We argue that "ridge" in 2-particle correlation function associated with hard trigger at RHIC heavy ion collisions is naturally explained by an interrelation of jet quenching and hydrodynamical transverse flow. The excess particles forming the ridge are produced by QCD bremsstrahlung along the beam (and thus have wide rapidity distribution) and then boosted by transverse flow. Nontrivial correlation between directions of the jet and the radial flow is provided by jet quenching: our straightforward and basically parameter-independent calculation reproduces the angular shape, width and other properties of the "ridge".
Hadron correlations in jets, ridges and opposite dijets at all $p_T$ above 2 GeV/c are discussed. Since abundant data are available from RHIC at intermediate $p_T$, a reliable hadronization scheme at that $p_T$ range is necessary in order to relate the semihard partonic processes to the observables. The recombination model is therefore first reviewed for that purpose. Final-state interaction is shown to be important for the Cronin effect, large B/M ratio and forward production. The effect of semihard partons on the medium is then discussed with particular emphasis on the formation of ridge wit…
An $η$-elongated same-side 2D peak ("soft ridge") in minimum-bias angular correlations from heavy ion collisions has been attributed both to jet formation and to initial-state geometry structure coupled to radial flow. We consider evidence for both interpretations.
An interpretation of the ridge phenomenon found in pp collisions at 7 TeV is given in terms of enhancement of soft partons due to energy loss of semihard jets. A description of ridge formation in nuclear collisions can directly be extended to pp collisions, since hydrodynamics is not used, and azimuthal anisotropy is generated by semihard scattering. Both the p_T and multiplicity dependencies are well reproduced. Some suggestions are made about other observables.
We attribute the phenomenon known as "the ridge" to long range initial state correlations from Color Glass Condensate flux tubes and later stage radial flow. We show that this description can explain the amplitude and azimuthal width of the soft ridge and nearly explain that of the hard ridge, suggesting that the two are essentially the same phenomenon.
Azimuthal anisotropy in heavy-ion collisions is studied by taking into account the ridges generated by semi-hard scattering of intermediate-momentum partons, which can be sensitive to the initial spatial configuration of the medium in non-central collisions. In a simple treatment of the problem where the recombination of only thermal partons is considered, analytical formulas can be derived that yield results in accord with the data on v_2 for p_T <1-2 GeV/c. Centrality dependence is described by a geometrical factor. Ridge phenomenology is used to determine the initial slopes of v_2 at low p_…
Within the AMPT Monte Carlo model, hot spots in the initial transverse parton density are shown to lead to harmonic flows which all contribute to dihadron azimuthal correlation. The net back-to-back dihadron correlation after subtraction of harmonic flows still has a double-peak that is independent of the initial geometric triangularity at a fixed impact-parameter and unique to the structure of jet-induced Mach cone and expanding hot spots dragged by radial flow. The longitudinal structure of hot spots also leads to a near-side ridge in dihadron correlation with a large rapidity gap. By succes…
We investigate the consequences of long range rapidity correlations in the Glasma. Particles produced locally in the transverse plane are correlated by approximately boost invariant flux tubes of longitudinal color electric and magnetic fields that are formed when two sheets of Colored Glass Condensate pass through one another, each acquiring a modified color charge density in the collision. We argue that such long range rapidity correlations persist during the evolution of the Quark Gluon Plasma formed later in the collision. When combined with transverse flow, these correlations reproduce ma…
We study untriggered di-hadron correlations in Pb+Pb at 2.76 TeV, based on an event-by-event simulation of a hydrodynamic expansion starting from flux tube initial conditions. The correlation function shows interesting structures as a function of the pseudorapidity difference $Δη$ and the azimuthal angle difference $Δϕ$, in particular comparing different centralities. We can clearly identify a peak-like nearside structure associated with very low momentum components of jets for peripheral collisions, which disappears towards central collisions. On the other hand, a very broad ridge structure f…
Glasma Flux Tubes, Mono Jets with squeeze out flow around them plus the Chiral Magnetic Effect(CME) are physical phenomenon that generate two particle correlation with respect to the reaction plane in mid-central 20\% to 30\% Au-Au collision $\sqrt{s_{NN}}$ = 200.0 GeV measured at RHIC.
In this study, the momentum-kick model is used to understand the ridge behaviours in dihadron $Δη$--$Δφ$ correlations recently reported by the LHC in high-multiplicity proton-proton (pp) collisions. The kick stand model is based on a momentum kick by leading jets to partons in the medium close to the leading jets. The medium where partons move freely is assumed in the model regardless of collision systems. This helps us apply the method to small systems like pp collisions in a simple way. Also, the momentum transfer is purely kinematic and this provides us a strong way to approach the ridge be…
A simple jet absorption model is used to study the influence of hadron pairs produced by quenched jets, on di-hadron angular correlations at intermediate transverse momentum ($p_T$). We demonstrate that such pairs can dominate both the yield and the shape of angular correlations, and may account for the similar properties between the near-side "ridge" and the away-side "double-humped" structure seen in recent data. These hadron pairs also show azimuthal anisotropy which is sensitive to the emission angle of hadrons relative to that of the jet. Measurement of this anisotropy may provide a const…
Pseudorapidity and azimuthal three-particle correlations are studied based on a correlated-cluster model of multiparticle production. The model provides a common framework for correlations in proton-proton and heavy-ion collisions allowing easy comparison with the measurements. It is shown that azimuthal cluster correlations are definitely required in order to understand three-particle correlations in the near-side ridge effect. This is similar to the explanation of the ridge phenomenon found in our previous analysis of two-particle correlations and generalizes the model to higher-order correl…
Di-jet correlations in nucleus-nucleus collisions are studied within the Hadron-String-Dynamics (HSD) transport approach taking into account the reaction of the medium on the jet energy loss nonperturbatively. A comparison with the STAR and PHENIX data in central Au+Au collisions at the RHIC energy $\sqrt{s}=200$ GeV is performed differentially, i.e. with respect to correlations in azimuthal angle $Δϕ$ and pseudorapidity $Δη$. The HSD results do not show enough suppression for the `away-side' jets in accordance with earlier perturbative studies. Furthermore, the `Mach-cone' structure for the a…
In this paper we report the effect of the jet-medium interplay as implemented in EPOS 3 on the ridge like structure observed in high multiplicity p-Pb collisions at $\sqrt{s_{NN}} = $ 5.02 TeV. EPOS 3 takes into account hydrodynamically expanding bulk matter, jets and the jet-medium interaction. The basis of this model is multiple scatterings where each scattering finally produces flux tube / string. In the higher multiplicity event classes where the flux tube/string density is higher, there is a finite probability that the strings will pick up quarks and antiquarks (or diquarks) from the bulk…
The QCD matter produced in nuclear collisions at the Relativistic Heavy Ion Collider (RHIC) has been found to have a very low shear viscosity, which is close to the lower bound allowed by unitarity. The matter has also been found to strongly suppress the emission of energetic hadrons. This phenomenon, called "jet quenching" is interpreted to be the result of a large energy loss by the precursor parton on its path through the dense matter, primarily due to gluon radiation. I discuss how the two phenomena are related. The RHIC data suggest, in some scenarios of jet quenching, that the quark-gluo…
Starting with a reminder of what is strongly coupled Quark-Gluon Plasma (sQGP), we proceed to recent advances in jet quenching and heavy quark diffusion, with a brief summary of various results based on AdS/CFT correspondence. The conical flow is a hydrodynamical phenomenon created by energy and entropy deposited by high energy jets propagating in matter, similar in nature to well known sonic boom from the supersonic planes. After a brief review, we discuss excitations of two hydro modes -- sound and ``diffuson'' -- which can be excited in this way. We also study expanding matter case, with a …
We review the models suggested, to date, as an explanation for the so called "ridge" phenomenon, an elongation in rapidity of 2-particle correlations seen at RHIC and LHC energies. We argue that these models can be divided into two phenomenologically distinct classes: "Hotspot+flow" driven correlations, where initial state correlations created by structures local in configuration space are collimated by transverse flow, and models where the azimuthal correlation is created through local partonic interactions in a high gluon density initial state. We further argue that the key to distinguish th…
Heavy ion collisions at RHIC are well described by the (nearly ideal) hydrodynamics. In the present paper we study propagation of perturbations induced by moving charges (jets) on top of the expanding fireball, using hydrodynamics and (dual) magnetohydrodynamics. Two experimentally observed structures, called a "cone" and a "hard ridge", have been discovered in dihadron correlation function with large-$p_t$ trigger, while "soft ridge" is a similar structure seen without hard trigger. All three can be viewed as traces left by a moving charge in matter, on top of overall expansion. A puzzle is w…
The suppression of high transverse momentum particles, recently discovered at RHIC, is commonly interpreted as due to parton energy loss. In high energy nuclear collisions, QCD jets would deposit a large fraction of their energy and into the produced matter. The question of how this energy is degraded and whether we can use this phenomenon to probe the properties of the produced matter is now under active discussion. It has been proposed that if this matter, which is now being referred to as a {\em strongly coupled Quark-Gluon Plasma} (sQGP), may behave as a liquid with a very small viscosity.…
We present the predictions of a hydrodynamic model for the flow observables recently measured in the highest-multiplicity p+Pb collisions at the LHC. We focus o the ridge phenomenon, which provides an important probe of the long-range dynamics and may be used to support the collective interpretation of the p+A data.
Two-particle angular correlation for charged particles emitted in Au+Au collisions at the center-of-mass of 200 MeV measured at RHIC energies revealed novel structures commonly referred to as a near-side ridge. The ridge phenomenon in relativistic A+A collisions is rooted probably in the initial conditions of the thermal evolution of the system. In this study we analyze the evolution of the bumping transverse structure of the energy density distribution caused by fluctuations of the initial density distributions that could lead to the ridge structures. We suppose that at very initial stage of …
The azimuthal anisotropy due to path-length dependent jet energy loss is studied in a simple jet absorption model that include event by event fluctuating Glauber geometry. Significant anisotropy coefficients v_n are observed for n=1,2 and 3, but they are very small for n>3. These coefficients are expected to result in a "ridge" for correlations between two independently produced jets. The correlations between the orientation of the n^{th}-order anisotropy induced by jet absorption (Φ_n^{QP}) and the n^{th}-order participant plane (Φ_n^{PP}) responsible for harmonic flow are studied. Tight corr…
The Monte Carlo event generator HYDJET++ is one of the few generators, designed for the calculations of heavy-ion collisions at ultrarelativistic energies, which combine treatment of soft hydro-like processes with the description of jets traversing the hot and dense partonic medium. The model is employed to study the azimuthal anisotropy phenomena, dihadron angular correlations and event-by-event (EbyE) fluctuations of the anisotropic flow in Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV. The interplay of soft and hard processes describes the violation of the mass hierarchy of meson and baryo…
The phenomenon of jet quenching provides essential information about the properties of hot and dense matter created in ultra-relativistic heavy-ion collisions. Recent results from experiments at the Large Hadron Collider (LHC) show evidence for an unexpectedly similar suppression of both light and heavy flavor jets. Furthermore, the role of radiative energy loss of heavy quarks is still under active discussion within the theoretical community. By employing the parton cascade Boltzmann Approach to Multi-Parton Scatterings (BAMPS), which numerically solves the 3+1D Boltzmann equation both for li…
The diffusion wake accompanying the jet-induced Mach cone provides a unique probe of the properties of quark-gluon plasma in high-energy heavy-ion collisions. It can be characterized by a depletion of soft hadrons in the opposite direction of the propagating jet. We explore the 3D structure of the diffusion wake induced by $γ$-triggered jets in Pb+Pb collisions at the LHC energy within the coupled linear Boltzmann transport and hydro model. We identify a valley structure caused by the diffusion wake on top of a ridge from the initial multiple parton interaction (MPI) in jet-hadron correlation …
