14 pages, 14 figures, Proceedings of the Workshop on Relativistic Nuclear Physics (WRNP) 2007, Kiev, Ukraine. Conference Info: http://wrnp2007.bitp.kiev.ua/. Final version published in "Physics of Atomic Nuclei"
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 system opening a new major window of study: the physics of jets on an event-by-event basis. We will concentrate on the expected performance for jet reconstruction in ALICE using the EMCal calorimeter.
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.
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.
Anisotropic flow is recognized as one of the main observables providing information on the early stage of a heavy-ion collision. At RHIC the large observed anisotropic flow and its successful description by ideal hydrodynamics is considered evidence for an early onset of thermalization and almost ideal fluid properties of the produced strongly coupled Quark Gluon Plasma. This write-up discusses some key RHIC anisotropic flow measurements and for anisotropic flow at the LHC some predictions.
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.
Anisotropic flow is recognized as one of the main observables providing information on the early dynamics in heavy-ion collisions. The large elliptic flow observed at RHIC is considered to be evidence for almost perfect liquid behavior of the strongly coupled Quark Gluon Plasma produced in the collisions. In this report we review our current understanding of this new state of matter and investigate the predictions for anisotropic flow at the LHC.
Measurements of $π^0$, identified charged hadrons, direct-single-$γ$, direct single-$e^{\pm}$ and jets are expected to be important probes of the Quark Gluon Plasma (QGP) at LHC as they are at RHIC. Recent results from RHIC will be presented, with implications, possibly grave, for LHC. Issues of soft-physics, such as $E_T$ distributions, will be discussed with questions as to: whether the soft multipicity or sum-transverse energy ($E_T$), may be the only quantity at LHC to exhibit number of collision scaling? or whether the anisotropic flow ($v_2$) will exceed the hydrodynamic limit?
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.
A new era has started in the field of relativistic heavy-ion physics with lead beams delivered by the Large Hadron Collider (LHC) in November 2010. In this proceedings I highlight the main results from experimental measurements with Pb-Pb collisions at the incident energy of 2.76 TeV/nucleon recorded by the LHC experiments. Recent experimental developments from the Relativistic Heavy Ion Collider (RHIC) at the GeV incident energy scale are also discussed. All together LHC and RHIC measurements provide new insights on the properties and features of the new hot and dense form of matter created i…
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.
The first heavy-ion run at the LHC with Pb+Pb collisions at roots_NN = 2.76 TeV took place in the fall of 2010. In a short and relatively low luminosity run, the three detectors, ALICE, ATLAS and CMS showcased an impressive performance and produced a wealth of a high quality results. This article compares the new LHC results with those accumulated over the last decade at RHIC, focussing on the quantitative and qualitative differences between the different energy regimes of these two facilities.
Recent experimental results at both the LHC and RHIC show evidence for hydrodynamic behavior in proton-nucleus and deuteron- nucleus collisions (p+A). This unexpected finding has prompted new measurements in p+A collisions in order to understand whether similar matter is created in A+A and p+A collisions or whether some another explanation is needed. In this proceedings, we will discuss the new experimental data and its interpretation within the context of heavy ion collisions.
For the past decade, measurements of semi-inclusive single identified particle spectra and two particle correlations in p-p and A+A collisions at RHIC have produced a treasure trove of results which indicate that the medium produced in Au+Au collisions is a strongly interacting quark gluon liquid in which both light and heavy quarks are suppressed, presumably by energy loss in the hot, dense medium. These results have been confirmed in Pb+Pb collisions at the LHC along with the addition of measurements of jets and di-jets. Results and methods at RHIC and LHC are compared which leads to some in…
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.
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…
The study of heavy-ion collisions has currently unprecedented opportunities with two first class facilities, the Relativistic Heavy Ion Collider (RHIC) at BNL and the Large Hadron Collider (LHC) at CERN, and five large experiments ALICE, ATLAS, CMS, PHENIX and STAR producing a wealth of high quality data. Selected results recently obtained are presented on the study of flow, energy loss and direct photons.
The progress over the 30 years since the first high-energy heavy-ion collisions at the BNL-AGS and CERN-SPS has been truly remarkable. Rigorous experimental and theoretical studies have revealed a new state of the matter in heavy-ion collisions, the quark-gluon plasma (QGP). Many signatures supporting the formation of the QGP have been reported. Among them are jet quenching, the non-viscous flow, direct photons, and Debye screening effects. In this article, selected signatures of the QGP observed at RHIC and the LHC are reviewed.
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 RHIC program was intended to identify and study the quark-gluon plasma formed in the collision of heavy nuclei. The discovery of the "perfect liquid" is an essential step towards the understanding of the medium formed in these collisions. Much of data relevant to this was provided by the study of "soft" observables, which involve many particles of low momentum produced in nearly every event, rather than high momentum particles produced in rare events. The main results related to soft physics at RHIC are discussed, as well as their implications for the physics of the LHC heavy ion program.
I will review RHIC data with respect to the intriguing possibility that the hadron production mechanism in the produced partonic medium might be different than in vacuum. I will use the measurements of collective features, such as flow and quenching of identified particles, to show that different regions of the particle momentum spectrum are likely populated through different mechanisms, and that the medium seems to play an important role in hadronization. Finally I will address the question whether the different initial conditions achievable in heavy ion collisions at LHC energies, compared t…
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 …
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.
From Pythia simulations of pp collisions we determine the mean transverse momentum <Pt> of partons producing the leading and associated particles studied in di-hadron correlations. The dependence of <Pt> on the associated particle transverse momentum and expected differences at RHIC and LHC centre of mass energies are discussed.
A selection of experimental results in high-energy nucleus-nucleus collisions after five years of operation of the Relativistic Heavy-Ion Collider (RHIC) is presented. Emphasis is put on measurements that provide direct information on fundamental properties of high-density QCD matter. The new experimental opportunities accessible at LHC are introduced, in particular those that may help clarify some of the current open issues at RHIC.
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 this article, we briefly review the recent progress related to extracting the quark-gluon plasma (QGP) specific shear viscosity from the flow data measured at Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC).
We present a calculation of Pi, D and B mesons production at RHIC and LHC energies based upon the KKT model of gluon saturation. We discuss dependence of the nuclear modification factor on rapidity and transverse momentum.
We analyse the recently available experimental data on direct photon productions from Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV RHIC and from Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV LHC energies. The transverse momentum ($p_T$) distributions have been evaluated with the assumption of an initial quark gluon plasma phase at temperatures $T_i$=404 and 546 MeV with initial thermalisation times $τ_i$=0.2 and 0.1 fm/c respectively for RHIC and LHC energies. The theoretical evalutions agree reasonably well with the experimental observations. The thermal window for the LHC energy is justified t…
The hydrodynamic model for the expansion of the fireball in relativistic heavy-ion collisions is presented. Calculations using relativistic hydrodynamics of a fluid with small viscosity yield a satisfactory description of the experimental data on the particle spectra, the elliptic flow or the interferometry radii.
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…
We study the mechanism and probability of in-medium hadronization in the deconfined medium produced in heavy-ion collisions at RHIC and LHC. We show the likelihood of color-neutral objects to be formed inside the partonic fireball and the probability of these states to escape the medium with reduced interaction strength and energy loss. We will suggest specific measurements that are sensitive to the early degrees of freedom and show predictions for these measurements at RHIC and the LHC
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…
Although Tevatron has discovered top quark and LHC (pp collisions) has discovered Higgs boson but the RHIC and LHC heavy-ion colliders have not discovered thermalized quark-gluon plasma (QGP). This is because the experimental data of top quark at Tevatron and the experimental data of Higgs boson at LHC are compared with the exact first principle calculation but the experimental data at RHIC and LHC are compared with simplistic models and assumptions which are not exact first principle calculation. In this paper we show that the exact first principle method to study quark-gluon plasma at RHIC a…
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.
In this letter we update our predictions for the photoproduction of vector mesons in coherent $pp$ and $AA$ collisions at RHIC and LHC energies using the color dipole approach and the Color Glass Condensate (CGC) formalism. In particular, we present our predictions for the first run of the LHC at half energy and for the rapidity dependence of the ratio between the $J/Ψ$ and $ρ$ cross sections at RHIC energies.
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…
We report results on event-by-event hard probe of soft matter geometry and fluctuations in heavy ion collisions. Geometric data ($v_2$ of high $p_t$ hadrons) from RHIC plus LHC clearly favors jet "monography" model with strong near-Tc enhancement of jet-medium interaction strength which also implies a less opaque medium at LHC. We also quantify the jet responses to all harmonic anisotropy $v_n$($n=1,2,3,4,5,6$) and their manifestation in hard-soft azimuthal correlations.
The expected connections between signatures in the soft and hard sectors of small collision systems, and the status of experimental attempts to identify them, are discussed. These proceedings summarize the talk as given at the International Symposium on Multi-Particle Dynamics in September 2019 in Santa Fe, NM (ISMD19). As such, the choice of content and focus are selective and not intended to be comprehensive.
Monte-Carlo implementations of kT -factorization formula with both KLN and running-coupling BK unintegrated gluon distributions for nucleus-nucleus collisions are used to analyze recent experimental data on the particle multiplicities from RHIC(Au+Au@200GeV) and LHC(Pb+Pb@2.76TeV). We also compare the predicted transverse energy at midrapidity to new data from ALICE.
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…
We present predictions for the J/psi and rho meson production in the heavy ion ultraperipheral collisions (UPC) for the current energy 2.76 TeV at the LHC. Both total cross sections and cross sections with the neutron emission from one or both nuclei are presented. We also analyse the RHIC rho meson photoproduction data and emphasize importance of these data to test the current model for nucleus break up in UPC.
The generic features of parton energy loss effects on the quenching of single hadron spectra in heavy-ion collisions are discussed, paying attention to the expected differences from RHIC to LHC. The need for precise baseline measurements in p-Pb collisions at the LHC is also emphasized. Finally I briefly mention the production of prompt photons in heavy-ion collisions as well as some open questions.
Construction of future Muon Collider (or dedicated mu-ring) tangential to nucleus colliders will give opportunity to realize mu-A collisions at multi-TeV center of mass energies at a luminosity of order of 10^29-10^30 cm^-2s^-1. Obviously, such colliders will essentially enlighten fundamentals of strong interactions from quark to nucleus levels as well as clarify QCD basics. This paper is devoted to estimation of main parameters of the FCC, SppC, HL-LHC, HE-LHC and RHIC based muon-nucleus collider proposals by the software AloHEP.
Fluid dynamical description of elementary particle collisions has a long history dating back to the works of Landau and Fermi. Nevertheless, it is during the last 10-15 years when fluid dynamics has become the standard tool to describe the evolution of matter created in ultrarelativistic heavy ion collisions. In this review I briefly describe the hydrodynamical models, what we have learned when analyzing the RHIC and LHC data using these models, and what the latest developments and challenges are.
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 (…
We study the emission characteristics of thermal photons at RHIC and LHC as affected by both the space-time evolution of the bulk medium and the thermal emission rates. For the former we compare the results of two evolution models (expanding fireball and hydrodynamics). For the latter, we detail the influence of hadronic emission components and study a speculative scenario by upscaling the default QGP and hadronic rates around the pseudo-critical region.
STAR collaboration at RHIC has recently measured the polarization of $Λ$ hyperons in non-central heavy ion collisions in the RHIC Beam Energy Scan (BES) program. The magnitude of the polarization was found to decrease from few percents at the lowest BES energies to $\approx0.2$% at the top RHIC energy. The polarization signal has been reproduced in different hydrodynamic calculations assuming a thermodynamic spin-vorticity coupling mechanism at the Cooper-Frye hypersurface. In this work an extension of our existing calculations of the $Λ$ polarization in the RHIC BES program to the top RHIC an…
We present a summary of the physics of gluon saturation and non-linear QCD evolution at small values of parton momentum fraction $x$ in the proton and nucleus in the context of recent experimental results at HERA and RHIC. The rich physics potential of low-x studies at the LHC, especially in the forward region, is discussed and some benchmark measurements in pp, pA and AA collisions are introduced.
I discuss Upsilon production in pp collisions at RHIC, Tevatron and LHC energies, in particular the behaviour of the differential cross section in rapidity and the impact of QCD corrections on the P_T differential cross section. I also emphasise the very good agreement between the parameter-free predictions of the Colour-Singlet Model (CSM) and the first LHC data, especially in the region of low transverse momenta, which is the most relevant one for heavy-ion studies. I also show that the CSM predicts Upsilon cross-section ratios in agreement with the most recent LHC data. I then briefly discu…
We briefly review the existing psi(2S) data taken at RHIC, the Tevatron and the LHC. We systematically compare them with colour-singlet-model predictions as a function of the center-of-mass energy, of the quarkonium rapidity and of the quarkonium transverse momentum. The overall agreement is good except for large transverse momenta. This points at the existence of large NNLO corrections or points at colour-octet dominance.
The ratio of nuclear modification factors of high-$p_T$ heavy-flavored mesons tolight-flavored hadrons (heavy-to-light ratio) is shown to be a sensitive tool to test medium-induced energy loss at RHIC and LHC energies. Heavy-to-light ratios of $D$ mesons at RHIC in the region $7<p_T<12$ GeV, and of $D$ and $B$ mesons at the LHC in the region $10<p_T<20$ GeV, are proposed for such a test. Finally, the different contributions to the nuclear modification factor for electrons at RHIC are analyzed. Preliminary PHENIX and STAR data are compatible with radiative energy loss provided the contribution …
An important ingredient for the non-equilibrium evolution of partons at RHIC and LHC is to have some physically reasonable initial conditions for the single particle phase space distribution functions for the partons. We consider several plausible parametrizations of initial conditions for the single particle distribution function f_i(x,p) and fix the parameters by matching \int f(x,p)p^μd σ_μto the invariant momentum space semi-hard parton distributions obtained using perturbative QCD (pQCD), as well as fitting low order moments of the distribution function. We consider parametrizations of f_…
We study the stochastic dynamics of c and b quarks in the hot plasma produced in nucleus-nucleus collisions at RHIC and LHC, providing results for the nuclear modification factor R_AA and the elliptic flow coefficient v_2 of the single-electron spectra arising from their semi-leptonic decays. The initial QQbar pairs are generated using the POWHEG code, implementing pQCD at NLO. For the propagation in the plasma we develop a relativistic Langevin equation (solved in a medium described by hydrodynamics) whose transport coefficients are evaluated through a first-principle calculation. Finally, at…
