Direct photon-hadron correlations greatly improve our ability to perform jet tomography in heavy-ion collisions because the momentum of the direct photon can be used to constrain the initial momentum of the opposing jet. By comparing the spectrum of away-side hadrons observed in heavy ion collisions to the spectrum seen in nucleon collisions we can quantify the medium modification to the fragmentation function due to energy loss of the away-side parton.
High $p_{T}$ direct photon-hadron correlations have been measured with the PHENIX detector using a statistical subtraction method to remove the photon contribution from meson decays. The increased integrated luminosity in the most recent Au+Au RHIC run at $\sqrt{s_{NN}}$ = 200 GeV provides substantially improved statistical precision and enhances the kinematic reach. These measurements are compared to PHENIX p+p results and several theoretical models of energy loss. In addition, we compare direct photon-hadron and $π^{0}$-hadron correlations.
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.
Recent results on identified hadrons from the PHENIX experiment in Au+Au collisions at mid-rapidity at $\sqrt{s_{NN}}$ = 200 GeV are presented. The centrality dependence of transverse momentum distributions and particle ratios for identified charged hadrons are studied.
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.
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.
The PHENIX collaboration has designed a conceptually new Hadron Blind Detector (HBD) for electron identification in high density hadron environment. The HBD will identify low momentum electron-positron pairs to reduce the combinatorial background in the mass region below 1 GeV/c^2. The HBD shall be installed in PHENIX during the 2007 physics run. The HBD is a windowless proximity focusing Cherenkov detector with a radiator length of 50 cm, CsI photocathode and three layers of Gas Electron Multipliers (GEM) for gas amplification. Pure CF_4 serves both as a radiator and as a detector gas. The ra…
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.
Dielectrons play an important role in heavy ion collisions since they are produced during all stages of the collision and interact only electromagnetically. The PHENIX experiment was upgraded with the Hadron Blind Detector which provides excellent background rejection by removing pairs from both partially reconstructed Dalitz decays and photon conversions. In these proceedings we will report on the results obtained from 2009 data in p+p collisions using the HBD as well as the Au+Au results obtained in 2010.
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…
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.
A novel Hadron Blind Detector (HBD) has been developed for an upgrade of the PHENIX experiment at RHIC. The HBD will allow a precise measurement of electron-positron pairs from the decay of the light vector mesons and the low-mass pair continuum in heavy-ion collisions. The detector consists of a 50 cm long radiator filled with pure CF4 and directly coupled in a windowless configuration to a triple Gas Electron Multiplier (GEM) detector with a CsI photocathode evaporated on the top face of the first GEM foil.
Recent observations of extended pseudorapidity correlations at the LHC in p+p and p+Pb collisions are of great interest. Here we present related re- sults from d+Au collisions at PHENIX. We present the observed v2 and discuss the possible origin in the geometry of the collision region. We also present new measurements of the pseudorapidity dependence of the ridge in d+Au collision. Future plans to clarify the role of geometry in small collision systems using 3He+Au collisions are discussed.
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.
The PHENIX experiment at RHIC measured production of the ω- and ϕ- mesons in p+p, d+Au and Au+Au collisions at \sqrt{s_NN} = 63 and 200 GeV. Particle properties were studied using hadronic and di-electron decay channels. Transverse momentum (mass) spectra measured in different decay modes are found to be in agreement with each other within the errors. Nuclear modification factors R_{AA} measured for both mesons are consistent with results previously obtained for other neutral mesons. Position of the meson mass peaks and their widths reconstructed in hadronic decay channels are in agreement wit…
In these proceedings, we discuss recent results from d+Au collisions in PHENIX ridge related measurements and their possible hydrodynamic origin. We present the v2 at midrapidity and measurements of the pseudorapidity dependence of the ridge, distinguishing between the d-going and Au-going directions. We investigate the possible geometrical origin by comparing v2 in d+Au to that in p+Pb, Au+Au and Pb+Pb collisions. Future plans to clarify the role of geometry in small collision systems at RHIC are discussed.
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…
Transverse momentum spectra of identified $π^{+}$, $π^{-}$, $K^{+}$, $K^{-}$, p and $\overline{p}$ were measured by the PHENIX experiment at mid-rapidity in Au-Au collisions at $\sqrt{s_{NN}}=130$ GeV over a broad momentum range. Inverse slope parameters and mean $p_{t}$ were measured in minimum bias events and as a function of the number of participating nucleons. The mass and centrality dependence of the inverse slope parameters and mean $p_{t}$ is presented and discussed.
Recent results on identified hadrons from the PHENIX experiment in Au+Au collisions at mid-rapidity at $\sqrt{s_{NN}}$ = 200 GeV are presented. The centrality dependence of transverse momentum distributions and particle ratios for identified charged hadrons are studied. The transverse flow velocity and freeze-out temperature are extracted from $p_{T}$ spectra within the framework of a hydrodynamic collective flow model. Two-particle HBT correlations for charged pions are measured in different centrality selections for a broad range of transverse momentum of the pair. Results on elliptic flow m…
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 suppression of hadrons with large transverse momentum ($p_{\rm T}$) in central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV compared to a binary scaled p+p reference is one of the major discoveries at RHIC. To understand the nature of this suppression PHENIX has performed detailed studies of the energy and system-size dependence of the suppression pattern, including the first RHIC measurement near SPS energies. An additional source of information is provided by direct photons. Since they escape the medium basically unaffected they can provide a high $p_{\rm T}$ baseline for hard-scatt…
The nature of the quark-hadron phase transition can be investigated through analyzing the space-time structure of the hadron emission source. For this, the Bose-Einstein or HBT correlations of identified charged particles are among the best observables. In this paper we present the latest results from the RHIC PHENIX experiment on such measurements.
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…
The PHENIX experiment at RHIC measured $ω$, $η$ and $K_{S}^{0}$-meson production at high $p_{T}$ in $p+p$, $d+Au$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ $GeV$. Measurements performed in different hadronic decay channels give consistent results. The measured ratios of all three mesons to $π^{0}$ are found to be flat as a function of $p_{T}$ in $p+p$ collisions and equal to $ω/π^{0}=0.81\pm0.02\pm0.07$, $η/π^{0}=0.48\pm0.02\pm0.02$ and $K_{S}^{0}/π^{0}=0.45\pm0.01\pm0.05$. Nuclear modification factor measured for $ω$-mesons in central Au+Au collisions is $R_{AA}=0.4\pm0.15$.
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 …
Direct photons are a powerful tool to study the hot and dense matter created in heavy-ion collisions at RHIC, since they are created in the different stages of the collision. Since they do not interact via the strong force, they can travel through the hot and dense matter mostly unaffected. The PHENIX experiment has measured direct photons using different methods, over a broad range of transverse momentum (\pt), in different collision systems, and at different energies. These measurements help interpreting the measurement of hadrons as well as understanding the temperature of the created quark…
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…
Forward hadron measurements in p(d)+A provide a signal to study nuclear shadowing, initial state energy loss and/or gluon saturation effects as a function of rapidity, centrality and energy. High $p_T$ identified $π^{0}$ measurements are an essential first step toward measuring prompt photon production. The $π^{0}$ measurements are enabled by the PHENIX MPC-EX detector, a Si-W preshower detector located in front of the Muon Piston Calorimeter (MPC), expanding the neutral pion reconstruction capabilities in the rapidity range $3.1< η<3.8$ out to high energies, $E < 80$ GeV. Previous PHENIX meas…
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.
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.
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…
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…
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…
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 …
PHENIX has measured $e^+e^-$ pairs from p+p and Au+Au collisions as function of mass and $p_T$. The data can be used to probe the properties of dense matter formed in Au+Au collision. The relation between electron pairs and virtual photons is discussed.
The transverse momentum ($p_{\rm T}$) and centrality dependence of the azimuthal anisotropy ($v_{2}$) are measured for charged hadrons in different energies and collision species by the PHENIX experiment at RHIC. We find that $v_{2}$ divided by the participant eccentricity of the initial geometry proportionally increases with the number of participants to the 1/3 power except at small $N_{\rm part}$ in Cu+Cu at $\sqrt{s_{\rm NN}}$ = 62.4 GeV. Taking the eccentricity and quark number scaling into account, there is a universal scaling for $v_{2}$ with different energies and collision sizes. The …
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…
The PHENIX experiment at RHIC measured K0S, eta and omega-meson production at high pT in p+p, d+Au and Au+Au collisions at sqrt(s_NN)=200 GeV. Measurements performed in different hadronic decay channels give consistent results. This paper presents measured meson-to-pi0 ratios and Nuclear Modification factors in the most central d+Au and Au+Au collisions. No suppression seen in d+Au interactions is in contrast to a strong suppression of meson yields revealed in central Au+Au collisions at the same energy.
PHENIX preliminary results on the $J/Ψ$ production in $Cu+Cu$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV are presented. They are compared to results from lower energy experiments NA50 and NA60 at CERN SPS and to expectations from various theoretical models.
This contribution presents the latest results on heavy quarkonia (j/psi and upsilon) production in d+A and A+A collisions at RHIC at a center of mass energy per nucleon-nucleon collision sqrt(s_NN) = 200 GeV, measured by the PHENIX experiment, as well as their implications in terms of understanding cold nuclear matter effects and the possible formation of a quark gluon plasma in central $\auau$ collisions.}
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 correlation functions are presented for charged hadrons produced in Au+Au collisions at RHIC ($\sqrt{s_{_{NN}}}=130$ GeV). The measurements allow for the determination of elliptic flow without event-by-event estimation of the reaction plane. The measured correlation functions indicate elliptic flow values ($v_2$) which show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons.
Heavy quarks are an ideal probe of the quark gluon plasma created in heavy ion collisions. They are produced in the initial hard scattering and therefore experience the full evolution of the medium. PHENIX has previously measured the modification of heavy quark production in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV via electrons from semileptonic decays, which indicated substantial modifications of the parent hadron momentum distribution. The PHENIX barrel silicon vertex detector (VTX), installed in 2011, allows for the separation of electrons from charm and bottom hadron decays through the…
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…
Results of identified charged hadrons produced in Au+Au collisions at ${\sqrt{s_{NN}}} = 130$ GeV as a function of centrality are discussed. The $<{p_{T}}>$ of protons and antiprotons is significantly larger than in p--p collisions at the same center of mass energy. Its scaling with the number of participant nucleons, an increase of $20 \pm 5%$ from peripheral to central, may be due to radial expansion. In a hydrodynamical picture a simultaneous fit of pions, kaons and protons is consistent with a radial flow velocity of $β_{\rm{Tsurface}} = 0.72 \pm 0.01$ and a temperature of $T = 122 \pm 4$ …
The last decades of high energy physics revealed, that in ultra-relativistic ion-ion collisions, a strongly interacting quark gluon plasma (sQGP) is created. Varying the collision energy allows for the investigation of the phase diagram of QCD matter. The nature of the quark-hadron transition can be studied via femtoscopy, as the investigation of momentum correlations in heavy ion reactions reveals the space-time structure of the hadron production of the sQGP. Going beyond the Gaussian assumption the shape of this source may be described by Lévy distributions. In this paper we report on recent…
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 …
The PHENIX experiment discovered a large excess of low-$p_{T}$ direct photons in Au+Au collisions at 200 GeV compared to reference p+p collisions, which has been attributed to thermal radiation from the medium produced in the collisions. At the same time the excess photons show a large azimuthal anisotropy, expressed as Fourier coefficients $v_{2}$ and $v_{3}$. These surprising results have not yet been fully described by theoretical models. We will present the results obtained from real photons in the electromagnetic calorimeter and photons converted on the outer shell of the Hadron Blind Det…
Measurements from the RHIC experiments show strong suppression of high-pT hadrons in central Au+Au collisions. The PHENIX experiment has observed strong suppression of $π^0$ and charged hadron yields in central Au+Au collisions for pT > 5 GeV/c regardless of pT and particle species. The observed suppression is interpreted in terms of energy loss of quarks in a high-density medium. The PHENIX Year-4 Au+Au measurements have extended the pT reach of the $π^0$ spectra to 20 GeV/c. And the PHENIX Year-5 Cu+Cu measurements performed for the study of particle production in a lighter system and they c…
In 2001, PHENIX measured particle correlations of identical charged pions and kaons at mid-rapidity in Au-Au collisions at sqrt(s_NN)=200GeV. Bertsch-Pratt radius parameters of pion pairs are studied for 9 kT regions from 0.2 to 2.0 GeV/c and for 9 selections of collision centralities. The pion radius parameters are consistent with the result at sqrt(s_NN)=130GeV, and the ratio Rout/Rside is below 1 in all <kT> ranges up to 1.2 GeV/c. The radius parameters from charged kaon correlations are compared with those of pions.
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…
We report recent results of strangeness and heavy flavor measurements from PHENIX. The topics are: Elliptic flow of strangeness and heavy flavor electron production comparing to the other hadrons, $ϕ$ meson production, and an exotic particle search.
Direct photon spectra measured at small $p_T$ in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV are presented. Several measurement techniques including statistical subtraction, tagging, and internal and external conversion were applied and found to produce consistent results. The p+p and d+Au results are found to be in very good agreement with pQCD predictions over the entire $p_T$ range. No excess of direct photons in Au+Au collisions with respect to binary scaled d+Au data is observed within systematic errors.
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.
First identical-pion correlations measured at RHIC energies by PHENIX are presented. Two analyses with separate detectors, systematics, and statistics provide consistent results. The resulting HBT radii are moderately larger than those measured at lower energies. The $k_t$ dependence of the Bertsch-Pratt HBT radii is also similar to previous measures and is consistent with the conjecture of an expanding source.
The intermediate $p_T$ region (2 - 5 GeV/$c$) in central Au+Au collisions at RHIC has a rich physics content. The (anti)proton to pion ratio at the intermediate $p_T$ gives us a powerful tool to investigate the bulk properties of the hot and dense matter created at RHIC and their hadronization processes. We present the preliminary results of identified charged hadron spectra at the lower beam energies at RHIC. The excitation function of (anti)proton to pion ratios from SPS to RHIC are shown. We also discuss the onset of the baryon enhancement at the high energy heavy ion collisions.
Large enhancement of (anti)protons relative to pions has been observed at intermediate pT $\sim$ 2-5 GeV/c in central Au+Au collisions at RHIC. To investigate the possible source of this baryon enhancement, we performed a systematic study of identified hadron spectra in Au+Au and Cu+Cu collisions at sqrt(s_NN) = 200 GeV, and Au+Au collisions at sqrt(s_NN) = 62.4 GeV. The data set allows us to study the energy dependence and system size dependence of the baryon enhancement. We also compare the nuclear modification factors on hadron production in two different collision systems.
We report the measurement of anisotropic flow at RHIC - PHENIX experiment. We present the v_4 results at sqrt(s_NN) = 200 GeV in Au+Au collision. The scaling ratio of v_4/(v_2)^2 is about 1.5 and it is found to be smaller than the prediction from simple coalescence model. The v_2 for high p_T identified particles ($\sim$ 5 GeV/c) measured with Aerogel Cherenkov Counter are presented. We discuss the constituent quark scaling of v_2 for identified particles. We also report the first observation of v_2 for inclusive charged hadrons as well as identified hadrons at sqrt(s_NN) = 200 GeV in Cu+Cu co…
PHENIX has performed an extensive study on the evolution of medium effects from small to large systems. PHENIX has continued searching for Quark-Gluon Plasma (QGP) in small systems by measuring collectivity, modification of light hadron and quarkonia production, and jet substructure. In large systems, detailed studies on the property of the QGP have been done using direct photon, $π^{0}$-hadron correlation, heavy-flavor electron, and $J/ψ$ flow with a large statistics of data collected in 2014. This report covers new results from the PHENIX experiment in various collision systems.
We present recent high transverse momentum measurements by the PHENIX experiment for Au+Au and p+p collisions at $\sqrt{s_{NN}} = 200$ GeV at the Relativistic Heavy Ion Collider (RHIC). We show particle spectra for neutral pions and charged hadrons, define and show the nuclear modification factor, and discuss particle composition. By means of the nuclear modification factor, we observe a suppression factor of 5-6 for neutral pions and 3-4 for charged hadrons in central collisions at high $p_T$. We find that the ratio of $π^0$ to $(h^++h^-)/2$ remains nearly constant at $\sim 0.5$ for $p_T = 2-…
Direct photons were measured with the PHENIX experiment in p+p, d+Au, and Au+Au at sqrt(s_NN) = 200 GeV. To tackle the p_T region below 5 GeV/c, direct photons were measured through their internal conversion into e^+e^- in Au+Au collisions.
