PHENIX has measured the transverse momentum ($p_{\rm T}$) spectra and two particle angular correlations for high $p_{\rm T}$ particles in $d$+Au collisions at $\sqrt{s_{_{NN}}}$=200\,GeV using the RHIC Year-2008 run data. The azimuthal angle correlations for two particles with a large rapidity gap exhibit a ridge like structure. Using the $π^0$ reconstructed in the EMCal, we have successfully extended the $p_{\rm T}$ reach of the correlation up to 8\,GeV/$c$. We find that the azimuthal anisotropy of hadrons found at low $p_{\rm T}$ persists up to 6\,GeV/$c$ with a significant centrality and $p_{\rm T}$ dependence, similar to what was observed in A+A collisions.
Since the earliest days of Heavy Ion Physics thermal soft photon radiation emitted during the reaction had been theorized as a smoking gun signal for formation of a quark-gluon plasma and as a tool to characterize its properties. In recent years the existence of excess photon radiation in heavy ion collisions over the expectation from initial hard interactions has been confirmed at both RHIC and LHC energies by PHENIX and ALICE respectively. There the radiation has been found to exhibit elliptic flow $v_2$ well above what can currently be reconciled with a picture of early emission from a plas…
Different regions on the QCD phase diagram can be investigated by varying the collision energy and the centrality in heavy-ion collisions. In our latest measurements at the PHENIX experiment at RHIC, we utilize Lévy-type sources to describe the measured HBT correlation functions. In this paper we report the current status of the analysis of the centrality and beam energy dependence of the Lévy source parameters in Au+Au collisions from $\sqrt{s_{NN}}$ = 15 GeV to $\sqrt{s_{NN}}$ = 200 GeV.
In this paper, new measurements of anisotropic flow ($v_{1}$, $v_{2}$) for identified particles such as pions and proton in Cu+Au collisions at 200 GeV and U+U collisions at 193 GeV are reported. The anisotropic flow is studied as a function of $p_{T}$ and centrality in these two collision systems. In ultra-central U+U collisions (0--2% centrality), $v_2$ of protons shows a weak $p_{T}$ dependence for $p_T<$~1.0 GeV/c. A positive $v_1$ for charged pions is observed for $p_{T} >$ 1 GeV/c with respect to the first-order event plane, the angle of which is determined by the Au-going spectators. Th…
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.
Investigation of femtoscopic correlation functions in relativistic heavy ion reactions is an important tool to access the space-time structure of particle production in the sQGP. The shape of the correlation functions is often assumed to be Gaussian, but a detailed analysis reveals that the statistically correct assumption could be the so-called Lévy distribution. The detailed analysis of correlation functions in various systems may shed light on the location of the critical endpoint on the QCD phase diagram. It could also reveal if there is partially coherent pion production or could indicate…
We obtain the first measurement of $J/ψ$ elliptic flow at RHIC energies in forward rapidity using data from the PHENIX detector and applying an event plane method. The dataset used contains 19 billion events from the PHENIX experiment's Run 14 Au + Au dataset at $\sqrt{s_{NN}}=200$ GeV. PHENIX has measured a $J/ψ$ $v_2$ in a centrality range of $10-60\%$ that is consistent with zero. Taken together with results from LHC the measurement of $v_2$, which is consistent with zero may indicate that $J/ψ$ production by coalescence is not significant at forward rapidity at RHIC energy.
Event anisotropy of identified $π^{0}$, photon and electron compared to charged $π$, $K$, $p$ and deuteron in $\sqrt{s_{NN}}$ = 200 GeV Au+Au at PHENIX
Transverse energy distributions at midrapidity have been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) for Au+Au, U+U, Cu+Au, Cu+Cu, He+Au, d+Au, and p+p collisions over a wide energy range from $\sqrt{s_{NN}}$ = 7.7 GeV to $\sqrt{s_{NN}}$ = 200 GeV as a function of centrality. For central Au+Au collisions, it is observed that the midrapidity Bjorken energy density demonstrates a power law behavior from $\sqrt{s_{NN}}$ = 7.7 GeV to $\sqrt{s_{NN}}$ = 2.76 TeV. At a given collision energy, the data presented as a function of $N_{part}$ are independent of the…
The phase diagram of strongly interacting matter can be explored by analyzing data of heavy-ion collisions at different center of mass collision energies. For investigating the space-time structure of the hadron emission source, HBT correlation measurements are among the best tools. In this paper we present the latest results from the RHIC PHENIX experiment on such measurements in $\sqrt{s_{\rm NN}}=$ 39 GeV and 62 GeV Au+Au collisions.
Collisions of small systems at RHIC exhibit a significant suppression of the nuclear modification factor $R_{xA}$ of jets and high momentum neutral pions in events with large event activity. This suppression is accompanied by an enhancement of $R_{xA}$ in events with low event activity. Since event activity is commonly interpreted as a measure of the centrality of the collisions, these results call into question any interpretation of the suppression in central collisions that invokes energy loss in a QGP produced small systems. In this talk, we will compare prompt photon to $π^0$ production me…
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.
The dissociation of quarkonia in the medium created in heavy ion collisions is still one of the most debated topics in the heavy ion community. Progress in understanding the effect relies on a broad range of measurements in collisions with different nuclear sizes, covering a broad rapidity range. This presentation will report the $J/ψ$ measurements performed by the PHENIX collaboration at forward and backward rapidities of 1.2 $< |y| <$ 2.2 in $p$+Al, $p$+Au, and $^3$He+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, and the corresponding nuclear modification factors.
The PHENIX experiment has conducted searches for the QCD critical point with measurements of multiplicity fluctuations, transverse momentum fluctuations, event-by-event kaon-to-pion ratios, elliptic flow, and correlations. Measurements have been made in several collision systems as a function of centrality and transverse momentum. The results do not show significant evidence of critical behavior in the collision systems and energies studied, although several interesting features are discussed.
The PHENIX experiment has published direct photon yields and elliptic flow coefficients $v_2$ from Au+Au collisions at RHIC energies. These results have sparked much theoretical discussion. The measured yields and flow parameters are difficult to reconcile in current model calculations of thermal radiation based on hydrodynamic time evolution of the collision volume. Our latest analyses which use high statistics data from the 2007 and 2010 runs allow the determination of direct photon yields with finer granularity in centrality and photon momentum and down to $p_T$ as low as 0.4 GeV/$c$. We wi…
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 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…
Recent PHENIX measurements of the elliptic (v2) and hexadecapole (v4) Fourier flow coefficients for charged hadrons as a function of transverse momentum (pT), collision centrality and particle species are presented and compared with results from the PHOBOS and STAR collaborations respectively. The status of extensions to future PHENIX measurements at lower beam energies is also discussed.
Hard scattering yields in centrality-selected proton-- and deuteron--nucleus ($p$+A) collisions are generally compared to nucleon--nucleon ($NN$) cross-sections scaled to the appropriate partonic luminosity using geometric models derived from an analysis of minimum bias $p$+A interactions. In general, these models assume that hard process rates and the magnitude of the soft event activity in the underlying $NN$ collisions is uncorrelated. When included, these correlations influence the measured yield in a nominal centrality interval, an effect typically referred to as a "centrality bias". In t…
Based on results obtained with event generators we have launched the core-corona model. It describes in a simplified way but quite successfully the centrality dependence of multiplicity and $<p_t>$ of identified particles observed in heavy-ion reaction at beam energies between $\sqrt{s}$ = 17 GeV and 200 GeV. Also the centrality dependence of the elliptic flow, $v_2$, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single particle spectra of $K^-$ and ${\bar p}$ measured by the PHENIX, STAR and BRAHM…
