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Cronin Effect in Hadron Production off Nuclei

B. Z. Kopeliovich, J. Nemchik, A. Schaefer, A. V. Tarasov

TL;DR

A phenomenological description based on the light-cone QCD-dipole approach is developed which allows one to explain data without fitting to them and to provide predictions for pA collisions at RHIC and LHC.

Abstract

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.

Cronin Effect in Hadron Production off Nuclei

TL;DR

A phenomenological description based on the light-cone QCD-dipole approach is developed which allows one to explain data without fitting to them and to provide predictions for pA collisions at RHIC and LHC.

Abstract

Recent data from RHIC for high- hadrons in gold-gold collisions raised again the long standing problem of quantitatively understanding the Cronin effect, i.e. nuclear enhancement of high- 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- hadron production. The only possibility to test models is to compare with available data for 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 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- hadrons are produced incoherently on different nucleons at low energies, whereas the production amplitudes interfere if the energy is sufficiently high.

Paper Structure

This paper contains 11 equations, 3 figures.

Figures (3)

  • Figure 1: Ratio of the charged pion production cross sections for tungsten and beryllium function of the transverse momentum of the produced pions. The curves correspond to the parameter-free calculation Eq. (\ref{['60']}), the data are from fixed target experiments cronin2e605
  • Figure 2: Ratio of $p-Au$ to $pp$ cross sections as function of transverse momentum of produced pions at the energy of LHC calculated with Eq. (\ref{['80']}). The dashed and solid curves correspond to calculations without and with gluon shadowing respectively.
  • Figure 3: Predictions for RHIC. The dotted and dashed curves are calculated at $\sqrt{s}=200\,\hbox{GeV}$ using Eqs. (\ref{['60']}) and (\ref{['70']}) respectively. The final prediction taking into account the coherence length is shown by the solid curve.