Low-mass dielectrons from the PHENIX experiment at RHIC

The production of the low-mass dielectrons is considered to be a powerful tool to study the properties of the hot and dense matter created in the ultra-relativistic heavy-ion collisions. We present the preliminary results on the first measurements of the low-mass dielectron continuum in Au + Au collisions and the φ-meson production measured in Au + Au and d + Au collisions at = 200GeV performed by the PHENIX experiment.     

Scaling properties of fluctuation results from the PHENIX experiment at RHIC

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has made measurements of event-by-event fluctuations in the charged-particle multiplicity as a function of collision energy, centrality, collision species, and transverse momentum in several heavy-ion collision systems. It is observed that the fluctuations in terms of σ ²/μ ² exhibit a universal power law scaling as a function of N_participants that is independent of the transverse momentum range of the measurement.     

Direct photons measured by the PHENIX experiment at RHIC

Results from the PHENIX experiment at RHIC on direct photon production in p+p, d+Au, and Au+Au collisions at  =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 supports jet quenching models, which attribute the suppression of high p_T hadrons to the energy loss of fast partons in the medium produced in the collision. Low p_T direct photons, measured via e⁺e^- pairs with small invariant mass, are possibly related to the production of thermal direct photons.     

Three-particle correlations from PHENIX to investigate the properties of the QGP at RHIC

There is now a consensus of opinion that in heavy ion collisions at RHIC energies a strongly interacting state of matter resembling a near-perfect liquid (termed sQGP) is formed. Attention is now being focused on elucidating the properties of this medium e.g. size, shape, collectivity, viscosity, closeness to the critical point etc. In this work we describe the efforts in the soft and hard sectors to quantify these properties. In particular, the study of jet-medium interactions are described via correlation based studies. Details of three particle correlation studies of RHIC data will be discussed. Such studies are important as they provide an avenue for estimates of the viscosity and the sound speed of the medium.     

Measurement of light mesons at RHIC by the PHENIX experiment

The PHENIX experiment at RHIC has measured a variety of light neutral mesons (π ⁰, K _S ⁰, η, ω, η ^′, φ) via multi-particle decay channels over a wide range of transverse momentum. A review of the recent results on the production rates of light mesons in p + p and their nuclear modification factors in d + Au, Cu + Cu and Au + Au collisions at different energies is presented.     

Open heavy flavor production from single muons in PHENIX at RHIC

The PHENIX experiment has studied open heavy flavor production in  =200 GeV p+p and d+Au collisions using the semi-leptonic decay into single muons. The results from these measurements and the details of the analysis technique are presented. The results from p+p collisions obtained at mid-rapidity are compared to perturbative QCD calculations. The production of light mesons is the major background source for the open flavor measurement using muons. The nuclear modification factor for light mesons were measured in Cu+Cu collisions at  =200 GeV is presented.     

A hadron blind detector for the PHENIX experiment at RHIC

A hadron blind detector (HBD) is to be installed in the PHENIX experiment for Run7, starting in fall 2006. The HBD is a threshold Čerenkov detector designed to measure electrons in a field free region surrounding the collision vertex. The HBD’s primary purpose is to tag background electrons originating from photon conversion and Dalitz decays. These background electrons can subsequently be excluded from a dilepton analysis, thereby reducing the combinatorial background by up to a factor of 100. The detector is realized by a proximity-focus windowless Čerenkov detector operating with pure CF₄ and read out by a reflective photocathode consisting of a stack of gas electron multipliers (GEM), the first of which is coated with 300 nm of CsI. The avalanche charge from the GEM stack is collected on a PCB with pads having similar size to the Čerenkov blob. Dalitz and photon conversions are tagged by having twice the amplitude of a single blob. An excellent Quantum Efficiency of the photocathode is thus crucial to the success of the device. Outstanding results have been accomplished using a vacuum evaporation facility on loan from INFN Rome. We will give an overview of the experimental methods to identify blobs and techniques developed for photocathode production.     

Results from STAR experiment at RHIC

We present some of the important experimental results from nucleus-nucleus collision studies carried out by the STAR experiment at Relativistic Heavy Ion Collider (RHIC). The results suggests that central Au+Au collisions at RHIC has produced a dense and rapidly thermalizing matter with initial energy densities above the critical values predicted by lattice QCD for establishment of a quark-gluon plasma (QGP).     

STAR results from the first year at RHIC

An overview of the latest results from the STAR experiment at RHIC is presented. Preliminary measurements of π,K,p,Λ and Ξ, plus their respective anti-particles atp _t < 2 GeV/c, where the majority of particle production occurs, allow us to probe the soft processes whilst the harder perturbative regime can be accessed by studying particle spectra and yields at higher momenta.     

Silicon-tungsten calorimeter for the forward direction in the PHENIX experiment at RHIC

The PHENIX detector at RHIC has been designed to study hadronic and leptonic signatures of the Quark Gluon Plasma in heavy ion collisions and spin dependent structure functions in polarized proton collisions. The baseline detector measures muons in two muon spectrometers located forward and backward of mid-rapidity, and measures hadrons, electrons, and photons in two central spectrometer arms, each of which covers 90. in azimuth and 0.35 units of rapidity. Further progress requires extending rapidity coverage for hadronic and electromagnetic signatures by upgrading the functionality of the PHENIX muon spectrometers to include photon and jet measurement capabilities. Tungsten calorimeters with silicon pixel readout and fine transverse and longitudinal segmentation are proposed to attain this goal. The use of such a design provides the highest density and finest granularity possible in a calorimeter. for the PHENIX Forward Calorimeter Collaboration Presented in the Poster Session “Future Experiments and Facilities” at the 18th International Conference “Quark Matter 2005”, Budapest, Hungary, 4–9 August 2005.     

Femtoscopic results in Au + Au and p + p from PHENIX at RHIC

Ultra-relativistic gold-gold and proton-proton collisions are investigated in the experiments of the Relativistic Heavy Ion Collider (RHIC). In the last several years large amount of results were revealed about the matter created in these collisions. The latest PHENIX results for femtoscopy and correlations are reviewed in this paper. Bose-Einstein correlations of charged kaons in 200 GeV Au + Au collisions and of charged pions in 200 GeV p + p collisions are shown. They are both compatible with previous measurements of charged pions in gold-gold collisions, with respect to transverse mass or number of participants scaling.     

Future of low-x forward physics at RHIC

Comparisons of particle production from high-energy ion collisions with next-to-leading order perturbative QCD calculations show good agreement down to moderate transverse momentum values. Distributions of azimuthal angle differences between coincident hadrons in these collisions support a partonic origin to the particle production, again down to moderate transverse momentum values. The rapidity dependence of inclusive and coincident particle production can therefore be used to probe parton distribution functions down to small momentum fractions where theory anticipates that parton saturation could be present. This paper describes how such experiments could be completed.Arrival of the final proofs: 27 July 2005PACS: 12.38 Qk, 13.88. + e, 24.85. + p     

High-pt probes of the quark-gluon plasma: STAR/PHENIX results at RHIC

In this talk I review the use of scattered high-pt partons as probes of the quark-gluon plasma formed at RHIC. Recent results from both STAR and PHENIX are used to assess our current understanding of how these partons lose energy as they travel through the plasma and the extent that energy-loss can be used to extract properties of the plasma.     

Spin physics at RHIC: Present and future

In 2001–2002 the relativistic heavy-ion collider (RHIC) at the Brookhaven National Laboratory (BNL) was first commissioned for polarized proton collisions. Polarized protons were injected into the RHIC, accelerated to 100 GeV, stored and the two beams were made to collide in four interaction regions. I will review the progress made by the RHIC spin program, followed by the physics goals for the next few years. After that I will present a brief overview of a proposal to build a high intensity polarized electron/positron beam facility at BNL which would enable deep inelastic scattering (DIS) experiments to be pursued at BNL by its collisions with the RHIC hadron beams.     

Extending physics capabilities of the PHENIX detector with calorimetry at forward rapidities

The PHENIX detector at RHIC has been designed to study different signatures of the states of matter created in heavy-ion collisions, and to investigate the spin structure of the nucleon. The PHENIX detector measures muons in two muon spectrometers, located at forward rapidities (1.2 < |η| < 2.4) and hadrons, electrons and photons in the two central spectrometers at midrapidity (|η| <0.35). To make a next step in the PHENIX research program, it is necessary to extend the rapidity coverage beyond the limits set by the existing central spectrometer. The functionality of the PHENIX muon detectors can be extended with added capabilities to measure photonic and hadronic jets. Tungsten calorimeters with silicon pixel readout and fine transverse and longitudinal segmentation are proposed to attain this goal. The proposed calorimeters will be located in the forward directions on either side of the PHENIX interaction point. In this talk we report on the studies of the functionality of the proposed calorimeters: the detector energy resolution, the jet reconstruction capabilities and the characteristics of pion rejection.     

Saturation physics and angular correlations at RHIC and LHC

We investigate the angular correlation between pions and photons produced in deuteron–gold collisions at RHIC and proton–lead collisions at LHC using the color glass condensate formalism. We make predictions for the dependence of the production cross section on the angle between the pion and the photon at different rapidities and transverse momenta. Measuring this dependence would shed further light on the role of the high gluon-density effects and saturation dynamics at RHIC and LHC.     

Polarized pp physics with internal jet targets at RHIC

The physics scope of RHIC could be extended to include fixed target experiments by the addition of a gas jet target. Two applications stand out among many possibilities. RHIC is the first accelerator to provide polarized proton beams with energy above 30 GeV. Extensive studies of pp colliding beams are planned for RHIC, but these will not cover the energy range covered with a fixed target, where the scattering of polarized protons from protons has not been adequately studied. Another important application is the possible use of a hydrocarbon jet to obtain a rapid and precise measurement of the polarization of the RHIC proton beams. A gas jet target with associated recoil detectors, electronics, and vacuum pumps is available and can be installed with low incremental costs on a short time scale.     

Production of light vector mesons in heavy-ion nuclear collisions at RHIC,measured by the PHENIX spectrometer

The production cross sections of ω and ? mesons in p + p, d + Au, and Au + Au collisions at energies √S _NN = 63 and 200 GeV have been measured in the PHENIX experiment at RHIC. The results of the measurements in different hadronic and dielectron decay channels are in agreement within the measurement error. The nuclear modification factors R _AA measured for both mesons are consistent with the results previously obtained for light neutral mesons. The position and width of the meson mass peaks reconstructed in hadronic decay channels are in agreement with the results of measurements in vacuum.     

Beyond the standard model physics at RHIC in polarized pp collision

An polarized hadron collider experiment must have a great discovery potential for a search of physics beyond the standard model. Experimental data of various symmetry tests at RHIC are going to be obtained within a few years. The author developed a simulation tool, studying a sensitivity of hunting contact interaction at RHIC by measuring parity violating spin asymmetries.     

Results from PHENIX: Year-1 and outlook

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory had its first physics run Summer 2000 colliding Au+Au ions at √ ^s NN=130 GeV energy. The PHENIX experiment measured global observables of the collision, spectra of electrons and identified hadrons as well as pair correlations. This talk gives an overview of the PHENIX results as presented at the Budapest'02 Workshop on Quark and Hadron Dynamics, Budapest, Hungary, March 3–7, 2002.