Parameter V2 Research Articles

AZIMUTHAL ASYMMETRY AND CORRELATIONS OF HARD PHOTONS IN INTERMEDIATE ENERGY HEAVY ION COLLISIONS

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we investigated the directed flow and elliptic flow for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive directed flow and negative elliptic flow of directed photons are illustrated and they seem to be anti-correlated to the free proton's flow. Also we calculated the two-photon correlation functions from which the information of photon source was extracted, and while two-photon azimuthal correlations are presented as a good method to extract the elliptic flow parameter v2 of direct hard photons.

Energy dependence of the v2-scaling and the QCD phase boundary

In high-energy nuclear collisions at RHIC ( = 60–200 GeV), quark coalescence has been suggested as one of the processes for hadronization. As a result, one observes a scaling in the elliptic flow parameter v2 and hadron-type dependence (within the 2 < pT < 5 GeV/c region) in the nuclear modification parameter RAA. On the other hand, in a given collision when the center of mass energy is not sufficiently high to create partonic matter, one would not expect the scaling in the final observed v2. Hence, the scaling provides us a sensitive tool for the search for the possible phase boundary in the hot/dense matter dominated by either partonic or hadronic degrees of freedom. In this paper, we will report the results from analyzing the energy dependence of v2 for identified hadrons from Au+Au collisions. Data from transport models are used in our analysis. In this model calculation, without the partonic coalescence the scaling in v2 is absent.

Order-dependent mappings: Strong-coupling behavior from weak-coupling expansions in non-Hermitian theories

A long time ago, it has been conjectured that a Hamiltonian with a potential of the form x2+ivx3, v real, has a real spectrum. This conjecture has been generalized to a class of the so-called PT symmetric Hamiltonians and some proofs have been given. Here, we show by numerical investigation that the divergent perturbation series can be summed efficiently by an order-dependent mapping (ODM) in the whole complex plane of the coupling parameter v2, and that some information about the location of level-crossing singularities can be obtained in this way. Furthermore, we discuss to which accuracy the strong-coupling limit can be obtained from the initially weak-coupling perturbative expansion, by the ODM summation method. The basic idea of the ODM summation method is the notion of order-dependent “local” disk of convergence and analytic continuation by an ODM of the domain of analyticity augmented by the local disk of convergence onto a circle. In the limit of vanishing local radius of convergence, which is the limit of high transformation order, convergence is demonstrated both by numerical evidence as well as by analytic estimates.

Negative elliptic flow of J/ψ’s: A qualitative signature for charm collectivity at RHIC

We discuss one of the most prominent features of the very recent preliminary elliptic flow data of J/ψ-mesons from the PHENIX Collaboration (PHENIX Collaboration (C. Silvestre), arXiv:0806.0475 [nucl-ex]). Even within the rather large error bars of the measured data a negative elliptic flow parameter (v2) for J/ψ in the range of p T = 0.5-2.5 GeV/c is visible. We argue that this negative elliptic flow at intermediate pT is a clear and qualitative signature for the collectivity of charm quarks produced in nucleus-nucleus reactions at RHIC. Within a parton recombination approach we show that a negative elliptic flow puts a lower limit on the collective transverse velocity of heavy quarks. The numerical value of the transverse flow velocity $ \beta_{T}^{}$ for charm quarks that is necessary to reproduce the data is $ \beta_{T}^{}$ (charm) ∼ 0.55-0.6c and therefore compatible with the flow of light quarks.

High-pT direct photon spectra and azimuthal anisotropy measurements in 200 GeV Au+Au collisions at RHIC-PHENIX

Direct photons are a powerful probe to study the property of quark–gluon plasma (QGP) in high energy heavy-ion collisions. In non-central collisions, the anisotropy of the collision region produces the different pressure gradients and particle density that results in different anisotropy of particle emission, depending on the production processes of photons. Therefore, an azimuthal anisotropy parameter v2 is a powerful tool to explore the source of direct photons. We report on the latest direct photon analysis of the nuclear modification factor in and 62.4 GeV Au + Au collisions, and v2 at high pT in 200 GeV Au + Au collisions at RHIC-PHENIX (Run4). We also present the analysis status, using a larger statistics and better reaction plane information from a new detector available from RHIC Run7 data.

Importance of Granular Structure in the Initial Conditions for the Elliptic Flow

We show the effects of the granular structure of the initial conditions of a hydrodynamic description of high-energy nucleus-nucleus collisions on some observables, especially on the elliptic-flow parameter v2. Such a structure enhances production of isotropically distributed high-pT particles, making v2 smaller there. Also, it reduces v2 in the forward and backward regions where the global matter density is smaller and, therefore, where such effects become more efficacious.

AZIMUTHAL ANISOTROPY MEASUREMENT OF DIRECT PHOTON IN $\sqrt{^SNN} = 200\ {\rm GeV}$Au + Au COLLISIONS AT RHIC-PHENIX

Azimuthal anisotropy of direct photons is measured in [Formula: see text] Au + Au collisions by the PHENIX experiment at RHIC. Direct photons are one of the most effective probes to study properties of hot dense medium at initial state (also QGP state) of heavy ion collisions because photons do not interact strongly with medium once produced. They keep their conditions when they are created. Within statistical and systematic errors, the elliptic flow parameter (v2) of direct photons is consistent with zero. Direct photons v2 is measured by the hadron decay photon background v2 from inclusive photon v2 in intermediate to high transverse momentum (pT) region (0 to 10 GeV/c) for 3 centrality selections (20% steps) and minimum bias.

K*(892) PRODUCTION IN Au+Au COLLISIONS AT RHIC

Short-lived resonances are useful tools to probe the property of the matter created in heavy ion collisions. Measurements of their production yields and elliptic flow allow us to understand particle production mechanisms as well as the system evolution after hadronization. We report the measurements of transverse momentum (pT) spectrum and anisotropic parameter v2 of K* resonance from a high statistics data set of Au + Au collisions at [Formula: see text] taken by the STAR experiment in year 2004. The K* are measured up to intermediate pT region pT &lt; 5 GeV /c at mid-rapidity through its hadronic decay channel. Its nuclear modification factor as well as elliptic flow are compared with corresponding results for [Formula: see text] and Λ up to intermediate pT to check the number of constituent quark scaling for resonances. Combined with the K*/K and φ/K* yield ratios, the production mechanism of K* is discussed. The first results on K* mT spectra from Au + Au 62.4 GeV are presented to understand the energy dependence of K* production.

PHENIX measurements of reaction plane dependence of high-pT photons and pions

Direct photon and neutral pion production with respect to the reaction plane at high-pT were measured with the PHENIX experiment in Au+Au collisions at at mid-rapidity. The azimuthal asymmetry parameter v2 for direct photons was found to be consistent with zero for all centrality classes. We evaluate the dependence of π0 suppression at high-pT on the emission angle Δϕ with respect to the event reaction plane for seven centrality bins. For the peripheral bins we observe no suppression for neutral pions aligned with the reaction plane while π0's produced perpendicular to the reaction plane are suppressed by factor 2. We found that a simple geometric picture can explain the observed suppression pattern.

Elliptic flow of electrons from heavy flavour decay by the PHENIX

The RHIC-PHENIX experiment has measured the azimuthal anisotropy parameter v2, the second harmonic of the azimuthal distribution, for electrons at mid-rapidity (|η| < 0.35) as a function of transverse momentum (0.5 <pT< 5.0 GeV/c) in Au+Au collisions at = 200 GeV. From the result, we have calculated heavy flavour (charm and bottom) electron v2 by subtracting v2 of electrons from other sources such as photon conversions and Dalitz decays. At the PHENIX experiment, the nuclear modification factor (RAA) for the heavy flavour electrons is also measured. The property of the medium-created Au+Au collisions at = 200 GeV can be provided to these measurements.

The azimuthal anisotropy of electrons from heavy flavour decays in GeV Au–Au collisions by PHENIX

The PHENIX experiment has measured the azimuthal anisotropy parameter v2, the second harmonic of the azimuthal distribution, for electrons at mid-rapidity (|η| < 0.35) as a function of transverse momentum (0.4 < pT < 5.0) in Au+Au collisions at GeV. From the result we have calculated non-photonic electron v2, which is expected to reflect the heavy-flavour azimuthal anisotropy, by subtracting v2 of electrons from other sources such as photon conversions, Dalitz decay, etc.

Azimuthal anisotropy of electrons from heavy flavor decays in $\sqrt{s_{NN}}$ =200 GeV Au-Au collisions at PHENIX

The PHENIX experiment has measured the azimuthal anisotropy parameter v2, the second harmonic of the azimuthal distribution, for electrons at mid-rapidity (|η|<0.35) as a function of transverse momentum (0.5<pT (GeV/c)<5.0) in Au+Au collisions at \(\sqrt{s_{NN}}\) =200 GeV. From the result we have calculated the non-photonic electron v2, which is expected to reflect charm quark azimuthal anisotropy, by subtracting the v2 of electrons from other sources such as photon conversions and Dalitz decays.

On triplet low-energy parameters of nucleon-nucleon scattering

Triplet low-energy parameters of neutron-proton scattering, including high-order shape parameters, are calculated on the basis of approximating the effective-range function k cot δ t by polynomials and rational functions with the aid of the latest experimental data on phase shifts from the SAID nucleon-nucleon database. With the resulting values of the low-energy parameters, a good description of phase shifts over a broad energy interval is obtained by using the effective-range expansion featuring a small number of terms. The properties of the deuteron that were calculated on the basis of the values found for the triplet low-energy parameters of scattering agree very well with experimental values. The triplet low-energy parameters and the properties of the deuteron that were obtained here by using present-day data from the SAID database differ markedly from the analogous results obtained for data of the Nijmegen group. Possible reasons behind this discrepancy are discussed. Highly precise new approximate formulas for determining the shape parameter v 2 are proposed and are shown to be efficient in calculations. The effective-range expansion for the D wave is considered, and preliminary results of calculations of low-energy scattering parameters for this case are obtained.

3D Relativistic Hydrodynamic Computations Using Lattice-QCD-Inspired Equations of State

In this communication, we report results of three-dimensional hydrodynamic computations, by using equations of state with a critical end point as suggested by the lattice QCD. Some of the results are an increase of the multiplicity in the mid-rapidity region and a larger elliptic-flow parameter v2. We discuss also the effcts of the initial-condition fluctuations and the continuous emission.

Particle dependence of elliptic flow in Au + Au collisions at

The elliptic flow parameter (v2) for K0S and has been measured at mid-rapidity in Au+Au collisions at by the STAR Collaboration. The v2 values for both K0S and saturate at moderate pT, deviating from the hydrodynamic behaviour observed in the lower pT region. The saturated v2 values and the pT scales where the deviation begins are particle dependent. The particle-type dependence of v2 shows features expected from the hadronization of a partonic ellipsoid by coalescence of co-moving quarks. These results will be discussed in relation to the nuclear modification factor (RCP) which has also been measured for K0S and by the STAR Collaboration.

Azimuthal anisotropy of K(0)(S) and Lambda+Lambda production at midrapidity from Au+Au collisions at sqrt[s(NN)]=130 GeV.

We report STAR results on the azimuthal anisotropy parameter v(2) for strange particles K(0)(S), Lambda, and Lambda at midrapidity in Au+Au collisions at sqrt[s(NN)]=130 GeV at the Relativistic Heavy Ion Collider. The value of v(2) as a function of transverse momentum, p(t), of the produced particle and collision centrality is presented for both particles up to p(t) approximately 3.0 GeV/c. A strong p(t) dependence in v(2) is observed up to 2.0 GeV/c. The v(2) measurement is compared with hydrodynamic model calculations. The physics implications of the p(t) integrated v(2) magnitude as a function of particle mass are also discussed.

Azimuthal anisotropy of KS0 and Λ at mid-rapidity from Au + Au collisions at √sNN = 130 GeV

We report STAR results on the azimuthal anisotropy parameter v2 for strange particles KS0 and Λ at mid-rapidity in Au + Au collisions at √sNN = 130 GeV at RHIC. The value of v2 as a function of transverse momentum pt and collision centrality is presented for both particles and compared with model calculations. A strong pt dependence in v2 is observed up to pt ∼ 2.0 GeV/c where v2 begins to saturate.

EPR of dynamic Jahn-Teller distortion in CuII doped magnesium Tutton's salt

The dynamic Jahn-Teller distortion in single crystals of CuII doped magnesium Tutton's salt, MgK2(SO4)2·6H2O was studied by EPR spectroscopy. The directions of the g tensor axes were found to coincide with those of A at room temperature as well as at 113 K and were correlated with the MgO directions in the lattice. Two spatially distinct sites of copper were detected in the crystal. The g and A values were also calculated from the polycrystalline samples at various temperatures. A dx2-y2 ground state has been assigned for CuII, as in the isomorphous zinc Tutton's salt. The Silver and Getz model was applied to understand the dynamics of Jahn-Teller (JT) activity. The system was found to undergo dynamic JT distortion at all temperatures. At low temperatures, the [Cu(H2O)6]2+ ion has three possible degenerate vibronic states corresponding to three possible directions for the long axis of the octahedron. The energy separations between the three inequivalent JT valleys were estimated as δ1,2 = 90 and δ1,3 = 370 cm−1. The lattice strain parameter V2 and the JT stabilization energy EJT were also estimated as 19,140 and 1030 cm−1 respectively. From the EJT value, the JT distortion present in the system was classified as a case of “strong” coupling.

A one-parameter expression of seismicity patterns in space and time

AbstractA technique to express changes in seismicity patterns by means of an objective criterion has been investigated. A parameter v2=(Δ¯)2/Δ¯2, where Δ is the distance between two adjacent earthquakes in space and time, was derived on the basis of the Weibull distribution function. This parameter can be related to an apparent interaction in the earthquake sequences and used to monitor changes of the seismicity patterns which may reflect the state of the crustal stress. The patterns are classified as regular, completely random, and clustered according to the value of v2.The technique was applied to the U.S. Geological Survey microearthquake catalog for central California. A total of 9740 earthquakes (M ≧ 1.5) was selected from along the 250-km-long creeping zone of the San Andreas and Calaveras faults for the period 1971 to 1981. The seismicity pattern was found to be generally a combination of highly clustered ones overlapped with a background, which was characterized as almost random or slightly clustered.

The Calculation of the Three-Dimensional Turbulent Boundary Layer: Part III. Comparison of Attachment-Line Calculations with Experiment

SummaryWind tunnel measurements have been made of the attachment-line boundary layer on a swept wing. The combination of a 4-5 in (114 mm) nose radius and 60° angle of sweep enabled a wide range of values of the parameter V2/(v dU/dx) (denoted here by C*), to be covered, and gave a thick enough boundary layer for the velocity profiles to be accurately measured. Pitot traverses were performed for values of C* from 0·59 × 105 to 3·7 × 105. Without a trip wire fitted the attachment-line flow was laminar over the full range and the measured velocity profiles agreed closely with the theory for an infinite swept wing. With a large trip wire fitted, a transition régime was observed in the range 0·6 × 105 &lt; C* &lt; 1·4 × 105, and at higher values of C* the flow was fully turbulent and showed good agreement with the earlier calculations of Cumpsty and Head. Preston tubes were used for skin friction measurements in fully turbulent conditions and a hot wire was used to explore the development of turbulence in the transition régime.