Theory summary. Hard Probes 2012

I provide a summary of the theoretical talks in Hard Probes 2012 together with some personal thoughts about the present and the future of the field.Comment: 8 pages. Proceedings of the conference Hard Probes 2012 - Sardinia - Italy - May 27 -June 1 2012 --- Comments welcom

Jet quenching

High-pt particles produced in nucleus-nucleus collisions constitute a powerful tool to study the medium properties. The energy loss resulting from the propagation of these particles in the produced medium translates into a suppression of the high-pt yields. These effects are usually associated to medium-induced gluon radiation which, in turn, predicts a broadening of the jet-like signals. Both the energy loss and the jet broadening are expected to increase proportionally to the medium density. In the more realistic case of a dynamically expanding medium, the gluon radiation becomes anisotropic due to the presence of a preferred direction in the transverse plane with respect to the axis of propagation. This anisotropy translates into deformed jet-shapes which provide new posibilities to study these flows by high-pt measurements.Comment: To appear in the proceedings of the XXXX Rencontres de Moriond. QCD and high energy hadronic interaction

Hard QCD probes to quark-gluon plasma

Completely unexplored regimes of QCD, dominated by high-density/temperature effects, are available in heavy ion experiments at collider energies. The successful RHIC program shows how relevant the high transverse momentum part of the spectrum is for the characterization of the properties of the created medium. It points, as well, to interesting properties of the nuclear wave function at small fraction of momentum x, probably dominated by saturated color fields. In both domains, the imminent LHC program will provide a phase space enlarged by orders of magnitude with respect to those studied at RHIC. I will review the present status of hard probes in heavy ion collisions as well as the expectations for the LHC.Comment: 8 pages, invited talk at the YKIS Seminar on New Frontiers in QC

Neutrino-nucleus DIS data and their consistency with nuclear PDFs

In this talk, we discuss the compatibility of different deeply inelastic neutrino-nucleus data sets and the universal nuclear PDFs. This is an issue that has lately been investigated by different groups but the conclusions have been surprisingly contradictory. While some studies have found a good overall agreement between the nuclear PDFs and the neutrino data, others have claimed for an incompatibility. Here, we demonstrate that the independent neutrino data sets from NuTeV, CHORUS and CDHSW collaborations differ in the absolute overall normalization and that it is not possible to accurately reproduce all the data simultaneously with a single set of PDFs. Our strategy to overcome this difficulty and allow a consistent use of all neutrino data in global PDF analyses is to normalize the data by the integrated cross-sections thereby cancelling possible inaccuracies in the absolute normalization. Indeed, this brings all data to a surprisingly good mutual agreement underscoring the x-dependence of the nuclear modifications in a model-independent way. The consistency of these data with the present nuclear PDFs is verified by introducing a method to test the effect of a new data set in an existing global fit that performed a Hessian error analysis.Comment: A transcription of the talk given in XXI International Workshop on Deep-Inelastic Scattering and Related Subjects, Marseilles, Franc

Introductory lectures on jet quenching in heavy ion collisions

Jet quenching has become an essential signal for the characterization of the medium formed in experiments of heavy-ion collisions. After a brief introduction to the field, we present the full derivation of the medium-induced gluon radiation spectrum, starting from the diagrammatical origin of the Wilson lines and the medium averages and including all intermediate steps. The application of this spectrum to actual phenomenological calculations is then presented, making comparisons with experimental data and indicating some improvements of the formalism to the future LHC program. The last part of the lectures reviews calculations based on the AdS/CFT correspondence on the medium parameters controlling the jet quenching phenomenon.Comment: 63 pages, 17 figures, Presented at the XLVII Cracow School of Theoretical Physics, Zakopane, Poland, June 14-22, 200