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 angle distribution in the `away-side' jet as well as `ridge' long rapidity correlations in the `near-side' jet - observed by the STAR and PHOBOS Collaborations - are not seen in the HSD results, thus suggesting a partonic origin.
A study of hadronic data up to TEVATRON energies in terms of relativistic hydrodynamics indicates an extended 1-dimensional stage of the expansion which suggests a jet like behaviour of the fireball along the collision axis.
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…
We study the medium modification factor $I_{pp}$ within the light-cone path integral approach to induced gluon emission. We use parametrization of the running coupling $α_s(Q,T)$ which has a plateau around $Q\sim κT$. We calculate $I_{pp}$ with no free parameters using $κ$ fitted to the LHC data on the nuclear modification factor $R_{AA}$. We find that the theoretical multiplicity dependence of the ratio $I_{pp}/\langle I_{pp}\rangle$ for $5.02$ TeV $pp$ collisions agrees reasonably with the recent preliminary data from ALICE [1].
Vacuum and medium modified fragmentation functions are used to study the properties of hadrons produced in hard interactions, in $p$-$p$ and $A$-$A$ collisions, respectively. We study the modification of reconstructed jets and high transverse momentum (high-$p_\mathrm{T}$) hadrons as they propagate through a dense medium. Jets and jet modification are studied within the framework of a factorized jet function. The vacuum jet function is found consistent with PYTHIA simulations. Both the modification of the fragmentation function and the jet function are carried out within the identical higher-t…
We study nonperturbative flavor correlations between pairs of leading and next-to-leading charged hadrons within jets at the Electron-Ion Collider (EIC). We introduce a charge correlation ratio observable $r_c$ that distinguishes same- and opposite-sign charged pairs. Using Monte Carlo simulations with different event generators, $r_c$ is examined as a function of various kinematic variables for different combinations of hadron species, and the feasibility of such measurements at the EIC is demonstrated. The precision hadronization study we propose will provide new tests of hadronization model…
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 JETSCAPE Collaboration has recently announced the first release of the JETSCAPE package that provides a modular, flexible, and extensible Monte Carlo event generator. This innovative framework makes it possible to perform a comprehensive study of multi-stage high-energy jet evolution in the Quark-Gluon Plasma. In this work, we illustrate the performance of the event generator for different algorithmic approaches to jet energy loss, and reproduce the measurements of several jet and hadron observables as well as correlations between the hard and soft sector. We also carry out direct comparis…
The event generator based on the higher-twist energy loss formalism -- Modular All Twist Transverse-scattering Elastic-drag and Radiation (MATTER) -- is further developed and coupled to a hydrodynamic model for studying jet modification in relativistic nuclear collisions. The probability of parton splitting is calculated using the Sudakov form factor that is constructed by a combination of vacuum and medium-induced splitting functions; and the full parton showers are simulated, including both energy-momentum and space-time evolutions of all jet partons. With the assumption that partons below a…
We review some recent experimental and theoretical work on the correlation among hadrons produced at intermediate $p_T$ at RHIC. The topics include: forward and backward asymmetry with and without trigger at mid-rapidity, associated-particle distribution on the near side, the $Ω$ puzzle and its solution, associated particles on the away side, and two-jet recombination at LHC.
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…
The moments of the single inclusive momentum distribution of hadrons in QCD jets, are studied in the next-to-modified-leading-log approximation (NMLLA) including next-to-leading-order (NLO) corrections to the alpha_s strong coupling. The evolution equations are solved using a distorted Gaussian parametrisation, which successfully reproduces the spectrum of charged hadrons of jets measured in e+e- collisions. The energy dependencies of the maximum peak, multiplicity, width, kurtosis and skewness of the jet hadron distribution are computed analytically. Comparisons of all the existing jet data m…
Correlation between shower partons is first studied in high $p_T$ jets. Then in the framework of parton recombination the correlation between pions in heavy-ion collisions is investigated. Since thermal partons play very different roles in central and peripheral collisions, it is found that the correlation functions of the produced hadrons behave very differently at different centralities, especially at intermediate $p_T$. The correlation function that can best exhibit the distinctive features is suggested. There is not a great deal of overlap between what we can calculate and what has been me…
Multiple parton scatterings in high-energy p+A collisions involve multi-parton correlation inside the projectile and color coherence of multiple jets which will lead to nuclear modification of final hadron spectra relative to that in p+p collisions. Such modification of final hadron spectra in p+A collisions is studied within HIJING 2.1 model which includes initial parton shadowing, transverse momentum broadening, parton flavor and momentum correlation inside the projectile through flavor and momentum conservation and fragmentation of multiple jets. They are shown to modify the partonic flavor…
High momentum jets and hadrons are important probes for the quark gluon plasma (QGP) formed in nuclear collisions at high energies. We investigate how fluctuations in the background density of the QGP and fluctuations in the spatial distribution of the hard process create azimuthal asymmetries of the high momentum hadron spectrum, described by the Fourier coefficients $v_n$, $n > 0$ . We estimate the coefficients up to $v_6$ in a simple energy loss model tuned to single inclusive hadron suppression.
Autocorrelation of two pions produced in heavy-ion collisions at intermediate $p_T$ is calculated in the framework of the recombination model. The differences of the pseudo-rapidities and azimuthal angles of the two pions are related to the angle between two shower partons in a jet. It is shown how the autocorrelation distribution reveals the properties of jet cone of the shower partons created by high-$p_T$ partons in hard collisions.
We study the transverse momentum distribution of hadrons within jets, where the transverse momentum is defined with respect to the standard jet axis. We consider the case where the jet substructure measurement is performed for an inclusive jet sample $pp\to\text{jet}+X$. We demonstrate that this observable provides new opportunities to study transverse momentum dependent fragmentation functions (TMDFFs) which are currently poorly constrained from data, especially for gluons. The factorization of the cross section is obtained within Soft Collinear Effective Theory (SCET), and we show that the r…
Jet quenching is considered to be one of the signatures of the formation of quark gluon plasma. In order to investigate the jet quenching, it is necessary to detect jets produced in relativistic heavy ion collisions, determine their properties and compare those with the jets one obtains in hadron-hadron or $e^+-e^-$ collisions. In this work, we propose that calculation of flow parameters may be used to detect and characterize jets in relativistic heavy ion collisions.
Correlation between trigger and associated particles in jets produced on near and away sides of high-p_T triggers in heavy-ion collisions is studied. Hadronization of jets on both sides is treated by thermal-shower and shower-shower recombination. Energy loss of semihard and hard partons traversing the nuclear medium is parametrized in a way that renders good fit of the single-particle inclusive distributions at all centralities. The associated hadron distribution in the near-side jet can be determined showing weak dependence on system size because of trigger bias. The inverse slope increases …
