By tuning several experimental observables, such as momentum and reaction plane, the PHENIX experiment has performed a systematic study of high $p_T$ parton energy loss in hot nuclear matter, as well as jet induced medium modifications, such as the ridge and shoulder. Baseline d+Au measurements are also studied to provide the comparison as control of cold nuclear matter effect.
Investigating partonic interactions is one of the primary goals of the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). RHIC is specially tailored for studying intrinsic partonic spin-momentum correlations due to its unique ability to collide polarized proton beams. Transverse single-spin asymmetries of order 10% have been measured in PHENIX at center of mass energies from 62.4 GeV to 200 GeV, similar to previous measurements. These results indicate that there exist partonic transverse momentum effects within the proton and/or within the process of hadronization. The MPC-EX, a …
The new forward Muon Piston Calorimeters allow PHENIX to explore low-$x$ parton distributions in d+Au collisions with hopes of observing gluon saturation. We present a two-particle azimuthal $Δϕ$ correlation measurement made between a mid-rapidity particle ($|η_1| < 0.35$) and a forward $π^0$ ($3.1 < η_2 < 3.9$) wherein we compare correlation widths in d+Au to p+p and compute $I_{dA}$.
We discussed methods used by the PHENIX to constrain the flow background in the two particle jet correlation. Both the background level and elliptic flow can be reliably decomposed from the jet contribution. We also studied the non-flow contribution to the reaction plane elliptic flow due to dijets. We found the jet bias is negligible in PHENIX, when the reaction plane is measured at Beam Beam Counter acceptance ($3<|η|<4$).
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.
In relativistic heavy-ion collisions, studying jet correlations and their dependence on the angle of emission with respect to the reaction plane can be used to shed light on the path length dependence of the energy lost by the jet. In this paper, we present recent PHENIX results on jet correlations versus reaction plane, as a function of centrality and transverse momentum.
The PHENIX experiment has established jet quenching at a center-of-mass energy of 200 GeV in Au+Au collisions. Recent measurements of Cu+Cu collisions at the same center-of-mass energy support a parton energy loss scenario. Furthermore, the onset of jet quenching was studied in Cu+Cu collisions for three center-of-mass energies 22.4, 62.4 and 200 GeV.
This is a status report on where PHENIX stands in terms of mapping out the landscape of jet correlation in $p_T$, hadron species, $\sqrt{s}$. We discuss separately high $p_T$ correlation results and low and intermediate $p_T$ correlation results. The former is sensitive to the quenching of the jet by medium, the later allows detailed study of the medium response to the (di-)jet.
We review recent progresses on jet quenching measurements by PHENIX. With increased statistics, PHENIX has gone beyond the single hadron suppression $R_{\rm AA}$, and made measurements on multiple jet quenching observables, such as $v_2$, $I_{\rm AA}$ and $v_2^{I_{\rm AA}}$. We argue that, by combining these observables together, one can achieve a better understanding of the energy loss mechanism. We present new $γ$-hadron correlation results with associated hadrons extended to low $p_T$; an enhancement has been observed, suggesting a contribution of genuine medium response that is relatively …
Modifications of jet properties resulting from the coupling of jets to the strongly interacting matter produced in RHIC collisions are of great current interest. In recent work, the PHENIX collaboration has applied a novel technique to the analysis of two particle azimuthal correlations which extinguishes the harmonic part of the underlying event revealing the true jet shape. Recent extensions of the method to three particle correlations allow for a more revealing study of jet topologies in Au+Au collisions at ($\sqrt{s_{_{\rm NN}}}$=200 GeV).
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.
PHENIX has measured the two particle azimuth correlation in Au + Au at $\sqrt{s}$ = 200 GeV. Jet shape and yield at the away side are found to be strongly modified at intermediate and low $p_T$, and the modifications vary dramatically with $p_T$ and centrality. At high $p_T$, away side jet peak reappears but the yield is suppressed. We discuss the possible physics pictures leading to these complicated modifications.
PHENIX has measured the two particle azimuth correlation in Au + Au at $\sqrt{s}$ = 200 GeV. Jet shape and yield at the away side are found to be strongly modified at intermediate and low $p_T$. The modifications vary dramatically with $p_T$ and centrality. At high $p_T$, away side jet peak reappears but the yield is suppressed. Similar jet strength is found for Au + Au and Cu + Cu collisions with similar number of participant nucleons.
Measurements of two particle azimuthal correlations in relativistic heavy ion collisions are useful tools to dissect the interplay between hard-scattered partons and hot dense medium. Correlations with trigger particle selection relative to second order event plane are sensitive to the path-length dependence of parton energy loss and to the influence of the medium on jet for high and intermediate transverse momenta pairs, respectively. To study the parton-medium coupling, it is also crucial to obtain correlations with rejection of contributions from higher harmonic flow. We present current res…
Two-particle azimuthal correlations have been shown to be a powerful probe for extracting novel features of the interaction between hard scattered partons and the medium produced in Au+Au collisions at RHIC. At intermediate $p_T$, 2-5GeV/c, jets have been shown to be significantly modified in both particle composition and angular distribution compared to p+pcollisions. We present recent PHENIX results from Au+Au collisions for a variety of $p_T$ and particle combinations.
Measurement of the in-medium energy loss of fast partons is one of the most active topics in heavy-ion physics. Such studies provide an opportunity to gain insight into the fundamental behavior of QCD processes by studying them away from vacuum conditions. A promising channel for relating theoretical models to data are two particle correlations using direct photon triggers. Recent results on this observeable using the PHENIX detector are presented.
The PHENIX MPC-EX detector is a Si-W preshower extension to the existing Muon Piston Calorimeters (MPC). Covering the pseudorapidity range 3.1 <eta < 3.8, the MPC-EX and MPC access high-x partons in the projectile nucleon The combined detectors will make possible a measurement of the prompt photon single spin asymmetry A_N in 200GeV transversely polarized p+p collisions, which will help elucidate the correlation of the transverse motion of valence partons in the proton with the proton spin.
We analyze the relative azimuthal ($Δϕ$) distribution of same-charge and opposite-charge particle pairs. We then remove elliptic flow background using the ZYAM method. Comparisons between near angle $Δϕ$ peak widths are presented for various centralities.
To interpret the measurements in heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) it is crucial to understand the initial state of the colliding gold (Au) nuclei. The parton distribution in Au nuclei is modified compared to protons, and their isospin composition is different due to the presence of neutrons. d+Au collisions at RHIC at the same collision energies are an important tool to study initial state modifications. PHENIX has measured pi0, eta, and reconstructed jets at high transverse momentum. These data are compared to predictions from nuclear parton distribution func…
In the first three years of the physics program at the Relativistic Heavy Ion Collider (RHIC) a picture was established in which the suppression of hadrons at high transverse momenta (p_T) in central Au+Au collisions is explained by energy loss of quark and gluon jets in a medium of high color-charge density. Measurements of single particle spectra for a smaller nucleus (Cu), for different center-of-mass energies and with higher statistics were performed in the subsequent years and are used to test predictions and assumptions of jet quenching models in more detail. The measurements presented h…
Measurements of two particle azimuthal correlations in relativistic heavy ion collisions provide information of the possible interplay between hard-scattered partons and the hot-dense medium. Toward an understanding of parton-medium coupling, it is indispensable to obtain correlations where contributions from higher harmonic flow($v_n$) are rejected. It is also important to produce correlation measurements where the trigger particle is selected relative to second and third order event planes. This enables us to explore path-length dependence of parton energy loss and the influence of the mediu…
Small, but significant non-random fluctuations in event-by-event average $p_T$ have been observed in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV by the PHENIX collaboration at RHIC. These are consistent with being caused by correlations due to jets at large $p_T$, where the measured suppression must be included to reproduce the centrality dependence of the non-random fluctuations.
The first evidence of jet quenching was observed at RHIC via suppression of single high $p_T$ hadron $R_{AA}$ and the disappearance of the away-side jet peak in two-particle correlations. Since then, hadron $R_{AA}$ and two-particle correlations continue to be useful probes of the QGP in heavy ion collisions, since the particles involved are fragments of the jets produced in the initial hard scattering. PHENIX recently improved the width measurements extracted from $π^0$-hadron correlations after removing the higher order flow terms in the underlying event subtraction. Measurements of the away…
Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta (p_T), elliptic flow, two-particle correlations, non-statistical fluctuations, and suppression of particle production at high p_T. The results are examined with an emphasis on implications for the formation of a …
Azimuthal two particle correlations at intermediate $p_{T}$ with one of the particles identified have been measured at PHENIX. Trigger ($2.5 < p_{T} < 4.0 GeV/c$) baryons and mesons show little significant difference in the number of associated particles ($1.7 < p_{T} < 2.5 GeV/c$) independent of centrality. For inclusive hadron triggers with $2.5 < p_{T} < 4.0 GeV/c$, associated fragmentation particles with $1.0 < p_{T} < 2.5 GeV/c$ show a higher baryon to meson ratio on the away side.
With the recent high statistics Au+Au and Cu+Cu runs at RHIC, it has become possible to systematically study jet properties in several different colliding systems with potentially different final state interactions. In this talk we present results from high-pT di-hadron and gamma-hadron correlations from p+p, d+Au, Cu+Cu, and Au+Au collisions where jets in vacuum, cold nuclear matter, and hot, dense nuclear matter are studied.
Azimuthal angle two particle correlations have been shown to be a powerful probe for extracting novel features of the interaction between hard scattered partons and the medium 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. Additionally, angular two particle correlations with identified hadrons provide information on the possible role of modified hadronization scenarios such as partonic recombination, which might allow medium…
We analyze PHENIX near-side ridge data for central Au+Au collisions at \sqrt{s_{NN}}=200 GeV with the momentum kick model, in which a near-side jet emerges near the surface, kicks medium partons, loses energy, and fragments into the trigger particle and fragmentation products. The kicked medium partons subsequently materialize as the observed ridge particles, which carry direct information on the early parton momentum distribution and the magnitude of the momentum kick. We find that the PHENIX ridge data can be described well by the momentum kick model and the extracted early partons momentum …
The PHENIX Experiment at the Relativistic Heavy Ion Collider has performed a survey of momentum correlations ranging from 200 MeV/c to 7 GeV in $\sqrt{s_{NN}}$ = 200 GeV p+p, d+Au, Au+Au, and $\sqrt{s_{NN}}$ = 62 GeV Au+Au collisions. The correlations are measured separately for like-sign and unlike-sign pairs. Comparisons of the properties of the near-side peak amplitude and width as a function of centrality and transverse momentum for each collision species are presented and discussed.
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.
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.
Angular correlation studies provide powerful insight into the energy loss of hard scattered partons as they traverse the partonic medium produced in heavy ion collisions at RHIC. These results are generally compared to jet correlations in p+p collsisions where all correlation strength is attributed to vacuum fragmentation. Strong modification to di-jet correlations has been observed in A+A collisions at RHIC, most notably for the away side jet. Many different effects, including the opacity of the medium, its response to energy deposited by partons as they propagate, and modifications to the pa…
Fully reconstructed jets and direct photon-tagged jet fragments significantly reduce energy-loss bias, the bias toward mostly measuring particles from partons which suffer little energy loss. In d+Au collisions, one accesses the physics at large $x$, which yields important constraints for nuclear parton distribution functions. In both d+Au and A+A collisions, coherent multiple-scattering models of energy loss can be tested. In this contribution, we present the current results from the PHENIX experiment on fully reconstructed jets and direct $γ$-hadron correlations. Baseline measurements of jet…
This poster presents the PHENIX results on high-p_T gamma-hadron and pi0-hadron correlations and shows the modification of away side jet shape by the medium. By comparing their jet shapes and yields, we see some evidence of the direct gamma contribution to correlation functions.
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…
The azimuthal anisotropy of high $p_{T}$ particle production in heavy ion collisions is a sensitive probe of the jet quenching mechanism. Recent PHENIX measurements for Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV show a $π^{0}$ $v_{2}$ signal that exceeds the pQCD energy loss calculations up to $p_{T} \sim 10$ GeV/c, challenging the traditional perturbative picture of the energy loss process. Here, we present an update and details of that measurement, as well as new high $p_T$ measurements at $\sqrt{s_{NN}}=62$ and 39 GeV. These measurements not only provide an important constraint for underst…
High $p_T$ jets are known to be strongly modified by the dense, strongly interacting medium created in heavy-ion collisions. The jet signal, extracted from two particle $Δϕ$ correlation, shows a systematic evolution of these modifications as function of $p_T$ and centrality. At intermediate $p_T$, both near side and away side correlations are modified. But the modifications are much stronger at the away side, resulting in a characteristic cone type of structure in central Au + Au collisions. The robustness of cone structure is strengthened by studying the jet shape as function of angle relativ…
A surprising excess of protons at intermediate $p_T$, 2-5GeV/c, has been observed in Au+Au collisions at RHIC, for which the source is not known. In p+p collisions, particles at this $p_T$ arise from jet fragmentation, however the observed baryon yield in central Au+Au collisions are not compatible with the usual jet fragmentation function. Two particle $Δϕ$ correlations are a powerful probe for quantitatively understanding the modifications to jet fragmentation from interactions with the medium. Earlier studies have shown that the excess baryons do have jet-like partners, indicating a hard sc…
PHENIX has measured many different two-particle azimuthal correlations in several different colliding systems, beam energies, $p_{T}$ windows, etc. The initial striking results from the first full energy Au+Au run have been confirmed, i.e. the observation of away-side suppression at intermediate $p_{T}$ and the shape modification at low $p_{T}$. With the new high-statistics data these results have been extended to further explore the physics resulting in these modified correlations. In this contribution we present a wide variety of correlation results at high-$p_{T}$ ($>$ 5 GeV/c) and at low $…
High-$p_T$ hadron-hadron correlations have been measured with the PHENIX experiment in $\Cu$ and $\pp$ collisions at $\sqrt{s_{NN}}=200$ GeV. A comparison of the jet widths and yields between the two colliding systems allows us to study the medium effect on jets. We also present a first measurement of direct photon-hadron correlations in $\Au$ and $\pp$ collisions. We find that the near-side yields are consistent with zero in both systems. By comparing the jet yields on the away side, we observe a suggestion of the expected suppression of hadrons associated with photons in $\Au$ collisions.
We present the application of a new jet reconstruction algorithm that uses a Gaussian filter to locate and reconstruct the jet energy to p+p and heavy ion data from the PHENIX detector. This algorithm is combined with a fake jet rejection scheme that provides efficient jet reconstruction with an acceptable fake rate. We show our first results on the measured jet spectra, jet--jet angular correlation in p+p and Cu+Cu collisions.
We review some important results from the PHENIX experiment at RHIC. They were obtained in a unique environment for studying QCD bulk matter at temperatures and densities that sur- pass the limits where hadrons exist as individual entities, so raising to prominence the quark- gluon degrees of freedom. We present measurements of nuclear modification factors for neutral pions, light favors (strange hadrons), direct-photons and non-photonic electrons from decays of particles carrying charm or beauty quarks. We interpret the large suppression of hadron produc- tion at high transverse momenta as re…
The PHENIX MPC-EX detector is a Si-W preshower extension to the existing PHENIX Muon Piston Calorimeters (MPC). The MPC-EX will consist of eight layers of alternating W absorber and Si mini-pad sensors and will be installed in time for RHIC Run-15. Covering a large pseudorapidity range, 3.1 < eta < 3.8, the MPC-EX and MPC access high-x partons in the projectile nucleon (and low-x partons in the target nucleon) in p+A and transversely polarized proton-proton collisions at 200 GeV. With the addition of the MPC-EX, the neutral pion reconstruction range extends to energies > 80 GeV, a factor of fo…
In this analysis we measure the azimuthal angle($ϕ$) dependence of hadrons with respect to the reaction plane ($Ψ_{RP}$) in events that were triggered by a high-$p_T$ $π^0$ of 5-10 GeV. Fitting the distribution of hadrons with a function of the type $ξ(1+2v_2\cos{(2(ϕ-Ψ_{RP})}))$, we observe that there is no significant statistical difference between $v_2$ inclusive hadrons and those hadrons from hard scattering events. We also compare the near-side jet widths using PYTHIA simulations with $h^{\pm}$-$h^{\pm}$ correlations in Au+Au at $\sqrt{s_{NN}}=200$ GeV.
We present measurements by the PHENIX experiment at RHIC of di-hadron pair production in \dAu collisions where the particles in the pair are varied across a wide range of pseudorapidity, out to $η= 3.8$. With di-hadrons, varying the $p_T$ and rapidity of the particles in the di-hadron pair allows studying any effects as a function of partonic $x$ in the nucleus. These di-hadron measurements might probe down to parton momentum fractions x $\sim$ $10^{-3}$ in the gold nucleus, where the interesting possibility of observing gluon saturation effects at RHIC is the greatest. Our measurements show t…
When studying the initial state and evolution of the matter created in relativistic heavy ion collisions, high-pT direct photons are a powerful probe. They are created in initial hard processes and in parton fragmentation, and possibly in interactions of partons with the hot and dense medium. We present systematic measurements of high-pT direct photon production in \sqrt{s_{NN}} = 200 GeV p+p and Au+Au collisions. The nuclear modification factor of direct photons is shown for 5 < pT < 18 GeV/c, and at very high transverse momenta it seems to be below unity in the most central Au+Au collisions.
Direct photons associated with jets provide a direct measurement of the effects of energy loss on the fragmentation of the parton as it propagates through the medium. Perturbative QCD calculations describe the direct photon cross section well at next-to-leading order, predicting a significant contribution from photons produced through parton fragmentation. Non-perturbative quantities such as the photon fragmentation function, which is poorly constrained, lead to large theoretical uncertainties. The measurement of photons correlated with jets in p+p collisions serves as an important test of the…
Jet tomography, the study of differential energy loss of hard scattered partons to infer the density profile of the medium, is greatly improved by precise knowledge of the initial energy of the hard probe. As photons are not strongly interacting, the momentum of the recoil jet from a direct photon trigger is balanced, to a good approximation, by the momentum of the photon. The energy loss of the away-side jet may be viewed as an effective modification of the fragmentation function. Direct photon-hadron correlations in A+A collisions should be sensitive to modified jet fragmentation as well as …
It has been observed that the yield of neutral pions at high transverse momentum (pT $>$ 5 GeV/c) region is strongly suppressed in central Au+Au collisions at Relativistic Heavy Ion Collider (RHIC), compared to the one expected in p+p collisions. This suppression may be due to an energy loss of hard scattered partons in the medium (jet quenching), that results in a decrease of the yield at a given pT. The magnitude of the suppression would depend on the path length of scattering partons in the medium, and therefore is associated with azimuthal angle from reaction plane in non-central collision…
Measurement of jet fragmentation property in p + p collisions provides a crucial baseline for the study of a possible, modified fragmentation behavior at the presence of the quark-gluon plasma. We describe the first measurement of jet fragmentation functions in sqrt(s) = 200 GeV p + p collisions at RHIC. This is facilitated by extending the linear least square unfolding technique employed by high energy and nuclear experiments to multidimensional spectra, which allows us to correct the inefficiencies in the jet energy response encountered at detectors such as PHENIX.
PHENIX has measured high transverse momentum (pT) identified hadrons in different collision species and energies in the last five RHIC runs. The systematic study of the high pT hadron production provides an idea on interaction of hard scattered partons and the matter created in relativistic heavy ion collision. The eta/pi0 ratio is measured in Au+Au collisions, which gives a hint on the system thermalization and particle production. A future measurement of hadron and photon measurement is discussed.
One of the most active areas of investigation in relativistic heavy-ion collisions is the study of the jet quenching phenomenon whereby hard partons lose their energy as they traverse the hot, dense matter created in such collisions. Strong parton energy loss has been observed in central nucleus-nucleus collisions as evidenced by the a large suppression of the yield of high pT hadrons as compared to the expected yield based on measurements in p+p collisions. Moreover, measurements of back-to-back correlations of charged hadrons suggest that jet shapes are strongly modified modified by the medi…
The PHENIX Run 4 Au+Au dataset provides a powerful opportunity for exploring the angular anisotropy of identified particle yields at high pT. Complementing traditional v2 measurements, we present pi0 yields as a function of angle with reaction plane, up to pT 10 GeV/c. The centrality dependence of the angular anisotropy allows us to probe the density and path-length dependence of the energy loss of hard-scattered partons. We will discuss various mechanisms for particle production in this high pT region.
The transverse momentum spectra, yields, and ratios of charged pions, protons, and antiprotons have been studied up to 5 GeV/c in $p_T$ in 5 different centrality classes in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. These results are compared and contrasted with the observables calculated in recombination models of hadronization. They are also used to examine the color charge dependence of parton energy loss in the medium.
Direct photon-hadron correlations are a golden channel to study parton in-medium energy loss in QGP. The modification of the effective fragmentation function for the away-side jet can be measured by comparing integrated away-side yields of direct photon-hadron pairs in heavy ion collisions to those in p+p. We measured per-trigger-yield of associated hadrons in Au+Au collisions and observed that there is a suppression compared to p+p for higher momentum fraction ($z_T$) hadrons. This can be explained by the opacity of the hot medium: energetic partons from the initial hard scattering lose energ…
Recent results from the PHENIX experiment at RHIC are presented. In this second part of the overview we discuss new results on direct photon production at low p_T in Au+Au collisions and a systematic study of J/psi production in various systems. Finally we summarize new results on the modification of jets in the medium.
Dihadron azimuthal correlation measurements have revealed striking modifications of the jets by the dense medium created in heavy-ion collisions at RHIC. One important question is to what extent the modification can be attributed to cold nuclear matter effects. In this analysis, we carried out a detailed mapping of the correlation patterns using high-statistics RUN8 d+Au minimum bias data. A striking scaling behavior of the jet pair yields is observed at low and intermediate $p_T$. The jet pair yields are found to be enhanced relative to $N_{\rm coll}$ scaled p+p jet pair yields. The nuclear m…
The Relativistic Heavy Ion Collider collides heavy nuclei at ultrarelativistic energies, creating a strongly interacting, partonic medium that is opaque to the passage of high energy quarks and gluons. Direct jet reconstruction applied to these collision systems provides a crucial constraint on the mechanism for in-medium parton energy loss and jet-medium interactions. However, traditional jet reconstruction algorithm operating in the large soft background at RHIC give rise to fake jets well above the intrinsic production rate of high-pT partons, impeding the detection of the low cross section…
Measurements from the RHIC experiments show a strong suppression in the yield of high-p$_\mathrm{T}$ single hadrons and a clear reduction in strength of the di-jet signal in two-hadron azimuthal-angle correlation functions in central Au+Au collisions at RHIC. These measurements should provide direct information on the properties of the medium within which hard-scattered partons propagate. The PHENIX preliminary results on single high-p$_\mathrm{T}$ hadron production and on particle azimuthal correlations are shown. The properties of the medium created in relativistic heavy ion collisions are d…
