我们测量了在$\sqrt{s_{NN}}$ = 200 GeV的$^{197}$ Au + $^{197}$ Au碰撞中与高$p_T$触发粒子相关的奇异介子、重子和反重子的相对丰度。在触发粒子的近侧和远侧提取粒子产率和比率。作为相对于触发粒子方位角$Δϕ$的角度的函数，研究了缔合粒子比。这样的研究应该有助于阐明以前观察到的相关性的起源和它们在Au+Au碰撞相对于p+p碰撞的强烈修改。我们讨论了这些测量可能与几种情况下的相互作用的快速部分子与介质中的Au+Au碰撞。
英文摘要：
We measure the relative abundances of strange mesons, baryons, and anti-baryons correlated with high-$p_T$ trigger particles in $^{197}$Au + $^{197}$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Particle yields and ratios are extracted on the near-side and away-side of the trigger particle. The associate-particle ratios are studied as a function of the angle relative to the trigger particle azimuth $Δϕ$. Such studies should help elucidate the origin of the previously observed correlations and their strong modifications in Au+Au collisions relative to p+p collisions. We discuss how these measurements might be related to several scenarios for interactions of fast partons with the medium in Au+Au collision.
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.
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 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.
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 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…
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 …
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…
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.
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…
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…
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…
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…
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…
When heavy ions with high energy collide, a hot and dense matter is produced. As the matter expands, the matter undergoes cross-over phase transition from partonic matter to hadronic matter. Jets are created by high pT partons in the early phase of the collisions. Leptons and photons can penetrate the matter without strong interaction. For that reason, jets, leptons and photons are good probes to study the partonic matter in the early phase of the collisions. We report about two probes associated with photon and their results for PHENIX.
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.
At RHIC kinematics, polarized jet hadroproduction is dominated by $gg$ and $qg$ scattering, making the jet double longitudinal spin asymmetry, $A_{LL}$, sensitive to gluon polarization in the nucleon. I will present STAR results of $A_{LL}$ from inclusive jet measurements for the RHIC 2006 run at center-of-mass energy 200 GeV. I will also discuss the current status of the analysis of data from the 2009 run, also at center-of-mass energy 200 GeV. The results are compared with theoretical calculations of $A_{LL}$ based on various models of the gluon density in the nucleon. The STAR data place si…
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…
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）
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 (…
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 mechanisms underlying hadronization are not well understood, both in vacuum and in hot QCD matter. Precise characterization of jet fragmentation to hadrons in p-p collisions will help elucidate the fundamental process of hadronization, and will serve as essential reference to measure the modification of hadronization in heavy ion collisions. We present measurements of fragmentation functions for unidentified particles in jets produced in p-p collisions at 200 GeV using the STAR detector at RHIC. The results from different jet reconstruction algorithms are compared, including variations of …
The spatial extents of particle emission source in high-energy collisions can be measured using two-particle femtoscopic correlations. In collisions with small multipli cities, such as proton-proton collisions, correlation functions can be distorted by non-femtos copic effects, for example due to the correlations that caused by energy-momentum conservatio n laws, jets and mini-jets. To estimate these effects, a simulation of p+p collisions at $\sqrt{s}$=200 and $\sqrt{s}$=510 GeV using PYTHIA 6.4.28 and HIJING 1.383, and p+Au collisions at $\sqrt{s_{NN}}$=200 GeV using HIJING were performed. C…
High pT π^0 and η, as well as jets are measured using high statistics d+Au collision data collected in RHIC Year-2008 run. Both R_{dA} and R_{cp} for three observables are found to be very consistent each other within quoted systematic and statistical uncertainties. It was found that the R_{dA} is strongly centrality dependent as opposed to the expectations from theoretical models. An explanation of the centrality dependence from the experimental point of view is presented.
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…
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…
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…
