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Register a new userInitial-state nuclear effects in proton-nucleus collisions
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Two important initial-state nuclear effects in hadron-nucleus collisions are considered. The ratios of inclusive differential cross sections for Drell-Yan dimuon production are calculated. The calculated results are compared to the E866 data. It is shown that consideration of multiple soft rescatterings of incident quarks in nuclei and initial-state quark energy loss effects allow to get a good agreement between the calculated results and the experimental data.
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Color fluctuations in hadron-hadron collisions are responsible for the presence of inelastic diffraction and lead to distinctive differences between the Gribov picture of high energy scattering and the low energy Glauber picture. We find that color fluctuations give a larger contribution to the fluctuations of the number of wounded nucleons than the fluctuations of the number of nucleons at a given impact parameter. The two contributions for the impact parameter averaged fluctuations are comparable. As a result, standard procedures for selecting peripheral (central) collisions lead to selection of configurations in the projectile which interact with smaller (larger) than average strength. We suggest that studies of pA collisions with a hard trigger may allow to observe effects of color fluctuations.
The energy dependence of light and heavy particle production in hadron-nucleus collisions is discussed. Whereas the production mechanism at lower energies can be understood in the Glauber rescattering picture, experimental data at RHIC indicate that particles are mostly produced in coherent processes. The importance of energy-momentum conservation is shown to be crucial at forward rapidities for the whole energy range. We also discuss the behaviour of $alpha (x_F)$ with energy for light particles and $J/psi$. Finally, we make predictions for the future LHC experiment.
We present an universal treatment for a substantial nuclear suppression representing a common feature of all known reactions on nuclear targets (forward production of high-pT hadrons, production of direct photons, the Drell-Yan process, heavy flavor production, etc.). Such a suppression at large Feynman xF, corresponding to region of minimal light-cone momentum fraction variable x2 in nuclei, is tempting to interpret as a manifestation of coherence or the Color Glass Condensate. We demonstrate, however, that it is actually a simple consequence of energy conservation and takes place even at low energies, where no effects of coherence are possible. We analyze this common suppression mechanism for several processes performing model predictions in the light-cone dipole approach. Our calculations agree with data.
Prompt photons produced in a hard reaction are not accompanied with any final state interaction, either energy loss or absorption. Therefore, besides the Cronin enhancement at medium transverse momenta pT and small isotopic corrections at larger pT, one should not expect any nuclear effects. However, data from PHENIX experiment exhibit a significant large-pT suppression in central d+Au and Au+Au collisions that cannot be accompanied by coherent phenomena. We demonstrate that such an unexpected result is subject to the energy sharing problem near the kinematic limit and is universally induced by multiple initial state interactions. We describe production of photons in the color dipole approach and find a good agreement with available data in p+p collisions. Besides explanation of large-pT nuclear suppression at RHIC we present for the first time predictions for expected nuclear effects also in the LHC energy range at different rapidities. We include and analyze also a contribution of gluon shadowing as a leading twist shadowing correction modifying nuclear effects at small and medium pT.
Proton-nucleus collisions provide a unique environment for studying the origin of anisotropic flows and the longitudinal properties of relativistic nuclear collisions. We perform the first event-by-event hydrodynamic simulations of asymmetric longitudinal decorrelations of elliptic, triangular and quadrangular flows in proton-lead collisions at the LHC. A set of rapidity-asymmetric decorrelation functions are proposed to measure the longitudinal flow decorrelations for asymmetric collision systems. Our result shows that the flow decorrelations in proton-going direction are larger than those in lead-going direction. We also compute rapidity-asymmetric and rapidity-symmetrized flow decorrelations in proton-gold collisions at RHIC, which exhibit larger decorrelation effects compared to the LHC. Further experimental and theoretical studies of longitudinal flow decorrelations in various symmetric and asymmetric systems across different colliding energies should provide powerful tools to probe the three-dimensional structure and evolution dynamics of relativistic nuclear collisions.
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