Punch-through jets in $A+A$ collisions at RHIC/LHC
Hanzhong Zhang, J. F. Owens, Enke Wang, X. -N. Wang
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4 pages, 4 figures, proceedings for the 20th international conference on ultra-relativistic nucleus-nucleus collisions (QM2008), Jaipur, India, February 4-10, 2008
High $p_T$ single and dihadron production is studied within a NLO pQCD parton model with jet quenching in high energy $A+A$ collisions at the RHIC/LHC energy. A simultaneous $χ^2$-fit to both single and dihadron spectra can be achieved within a narrow range of energy loss parameter. Punch-through jets are found to result in the dihadron suppression factor slightly more sensitive to medium than the single hadron suppression factor at RHIC. Such jets at LHC are found to dominate high $p_T$ dihadron production and the resulting dihadron spectra are more sensitive to the initial parton distribution functions than the single hadron spectra.
We solve (3+1)-dimensional ideal hydrodynamical equations with source terms that describe punch-through and fully stopped jets in order to compare their final away-side angular correlations in a static medium. For fully stopped jets, the backreaction of the medium is described by a simple Bethe-Bloch-like model which leads to an explosive burst of energy and momentum (Bragg peak) close to the end of the jet's evolution through the medium. Surprisingly enough, we find that the medium's response and the corresponding away-side angular correlations are largely insensitive to whether the jet punch…
The suppression of single jets at high transverse momenta in a quark-gluon plasma is studied at RHIC energies, and the additional information provided by a photon tag is included. The energy loss of hard jets traversing through the medium is evaluated in the AMY formalism, by consistently taking into account the contributions from radiative events and from elastic collisions at leading order in the coupling. The strongly-interacting medium in these collisions is modelled with (3+1)-dimensional ideal relativistic hydrodynamics. Putting these ingredients together with a complete set of photon-pr…
The dependence of the radiative energy loss of fast partons on the initial thermodynamic parameters is studied for deconfined matter to be expected at RHIC. We demonstrate that the specific QCD radiation pattern with a quadratic dependence of the energy loss on the propagated distance leads to a strong increase of the energy loss with increasing initial entropy of deconfined matter supposed its life-time is less than the average time to pass through the medium. This is in contrast to a parameterization with constant energy loss per unit length of propagation. For a sufficiently high initial te…
We evaluate the azimuthal asymmetries for the distributions of leading pions inside a jet, produced in high-energy proton-proton collisions, in kinematic configurations currently under active investigation at RHIC. Adopting a transverse momentum dependent approach, which assumes the validity of a perturbative QCD factorization scheme and takes into account all the spin and intrinsic parton motion effects, we show how the main mechanisms underlying these asymmetries, namely the Sivers and the Collins effects, can be disentangled. Furthermore, we consider the impact of color-gauge invariant init…
Impact of the cone algorithm parameters Ecut, Eseed, R on the efficiency and characteristics of the reconstructed jets in p-p collisions at the energy sqrt s = 200 GeV is studied. The PYTHIA Monte Carlo generator is used for event generation. The dependence of dijet production fraction on the parton transverse momentum at different algorithm parameters is analyzed. The dependence of reconstruction efficiency of parton energy in dijet events and two leading jets in N-jet events on Ecut, Eseed, R is studied. Monte Carlo results are compared with predictions made in the framework of z-scaling and…
We review the current status of jet measurements in heavy-ion collisions at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). We discuss how the current measurements provide information about the quark-gluon plasma and discuss near future opportunities at both RHIC and the LHC.
High P_T observables associated with hard pQCD processes are regarded as tomographic probes of the medium created in ultrarelativistic heavy-ion collisions. Unfortunately, tomography is unexpectedly complicated in practice due to model uncertainties and the highly averaged nature of many observables. However, a systematic comparison study demanding a simultaneous description of many observables within the same framework is sufficiently powerful to rule out a large fraction of conjectured models about the physics mechanism of parton-medium interaction. From this study, it can be inferred that t…
Dynamical net charge fluctuations have been studied in ultra-relativistic heavy-ion collisions from the beam energy scan at RHIC and LHC energies by carrying out the hadronic model simulation. Monte Carlo model, HIJING is used to generate events in two different modes, HIJING-default with jet quenching switched off and jet/minijet production switched off. A popular variable, $ν_{[+-,dyn]}$ is used to study the net charge fluctuations in different centrality bins and the findings are compared with the available experimental values reported earlier. Although the broad features of net charge fluc…
Typically the materialization of high energetic transverse partons to hadronic jets is assumed to occur outside the reaction zone in a relativistic heavy ion collision. In contrast, a quantum mechanical estimate yields a time on the order of only a few fm/c for building up the hadronic wavefunction for jets with typical transverse momenta of pT < 10 GeV as accessible at RHIC facilities. The role of possible elastic or inelastic collisions of these high pT particles with the bulk of hadrons inside the fireball is addressed by means of an opacity expansion in the number of collisions. This analy…
Hard probes are a cornerstone in the ongoing program to determine the properties of hot and dense QCD matter as created in ultrarelativistic heavy ion collisions. LHC measurements have so far resulted in a wealth of high P_T data, opening new kinematic windows with high statistics. Yet on first glance, several observations are counter-intuitive and seem to contradict results from the RHIC high P_T program. This calls for a combined analysis of high P_T hadrons and reconstructed jets at RHIC and LHC in a unified framework testing a large number of theoretical models for both medium evolution an…
We present POWHEG predictions for photon-jet correlations at RHIC and the LHC. We show that the total transverse-momentum spectrum of photons and jets is modified not only by medium, but also by higher-order QCD effects, as is the distribution in their relative azimuthal angle. At the LHC, photon-jet measurements in the forward region allow to probe parton momentum fractions of lead ions down to 10$^{-4}$.
We study the induced photon bremsstrahlung from a fast quark produced in AA-collisions due to multiple scattering in quark-gluon plasma. For RHIC and LHC conditions the induced photon spectrum is sharply peaked at photon energy close to the initial quark energy. In this region the contribution of the induced radiation to the photon fragmentation function exceeds the ordinary vacuum radiation. Contrary to previous analyses our results show that at RHIC and LHC energies the final-state interaction effects in quark-gluon plasma do not suppress the direct photon production, and even may enhance it…
We compare results of $k_t$-factorization approach and next-to-leading order collinear-factorization approach for dijet correlations in proton-proton collisions at RHIC energies. We discuss correlations in azimuthal angle as well as correlations in two-dimensional space of transverse momenta of two jets. Some $k_t$-factorization subprocesses are included for the first time in the literature. Different unintegrated gluon/parton distributions are used in the $k_t$-factorization approach. The results depend on UGDF/UPDF used. For collinear NLO case the situation depends significantly on whether w…
Higher-order pQCD corrections play an important role in the reproduction of data at high transverse momenta in the energy range 20 GeV $ \leq \sqrt{s} \leq 200$ GeV. Recent calculations of photon and pion production in $pp$ collisions yield detailed information on the next-to-leading order contributions. However, the application of these results in proton-nucleus and nucleus-nucleus collisions is not straightforward. The study of nuclear effects requires a simplified understanding of the output of these computations. Here we summarize our analysis of recent calculations, aimed at handling the …
We attempt to deduce simple options of `jet quenching' phenomena in heavy-ion collisions at $\snn=5.5 \tev$ at the LHC from the present knowledge of leading-hadron suppression at RHIC energies. In light of the nuclear modification factor for leading particles we introduce the nuclear modification factor for jets, $\RAA^{jet}$, and for the longitudinal momenta of particles along the jet axis, $\RAA^{p_{\rm L}}$.
The method to simulate the rescattering and energy loss of hard partons in ultrarelativistic heavy ion collisions has been developed. The model is a fast Monte-Carlo tool introduced to modify a standard PYTHIA jet event. The full heavy ion event is obtained as a superposition of a soft hydro-type state and hard multi-jets. The model is applied to analysis of the jet quenching pattern at RHIC.
Energy and momentum lost by hard jets propagating through hot and dense nuclear matter have to be redistributed in the medium. It has been conjectured that collective sound modes are excited. Those lead to Mach cone nuclear shock waves in the nuclear medium that are shown to account for three and four particle angular correlation structures of hadrons with a (semi-)hard trigger hadron in heavy-ion collisions at RHIC.
Kinematical correlations between outgoing partons (elementary particles) are discussed in the framework of $k_t$-factorization. Different unintegrated gluon distributions are used. I discuss correlations between charm-anticharm, jets, photon and jet, and between leptons from semileptonic decays of heavy quarks as well as leptons produced in the Drell-Yan mechanism. Both correlations in azimuth as well as in the length of transverse momenta are shown. General conclusions are drawn.
We compare results of $k_t$-factorization approach and next-to-leading order collinear-factorization approach for dijet correlations in proton-proton collisions at RHIC energies. We discuss correlations in azimuthal angle as well as correlations in two-dimensional space of transverse momenta of two jets. Some $k_t$-factorization subprocesses are included for the first time in the literature. Different unintegrated gluon/parton distributions are used in the $k_t$-factorization approach. The results depend on UGDF/UPDF used. Limitations due to leading jet condition are discussed.
High transverse momentum (P_T) processes are considered to be an important tool to probe and understand the medium produced in ultrarelativistic heavy-ion collisions via the interaction of hard, perturbatively produced partons with the medium. In this context, triggered hard dihadron correlations constitute a class of observables set between hard single inclusive hadrons (dominated by the leading jet fragments) and fully reconstructed jets - while they probe some features of the perturbative QCD evolution of a parton shower in the medium, they do not suffer from the problem of finding a suitab…
The model to simulate rescattering and partonic energy loss in ultrarelativistic heavy ion collisions is presented. The full heavy ion event is obtained as a superposition of a soft hydro-type state and hard multi-jets. This model is capable of reproducing main features of the jet quenching pattern at RHIC, and is applied to probe jet quenching in various novel channels at LHC.
We discuss the emission of high momentum lepton pairs in central Au+Au collisions at RHIC ($\sqrt{s_{NN}}=$200 GeV) and Pb+Pb collisions at the LHC ($\sqrt{s_{NN}}=$5500 GeV). Yields of dileptons produced through interactions of jets with thermal partons have been calculated, with next-to-leading order corrections through hard thermal loops (HTL) resummation. They are compared to thermal dilepton emission and the Drell-Yan process. A complete leading order treatment of jet energy loss has been included. Jet-plasma interactions are found to dominate over thermal dilepton emission for all values…
The Monte Carlo HYDJET++ model, that contains both hydrodynamic state and jets, is applied to study the influence of the interplay between soft and hard processes on the formation of the elliptic flow in heavy-ion collisions at RHIC and LHC energies. Jets are found to cease the hydro-like increase of the elliptic flow with rising p_T. Since jets are more influential at LHC than at RHIC, the v_2 at LHC should be weaker than that at RHIC. Violation of the number-of-constituent-quark (NCQ) scaling is predicted. The decays of resonances are found to enhance the low-p_T part of the elliptic flow of…
We report the results of $γ_{\rm dir}$ and $π^{0}$-hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at $\sqrt{s_{_{NN}}}$=200 GeV in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity with respect to high-$p_{T}$ $γ_{\rm dir}$ and $π^{0}$ in central Au+Au collisions are compared with p+p collisions. Within uncertainties, the same $z_{T}$ (~$p_{T}^{\mathrm{assoc}}$ / $p_{T}^{\mathrm{trig}}$) dependence of the suppression is observed for $γ_{\rm dir}$ and $π^{0}$ - triggers. The results are compared…
The model to simulate jet quenching effect in ultrarelativistic heavy ion collisions is presented. The model is the fast Monte-Carlo tool implemented to modify a standard PYTHIA jet event. The model has been generalized to the case of the "full" heavy ion event (the superposition of soft, hydro-type state and hard multi-jets) using a simple and fast simulation procedure for soft particle production. The model is capable of reproducing main features of the jet quenching pattern at RHIC and is applyed to analyze novel jet quenching features at LHC.
Jet substructure of light and heavy flavor jets at RHIC
Stony Brook University（石溪大学）；Georgia State University（佐治亚州立大学）；Center for Frontiers in Nuclear Science, Stony Brook University（石溪大学核科学前沿中心）；Jefferson Lab（杰斐逊实验室）
We discuss recent applications of the partonic pQCD based cascade model BAMPS with focus on heavy-ion phenomeneology in hard and soft momentum range. The nuclear modification factor as well as elliptic flow are calculated in BAMPS for RHIC end LHC energies. These observables are also discussed within the same framework for charm and bottom quarks. Contributing to the recent jet-quenching investigations we present first preliminary results on application of jet reconstruction algorithms in BAMPS. Finally, collective effects induced by jets are investigated: we demonstrate the development of Mac…
We investigate the Collins azimuthal asymmetry of hadrons produced inside jets in transversely polarized proton-proton collisions. Recently, the quark transversity distributions and the Collins fragmentation functions have been extracted within global analyses from data of the processes semi-inclusive deep inelastic scattering and electron-positron annihilation. We calculate the Collins azimuthal asymmetry for charged pions inside jets using these extractions for RHIC kinematics at center-of-mass energies of 200 and 500 GeV. We compare our results with recent data from the STAR Collaboration a…
Fluctuation measurements of event-wise mean transverse momentum $\langle p_t \rangle$ for p-p and Pb-Pb collisions at the large hadron collider (LHC) have been reported recently. In that study it was concluded that the strength of "nonstatistical" $\langle p_t \rangle$ fluctuations decreases with increasing particle multiplicity $n_{ch}$ (or A-A centrality) and is nearly independent of collision energy over a large interval. Among several potential mechanisms for those trends onset of thermalization and collectivity are mentioned. The LHC analysis employed one fluctuation measure selected from…
We argue that if the growing part of hadron-hadron cross section (described phenomenologically by the supercritical soft Pomeron) is due to instanton/sphaleron mechanism, one should find certain qualitative features of the produced cluster which differ from the usual string fragmentation. Furthermore, we suggest that this mechanism should be even more important for heavy ion collisions in the RHIC energy domain. Large number of parton-parton collisions should result in hundreds of produced sphaleron-like gluomagnetic clusters per unit rapidity. Unlike perturbative gluons (or mini-jets), these …
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 arg…
We consider the single-inclusive minijet cross section in pA at forward rapidity within the Color Glass Condensate model of high energy collisions. We show that the nucleus appears black to the incident quarks except for very large impact parameters. A markedly flatter p_t distribution as compared to QCD in the dilute perturbative limit is predicted for transverse momenta about the saturation scale, which could be as large as Q_s^2 ~ 10 GeV^2 for a gold nucleus boosted to rapidity ~10 (as at the BNL-RHIC).
Selected aspects of the theory and phenomenology of production of forward jets at the LHC and RHIC are overviewed. In the theory part we discuss basics of frameworks originating from the BFKL dynamics while in the phenomenology part we present results for forward-central jet correlations at the LHC and forward di-jet production at RHIC.
Jet energy loss, photon production and photon-hadron correlations are studied together at high transverse momentum in relativistic heavy-ion collisions at RHIC energies. The modification of hard jets traversing a hot and dense nuclear medium is evaluated by consistently taking into account induced gluon radiation and elastic collisions. The production of high transverse momentum photons in Au+Au collisions at RHIC is calculated by incorporating a complete set of photon-production channels. Comparison with experimental photon production and photon-hadron correlation data is performed, using a (…
The production of the intermediate mass dileptons originating from the annihilation and Compton scattering of the jets and high energy photons (resolved photons) passing through the quark-gluon plasma is calculated. The contribution of the dilepton yield due to the jet-plasma and high energy photon-plasma interaction is pronounced compared to the thermal and Drell-Yan dilepton spectrum at intermediate mass. The ordinary spectrum of thermal and Drell-Yan processes is enhanced by the jet and photon-plasma mechanism. The numerical results match to the PHENIX data accurately in the intermediate ma…
In all modern hadronic colliders, jets recieve a large contribution from a soft background: pileup in the case of proton-proton collisions at the LHC, or the underlying event for heavy-ion collisions at RHIC or the LHC. In these proceedings, we present a generic and simple method, based on jet areas, to subtract the contribution of the soft background from the jets. This allows for more precise kinematic reconstruction of jets in dense environments.
We investigate single-inclusive high-pT jet production in longitudinally polarized pp collisions at RHIC, with particular focus on the algorithm adopted to define the jets. Following and extending earlier work in the literature, we treat the jets in the approximation that they are rather narrow, in which case analytical results for the corresponding next-to-leading order partonic cross sections can be obtained. This approximation is demonstrated to be very accurate for practically all relevant situations, even at Tevatron and LHC energies. We confront results for cross sections and spin-asymme…
High energetic particles traversing a dense medium lose a sizable part of their energy in form of gluon radiation. As a result, the rate of high-$p_t$ particles is expected to be suppressed in heavy ion collisions with respect to the proton case. Recent experimental data from RHIC strongly support this scenario. This allows to study the properties of the medium by the amount of jet quenching it produces. The angular dependence of the radiation is modified in the medium in a characteristic way. This provides another tool to study the medium properties in a more differential measurement.
The measured data on the nuclear modification factor for pions and reconstructed jets as well as on the high-pT elliptic flow at RHIC and LHC energies are compared to results from a linear pQCD and a highly non-linear hybrid AdS holographic model of jet-energy loss. We find that the high-pT ellitic flow requires to include realistic medium transverse flow fields and a jet-medium coupling including the effects of the energy of the jet, the temperature of the bulk medium, and non-equilibrium effects close to the phase transition. We extend our jet-energy loss model that is coupled to state-of-th…
The dihadron spectra in high energy $AA$ collisions are studied within the NLO pQCD parton model with jet quenching taken into account. The high $p_T$ dihadron spectra are found to be contributed not only by jet pairs close and tangential to the surface of the dense matter but also by punching-through jets survived at the center while the single hadron high $p_T$ spectra are only dominated by surface emission. Consequently, the suppression factor of such high-$p_T$ hadron pairs is found to be more sensitive to the initial gluon density than the single hadron suppression factor.
We present a phenomenological study of the single-transverse spin asymmetry in azimuthal correlations of two jets produced nearly "back-to-back" in pp collisions at RHIC. We properly take into account the initial- and final-state interactions of partons that can generate this asymmetry in QCD hard-scattering. Using distribution functions fitted to the existing single-spin data, we make predictions for various weighted single-spin asymmetries in dijet correlations that are now readily testable at RHIC.
Recent RHIC data have suggested an interesting scenario where jets, after being formed in the very first instants of the nuclear collision, interact strongly and are absorbed by the hot and dense matter subsequently created. In this respect, electromagnetic signals constitute another class of penetrating radiation. We first propose the study of large mass dileptons induced by the passage of high-energy quark jets through quark-gluon plasma. We find that the yield due to the jet-plasma interaction gets progressively larger as the collision energy increases: it is slightly less than the Drell-Ya…
In collisions of ultra-relativistic nuclei, photon-tagged jets provide a unique opportunity to compare jet production and modification due to parton shower formation and propagation in strongly-interacting matter at vastly different center-of-mass energies. We present first results for the cross sections of jets tagged by an isolated photon to ${\cal O}(α_{\rm em} α_s^2)$ in central Au+Au reactions with $\sqrt{s_{NN}}=200$ GeV at RHIC and central Pb+Pb reactions with $\sqrt{s_{NN}}=2.76$ TeV at LHC. We evaluate the increase in the transverse momentum imbalance of the observed $γ$+jet state, in…
Angular correlations measured in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) include a same-side (SS) 2D peak which is strongly elongated on pseudorapidity $η$ in more-central \auau collisions. The elongated peak has been referred to as a ``soft ridge.'' The SS peak is consistent with expected jet correlations in peripheral åand p-p collisions. A saturation-scale argument has been proposed to explain the origin of the elongated SS peak in terms of correlations from Glasma flux tubes interacting with radial flow. In this analysis we review the details of the proposed argu…
We investigate the contribution of medium-modified jets and initial state fluctuations to the asymmetry in charged particle production with respect to the reaction plane. This asymmetry has been suggested as a compelling signature of the Chiral Magnetic Effect in QCD and make a study of "conventional" scenarios for the creation of such charged particle multiplicity fluctuations a timely endeavor. The different pathlength combinations of jets through the medium in non-central heavy ion collisions result in finite correlations of like and different charged particles emitted in the different hemi…
We present fully dynamic simulations of heavy ion collisions at RHIC energies within the perturbative QCD-based partonic transport model BAMPS, focusing on the simultaneous investigation of jet-quenching and elliptic flow. The model consistently features elastic and inelastic 2 -> 3 processes, the latter being based on the Gunion-Bertsch matrix element. We discuss first attempts to extend the model to include light quark degrees of freedom and study the energy loss of high energy gluons and quarks in a static partonic medium. The difference between gluons and quarks in inelastic processes is f…
Quenching of gluonic jets and heavy quark production in Au+Au collisions at RHIC can be understood within the pQCD based 3+1 dimensional parton transport model BAMPS including pQCD bremsstrahlung $2 \leftrightarrow 3$ processes. Furthermore, the development of conical structures induced by gluonic jets is investigated in a static box for the regimes of small and large dissipation.
Monte Carlo approaches are a powerful tool in collider physics as they allow to make theory-data comparison on complex multi-particle observables, otherwise difficult for perturbative calculations. In heavy-ion collisions, there is a multitude of Monte Carlo approaches that try to address jet quenching phenomena, name given to the collection of medium-induced modifications that high momentum particles and jets undergo when traversing the hot and dense medium that is produced in such collisions. These models are being continuous developed alongside the theoretical efforts to understand and accu…
Within a hadron-string dynamical transport approach (HSD) we investigate the attenuation of high transverse momentum ($\pT$) hadrons as well as the suppression of 'near-side' and 'far-side' jets in $Au+Au$ collisions at invariant energies $\sqrt{s}$ = 200 GeV and $\sqrt{s}$ = 62.4 GeV in comparison to the data available from the Relativistic Heavy-Ion Collider (RHIC). From our transport studies we find that a significant part of the high $\pT$ hadron attenuation seen experimentally can be attributed to inelastic interactions of 'leading' pre-hadrons with the dense hadronic environment. In addi…
We calculate the emission of large mass dileptons originating from the annihilation of quark jets passing through quark gluon plasma. Considering central collisions of heavy nuclei at SPS, RHIC and LHC energies, we find that the yield due to the jet-plasma interaction gets progressively larger as the collision energy increases. We find it to be negligible at SPS energies, of the order of the Drell-Yan contribution and much larger than the normal thermal yield at RHIC energies and up to a factor of ten larger than the Drell-Yan contribution at LHC energies. An observation of this new dilepton s…
The coherent hadron production analogous to Cherenkov radiation of photons gives rise to the ring-like events. Being projected on the ring diameter they produce the two-bump structure recently observed for the away-side jets at RHIC. The position of the peaks and their height determine such properties of the hadronic medium as its nuclear index of refraction, the parton density, the free path length and the energy loss of Cherenkov gluons. Beside comparatively low energy gluons observed at RHIC, there could be high energy gluons at LHC, related to the high energy region of positive real part o…
Generalization of z-scaling observed in the inclusive high-pT charged hadron and jet production is proposed. The scaling function psi(z) describing both charged hadrons and jets produced in proton-(anti)proton collisions for various multiplicity densities and collision energies is constructed. Anomalous fractal dimensions and parameters characterizing associated medium for both classes of events are established. The basic features of the scaling established in minimum bias events are shown to be preserved up to the highest multiplicity densities measured in experiments UA1, E735, CDF and STAR.…
Fast thermalization and a strong buildup of elliptic flow of QCD matter as found at RHIC are understood as the consequence of perturbative QCD (pQCD) interactions within the 3+1 dimensional parton cascade BAMPS. The main contributions stem from pQCD bremsstrahlung $2 \leftrightarrow 3 $ processes. By comparing to Au+Au data of the flow parameter $v_2$ the shear viscosity to entropy ratio $η/s$ has been extracted dynamically and lies in the range of 0.08 and 0.2. Also jet-quenching has been investigated consistently within a full dynamical picture of the heavy ion collision. The results for glu…
The collective effect of emission by the forward moving partons of high energy Cherenkov gluons in nucleus-nucleus collisions at RHIC and LHC energies is considered. It can reveal itself as peaks in the pseudorapidity distribution of jets at midrapidities or as a ring-like structure of individual events in event-by-event analysis. The pseudorapidity distribution of centers of dense isolated groups of particles in HIJING model is determined. It can be considered as the background for Cherenkov gluons. If peaks above this background were found in experiment, they would indicate new collective ef…
In nucleus--nucleus collisions, high-pT partons interact with a dense medium, which possesses strong collective flow components. Here, we demonstrate that the resulting medium-induced gluon radiation does not depend solely on the energy density of the medium, but also on the collective flow. Both components cannot be disentangled on the basis of leading hadron spectra, but the measurement of particle production associated to high-pT trigger particles, jet-like correlations and jets, allows for their independent characterization. In particular, we show that flow effects lead to a characteristic…
Formation and evolution of the elliptic flow pattern in Pb+Pb collisions at sqrt{s}=5.5 ATeV and in Au+Au collisions at sqrt{s}=200 AGeV are analyzed for different hadron species within the framework of HYDJET++ Monte-Carlo model. The model contains both hydrodynamic state and jets, thus allowing for a study of the interplay between the soft and hard processes. It is found that jets are terminating the rise of the elliptic flow with increasing transverse momentum. Since jets are more influential at LHC compared to RHIC, the elliptic flow at LHC should be weaker than that at RHIC. The influence…
We present a global fit to all data on the suppression of high energy jets and high energy hadrons in the most central heavy ion collisions at the LHC for two different collision energies, within a hybrid strong/weak coupling quenching model. Even though the measured suppression factors for hadrons and jets differ significantly from one another and appear to asymptote to different values in the high energy limit, we obtain a simultaneous description of all these data after constraining the value of a single model parameter. We use our model to investigate the origin of the difference between t…
The production of jets, and high momentum hadrons from jets, produced in deuteron ($d$)-$Au$ collisions at the relativistic heavy-ion collider (RHIC) and proton ($p$)-$Pb$ collisions at the large hadron collider (LHC) are studied as a function of centrality, a measure of the impact parameter of the collision. A modified version of the event generator PYTHIA, widely used to simulate $p$-$p$ collisions, is used in conjunction with a nuclear Monte-Carlo event generator which simulates the locations of the nucleons within a large nucleus. We demonstrate how events with a hard jet may be simulated,…
