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   cronin effect
Tuesday 30 June 1998
Disappearance of the Cronin Effect at RHIC
Xiao-ming Xu  (Shanghai/China)

The large pt spectra of produced hadrons in high-energy pA collisions are known to be enhanced relative to superposition of pp collisions. Such a phenomenon is often referred to as the Cronin effect. It is shown in a pQCD-based parton model that this arises from multiple parton scattering in pA collisions. Within this model, one can demonstrate that the enhancement decreases like 1/pt**2 at large pt. It will also be shown that the overall Cronin effect will disappear at high collider energies such as RHIC. Consequently, this will reduce the uncertainties of high pt hadron spectra due to normal nuclear effect.


X.-N. Wang, Phys. Rep. 280, 287 (1997)
M. Lev and B. Petersson, Z. Phys. C21, 155 (1983).
J. W. Cronin et al., Phys. Rev. D11, 3105 (1975).

Cronin Effect in Hadron Production off Nuclei
Authors: B.Z. Kopeliovich, J. Nemchik, A. Schaefer, A.V. Tarasov
Comments: the final version to appear in Phys. Rev. Lett
Journal-ref: Phys.Rev.Lett. 88 (2002) 232303

Recent data from RHIC for high-$p_T$ hadrons in gold-gold collisions raised again the long standing problem of quantitatively understanding the Cronin effect, i.e. nuclear enhancement of high-$p_T$ hadrons due to multiple interactions in nuclear matter. In nucleus-nucleus collisions this effect has to be reliably calculated as baseline for a signal of new physics in high-$p_T$ hadron production. The only possibility to test models is to compare with available data for $pA$ collisions, however, all existing models for the Cronin effect rely on a fit to the data to be explained. We develop a phenomenological description based on the light-cone QCD-dipole approach which allows to explain available data without fitting to them and to provide predictions for $pA$ collisions at RHIC and LHC. We point out that the mechanism causing Cronin effect drastically changes between the energies of fixed target experiments and RHIC-LHC. High-$p_T$ hadrons are produced incoherently on different nucleons at low energies, whereas the production amplitudes interfere if the energy is sufficiently high



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