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We present an analysis of the role that the quark-gluon plasma (QGP) resolution length, the minimal distance by which two nearby colored charges in a jet must be separated such that they engage with the plasma independently, plays in understanding the modification of jet substructure due to interaction with QGP. We identify a set of observables that are sensitive to whether jets are quenched as if they are single energetic colored objects or whether the medium that quenches them has the ability to resolve the internal structure of the jet. Using the hybrid strong/weak coupling model, we find that although the ungroomed jet mass is not suitable for this purpose (because it is more sensitive to effects coming from particles reconstructed as a part of a jet that originate from the wake that the jet leaves in the plasma), groomed observables such as the number of Soft Drop splittings $n_{\rm SD}$, the momentum sharing fraction $z_g$, or the groomed jet mass are particularly well-suited to discriminate the degree to which the QGP medium resolves substructure within a jet. In order to find the optimal grooming strategy, we explore different cuts in the Lund plane that allow for a clear identification of the regions of Soft Drop phase space that enhance the differences in the jet substructure between jets in vacuum and quenched jets. Comparison with present data seems to disfavor an "infinite resolution length", which is to say the hypothesis that the medium interacts with the jet as if it were a single energetic colored object. Our analysis indicates that as the precision of experimental measurements of jet substructure observables and the control over uncertainties in their calculation improves, it will become possible to constrain the value of the resolution length of QGP, in addition to seeing how the substructure of jets is modified via their passage through it., Comment: 50 pages, 5 figures

We propose a novel hybrid model for jet quenching, including both strong and weak coupling physics where each seems appropriate. Branching in the parton shower is assumed to be perturbative and described by DGLAP evolution, while interactions with the medium result in each parton in the shower losing energy as at strong coupling, as realized holographically. The medium-modified parton shower is embedded into a hydrodynamic evolution of hot QCD plasma and confronted with LHC jet data., Comment: 5 pages, 6 figures, Quark Matter 2014 proceedings

The strong modifications of dijet properties in heavy ion collisions measured by ATLAS and CMS provide important constraints on the dynamical mechanisms underlying jet quenching. In this work, we show that the transport of soft gluons away from the jet cone - jet collimation - can account for the observed dijet asymmetry with values of $\hat{q}\, L$ that lie in the expected order of magnitude. Further, we show that the energy loss attained through this mechanism results in a very mild distortion of the azimuthal angle dijet distribution., Comment: 4 pages, 2 figures; Proceedings of the "Quark Matter 2011" conference

This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from May 14th to June 10th 2007., Comment: LaTeX, 185 pages, uses iop styles; writeup of the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from May 14th to June 10th 2007

Monte Carlo simulations have been performed to determine the excess energy and the equation of state of fcc solids with Sutherland potentials for wide ranges of temperatures, densities and effective potential ranges. The same quantities have been determined within a perturbative scheme by means of two procedures: i) Monte Carlo simulations performed on the reference hard-sphere system and ii) second order Barker-Henderson perturbation theory. The aim was twofold: on the one hand, to test the capability of the 'exact' MC-perturbation theory of reproducing the direct MC simulations and, on the other hand, the reliability of the Barker-Henderson perturbation theory, as compared with direct MC simulations and MC-perturbation theory, to determine the thermodynamic properties of these solids depending on temperature, density and potential range. We have found that the simulation data for the excess energy obtained from the two procedures are in close agreement with each other. For the equation of state, the results from the MC-perturbation procedure also agree well with direct MC simulations except for very low temperatures and extremely short-ranged potentials. Regarding the Barker-Henderson perturbation theory, we have found that, surprisingly, the first-order approximation is in closer agreement with simulations than the second-order one., Comment: 19 pages, 2 figures

We study the interaction of a fast moving particle in the Quark Gluon Plasma with linearized hydrodynamics. We derive the linearized hydrodynamic equations on top of an expanding fireball, and detail the solutions for a static medium. There are two modes far from the jet -- a sound mode and a diffusion mode. The diffusion mode is localized in a narrow wake behind the jet while the sound mode propagates at the Mach angle, $\cos(\theta_M) = c_s/c$. A general argument shows that the strength of the diffusion mode relative to the sound mode is directly proportional to the entropy produced by the jet-medium interaction. This argument does not rely on the linearized approximation and the assumption of local thermal equilibrium close to the jet. With this insight we calculate the spectrum of secondaries associated with the fast moving particle. If the energy loss is large and the jet-medium interaction does not produce significant entropy, the flow at the Mach angle can be observed in the associated spectrum. However, the shape of associated spectra is quite fragile and sensitive to many of the inputs of the calculation., Comment: 31 pages, 8 figures

In high energy nuclear collisions, QCD jets deposit a large fraction of their energy into the produced matter. It has been proposed that as such matter behaves as a liquid with a very small viscosity, a fraction of this energy goes into a collective excitation called the ``conical flow'', similar e.g. to the sonic booms generated by the supersonic planes. In this work we study the effect of time-dependent speed of sound on the development of the conical wave. We show that the expansion of matter and the decrease of $c_s$ leads to an increase of observable manifestations of the conical flow. We also show that if the QCD phase transition is of the first order (and thus with vanishing speed of sound in the mixed phase) the wave must split into two, with opposite directions. We then argue that it is not the case experimentally, which supports the conclusion that the QCD phase transition is $not$ of the first order.

Quenching is a recently discovered phenomenon in which QCD jets created in heavy ion collisions deposit a large fraction or even all their energy and momentum into the produced matter. At RHIC and higher energies, where that matter is a strongly coupled Quark-Gluon Plasma (sQGP) with very small viscosity, we suggest that this energy/momentum propagate as a collective excitation or ``conical flow''. Similar hydrodynamical phenomena are well known, e.g. the so called sonic booms from supersonic planes. We solve the linearized relativistic hydrodynamic equations to detail the flow picture. We argue that for RHIC collisions the direction of this flow should make a cone at a specific large angle with the jet, of about $70^o$, and thus lead to peaks in particle correlations at the angle $\Delta\phi=\pi\pm 1.2$ rad relative to the large-$p_t$ trigger. This angle happens to matchperfectly the position of the maximum in the angular distribution of secondaries associated with the trigger recently seen by the STAR and PHENIX collaborations. We also discuss briefly possible alternative explanations and suggest some further tests to clarify the mechanism., Comment: Extended version submitted to Journal of Physics G: Conference Series, Workshop on Correlations and Fluctuations in Relativistic Nuclear Collisions, MIT, April 21-23, 2005

We have performed extensive Monte Carlo simulations in the canonical (NVT) ensemble of the pair correlation function for square-well fluids with well widths $\lambda-1$ ranging from 0.1 to 1.0, in units of the diameter $\sigma$ of the particles. For each one of these widths, several densities $\rho$ and temperatures $T$ in the ranges $0.1\leq\rho\sigma^3\leq 0.8$ and $T_c(\lambda)\lesssim T\lesssim 3T_c(\lambda)$, where $T_c(\lambda)$ is the critical temperature, have been considered. The simulation data are used to examine the performance of two analytical theories in predicting the structure of these fluids: the perturbation theory proposed by Tang and Lu [Y. Tang and B. C.-Y. Lu, J. Chem. Phys. {\bf 100}, 3079, 6665 (1994)] and the non-perturbative model proposed by two of us [S. B. Yuste and A. Santos, J. Chem. Phys. {\bf 101}, 2355 (1994)]. It is observed that both theories complement each other, as the latter theory works well for short ranges and/or moderate densities, while the former theory does for long ranges and high densities., Comment: 10 pages, 10 figures

We propose a model aimed at explaining jet quenching, large azimuthal asymmetry and baryon/meson ratio at large transverse momenta pt=2-10 GeV observed at RHIC. Its main point is that a QCD string can be cut by matter quarks and/or diquarks before its natural breaking. We model the early quark/diquark production via QCD sphalerons., Comment: 4 pages, 4 figures

We have obtained by Monte Carlo NVT simulations the constant-volume excess heat capacity of square-well fluids for several temperatures, densities and potential widths. Heat capacity is a thermodynamic property much more sensitive to the accuracy of a theory than other thermodynamic quantities, such as the compressibility factor. This is illustrated by comparing the reported simulation data for the heat capacity with the theoretical predictions given by the Barker-Henderson perturbation theory as well as with those given by a non-perturbative theoretical model based on Baxter's solution of the Percus-Yevick integral equation for sticky hard spheres. Both theories give accurate predictions for the equation of state. By contrast, it is found that the Barker-Henderson theory strongly underestimates the excess heat capacity for low to moderate temperatures, whereas a much better agreement between theory and simulation is achieved with the non-perturbative theoretical model, particularly for small well widths, although the accuracy of the latter worsens for high densities and low temperatures, as the well width increases., Comment: 11 pages, 4 figures; figures now include additional perturbation data; to be published in Mol. Phys