Characteristics of Parton Energy Loss Studied with High-p_T Particle Spectra from PHENIX
Klaus Reygers
备注：
To appear in the proceedings of 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 04-10 Feb 2008
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 here are consistent with a parton energy loss scenario so that these models can be used to relate the observed suppression to properties of the created medium.
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 …
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.
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 $I_{dA}$.
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.
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…
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.
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…
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…
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 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 …
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…
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.
Recent PHENIX elliptic flow ($v_2$) measurements for identified particles produced in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV are presented and compared to other RHIC measurements. They indicate universal scaling of $v_2$ compatible with partonic collectivity leading to the flow of light, strange and heavy quarks with a common expansion velocity field.
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.
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…
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…
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.
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…
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…
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…
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.
The first decade of RHIC physics and the first heavy ion running at the LHC have produced a wealth of data and discoveries. It is timely to now evaluate what has been learned and ask what compelling new questions have been raised. In this talk, several key unanswered questions about the properties of the strongly coupled quark gluon plasma and the distribution of partons inside nucleons and nuclei will be discussed along with how they can be addressed experimentally. The PHENIX Collaboration has developed a plan for upgrading the experiment in order to address these new questions. The current …
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…
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…
The observation of jet quenching in ultra-relativistic heavy ion collisions demonstrates significant energy loss of fast partons when passing through the created medium. Correlations between final-state particles at intermediate transverse momentum (1.0 $\lesssim$ $p_{T}$ $\lesssim$ 4.0 GeV/$c$) allow for study of the medium and its response to deposited energy. Comparison of these measurements in heavy ion collisions with measurements in proton collisions show strong modification of the correlation shape and particle yields. Two new structures are created, both extended in $Δη$, one centered …
Results from PHENIX at RHIC in p-p and Au+Au collisions are presented from the perspective of measurements in p-p collisions at the CERN ISR which serve as a basis for many of the techniques used. Notable results include the equality of the suppression of inclusive pi0 and direct electrons (from the decay of heavy quarks) in the range of transverse momentuum 4 < pT < 9 GeV/c in central Au+Au collisions. This result appears to strongly disfavor the explanation of suppression as due to radiative energy loss of partons traversing a Quark Gluon Plasma but opens up a fundamental discussion of how F…
The origin of the azimuthal anisotropy in particle yields at high pT (pT > 5 GeV/c) in RHIC collisions remains an intriguing puzzle. Traditional flow and parton energy loss models have failed to completely explain the large v2 observed at high pT. Measurement of this parameter at high pT will help to gain an understanding of the interplay between flow, recombination and energy loss, and the role they play in the transition from soft to hard physics. Neutral mesons measured in the PHENIX experiment provide an ideal observable for such studies. We present recent measurements of \piz yields with …
At the Relativistic Heavy Ion Collider (RHIC), key insights into the bulk properties of the hot and dense partonic matter arise from the study of azimuthal anisotropy ($v_2$) of the produced particles. These insights include indicating the matter undergoes rapid thermalization and behaves hydrodynamically at low $p_T$. Recently a low energy scan ($\le \sqrt{s_{NN}}$ = 62.4 GeV) began at RHIC to search for the QGP critical point, where a change in $v_2$ from higher energies could play a key role in its identification. Additionally, higher order flow harmonics have recently been shown to provide…
Throughout the history of the RHIC physics program, questions concerning the dynamics of heavy quarks have generated much experimental and theoretical investigation. A major focus of the PHENIX experiment is the measurement of these quarks through their semi-leptonic decay channels at mid and forward rapidity. Heavy quark measurements in $p+p$ collisions give information on the production of heavy flavor, without complications from medium effects. New measurements in $d+$Au and Cu+Cu indicate surprising cold nuclear matter effects on these quarks at midrapidity, and provide a new baseline for …
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…
At the Relativistic Heavy Ion Collider (RHIC), key insights into the bulk properties of the hot and dense partonic matter arise from the study of azimuthal anisotropy (v_2) of the produced particles. The v_2 values indicate that the matter undergoes rapid thermalization and behaves hydrodynamically at low p_T. Furthermore, the quark scaling of v_2 for different particle species suggests that thermalization occurs at the quark level and that v_2 is the same for all quark flavors. Recently, higher order harmonic measurements (v_3, v_4) have shown the potential for insights into the medium's init…
PHENIX has measured transverse momentum spectra of charged particles at mid-rapidity up to 10 GeV/c in Au+Au collisions at sqrt{s}=200 GeV. For central collisions, the yield at high pT is significantly suppressed comparing to binary scaled p+p data, and this suppression is stronger than observed at 130 GeV. Above 4 GeV/c, the deficit of high momentum particles is almost independent of pT.
Transverse momentum spectra for identified $π^0$'s in the range 1 GeV/c $< p_T <$ 4 GeV/c have been measured by the PHENIX experiment in Au-Au collisions at $\sqrt{s}=130$ GeV. The spectra from peripheral nuclear collisions are consistent with the simple expectation of scaling the spectra from p+p collisions by the average number of nucleon-nucleon binary collisions. The spectra from central collisions and the ratio of central/peripheral spectra are significantly suppressed when compared to point-like scaling.
It has been observed in central Au+Au collisions at Relativistic Heavy Ion Collider (RHIC) that the yield of neutral pions at high transverse momentum (pT> 5 GeV/c) is strongly suppressed compared to the one expected from p+p collisions scaled by the number of binary collisions. This suppression is considered to be due to the energy lost by hard scattered partons in the medium (jet quenching), which results in a decrease of the yield at a given pT. The magnitude of the suppression depends on the path length of scattered partons in the medium. Studying the path length dependence of energy loss …
During the past several years, experiments at RHIC have established that a dense partonic medium is produced in Au+Au collisions at sqrt(s)=200 GeV. Subsequently, a primary goal of analysis has been to understand and characterize the dynamics underlying this new form of matter. Among the many probes available, the measurements with respect to the reaction plane has proven to be crucial to our understanding of a wide range of topics, from the hydrodynamics of the initial expansion of the collision region to high-pt jet quenching phenomena. Few tools have the ability to shed light on such a wide…
One unexpected recent result from heavy-ion collisions is the large suppression and elliptic flow of electrons from heavy flavor decay. Further measurements of properties of electrons from heavy flavor decay are crucial to understanding the origin of this suppression and its implications for the properties of the hot matter produced at RHIC. Two particle correlations have been used extensively to study the propagation of hard partons through the produced matter in heavy-ion collisions. Measurements in p+p collisions are important both as reference for heavy ion measurements and to study heavy …
Mid-rapidity transverse momentum distributions for $π^\pm$, $K^\pm$, p and $\pbar$ are measured by the PHENIX experiment at RHIC in Au+Au, d+Au and p+p collisions at \ssnn=200GeV up to ~2--4GeV. Also particle ratios of $π^{-}/π^{+}$, $K^{-}/K^{+}$, $\pbar/p$, $p/π$ and $\pbar/π$ are measured, as well as the nuclear modification factor, all as a function of \pt and in every of the above collision systems. Finally, the measured p+p and Au+Au spectra are compared to the Buda-Lund hydro model.
The heavy quarks produced in the early stage of heavy-ion collisions are very effective probes of the dense partonic medium produced at RHIC. PHENIX has the ability to measure heavy quark production through single electrons in the central arm spectrometers ($|η|<0.35$) and single muons in the forward (backward) muon spectrometers ($1.2<|η|<2.2$). As these single leptons are from open heavy-flavor meson semi-leptonic decays, initial state cold nuclear matter effects on heavy quark production can be probed by measuring the single leptons in $d$$+$Au collisions. PHENIX have observed a large enhan…
The PHENIX experiment has measured single electron spectra at RHIC in proton-proton (p-p), deuteron-gold (d-Au), and gold-gold (Au-Au) collisions at an available energy per nucleon-nucleon pair of sqrt{s_NN} = 200 GeV. Contributions from photonic sources, i.e. Dalitz decays of light mesons and photon conversions, are subtracted from the inclusive spectra. The remaining non-photonic single electron spectra are dominated by semileptonic decays of particles carrying heavy flavor. Implications of these systematic measurements for heavy flavor production in cold and hot nuclear systems are discusse…
Results from the PHENIX experiment at RHIC on direct photon production in p+p, d+Au, and Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. In p+p collisions, direct photon production at high p_T behaves as expected from perturbative QCD calculations. The p+p measurement serves as a baseline for direct photon production in Au+Au collisions. In d+Au collisions, no effects of cold nuclear matter are found within the large uncertainty of the measurement. In Au+Au collisions, the production of high p_T direct photons scales as expected for particle production in hard scatterings. This support…
The PHENIX experiment at RHIC has measured single electron spectra in proton-proton, deuteron-gold and gold-gold collisions at sqrt(s_NN)=200 GeV. The photonic contribution (photon conversions and Daltiz decays) is subtracted from the inclusive spectra resulting in non-photonic electron spectra. The principal source of non-photonic electrons is the semi-leptonic decay of charm and bottom mesons. The implications for heavy flavor production in hot and cold nuclear systems are discussed.
Results from the PHENIX experiment for the first RHIC run with Au-Au collisions at a nucleon-nucleon center-of-mass energy of 130 GeV are presented. The systematic variation with centrality of charged particle multiplicity, transverse energy, elliptic flow, identified particle spectra and yield ratios, and production of charged particles and neutral pions at high transverse momenta are presented. Results on two-pion correlations and electron spectra are also provided, along with a discussion of plans for the second run at RHIC.
Recent results on high $p_T$ identified hadrons in Au+Au collisions from the PHENIX experiment are presented. The $R_{\rm AA}$ for $π^0$ and $η$ are found to be very consistent. The second and fourth order collective flow of $π^0$s have been measured and found that $v_4/v_2^2$ is consistent with the one observed in lower $p_T$ region. Assuming the suppression of the $π^0$ yield at highest $p_T$ arises from energy loss of partons, we found that the energy loss is $L^3$ dependent, where $L$ is the path length of the partons in the medium. The $δp_T/p_T$'s of high $p_T$ hadrons are computed from …
Heavy quarks are a valuable probe of the hot, dense medium created in a heavy ion collision, and are an important test of proposed mechanisms of energy loss. It was discovered that single non-photonic electrons are suppressed at a similar level to light hadrons, implying a comparable level of energy loss between light and heavy partons. Because theory has had a difficult time explaining the level of heavy quark energy loss, it is crucial to better understand charm and bottom suppression. Electron-hadron correlations have been used at PHENIX to study heavy flavor in both p+p and Au+Au collision…
Measurements of inclusive spectra of hadrons at large transverse momentum over a broad range of energy in different collision systems have been performed with the PHENIX experiment at RHIC. The data allow to study the energy and system size dependence of the suppression observed in RAA of high-pT hadrons at sqrt(s_NN)= 200 GeV. Due to the large energy range from sqrt(s_NN)= 22 GeV to 200 GeV, the results can be compared to results from CERN SPS at a similar energy. The large Au+Au dataset from the 2004 run of RHIC also allows to constrain theoretical models that describe the hot and dense matt…
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 …
Charm and bottom quarks are formed predominantly by gluon fusion in the initial hard scatterings at RHIC, making them good probes of the full medium evolution. Previous measurements at RHIC have shown large suppression and azimuthal anisotropy of open heavy-flavor hadrons in Au+Au collisions at $\sqrt{s_{NN}}=200~{\rm GeV}$. Explaining the simultaneously large suppression and flow of heavy quarks has been challenging. To further understand the heavy-flavor transport in the hot and dense medium, it is imperative to also measure cold nuclear matter effects which affect the initial distribution o…
PHENIX has extended the measurement of the pi0, eta, identified and inclusive charged hadron up to 20 GeV/c, and extended the measurement to the Cu+Cu collision system. A strong suppression is observed for both pi0 and charged hadron yields in central Au+Au and Cu+Cu collisions. Comparing Au+Au and Cu+Cu systems, RAA becomes independent of pT above 5 GeV/c. Its centrality dependence is compared with two models in order to test for universal Npart scaling that is independent of system; results are inconclusive. The results are compatible with energy loss predictions. In addition, the ratio of e…
The first results from Au-Au collisions at $\sqrt{s_{NN}}$=130 GeV obtained with the PHENIX detector in the Year 2000 run at RHIC are presented. The mid-rapidity charged particle multiplicity and transverse energy per participating nucleon rise steadily with the number of participants, such that transverse energy per charged particle remains relatively constant as a function of centrality. Identified charged hadron spectra as well as $\bar{p}/p$ and $K^+/K^-$ ratios are discussed. Charged particle and neutral pion transverse momentum distributions in peripheral nuclear collisions are consisten…
The characteristics of the particle emitting source are deduced from low transverse momentum identified hadron spectra (transverse mass less than 1 GeV) and HBT radii using a hydrodynamic interpretation. From the most peripheral to the most central data, the single particle spectra are fit simultaneously for all pions, kaons, and (anti-)protons using the parameterization in [1] and assuming a linear transverse flow profile. Within the systematic uncertainties, the expansion parameters called the freeze-out temperature and flow velocity, respectively decrease and increase with the number of par…
Transverse momentum (p_T) spectra of neutral pions and charged hadrons measured in Au+Au and d+Au collisions at sqrt{s_NN}=200 GeV by the PHENIX experiment at RHIC are compared to p+p reference spectra at the same sqrt{s_NN}. In central Au+Au collisions a factor 4-5 suppression for neutral pions and charged hadrons with p_T > 5 GeV/c is found relative to the p+p reference scaled by the nuclear overlap function <T_AB>. In contrast, such a suppression of high p_T particles is absent in d+Au collisions.
The first measurement of the dielectron continuum at RHIC energies was performed by the PHENIX experiment for Au+Au collisions at sqrt(s_{NN}) = 200 GeV. Mass spectra for different centralities are presented and compared with the expectations from hadron decays.
PHENIX measurements of high transverse momentum ($p_T$) identified hadrons in $d$+Au and Au+Au collisions are presented. The nuclear modification factors ($R_{d{\rm A}}$ and $R_{\rm AA}$) for $π^0$ and $η$ are found to be very consistent in both collision systems, respectively. Using large amount of $p+p$ and Au+Au datasets, the fractional momentum loss ($S_{\rm loss}$) and the path-length dependent yield of $π^0$ in Au+Au collisions are obtained. The hadron spectra in the most central $d$+Au and the most peripheral Au+Au collisions are studied. The spectra shapes are found to be similar in bo…
