Energy losses in the black disc regime and correlation effects in the STAR forward pion production in dAu collisions

Abstract

We argue that in the small x processes, in the black disc QCD regime (BDR) a very forward parton propagating through the nuclear matter should loose a significant and increasing with energy and atomic number fraction of its initial energy as a result of dominance of inelastic interactions, causality and energy-momentum conservation. We evaluate these energy losses and find them to lead to the significant suppression of the forward jet production in the central NA collisions at collider energies with a moderate suppression of recoiling jet at central rapidities. We confront our expectations with the recent RHIC data of the STAR collaboration on the probability, $P$, for emission of at least one fast hadron at a central rapidity in association with production of a very forward high $p_t$ neutral pion in $pp$ and $dAu$ collisions. We calculate the A-dependence of $P$, and find that the data imply a strong suppression of leading pion production at central impact parameters. We also conclude that production of recoil jets in the hard subprocess is not suppressed providing further evidence for the dominance of peripheral collisions. Both features of the data are consistent with the onset of BDR. We suggest new phenomena and new observables to investigate BDR at RHIC and LHC.

18 pages,final text to be published in Phys.Lett.B, evaluation of the fractional energy energy losses in the black disk regime is ellaborated

References in corpus (2)

• Azimuthal Angle Correlations for Rapidity Separated Hadron Pairs in d+Au Collisions at sqrt(s_NN) = 200 GeV
• The casuality and/or energy-momentum conservation constraints on QCD amplitudes in small x regime

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• Particle Production at High Energy and Large Transverse Momentum - "The Hybrid Formalism" Revisited
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• Evidence for Nonlinear Gluon Effects in QCD and their $A$ Dependence at STAR
• Impact of fully coherent energy loss on heavy meson production in pA collisions
• Baryon Stopping in Proton-Nucleus Collisions
• Single and double inclusive particle production in d+Au collisions at RHIC, leading twist and beyond
• Large t diffractive rho-meson photoproduction with target dissociation in ultraperipheral pA and AA collisions at LHC
• Leading twist shadowing, black disk regime and forward hadron production