This article reviews several important results from RHIC experiments and discusses their implications. They were obtained in a unique environment for studying QCD matter at temperatures and densities ...that exceed the limits wherein hadrons can exist as individual entities and raises to prominence the quark-gluon degrees of freedom. These findings are supported by major experimental observations via measuring of the bulk properties of particle production, particle ratios and chemical freeze-out conditions, and elliptic flow; followed by hard probe measurements: high- hadron suppression, dijet fragment azimuthal correlations, and heavy-flavor probes. These measurements are presented for particles of different species as a function of system sizes, collision centrality, and energy carried out in RHIC experiments. The results reveal that a dense, strongly interacting medium is created in central collisions at GeV at RHIC. This revelation of a new state of nuclear matter has also been observed in measurements at the LHC. Further, the IP-Glasma model coupled with viscous hydrodynamic models, which assumes the formation of a QGP, reproduces well the experimental flow results from at GeV. This implies that the fluctuations in the initial geometry state are important and the created medium behaves as a nearly perfect liquid of nuclear matter because it has an extraordinarily low ratio of shear viscosity to entropy density, . However, these discoveries are far from being fully understood. Furthermore, recent experimental results from RHIC and LHC in small , and 3He+Au collision systems provide brand new insight into the role of initial and final state effects. These have proven to be interesting and more surprising than originally anticipated; and could conceivably shed new light in our understanding of collective behavior in heavy-ion physics. Accordingly, the focus of the experiments at both facilities RHIC and the LHC is on detailed exploration of the properties of this new state of nuclear matter, the QGP.
Charged particle multiplicities in A+A and p(p̄)+p collisions as a function of pseudorapidity, centrality and energy are studied in both the nucleon and the constituent quark frameworks. In the ...present work, the calculation using the nuclear overlap model takes into account the fact that for the peripheral A+A and p+p collisions the number of nucleon and constituent quark participants cannot be smaller than two. A striking agreement is seen between the particle density in A+A and p(p̄)+p collisions, both at mid-rapidity and in the fragmentation regions, when normalized to the number of participating constituent quarks. The observations presented in this paper imply that the number of constituent quark pairs participating in the collision controls the particle production.
In relativistic heavy-ion collisions, anisotropic collective flow is driven, event by event, by the initial eccentricity of the matter created in the nuclear overlap zone. Interpretation of the ...anisotropic flow data thus requires a detailed understanding of the effective initial source eccentricity of the event sample. In this paper, we investigate various ways of defining this effective eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we examine the participant eccentricity, which quantifies the eccentricity of the initial source shape by the major axes of the ellipse formed by the interaction points of the participating nucleons. We show that reasonable variation of the density parameters in the Glauber calculation, as well as variations in how matter production is modeled, do not significantly modify the already established behavior of the participant eccentricity as a function of collision centrality. Focusing on event-by-event fluctuations and correlations of the distributions of participating nucleons, we demonstrate that, depending on the achieved event-plane resolution, fluctuations in the elliptic flow magnitude v{sub 2} lead to most measurements being sensitive to the root-mean-square rather than the mean of the v{sub 2} distribution. Neglecting correlations among participants, we derive analytical expressions for the participant eccentricity cumulants as a function of the number of participating nucleons, N{sub part}, keeping nonnegligible contributions up to O(1/N{sub part}{sup 3}). We find that the derived expressions yield the same results as obtained from mixed-event MCG calculations which remove the correlations stemming from the nuclear collision process. Most importantly, we conclude from the comparison with MCG calculations that the fourth-order participant eccentricity cumulant does not approach the spatial anisotropy obtained assuming a smooth nuclear matter distribution. In particular, for the Cu+Cu system, these quantities deviate from each other by almost a factor of 2 over a wide range in centrality. This deviation reflects the essential role of participant spatial correlations in the interaction of two nuclei.
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This article reviews several important results from RHIC experiments and discusses their implications. They were obtained in a unique environment for studying QCD matter at temperatures and ...densities that exceed the limits wherein hadrons can exist as individual entities and raises to prominence the quark-gluon degrees of freedom. These findings are supported by major experimental observations via measuring of the bulk properties of particle production, particle ratios and chemical freeze-out conditions, and elliptic flow; followed by hard probe measurements: high-
hadron suppression, dijet fragment azimuthal correlations, and heavy-flavor probes. These measurements are presented for particles of different species as a function of system sizes, collision centrality, and energy carried out in RHIC experiments. The results reveal that a dense, strongly interacting medium is created in central
collisions at
GeV at RHIC. This revelation of a new state of nuclear matter has also been observed in measurements at the LHC. Further, the IP-Glasma model coupled with viscous hydrodynamic models, which assumes the formation of a QGP, reproduces well the experimental flow results from
at
GeV. This implies that the fluctuations in the initial geometry state are important and the created medium behaves as a nearly perfect liquid of nuclear matter because it has an extraordinarily low ratio of shear viscosity to entropy density,
. However, these discoveries are far from being fully understood. Furthermore, recent experimental results from RHIC and LHC in small
,
and
3
He+Au collision systems provide brand new insight into the role of initial and final state effects. These have proven to be interesting and more surprising than originally anticipated; and could conceivably shed new light in our understanding of collective behavior in heavy-ion physics. Accordingly, the focus of the experiments at both facilities RHIC and the LHC is on detailed exploration of the properties of this new state of nuclear matter, the QGP.
The PHENIX Collaboration carries out a comprehensive physics program which studies heavy flavor production in relativistic heavy ion collisions at RHIC. The discovery at RHIC of large high-pT ...suppression and flow of electrons from heavy quarks flavors have altered our view of the hot and dense matter formed in central Au+Au collisions at sNN=200 GeV. These results suggest a large energy loss and flow of heavy quarks in the hot, dense matter. In recent years, the PHENIX has installed a silicon vertex tracker both in central rapidity (VTX) and in forward rapidity (FVTX) regions, and has collected large data samples. These two silicon trackers enhance the capability of heavy flavor measurements via precision tracking. This paper summarizes some of the latest PHENIX results concerning open heavy flavor and quarkonia production as a function of rapidity, energy and system size.
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 surpass 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 production at high transverse momenta as resulting from a large energy loss by the precursor parton on its path through the dense matter, primarily driven by gluon radiation. This dense QCD matter responds to energy loss in a pattern consistent with that expected from a hydrodynamic fluid. Further, its elliptic flow measurements suggest that the hadronization of bulk partonic matter exhibits collectivity with effective partonic degrees of freedom. The results are shown as a function of transverse momentum, centrality in different collision systems and energies.
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 surpass 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 production at high transverse momenta as resulting from a large energy loss by the precursor parton on its path through the dense matter, primarily driven by gluon radiation. This dense QCD matter responds to energy loss in a pattern consistent with that expected from a hydrodynamic fluid. Further, its elliptic flow measurements suggest that the hadronization of bulk partonic matter exhibits collectivity with effective partonic degrees of freedom. The results are shown as a function of transverse momentum, centrality in different collision systems and energies.
Silicon vertex tracker for RHIC PHENIX experiment Taketani, A.; Akiba, Y.; Apdula, N. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2010, Letnik:
623, Številka:
1
Journal Article
Recenzirano
The PHENIX experiment at Relativistic Heavy Ion Collider will be equipped with Silicon Vertex tracker to enhance its physics capability. There are four layers of silicon sensor to reconstruct charged ...tracks with 50μm resolution of decay length measurement. The VTX surrounds the collision point. The inner two layers and the outer two layers are composed of 30 pixel ladders and 44 stripixel ladders, respectively. We have been developing these detectors and done a performance test with 120GeV proton beam.
New design of silicon stripixel sensor has been developed at BNL for PHENIX upgrade. The sensor is a single-sided, DC-coupled, two-dimensional position sensitive device with good position resolution. ...This design is simpler for sensor fabrication and signal processing than the conventional double-sided strip sensor. HPK has produced pre-production stripixel sensors with thickness of 625μm. The quality assurance tests show that the very low leakage current 0.12nA per strip allows the use of the SVX4 chip. A long term stability test shows that the leakage current is stable over a long period of time. The study of the effects of irradiation on the performance of the stripixel sensor has been made using p+p collisions at 200GeV at PHENIX, 14MeV neutron and 20MeV proton beams.
We are constructing a Silicon Vertex Tracker detector (VTX) for the PHENIX experiment at RHIC. Our main motivation is to enable measurements of heavy flavor production (charm and beauty) in p+p, p+d ...and A+A collisions. Such data will illuminate the properties of the matter created in high-energy heavy-ion collisions. The measurements also will reveal the distribution of gluons in protons from p+p collisions. The VTX detector consists of four layers of barrel detectors and covers |{eta}|<1.2, and almost a 2{pi} in azimuth. The inner two silicon barrels consist of silicon pixel sensors; their technology accords with that of the ALICE1LHCB sensor-readout hybrid. The outer two barrels are silicon stripixel detectors with a new 'spiral' design, and a single-sided sensor with 2-dimensional (X, U) readout. In this paper, we describe the silicon stripixel detector and discuss its performance, including its response to electrons from a beta source ({sup 90}Sr), muons from cosmic-rays, and a 120 GeV proton beam. The results from the proton beam demonstrate that the principle of two-dimensional position sensitivity based on charge sharing works; the signal-to-noise value is 10.4, the position resolution is 33.6 {micro}m for X-stripixel (35.2 {micro}m for U-stripixel), and the tracking efficiencies in the X- and U-stripixels are, over 98.9 {+-} 0.2%. The stripixel detector within the VTX project is in the pre-production phase.
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