Heavy quarkonia production in p+p, d+Au and Cu+Cu collisions by PHENIX experiment at ?{sNN }\sqrt {s_{NN} } = 200 GeV

The PHENIX experiment has measured, J/ψ, ψ′ and γ productions for different collision systems in the forward rapidities 1.2 < | η | < 2.2 at ?{S_NN }\sqrt {S_{NN} } = 200 GeV. We have observed significant suppressions of J/ψ production in both Cu+Cu and Au+Au collisions relative to the yield in p+p system. The measurements of higher mass heavy quarkonia states (ψ′ and γ) will help us to constrain various quarkonium suppression models in heavy ion collisions. A first hint of ψ′ and γ productions in 200GeV p+p collisions has been observed at forward and backward rapidities at PHENIX.     

Antikaon production and medium effects in proton-nucleus reactions at subthreshold beam energies

The inclusive K ^--meson production in proton-nucleus collisions in the subthreshold energy regime is analyzed in the framework of an appropriate folding model for incoherent primary proton-nucleon and secondary pion-nucleon production processes, which takes properly into account the struck target nucleon momentum and removal energy distribution (nucleon spectral function), novel elementary cross-sections for proton-nucleon reaction channel close to threshold as well as nuclear mean-field potential effects on the one-step and two-step antikaon creation processes. A detailed comparison of the model calculations of the K ^- differential cross-sections for the reactions p + ⁹Be and p + ⁶³Cu at subthreshold energies with the first experimental data obtained at the ITEP proton synchrotron is given, that displays both the relative role of the primary and secondary production channels at considered incident energies and the contributions to the K ^- production coming from the use of the single-particle part as well as high-momentum-energy part of the nucleon spectral function. It is found that the pion-nucleon production channel does not dominate in the subthreshold “hard” antikaon production in p ⁹Be-, p ⁶³Cu-collisions and the main contributions to the antikaon yields here come from the direct K ^- production mechanism. The influence of the nucleon, kaon and antikaon mean-field potentials on the K ^- yield is explored. It is shown that the effect of the nucleon mean-field is of importance in explaining the considered experimental data on “hard” antikaon production, whereas the K ⁺ and K ^- optical potentials play a minor role. The sensitivity of the subthreshold “soft” antikaon production in p ⁹Be-, p ¹²C-reactions to the nucleon, kaon and antikaon mean fields is studied. It is demonstrated that, contrary to the case of “hard” antikaon production, the K ^- potential has a very strong effect on the K ^- yield, which is greater than that from nucleon effective potential. Received: 20 July 2000 / Accepted: 4 December 2000     

Development of the PHENIX silicon pixel detector

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) is being upgraded with a novel four-layer silicon vertex tracker. The detector will enhance the physics capabilities of PHENIX in the future phase of the heavy-ion and the polarized proton-proton programs at RHIC. The silicon vertex tracker will allow the direct measurement of heavy quark production by identifying displaced decay vertices, and will reconstruct jets with nearly full azimuthal coverage over |η| < 1.2. We are developing a novel Silicon Pixel Detector for the inner two barrel layers of the silicon vertex tracker. In this paper, the status of the development is reported. for the PHENIX collaboration Presented in the Poster Session “Future Experiments and Facilities” at the 18th International Conference “Quark Matter 2005”, Budapest, Hungary, 4–9 August 2005.     

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.     

Correlations of polarizations and entangled states in the two-photon system

The correlations of the linear and circular polarizations in the system of two photons have been theoretically investigated. The polarization of a two-photon state is described by the one-photon Stokes parameters and by the components of the correlation “tensor” in the Stokes space. It is shown that in the case of two-photon decays π⁰ → 2γ, η → 2γ, K _L ⁰ → 2γ, K _S ⁰ → 2γ and the cascade process |0〉 → |1〉 + γ → |0〉 + 2γ(|0〉 and |1〉 are states with the spin 0 and 1, respectively) the final two-photon state represents a characteristic example of the entangled (nonfactorizable) state, and the correlations between the Stokes parameters in all these decays have the purely quantum character: the incoherence inequalities of the Bell type for the components of the correlation “tensor”, established previously for the case of classical “mixtures”, are violated. The general analysis of the registration procedure for two correlated photons by two one-photon detectors is performed.     

Direct photons in ATLAS@LHC

The ATLAS detector at the LHC is capable of efficiently separating photons and neutral hadrons based on their shower shapes over a wide range in η, ϕ and E _T , either in addition to or instead of isolation cuts. This provides ATLAS with a unique strength for direct photon and γ-jet physics (“tomography”) as well as access to the unique capability to measure non-isolated photons from fragmentation or from the medium. We present a first look at the ATLAS direct photon measurement capabilities in p+p and Pb+Pb collisions at LHC energies over the region |η| < 2.4.     

Subthreshold and near threshold K+ meson photoproduction\newline on nuclei

The inclusive K⁺ meson production in photon–induced reactions in the near threshold and subthreshold energy regimes is analyzed with respect to the one–step (γN→K ⁺ Y, Y=Λ,Σ) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account the struck target nucleon removal energy and internal momentum distribution (nucleon spectral function), extracted from recent quasielastic electron scattering experiments and from many–body calculations with realistic models of the NN interaction. Simple parametrizations for the total and differential cross sections of the K⁺ production in photon–nucleon collisions are presented. Comparison of the model calculations of the K⁺ differential cross sections for the reaction γ+C¹² in the threshold region with the existing experimental data is given, that displays the contributions to the K⁺ production at considered incident energies coming from the use of the single–particle part as well as high momentum and high removal energy part of the nucleon spectral function. Detailed predictions for the K⁺ total and differential cross sections from γH², γC¹² and γPb²⁰⁸ reactions at subthreshold and near threshold energies are provided. The influence of the uncertainties in the elementary K⁺ production cross sections on the K⁺ yield is explored. Received: 12 April 1999 / Revised version: 11 September 1999     

A fast muon trigger for the PHENIX forward spectrometer upgrade

The PHENIX forward upgrade adds nosecone calorimeters and level-1 trigger (LVL-1) detectors to the muon forward spectrometers. The muon detector will trigger on high pT muons from W decay and reject background. This will enable study of quark and anti-quark polarizations in the proton. The upgrade will add momentum and timing information to the present muon trigger. Signals from 3 Resistive Plate Chambers (RPCs) will provide momentum and timing information for the LVL-1 trigger. Each RPC carries a plane with coarse structure to establish a space point for timing and one with radial cathode strips for azimuthal resolution. Timing resolution of ≈ 2 ns rejects beam-related backgrounds and tracking from RPCs minimizes muons from hadron decays. RPC information is sent by optical. bers to LVL-1 trigger processors. A discussion of physics measurements possible, layout of the upgrade and details of RPC design and tests are given below. for the PHENIX collaboration Presented in the Poster Session “Future Experiments and Facilities” at the 18th International Conference “Quark Matter 2005”, Budapest, Hungary, 4–9 August 2005.     

Determination of the gluon polarization at RHIC and COMPASS

The most recent determinations of the gluon polarization in the nucleon, , obtained at RHIC and COMPASS experiments, are reviewed. The former accesses the gluon polarization mainly through the production of neutral pions (PHENIX) or jets (STAR) in polarized proton collisions. The latter uses the photon-gluon fusion in polarized lepton-nucleon scattering, tagged either by open charm or high-p_T hadrons production. All the results are in good agreement, and favour values of ΔG roughly between 0 and 0.5 at a few (GeV/c)² , thus in contradiction with what could be derived from the Ellis-Jaffe sum rule and the axial anomaly. Much stronger constraints will be obtained in a near future by both programs, helping us to clarify the role of gluons in the nucleon spin.     

Medium effects in the production and π0γ decay of ω-mesons in pA collisions in the GeV region

The ω resonance production and its π⁰γ decay in pA reactions close to threshold is considered within the Intranuclear Cascade (INC) model. The π⁰γ invariant-mass distribution shows two components which correspond to the ω decay “inside” and “outside” the nucleus, respectively. The “inside” component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the ω-meson and its decaying pion. The relative contribution of the “inside” component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the π⁰ and γ momenta allows to separate events related to the “inside”ω decay from different sources of background when uncorrelated π⁰'s and γ's are produced. Received: 2 April 2001 / Accepted: 5 June 2001     

Coherent inelastic processes on nuclei at ultrarelativistic energies

The coherent inelastic processes of the type a → b, which may take place in the interaction of hadrons and γ quanta with nuclei at very high energies (the nucleus remains the same), are theoretically investigated. For taking into account the influence of the nucleus matter, the optical model, based on the conception of the refraction index, is used. Analytical formulas for the effective cross section σ _coh (a → b) are obtained, taking into account that, at ultrarelativistic energies, the main contribution into σ _coh (a → b) is provided by very small transferred momenta in the vicinity of the minimal longitudinal momentum transferred to the nucleus. It is shown that the cross section σ _coh (a → b) may be expressed through the “forward” amplitudes of inelastic scattering f _a+N+b+N (0) and elastic scattering f _a+N+a+N(0), f _b+N+b+N(0) on a separate nucleon, and it depends on the ratios L _a /R and L _b /R (L _a and L _b are the mean lengths of the free path in the nucleus matter for the particles a and b, respectively, and R is the nucleus radius). In particular, when L _a /R ≫ 1, but L _b /R ≪ 1 (or L _a /R ≪ 1, but L _b /R ≫ 1), σ _coh (a → b) is equal to the ratio of the “forward” cross sections of inelastic scattering a + N → b + N and elastic scattering of the particle b (or a) on a nucleon, multiplied by the cross section of scattering on the “black” nucleus πR ². When both conditions L _a /R ≫ 1 and L _b /R ≫ 1 are satisfied, σ _coh (a → b) is proportional to the factor R ⁴/k ², where k is the initial energy of particle a in the laboratory frame. The text was submitted by the authors in English.     

Study of the isobar configurations in the <Superscript>12</Superscript>C and <Superscript>16</Superscript>O ground states

Experimental research on positive-pion photoproduction on the oxygen nucleus in the ¹⁶O(γ, π⁺p) reaction at high recoil momenta of the residual nuclear system was performed. The yield for the ¹⁶O(γ, π⁺p) reaction was analyzed using a model that takes Δ-isobar configurations in nuclei ground states into account, together with the earlier-measured yield of the¹²C(γ, π⁺p) reaction. The estimated number of isobars per nucleon N _Δ = 0.012 ± 0.005 was obtained for the ¹²C nucleus, and ¹⁶O N _Δ = 0.018 ± 0.004 was obtained for the ¹⁶O nucleus.     

First measurement of J/ψ anisotropy by PHENIX experiment at RHIC

Understanding the J/ψ suppression and possible recombination mechanisms at RHIC is one of the outstanding challenges for theorists and experimentalists. Recent results provided by PHENIX showed a stronger suppression at forward rapidity, while at mid-rapidity the suppression is similar to lower energy collision experiments. A large sample of Au + Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV was collected in 2007 with the PHENIX experiment at RHIC. Using this sample, J/ψs were identified in the di-electron decay channel. In order to probe the charm coalescence as an additional J/ψ production mechanism at RHIC, we studied the first determination of its v ₂ elliptic flow parameter at mid-rapidity.     

Quark momentum-space charge distribution in deuteron and neutron/proton structure functions ratio

The electromagnetic polarizabilities of the nucleon are shown to be essentially composed of the nonresonant α _p(E ₀₊) = + 3.2, α _n(E ₀₊) = + 4.1, the t-channel α ^t _{p, n} = - β ^t _{p, n} = + 7.6 and the resonant β _{p, n}(P ₃₃(1232)) = + 8.3 contributions (in units of 10^-4fm^3). The remaining deviations from the experimental data Δα _p = 1.2±0.6, Δβ _p = 1.2±0.6, Δα _n = 0.8±1.7 and Δβ _n = 2.0±1.8 are contributed by a larger number of resonant and nonresonant processes with cancellations between the contributions. This result confirms that dominant contributions to the electric and magnetic polarizabilities may be represented in terms of two-photon coupling to the σ-meson having the predicted mass m _σ = 666MeV and two-photon width Γ _γγ = 2.6keV.     

Precision calculation of γd↦πnn within chiral perturbation theory

The reaction γd↦π⁺nn is calculated up to order χ^5/2 in chiral perturbation theory, where χ denotes the ratio of the pion to the nucleon mass. Special emphasis is put on the role of nucleon recoil corrections that are the source of contributions with fractional power in χ. Using the known near-threshold production amplitude for γp↦π⁺n as the only input, the total cross-section for γd↦π⁺nn is described very well. A conservative estimate suggests that the theoretical uncertainty for the transition operator amounts to 3% for the computed amplitude near threshold.     

Structure of turbulent flows of incompressible fluids and the parametrization of turbulence

The structure of stationary isotropic, homogeneous turbulence in an incompressible fluid with Re ≫ 1 set into motion by a force with amplitude f ₀ and spatial and temporal time scales of r ₀ and τ ₀, respectively, is examined. It is found that, depending on the magnitude of the force that sets the fluid into motion, three fundamentally different turbulent stationary states of the fluid can develop and the dimensionless parameters responsible for transitions from one state to another, γ=f ₀ τ ₀ ² /r ₀ and Γ=γ ^4/3 Re, are determined. It is shown that for γ≪1 and Γ≪1 a Kolmogorov spectrum with E(k)∝1/k ^5/3 develops in the inertial range. During the transition to turbulent flows driven by large amplitude forces f ₀, i.e., during the transition to a regime with γ≪1 and Γ ≫ 1, a segment of the spectrum with E(k)∝1/k ² develops near the viscous range and “detaches” the Kolmogorov spectrum from the viscous range. Further increases in the amplitude f ₀ of the force, i.e., approaching the parameter range with γ≫1 and Γ≫1, causes the entire inertial range to be “occupied” by a spectrum E(k)∝1/k ², and outside the inertial range, large scale structures with a characteristic size extending to γ ^2/5 r ₀ begin to be generated. In the regime with Γ≪1, the power dissipated per unit mass of fluid is independent of the viscosity, but on going to turbulent regimes with Γ≫1, the viscous losses begin to depend on the viscosity of the fluid. The “turn-off” of viscous dissipation for Γ≫1 shows that a drag crisis can occur simply as the source power is increased, without any further conditions. With this method for the excitation of turbulence, the Loitsyanskii integral diverges for arbitrary values of γ and Γ. A physical mechanism is proposed to explain the readjustment of the spectrum of the turbulent fluctuations at different γ and Γ. These results have all been obtained neglecting intermittency. Zh. éksp. Teor. Fiz. 116, 1630–1647 (November 1999)     

Experimental investigation of ligand effects on the conversion electron spectrum of the 22.5 keV M1 + E2 nuclear transition in <Superscript>149</Superscript>Sm

The conversion electron spectrum of the 22.5keV M1 + E2 nuclear transition in ¹⁴⁹Sm from the electron capture decay of ¹⁴⁹Eu was experimentally studied for the “Eu₂O₃” and “EuF₃” compounds in which ¹⁴⁹Eu ions have the same assumed oxidation number +3 . While the energies of the L, M, N, O, and P₁ conversion lines for “EuF₃” were lower, on average, by 1.7(1), 2.7(2), 2.3(3), 4.1(2), and 5.7(9)eV, respectively, than those for “Eu₂O₃”, no changes between the two ligand complexes were observed for relative intensities of the conversion lines and their natural widths within the error limits.     

Spin structure of the “Forward” nucleon charge-exchange reaction <Emphasis Type="Italic">n</Emphasis> + <Emphasis Type="Italic">p</Emphasis> → <Emphasis Type="Italic">p</Emphasis> + <Emphasis Type="Italic">n</Emphasis> and the deuteron charge-exchange breakup

The structure of the nucleon charge-exchange process n + p → p + n is investigated basing on the isotopic invariance of the nucleon-nucleon scattering. Using the operator of permutation of the spin projections of the neutron and proton, the connection between the spin matrices, describing the amplitude of the nucleon charge-exchange process at zero angle and the amplitude of the elastic scattering of the neutron on the proton in the “backward” direction, has been considered. Due to the optical theorem, the spin-independent part of the differential cross section of the process n + p → p + n at zero angle for unpolarized particles is expressed through the difference of total cross sections of unpolarized proton-proton and neutron-proton scattering. Meantime, the spin-dependent part of this cross section is proportional to the differential cross section of the deuteron charge-exchange breakup d + p → (pp) + n at zero angle at the deuteron momentum k _d = 2 k _n (k _n is the initial neutron momentum). Analysis shows that, assuming the real part of the spin-independent term of the “forward” amplitude of the process n + p → p + n to be smaller or of the same order as compared with the imaginary part, in the wide range of neutron laboratory momenta k _n > 700 MeV/c the main contribution into the differential cross section of the process n + p → p + n at zero angle is provided namely by the spin-dependent term.     

Open heavy flavor production from light ion collisions at RHIC

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 $\sqrt {s_{NN} } = 200$ GeV. The measured cross section for p+p collisions is compared with the NLO prediction, and a possible excess over the prediction is noted. The measured cross section for d+Au collisions scales with the number of colliding nucleon pairs from the p+p spectra.