The presented results are the first measurements at RHIC for direct $γ$-charged hadron azimuthal correlations in heavy ion collisions. We use these correlations to study the color charge density of the medium through the medium-induced modification of high-p$_T$ parton fragmentation. Azimuthal correlations of direct photons at high transverse energy (8 $<$ p$_T$ $<$ 16 GeV) with away-side charged hadrons of transverse momentum (3 $<$ p$_T$ $<$ 6 GeV/c) have been measured over a broad range of centrality for $Au+Au$ collisions and $p+p$ collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment. A transverse shower shape analysis in the STAR Barrel Electromagnetic Calorimeter Shower Maximum Detector is used to discriminate between the direct photons and photons from the decays of high p$_T$ $π^{0}$. The per-trigger away-side yield of direct $γ$ is smaller than from $π^{0}$ trigger at the same centrality class. Within the current uncertainty the I$_{CP}$ of direct $γ$ and $π^{0}$ are similar.
Latest results from the PHENIX experiment at RHIC on these topics will be presented. Results will be shown for Au+Au compared to p-p collisions as well as compared to results from fully reconstructed jets at LHC.
Azimuthal angle two particle correlations have been shown to be a powerful probe for extracting novel features of jet induced correlations produced in Au+Au collisions at RHIC. At intermediate $p_T$, 2-5GeV/c, the jets have been shown to be significantly modified in both their particle composition and their angular distribution compared to p+p collisions. Two-particle angular correlations with identified particles provide sensitive probes of both the interactions between hard scattered partons and the medium. The systematics of these correlations are essential to understanding the physics of i…
The first measurements of charged particle pseudorapidity distributions obtained from Au + Au collisions at the maximum RHIC energy sqrt(s_{NN}) = 200 GeV) using the PHOBOS detector are presented. A comparison of the pseudorapidity distributions at energies 130 and 200 GeV for different centrality bins is made, including an estimate of the total number of charged particles. Away from the mid-rapidity region, a comparison between Pb + Pb at SPS energy sqrt(s_{NN}) = 17.3 GeV and Au + Au at RHIC energy sqrt(s_{NN}) = 130 GeV indicates that the extent of the limiting fragmentation region grows by…
Measurements of inclusive hadron suppression and di-hadron azimuthal correlations have provided important insights into jet quenching in hot QCD matter. However, they do not provide access to the energy of the hard scattering and are limited in their sensitivity since they can be affected by biases toward hard fragmentation and small energy loss. Full jet reconstruction in heavy-ion collisions enables a complete study of the modification of jet structure due to energy loss, but is challenging due to the high-multiplicity environment. We present measurements of fully reconstructed di-jets at mi…
The status of the use of hard probes in heavy ion collisions at RHIC is reviewed. The discovery of strong jet quenching at RHIC is a major success. However, in order to make full use of this new phenomenon for full jet emission tomography of the properties of the collision zone further development is needed, both experimentally and theoretically.
Full jet reconstruction in heavy-ion collisions is expected to provide more sensitive measurements of jet quenching in hot QCD matter at RHIC. In this paper we review recent studies of jets utilizing modern jet reconstruction algorithms and their corresponding background subtraction techniques.
Two-particle correlations and event-wise fluctuations in transverse momentum p_t are reported for Au-Au collisions at sqrt{s_{NN}} = 62 and 200 GeV on pseudorapidity (eta) and azimuth (phi). Distributions of all pairs of particles (no leading trigger particle) reveal jet-like correlations, or peaks at pair-wise opening angles of order 1 radian or less. The width of this same-side correlation peak increases dramatically on pseudorapidity and decreases on azimuth for increasing collision centrality. Evolution of the same-side peak with centrality suggests dissipation of low-Q^2 partons via stron…
Exciting results from the Relativistic Heavy Ion Collider (RHIC) have been presented at this Workshop. However, fundamental questions remain to be addressed in the future regarding whether the system is deconfined, chiral symmetry is restored, a color glass condensate exists in the initial state, and how the system evolves through eventual hadronization. Jets, heavy flavors and electromagnetic probes are sensitive to the initial high density stage of RHIC collisions, and should provide new insight. Significant additional capabilities will be added with a luminosity upgrade of RHIC (to RHIC II)…
Full jet reconstruction in heavy-ion collisions enables a complete study of the modification of jet structure due to energy loss in hot and dense QCD matter, but is challenging due to the high multiplicity environment. The STAR and PHENIX collaborations at RHIC have recently presented measurements of fully reconstructed jets from p+p, Cu+Cu and Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 200 \mathrm{GeV}$. We review the first results on inclusive jet spectra, di-jets and fragmentation functions and discuss their implications on understanding of jet quenching.
The STAR detector is well suited for investigating jet production at RHIC. It has a large acceptance for both charged particles and electromagnetic radiation, so that reconstructed jets contain a large fraction of the particles descending from an initial hard scattered parton. Inclusive jets can be used to measure $j_T$, which characterizes the transverse jet shape. Di-jet angular distributions in d+Au and p+p collisions at RHIC provide a determination of intrinsic and nuclear $k_{T}$. The most recent results from this analysis based on year 2003 d+Au and p+p data are presented and compared to…
Recent progress in full jet reconstruction in heavy-ion collisions at RHIC makes it a promising tool for the quantitative study of the QCD at high energy density. Measurements in d+Au collisions are important to disentangle initial state nuclear effects from medium-induced k_T broadening and jet quenching. Furthermore, comparison to measurements in p+p gives access to cold nuclear matter effects. Inclusive jet p_T spectra and di-jet correlations (k_T) in 200 GeV p+p and d+Au collisions from the 2007-2008 RHIC run are presented.
Full jet reconstruction in heavy-ion collisions is a promising tool for the quantitative study of properties of the dense medium produced at RHIC. In addition to baseline measurements in p+p, results from d+Au collisions are needed to disentangle initial state nuclear effects from medium-induced k_T broadening and jet quenching. We present mid-rapidity inclusive jet p_T spectra and di-jet correlations (k_T) in 200~GeV p+p and d+Au collisions from the 2007-2008 RHIC run.
Recent results on jet production in heavy ion collisions at RHIC and the LHC are discussed, with emphasis on inclusive jet yields and semi-inclusive hadron-triggered and vector boson-triggered recoil jet yields as well as their azimuthal angular correlations. I will also discuss the constraints that these observables impose on the opacity of the medium, the flavour dependence of energy loss, the interplay of perturbative and non perturbative effects and the change of the degrees of freedom of the medium with the resolution of the probe.
To precisely measure jets over a large background such as pile up in high luminosity p+p collisions at LHC, a new generation of jet reconstruction algorithms is developed. These algorithms are also applicable to reconstruct jets in the heavy ion environment where large event multiplicities are produced. Energy loss in the medium created in heavy ion collisions are already observed indirectly via inclusive hadron distributions and di-hadron correlations. Jets can be used to study this energy loss in detail with reduced biases. We review the latest results on jet-medium interactions as seen in A…
We show that with a realistic treatment of spectator momentum distributions the RHIC detector trigger sensitivity is high even when RHIC is run below injection energies. In particular, a problem region with $\sqrt{s_{NN}}$=10 to 60 or 80 GeV assuming a simple Fermi step model is not found when using a more realistic one. We argue also that production of fast nucleons (with momenta $> p_F$ in the nucleus rest frame) provides complementary information about the collision process.
Full jet reconstruction in heavy-ion collisions is a promising tool for the quantitative study of properties of the dense medium produced at RHIC. Measurements of d+Au collisions are important to disentangle initial state nuclear effects from medium-induced kT broadening and jet quenching. Study of jet production and properties in d+Au in combination with similar studies in p+p is an important baseline measurement needed to better understand heavy-ion results. We present mid-rapidity inclusive jet pT spectra and di-jet correlations (kT) in 200 GeV p+p and d+Au collisions from the 2007-2008 RHI…
The hot and dense medium created at RHIC, called Quark and Gluon Plasma (QGP) has been a hot topic in the last ten years. Due to the high multiplicities in such heavy-ion collision events, particle correlations using either trigger particles, or fully-reconstructed jets, become not only useful but necessary, in addition to the single particle observables. In this paper the most recent work studying this medium will be shown, including both on bulk properties and tagged events.
Jet quenching in the matter created in high energy nucleus-nucleus collisions provides a tomographic tool to probe the medium properties. Recent experimental results on jet production at the Relativistic Heavy-Ion Collider (RHIC) are reviewed. Jet properties in p+p and d+Au collisions have been measured, establishing the baseline for studying jet modification in heavy-ion collisions. Current progress on detailed studies of high transverse momentum production in Au+Au collisions is discussed, with an emphasis on dihadron correlation measurements.
Two-particle azimuthal correlations have allowed detailed study of the modification to di-jets in the hot, dense medium created in RHIC collisions. Light can be shed by such correlations on many novel effects discovered at RHIC such as the enhanced p/pi ratio and conical structure of events with energy loss. Using pi0 triggers to reduce the effect of recombination we utilize high-pT correlations to explore the away-side structure.
The relationship between jet properties and the underlying geometry of the medium produced in heavy ion collisions can be explored through a measurement of the correlation between the axes of reconstructed jets and the reaction plane, defined as "jet v2." Such a measurement provides information on the pathlength dependence of medium-induced parton energy loss and may also be used to assess biases in jet-finding methods. We present first measurements of jet v2 in sqrt(sNN) = 200 GeV Au+Au collisions in the STAR experiment at RHIC. In order to reduce the artificial jet - event plane bias, which …
Jet fragmentation functions measured in e^+e^- and p+\bar{p} experiments are well-described on an inclusive hadron level by QCD-based calculations. Fragmentation is expected to be modified by the presence of a strongly interacting medium, but full theoretical description of this modification must still be developed. It has recently been suggested that particle-identified fragmentation functions may provide additional insight into the processes underlying jet quenching. To assess the applicability of QCD-based fragmentation calculations to RHIC data, and to provide a baseline with which to comp…
Differential measurements of various particle species over an extended momentum range provide a sensitive experimental tool for investigation of energy loss mechanisms in the medium created in nucleus-nucleus collisions at RHIC. In these proceedings, a systematic study of transverse momentum spectra for charged pions, protons and antiprotons from Cu+Cu data at $\sqrt{s_{NN}}=200$GeV as a function of collision centrality will be presented. Such systematic studies provide additional insights into the interplay between fragmentation and non-fragmentation contributions to the particle production. …
We present recent results for heavy flavor and jets produced in $\sqrt{s_{NN}} = 200$ GeV p-p, d-Au, Cu-Cu and Au-Au collisions at at RHIC. We find J/$ψ$ production is suppressed in Au-Au, but high energy J/$ψ$ are not suppressed in d-Au or Cu-Cu. Non-photonic electrons from D and B mesons are both suppressed in Au-Au. We study jets using two-particle 2D angular correlations as well as jet reconstruction algorithms. We find that jets show little if any suppression, but are highly modified in central Au-Au, becoming elongated in the $η$ direction and having fewer high-$p_t$ particles but many m…
I will present the latest results on particle identified spectra and two particle correlations at high transverse momentum measured with the STAR detector at RHIC. I will compare those measurements with the projected capabilities for the LHC using the ALICE detector. The effects of string fragmentation and quark recombination in the intermediate momentum range will be discussed in the context of hadron formation in proton-proton and Au-Au collisions, as well as energy loss mechanisms in the dense partonic phase. The necessity for gamma-jet and heavy quark jet measurements will be detailed base…
We present the recent results from the STAR experiment on charged and neutral particle measurements at the forward rapidity in d+Au collisions at sqrt{s_{NN}} = 200 GeV and Au+Au collisions at sqrt{s_{NN}} = 62.4 GeV. The nuclear modification factor for charged and neutral hadrons in d+Au collisions are presented. Measurements of Lambda and anti-Lambda production at forward rapidity and the variation of net baryon density as a function of collision centrality are discussed. We have also studied the limiting fragmentation of photons and charged particles in Au+Au collisions. The photons and cha…
Jet fragmentation functions provide insight into jet structure and are expected to be modified by the nuclear medium in A+A collisions with respect to p+p reference measurements. If jet reconstruction is unbiased then a softening of the fragmentation functions is expected and should be observed in Au+Au collisions at RHIC. In these proceedings we present measurements of fragmentation functions in p+p for charged particles for different jet finding algorithms; these measurements are understood and therefore can be used as a reference for comparison with Au+Au results. We report the effect of ba…
The measurement of jet fragmentation functions in p+p collisions at 200 GeV is of great interest because it provides a baseline to study jet quenching in heavy-ion collisions. It is expected that jet quenching in nuclear matter modifies the jet energy and multiplicity distributions, as well as the jet hadrochemical composition. Therefore, a systematic study of the fragmentation functions for charged hadrons and identified particles is a goal both in p+p and Au+Au collisions at RHIC. Studying fragmentation functions for identified particles is interesting in p+p by itself because it provides a …
The observation of the strong suppression of high pT hadrons in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at BNL has motivated a large experimental program using hard probes to characterize the deconfined medium created. However what can be denoted as ``leading particle physics'' accessible at RHIC presents some limitations which motivate at higher energy the study of much more penetrating objects: jets. The gain in center of mass energy expected at the Large Hadron Collider (LHC) at CERN will definitively improve our understanding on how the energy is lost in the syst…
Recent RHIC data show evidence of multiple hadron production mechanisms in heavy ion collisions compared to simple fragmentation in vacuum. I will review the measurements of collective flow, high momentum quenching, and two particle angular correlations to show that neither thermal production nor string fragmentation can describe the abundances, the angular distributions or the kinematic properties of all hadrons produced at RHIC. The proposed new hadronization mechanisms not only serve as evidence for a deconfined partonic phase of matter, but also for strong coupling of the degrees of freedo…
Predictions for some experimental physical observables in nucleus-nucleus collisions at RHIC energies are presented. I utilize the previous suggestion that the retarded, by time about 2-3 fm/c, jet absorption in opaque core is a natural explanation of many experimental data. This assumption is applied only to the particles with high transverse momentum above 4 GeV/c resulting from parton fragmentation. I calculate nuclear modification factor $R_{AA}$, $R_{AA}$ in- and out of the reaction plane, azimuthal anisotropy parameter $v_2$, jet suppression $I_{AA}$ for the away side jet and its depende…
Hard scattered partons are predicted to be well calibrated probes of the hot and dense medium produced in heavy ion collisions. Interactions of these partons with the medium w ill result in modifications of internal jet structure in Au+Au events compared to that observed in the p+p/d+Au reference. Full jet reconstruction is a promising tool to measu re these effects without the significant biases present in measurements with high-$\pT$ hadrons. One of the most significant challenges for jet reconstruction in the heavy ion environment comes from the correct characterization of the background fl…
At this conference first data from RHIC has been presented. Spectra of charged hadrons and identified neutral pions obtained in central collisions exhibit a depletion at large transverse momenta compared to expectations deduced from $pp$ and $\bar{p}p$ data and lower energy heavy ion data. While spectra measured in peripheral collisions exhibit the expected power-law shape, spectra from central collisions are closer to exponential. In addition, a significant azimuthal anisotropy of high momentum charged particle production has been found. All observations are in qualitative agreement with theo…
These proceedings present a brief overview of the main results on jet-modifications in heavy ion collisions at RHIC. In heavy ion collisions, jets are studied using single hadron spectra and di-hadron correlations with a high-\pt{} trigger hadrons. At high pt, a suppression of the yields due to parton energy loss is observed. A quantitative confrontation of the data with various theoretical approaches to energy loss in a dense QCD medium is being pursued. First results from $γ$-jet events, where the photon balances the initial jet energy, are also presented and compared to expectations from mo…
Hard scattering in p-p collisions, discovered at the CERN ISR in 1972 by the method of leading particles, proved that the partons of Deeply Inelastic Scattering strongly interacted with each other. Further ISR measurements utilizing inclusive single or pairs of hadrons established that high pT particles are produced from states with two roughly back-to-back jets which are the result of scattering of constituents of the nucleons as desribed by Quantum Chromodynamics (QCD), which was developed during the course of these measurements. These techniques, which are the only practical method to study…
Charged hadrons (0.15 < pt < 4 GeV/c) associated with a large pt trigger particle (4 < pt < 6 GeV/c) are statistically reconstructed in the large acceptance STAR TPC for p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. Preliminary results on transverse momentum distributions of these hadrons are presented, separately on the near and away side from the trigger particle. An increase in the multiplicity and total scalar pt of these hadrons from p+p to central Au+Au collisions is observed. The away side distribution is found to be significantly softened in central Au+Au with respect to p+p collisio…
Jets are studied in A-A collisions at RHIC and LHC with the goal to understand how they are affected by the medium and how they affect the medium. It is widely believed that hard-scattered partons lose energy when propagating through a medium before hadronizing. Partons losing enough energy may not even make it out of the medium as identifiable jets (although the momentum will be shared among whatever particles are emitted). "Full" jet reconstruction attempts to determine the partonic energy loss as well as possible changes in jet shape. Heavy ion collisions typically produce many unrelated pa…
Jet fragmentation in p+p and Au+Au collisions is studied via back-to-back correlations of direct photons and charged hadrons. The direct photon correlations are obtained by statical subtraction of the background from decay photons. Results on the nuclear modification to the associated charged hadron yields are reviewed. Further studies of jet fragmentation in p+p using isolated direct photons are also presented. A kT-smeared LO pQCD calculation is used to interpret the data. The sensitivity of the data to the underlying fragmentation function is tested and the results are found to be compatibl…
We review recent progress in the study of medium-induced modification of jet fragmentation in high energy nuclear collisions at the SPS and RHIC and present an outlook on jet physics at the LHC.
Hard scattering in p-p collisions, discovered at the CERN ISR in 1972 by the method of leading particles, proved that the partons of Deeply Inelastic Scattering strongly interacted with each other. Further ISR measurements utilizing inclusive single or pairs of hadrons established that high pT particles are produced from states with two roughly back-to-back jets which are the result of scattering of constituents of the nucleons as described by Quantum Chromodynamics (QCD), which was developed during the course of these measurements. These techniques, which are the only practical method to stud…
Experimental evidence from RHIC indicates that matter having an energy density far in excess of the value required for the creation of a deconfined phase is produced in ultrarelativistic Au+Au collisions at a center of mass energy of 200 GeV. This matter thermalizes rapidly, is strongly interacting, and displays hydrodynamic properties akin to a fluid with very low viscosity. Studies of the interaction of hard scattered partons with this matter provide an important probe of its properties. In fact, studies of the suppression of high-p_T hadrons have been one of the key arguments used by the RH…
Jets in hadron collisions are very complicated with a long learning curve replete with errors. In relativistic heavy ion (RHI) collisions, it is likely that jets will be much more complicated with an even longer and more difficult learning curve. Hard scattering is more easily observed via single particle and few particle correlation measurements. The main advantage of jets is higher rate at large $p_T$, plus the possibility of detailed studies of soft fragmentation if the soft fragments can be separated from the background. A critical review of the possibility of using jets as a probe of hard…
We present high transverse momentum ($p_T$) measurements made at the Relativistic Heavy Ion Collider (RHIC) for Au+Au, d+Au, and p+p collisions at $\sqrt{s_{NN}} = 200$ GeV, as well as for Au+Au collisions at $\sqrt{s_{NN}} = 62$ GeV. We observe a suppression in the yield of high $p_T$ hadrons measured in central Au+Au collisions, relative to the yield in p+p collisions scaled by the number of binary nucleon-nucleon collisions. This observation, together with the absence of such a suppression in d+Au collisions, leads to the conclusion that a dense medium is formed in central Au+Au collisions.
We review the di-hadron correlation results from RHIC. A consistent physical picture was constructed based on the correlation landscape in $p_T$, $Δϕ$, $Δη$ and particle species. We show that the data are consistent with competition between fragmentation of survived jets and response of the medium to quenched jets. At intermediate $p_T$ where the medium response are important, a large fraction of trigger hadrons do not come from jet fragmentation. We argue that these hadrons can strongly influence the interpretation of the low $p_T$ correlation data. We demonstrate this point through a simple …
The measurement of gamma+jet events with a direct photon in coincidence with an energetic parton can provide unique insights into the propagation and fragmentation of the parton in the presence of the hot and dense medium created in heavy-ion collisions. One way to explore these effects is the study of azimuthal correlations between the direct photon and hadrons produced in the fragmentation. We present azimuthal correlations between photons with a transverse momentum of more than 10 GeV and charged hadrons with a transverse momentum of more than 2 GeV in Au+Au collisions at sqrt(s_NN) = 200 G…
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.
We present an update to the analysis of fully reconstructed jets in heavy ion collisions by the STAR Collaboration at RHIC. We analyse the response of the anti-$k_{T}$ algorithm in the presence of background, and present a new observable for the measurement of inclusive jet production that is expected to be more robust against background model assumptions than previous jet analyses at RHIC and LHC.
In a coalescence plus independent fragmentation approach we calculate the $p_T$ spectra of the main hadrons: $π, K, p, \bar p, Λ, ϕ$ in a wide range of transverse momentum from low $p_T$ up to about 10 GeV. The approach in its main features was developed several years ago at RHIC energy. Augmenting the model with the inclusion of some more main resonance decays, we show that the approach correctly predicts the evolution of the $p_T$ spectra from RHIC to LHC energy and in particular the baryon-to-meson ratios $p/π,\bar p/π,Λ/K$ that reach a value of the order of unit at $p_T \sim 3\, \rm GeV$. …
We present data-driven methods for the full reconstruction of jets in heavy ion collisions, for inclusive and co-incidence jet measurements at both RHIC and LHC. The complex structure of heavy ion events generates a large background of combinatorial jets, and smears the measured energy of the true hard jet signal. Techniques to correct for these background effects can induce biases in the reported jet distributions, which must be well controlled for accurate measurement of jet quenching. Using model studies, we evaluate the proposed methods for measuring jet distributions accurately while mini…
Parton energy loss in Au+Au collisions at RHIC energies is studied by numerically solving the relativistic Boltzmann equation for the partons including $2 \leftrightarrow 2$ and $2 \to 2 + final state radiation$ collision processes. Final particle spectra are obtained using two hadronization models; the Lund string fragmentation and independent fragmentation models. Recent, preliminary $π^0$ transverse momentum distributions from central Au+Au collisions at RHIC are reproduced using gluon-gluon scattering cross sections of 5-12 mb, depending upon the hadronization model. Comparisons with the H…
I present an overview of some of the recent results on jets and jet-like correlation measurements from the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory. Jets are produced in the initial hard scatterings of an event and can therefore be exploited as probes of the hot and dense medium produced in heavy-ion collisions. Previous RHIC results indicate that this medium, the Quark Gluon Plasma (sQGP), is strongly coupled, with partonic degrees of freedom. High pT colored partons passing through the sQGP are therefore believed to suffer energy loss via induced gluon radiati…
We discuss the latest results from jet fragmentation and jet substructure measurements performed with the ALICE experiment in proton-proton and heavy-ion collisions in a wide range of jet transverse momentum. The jet production cross sections and cross section ratios for different jet resolution parameters will be shown in a wide range of $p_{\textrm{T}}$. Results will be compared to next-to-leading order pQCD calculations.
Jets represent an important tool to explore the properties of the hot and dense nuclear matter created in heavy-ion collisions. However, full jet reconstruction in such events is a challenging task due to extremely large and fluctuating background, which generates a large population of combinatorial jets that overwhelm the true hard jet population. In order to carry out accurate, data-driven jet measurements over a broad kinematic range in such conditions of small signal to background, we use several novel approaches in order to measure inclusive charged jet distributions and semi-inclusive ch…
The current experimental and theoretical status of hadron and jet production at large transverse momentum in high-energy nucleus-nucleus collisions is summarised. The most important RHIC results are compared to theoretical parton energy loss predictions providing direct information on the (thermo)dynamical properties of hot and dense QCD matter. Prospects for the LHC are also outlined.
High-energy jets offer rich opportunities to study quantum chromodynamics, from investigating the limits of perturbative calculability to constraining the emergent properties of the quark-gluon plasma (QGP). In these proceedings, we present new measurements of the fragmentation properties of jets. We report distributions of the sub-jet momentum fraction $z_r$ measured in pp and Pb-Pb collisions with ALICE at the Large Hadron Collider. These measurements serve as input to test the universality of jet fragmentation in the QGP, and offer a path to elucidate jet quenching effects in the large-$z$ …
The property of limiting fragmentation of various observables such as rapidity distributions ($dN/dy$), elliptic flow ($v_{2}$), average transverse momentum ($\langle p_{T} \rangle$) etc. of charged particles is observed when they are plotted as a function of rapidity ($y$) shifted by the beam rapidity ($y_{beam}$) for a wide range of energies from AGS to RHIC. Limiting fragmentation (LF) is a well studied phenomenon as observed in various collision energies and colliding systems experimentally. It is very interesting to verify this phenomenon theoretically. We study such a phenomenon for pion…
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 (…
Jet reconstruction and jet fragmentation variables provide important information to study the interaction between hard scattered partons and the Quark-Gluon Plasma. This paper presents the measurement of the inclusive cross section for fully reconstructed jets in pp collisions at sqrt(s) = 2.76 TeV, which provides an essential reference for jet measurements in Pb-Pb collisions at the same sqrt(s_NN). In addition, we report jet fragmentation measurements for charged particle jets in pp collisions at sqrt(s) = 7 TeV. These measurements utilize the ALICE central barrel tracking system to detect c…
A generic jet-energy loss model that is coupled to state-of-the-art hydrodynamic fields and interpolates between a wide class of running coupling pQCD-based and AdS/CFT-inspired models is compared to recent data on the azimuthal and transverse momentum dependence of high-pT pion nuclear modification factors and high-pT elliptic flow measured at RHIC and LHC. We find that RHIC data are surprisingly consistent with various scenarios considered. However, extrapolations to LHC energies favor running coupling pQCD-based models of jet-energy loss. While conformal holographic models are shown to be i…
The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is carrying out a spin physics program colliding transversely or longitudinally polarized proton beams at = 200-500 GeV to gain deeper insigh t into the spin structure and dynamics of the proton. These studies provide fundamental insight into Quantum Chromodynamics (QCD). One of the main objectives is the determination of the polarized gluon distribution function, g, through the measurement of the longitudinal double-spin asymmetry, ALL, for various processes. Inclusive hadron and jet prod…
