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.
We report on two new measurements by the PHENIX collaboration regarding open heavy flavor. The first is an additional contribution to the background in the measurement of the yield of electrons at mid-rapidity from open heavy flavor decays. We found that the $J/Ψ$ can contribute substantially to the yield at high $p_T$. PHENIX has also measured the spectrum of muons at forward rapidity from open heavy flavor decays in Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV.
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.
The paper presents recent PHENIX results for the nuclear modification factor R_AA in Au + Au Collisions at sqrt(s_NN) = 200 GeV for the electrons originating from semi-leptonic decays of open heavy flavor carrying particles. We also report the results of the azimuthal asymmetry (v_2) measurement for those electrons, which is directly related to the heavy quark elliptic flow.
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…
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.
The transverse momentum dependence of the azimuthal anisotropy parameter v_{2}, the second harmonic of the azimuthal distribution, for electrons at mid-rapidity (|eta|<0.35) has been measured with the PHENIX detector in Au+Au collisions at sqrt(s_NN) = 200 GeV with respect to the reaction plane defined at high rapidities (|eta|=3-4). From the result we have calculated non-photonic electron v_{2}, which is expected to reflect the heavy-flavor azimuthal anisotropy, by subtracting v_{2} of electrons from other sources such as photon conversions, Dalitz decay etc.
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 …
A study of heavy flavor production in different collision systems in various kinematic regions presents an opportunity to probe cold nuclear medium and hot dense matter effects. Results from the PHENIX experiment on $J/ψ$ and open charm production in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ =200 GeV are presented. The data show strong $J/ψ$ suppression in central AA collisions, similar to NA50 results, and strong suppression in high $p_T$ open charm production. The $J/ψ$ production in Au+Au and d+Au collisions is compared to understand the cold nuclear medium effects. The data show signif…
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 …
In recent years, PHENIX has studied many important observables related to heavy-flavor physics through their leptonic decay measurements including the invariant yield of electrons from nonphotonic sources, and prompt single muons, both of which are dominated by D and B mesons. Charm and beauty cross-sections were measured and compared through single lepton, and lepton-hadron correlations in p+p collisions at $\sqrt{s}$ = 200 GeV. Observables for quarkonia production such as invariant yield and polarization were also measured in p+p collisions. In Au+Au collisions, preliminary results for the $…
The PHENIX experiment uses semileptonic decay channels to measure open and closed heavy flavor cross sections across the rapidity range $-2.2 < y < 2.4$. High luminosity data are now available for p+p, d+Au, Cu+Cu and Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV, and for Au+Au collisions at $\sqrt{s_{NN}}$= 62 GeV. We discuss recent d+Au results for open heavy flavor and $J/ψ$ production, and discuss their implications for the cold nuclear matter contributions to heavy flavor production in heavy ion collisions.
Cold nuclear matter (CNM) effects provide an important baseline for the interpretation of data in heavy ion collisions. Such effects include nuclear shadowing, Cronin effect, and initial patron energy loss, and it is interesting to study the dependence on impact parameter and kinematic region. Heavy quark production is a good measurement to probe the CNM effects particularly on gluons, since heavy quarks are mainly produced via gluon fusions at RHIC energy. The PHENIX experiment has experiment has ability to study the CNM effects by measuring heavy quark production in $d$$+$Au collisions at va…
The measurement of the nuclear modification factor ($R_{\rm AA}$) for heavy-flavor production in heavy-ion collisions tests predictions for cold- and hot-nuclear-matter effects. Heavy-flavor production in \pp\ collisions tests pQCD calculations and serves as a reference for understanding heavy-flavor production in heavy-ion collisions. Using the PHENIX muon-arm spectrometers, the transverse momentum spectra of inclusive muon candidates are measured for \pp\ and $\cucu$ collisions at $\snn = 200$\,GeV. After subtracting backgrounds, we obtain the measured invariant yields of negative muons from…
Heavy quarks are good probes of the hot and dense medium created in relativistic heavy ion collisions since they are mainly generated early in the collision and interact with the medium in all collision stages. In addition, heavy flavor quarkonia production is thought to be uniquely sensitive to the deconfined medium of the Quark Gluon Plasma (QGP) through color screening. Heavy quark production has been studied by the PHENIX experiment at RHIC via measurements of single leptons from semi-leptonic decays, in both the electron channel at mid-rapidity and in the muon channel at forward rapidity.…
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…
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…
The measurement of single leptons from the semi-leptonic decay of heavy-flavor hadrons has long been a means for studying heavy-quark production. PHENIX has measured single muons in pp collisions at forward rapidity and single electrons in both pp and AuAu collisions at mid-rapidity at sqrt(s_NN)=200 GeV. The most recent PHENIX single lepton results are presented in the context of state-of-the-art pQCD calculations. An updated azimuthal anisotropy, v2(pT), measurement for heavy-flavor single electrons in AuAu collisions is also presented.
Heavy quarks (charm and bottom) are good probes of the hot and dense medium created in relativistic heavy ion collisions since they are mainly generated at the beginning of collisions and interact with the media in all collision stages. In addition, heavy flavor quarkonia production is thought to be uniquely sensitive to the deconfined medium of the Quark Gluon Plasma (QGP) through color screening. Heavy quark production has been studied by the PHENIX experiment at RHIC via measurements of single leptons from semi-leptonic decays in both the electron channel at mid-rapidity and in the muon cha…
Heavy flavor production is an ideal tool to study the properties of the Quark Gluon Plasma (QGP). The heavy flavor production at the Relativistic Heavy Ion Collider (RHIC) has its unique kinematic coverage and different production mechanisms from the Larger Hadron Collider (LHC) measurements. Heavy flavor products created in heavy ion collisions experience the whole evolution of nuclear medium. It's critical to measure both open and closed heavy flavor products in different collision systems to isolate cold/hot nuclear medium effects and initial/final state interactions. We report recent heavy…
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…
Hadrons carrying heavy quarks, i.e. charm or bottom, are important probes of the hot and dense medium created in relativistic heavy ion collisions. Heavy quark-antiquark pairs are mainly produced in initial hard scattering processes of partons. While some of the produced pairs form bound quarkonia, the vast majority hadronize into particles carrying open heavy flavor. Heavy quark production has been studied by the PHENIX experiment at RHIC via measurements of single leptons from semi-leptonic decays in both the electron channel at mid-rapidity and in the muon channel at forward rapidity. A lar…
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.
PHENIX measures leptons at mid and forward rapidities and extracts leptons resulting from semi-leptonic decays of heavy quarks. We present PHENIX results related to heavy quark production, specifically the invariant cross section of the non-photonic single electrons produced at midrapidity in p+p and d+Au collisions at sqrt(sNN) = 200 GeV. The measured cross section for {\it p+p} collisions is compared with the NLO prediction, and a possible excess over the prediction is noted. The measured cross section for {\it d+Au} collisions scales with the number of colliding nucleon pairs from the {\it …
From the wealth of data obtained from the first three years of RHIC operation, the four RHIC experiments, BRAHMS, PHENIX, PHOBOS and STAR, have concluded that a high density partonic matter is formed at central Au+Au collisions at 200 GeV. The research focus now shifts from initial discovery to a detailed exploration of partonic matter. Particles carrying heavy flavor, i.e. charm or beauty quarks, are powerful tool for study the properties of the hot and dense medium created in high-energy nuclear collisions at RHIC. At the relatively low transverse momentum region, the collective motion of th…
Heavy flavor and quarkona production are important hard probes to test the Quantum Chromodynamics (QCD) and measure the properties of the Quark Gluon Plasma (QGP) created in high energy heavy ion collisions. The new PHENIX mid- and forward-rapidity silicon vertex detectors provide precise Distance of Closest Approach (DCA) determination, allowing charm and bottom yields identification, and improve di-muon mass resolution for charmonia studies. The relative $ψ(2S)$ over $J/ψ$(1S) yields measured in $p$+$p$, $p$+Al and $p$+Au data at $\sqrt{s}=$200 GeV help us to understand final state effects o…
We present results on identified particle production in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV at mid-rapidity measured by the PHENIX experiment. The centrality and flavor dependence of the Cronin effect in d+Au collisions is measured. The Cronin effect for the protons in d+Au is larger than that for the pions, but not large enough to account for the ``anomalous'' proton to pion ratio in central Au+Au collisions.
Measurement of electrons from heavy quarks by PHENIX has been done for various collision species and energy.PHENIX has measured single electron spectra from heavy flavor decays in Au+Au collisions at $sqrt{S_{NN}} = 200$ GeV.The measurement of heavy flavor production for p + p in PHENIX has also been measured which provided the baseline for studying hot and dense matter effects in heavy ion reactions. In Au + Au we observe a strong suppression of single electron compared with scaled p + p which challenges radiative energy loss models because heavy quarksare expected to radiate less than light …
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…
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…
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.
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…
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 Experiment at RHIC has conducted a beam energy scan at several collision energies in order to search for signatures of the QCD critical point and the onset of deconfinement. PHENIX has conducted measurements of transverse energy production, muliplicity fluctuations, the skewness and kurtosis of net charge distributions, Hanbury-Brown Twiss correlations, charged hadron flow, and energy loss. The data analyzed to date show no significant indications of the presence of the critical point.
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…
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…
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 …
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…
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…
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.
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…
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 …
Transverse momentum ($p_\mathrm{T}$) distribution of electrons for $0.3<p_\mathrm{T}<9.0$ GeV/$c$ have been measured in midrapidity ($|η|<0.35$) in Au + Au collisions and $p$ + $p$ collisions at $\sqrt{s_{NN}} = 200$ GeV by the RHIC-PHENIX experiment. Two methods for background subtraction were applied to determine the electron yield from open charm and bottom decays. The nuclear modification factor was calculated, and significant suppression at high-$p_\mathrm{T}$ was observed in Au + Au collisions, indicating substantial energy loss of heavy quarks in the dense medium.
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 PHENIX collaboration has developed novel methodologies for reliable extraction of jet functions from two and three particle azimuthal correlation functions measured at mid-rapidity in Au+Au collisions at $\sqrt s=200$ GeV. The extracted jet shape and the yield of jet-associated partner hadrons (per trigger hadron) are found to vary with particle type and collision centrality, indicating a significant effect of the nuclear collision medium on the (di)jet fragmentation process.
The heavy flavor studies at RHIC help improve the knowledge of the bottom/charm quark production and can test Quantum Chromodynamics (QCD). Compared to the LHC/Tevatron, the RHIC heavy flavor production originates from different partonic sub-processes and has a complementary kinematic coverage. The PHENIX forward rapidity silicon vertex detector (FVTX) provides precise determination of the event vertex, tracking and the Distance of Closest Approach (DCA) of charged tracks. This detector allows direct access to the $B$ meson production via measurements of non-prompt $J/ψ\to μ^{+} + μ^{-}$ withi…
Quarks of heavy flavors are useful tool to study quark-gluon plasma created in heavy-ion collisions. Due to their high mass and early production time, heavy quarks experience the entire evolution of the system created in these collisions. Open heavy flavor meson measurements are sensitive to the energy loss in the QGP, while quarkonia are sensitive to the temperature of the QGP as they dissociate because of Debye-like screening of color charges. This presentation is a summary of the latest heavy flavor studies performed at RHIC. Results from both STAR and PHENIX experiments are presented, comp…
The double-helicity asymmetries ($A_{LL}$) of $π^{+}$ and $π^{-}$ production in polarized proton proton collisions are specially interesting probes of the gluon's polarization. Relative differences among $A_{LL}$ of positive, neutral, and negative pions at high transverse momentum are sensitive to the sign and of magnitude of $Δ$G. Quark-gluon (qg) scattering starts to dominate mid-rapidity pion production at RHIC at transverse momenta above 5GeV/c. In this kinematic region the favored and unfavored fragmentation functions for each pion species are sensitive to both the gluon and the quark dis…
We present the first measurements of the nuclear modification factor (RAA) for flavor-separated b, c-quark electrons in Au+Au collisions at 200 GeV. The newly installed Silicon Vertex Tracker is used to measure the distance of closest approach distributions of electrons at midrapidity (|eta|< 0.35) over the transverse momentum range 1 < pt < 5 GeV/c. From this, the relative fraction of bottom (b) and charm (c) quarks is determined in both the p+p and Au+Au collision systems, which form the basis of the measured RAA . In p+p, we observe that a FONLL perturbative QCD calculation of b->e/(c->e+b-…
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…
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 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.
Heavy flavor production in hadronic collisions is dominated by gluonic processes and so is a sensitive probe of the gluon structure function in the nucleon and its modification in nuclei. A study of heavy flavor production in p+p and d+Au collisions in various kinematic regions presents an opportunity to probe cold nuclear medium effects; parton shadowing, color glass condensate, initial state energy loss, and coherent multiple scattering in final state interactions. The PHENIX muon arms cover both forward and backward directions in the rapidity range of $1.2 < |η| < 2.4$. We investigate singl…
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…
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 $…
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 …
Inclusive transverse momentum spectra of single electrons from Au+Au collisions have been measured at $\sqrt{s_{NN}}$ = 130 GeV and 200 GeV at midrapidity by the PHENIX experiment at RHIC. After subtraction of background from photon conversions and light hadron decays, the spectra appear consistent with semileptonic decays of charmed particles.
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 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 …
