Recent results on hard probes with ALICE and STAR

This paper reviews recent experimental results on hard probes in heavy-ion collisions from the ALICE and STAR Collaboration. These studies include various observables characterizing jet properties like nuclear modification factors, recoil jet yields, di-jet and photon-jet energy imbalance, and the observables characterizing jet properties like jet fragmentation function and jet shapes; and measurements of high-$p_T$ charged hadrons from jet fragmentation and triggered particle correlations will be highlighted.Comment: Proceedings of XLVIII International Symposium on Multiparticle Dynamics (ISMD2018) Conference, Singapore, September 3-7, 201

Medium Recoils and background subtraction in JEWEL

\textsc{Jewel} is a fully dynamical event generator for jet evolution in a dense QCD medium, which has been validated for multiple jet and jet-like observables. Jet constituents (partons) undergo collisions with thermal partons from the medium, leading to both elastic and radiative energy loss. The recoiling medium scattering centers carry away energy and momentum from the jet. Keeping track of these recoils is essential for the description of intra-jet observables. Since the thermal component of the recoils is part of the soft background activity, comparison with data on jet observables requires the implementation of a background subtraction procedure. We will show two independent procedures through which background subtraction can be performed and discuss the impact of the medium recoil on jet shape observables and jet-background correlations. Keeping track of the medium recoil significantly improves the \textsc{Jewel} description of jet shape measurements.Comment: Proceedings for talk given at HP 2016 at Wuhan Chin

Jet injection studies for partially baffled mixing reactors: a general correlation for the jet trajectory and jet penetration depth

This paper is devoted to the analysis of the jet trajectories, obtained using computational fluid dynamics (CFD), at two different scales (laboratory and industrial) with application to quenching of runaway reactions. One of the goals was to describe how the jet penetrates the fluid in the stirred vessel and to build an easy to use correlation for research and industrial purposes. A model of the jet trajectory based on the analogy with a jet in a cross-flow has been used to predict the jet trajectory at the pilot and industrial scales. The correlation, built using a statistical analysis, has shown that the jet in a cross-flow model performs very well to describe the jet trajectories. A very interesting conclusion is that the correlation constants were found to be independent of scale. Finally, the authors proposed a definition of the penetration depth and use it in its dimensionless form to predict how the jet penetrates in the industrial vessel with the current injection conditions

The polarisation of afterglow emission reveals GRB jet structure

We numerically compute light and polarisation curves of gamma-ray burst afterglows for various configurations of the jet luminosity structure and for different dynamical evolutions. We especially consider the standard homogeneous ``top hat'' jet and the ``universal structured jet'' with power-law wings. We also investigate a possible more physical variation of the ``top hat'' model: the ``Gaussian jet''. The polarisation curves for the last two jet types are shown here for the first time together with the computation of X-ray and radio polarised fluxes. We show that the lightcurves of the total flux from these configurations are very similar to each other, and therefore only very high quality data could allow us to pin down the underlying jet structure. We demonstrate instead that polarisation curves are a powerful means to solve the jet structure, since the predicted behaviour of polarisation and its position angle at times around the jet break are very different if not opposite. We conclude that the afterglow polarisation measurements provide clear footprints of any outflow energy distribution (unlike the lightcurves of the total flux) and the joint analysis of the total and polarised flux should reveal GRBs jet structure.Comment: 16 pages, 18 figures, MNRAS, temp, 321. Light curves and polarisation curves for a Gaussian jet added. Cartoon of the three jet structures adde

Separated at Birth: Jet Maximization, Axis Minimization, and Stable Cone Finding

Jet finding is a type of optimization problem, where hadrons from a high-energy collision event are grouped into jets based on a clustering criterion. As three interesting examples, one can form a jet cluster that (1) optimizes the overall jet four-vector, (2) optimizes the jet axis, or (3) aligns the jet axis with the jet four-vector. In this paper, we show that these three approaches to jet finding, despite being philosophically quite different, can be regarded as descendants of a mother optimization problem. For the special case of finding a single cone jet of fixed opening angle, the three approaches are genuinely identical when defined appropriately, and the result is a stable cone jet with the largest value of a quantity J. This relationship is only approximate for cone jets in the rapidity-azimuth plane, as used at the Large Hadron Collider, though the differences are mild for small radius jets.Comment: 7 pages, 2 tables; v2: references added; v3: small clarifications and table 2 added to match journal versio

Theory of Jet Quenching in Ultra-Relativistic Nuclear Collisions

We present a short overview of recent progress in the theory of jet quenching in ultra-relativistic nuclear collisions, including phenomenological studies of jet quenching at RHIC and the LHC, development in NLO perburbative QCD calculation of jet broadening and energy loss, full jet evolution and modification, medium response to jet transport, and lattice QCD and AdS/CFT studies of jet quenching.Comment: 8 pages, 2 figures, proceedings of the XXIV Quark Matter conference, May 19-24 2014, Darmstadt (Germany

Review on recent developments in jet finding

We review recent developments related to jet clustering algorithms and jet finding. These include fast implementations of sequential recombination algorithms, new IRC safe algorithms, quantitative determination of jet areas and quality measures for jet finding, among many others. We also briefly discuss the status of jet finding in heavy ion collisions, where full QCD jets have been measured for the first time at RHIC.Comment: 5 pages, 5 figures, proceedings of the International Symposium on Multiparticle Dynamics 08, 15-20 september 2008, DES