a direct measurement of the inelastic dAu cross sections at RHIC. Also d − Au collisions with a tagged spectator nucleon may serve as a sensitive probe for nuclear transparency and inelastic shadowing. We found an illuminating quantum-mechanical effect: the nucleus acts like a lens focusing spectators into a very narrow cone.