Transparent nuclei and deuteron-gold collisions at relativistic energies

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 d-Au cross section. These calculations should be corrected for diffraction. Moreover, they miss Gribov’s inelastic shadowing which makes nuclei more transparent (color transparency) and reduces 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 data for high-p_T hadron production in d-Au collisions. 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 eliminates the Cronin enhancement in the PHENIX data for pions. The largest theoretical uncertainty comes from the part of 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 restriction and predict much stronger gluon shadowing. Thus, one arrives at quite diverse predictions for the correction factor which may be even as small as K=0.65. Therefore, one should admit that the current data for high-p_T hadron production in d-Au collisions at RHIC cannot exclude in a model independent way a possibility of initial state suppression proposed by Kharzeev-Levin-McLerran. To settle this uncertainty one should directly measure the inelastic d-Au cross sections at RHIC. Also, 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.