The Nuclear Modification Factor at Large Rapidities

RHIC data on high-$p_T$ hadron production display strong suppression in a wide rapidity region, indicating strong induced energy loss for both transversally and longitudinally traveling partons. We investigate the interplay of energy loss and rapidity dependence in a perturbative QCD improved parton model, and estimate the opacity of the produced hot matter in $AuAu$ collisions at energies $\sqrt{s}=200$ $A$GeV and 63 $A$GeV at different rapidity values. Direction-dependent suppression offers the possibility to study the geometry of the hot matter.Comment: 4 pages, 2 figures, Contribution to the Poster Proceedings of the Quark Matter 2005 Conference. To be published in Nuclear Physics

Jets and Underlying Events at LHC Energies

Jet-matter interaction remains a central question and a theoretical challenge in heavy-ion physics and might become important in high-multiplicity events in proton-proton collisions at LHC energies. Full jet measurement at LHC offer the proper tool to investigate energy loss process and fragmentation of hard parton in the medium. Since jet reconstruction will be constrained to small cone sizes, then study of the connection between jets and surrounding environment provides a further possibility to extend our exploration. We study jets at s = (14 TeV)^2 and pp collisions at s = (7 TeV)^2. We analyze the flavor components in jet-like environments. We introduce a definition for surrounding cones/belts and investigate flavor dependence and correlation of different hadron species produced in jets. Here, we focus on proton-triggered correlations. Our analysis can be extended for heavy ion collisions.Comment: 4 pages, 2 figures, Proceedings of Hot Quarks 2010, 21-26 June 2010 Las Londe Les Maures; to appear in Journal of Physics: Conference Serie

Underlying events in p+p collisions at LHC energies

General properties of hadron production are investigated in proton-proton collisions at LHC energies. We are interested in the characteristics of hadron production outside the identified jet cones. We improve earlier definitions and introduce surrounding rings/belts around the cone of identified jets. In this way even multiple jet events can be studied in details. We define the underlying event as collected hadrons from outside jet cones and outside surrounding belts, and investigate the features of these hadrons. We use a PYTHIA generated data sample of proton-proton collisions at s = (7 TeV)^2. This data sample is analysed by our new method and the widely applied CDF method. Angular correlations and momentum distributions have been studied and the obtained results are compared and discussed.Comment: 5 pages, 5 figures, to appear in the EPJ Web of Conferences, Proceedings of the International Workshop on Hot and Cold Baryonic Matter 2010 (Budapest, Hungary, 15-20 August 2010

Where Does the Energy Loss Lose Strength?

Nuclear modification factors for pion production in AuAu and CuCu collisions are analyzed at very high transverse momenta. At p_T > 10 GeV/c, the R_{AA}(p_T) is determined mostly by the initial state nuclear modifications (e.g. EMC effect) and the non-Abelian jet-energy loss in the final state. At high momenta these effects together are strong enough to suppress R_{AA}(p_T) to below 1 at RHIC energies. We display results using HKN shadowing in our pQCD improved parton model. Result of a similar calculation at LHC energies for PbPb collisions are also displayed. Based on dN/dy estimates, a larger opacity value, L/\lambda_g = 10 +/- 2, is used for the produced partonic matter in central collisions at the LHC.Comment: QM 2008, Submitted to Jour. Phys. G, 4 pages and 4 figure