Hadron Pt spectra from 0.03 to 6 GeV/c from PHOBOS

We review some of the latest results on identified and non-identified particle spectra for d+Au and Au+Au collisions at √s _NN =200 GeV from the PHOBOS Experiment at RHIC. No enhancement of hadron yields at very low PT is observed. Analysis of the high-PT spectra in d+Au and Au+Au collisions reveal the strong final state effects for central Au+Au collisions. The first measurements of identified particle spectra and particle ratios from the PHOBOS Time of Flight (ToF) detector are presented for d+Au collisions. Detailed results on centrality and pseudorapidity dependence of transverse momentum spectra, which may have important physics implications. are also shown.     

Results from the first physics run of PHENIX at RHIC

First results from measurements of Au?Au collisions at $\sqrt {s_{NN} } = 130$ GeV, performed with the PHENIX experiment during the initial physics run of Brookhaven National Laboratory’s Relativistic Heavy Ion Collider in summer 2000, are summarized. Global characterization of the collisions was obtained from charged-particle multiplicity and transverse energy densities. At mid-rapidity, dN _ch /dν and dE _T /dν rise steadily with the event centrality, while the ratio <E _T >/<N _ch > remains constant. Transverse momentum spectra of charged particles up to 5 GeV/c yield a suppression of high-momentum particles in the most central events when compared to a simple scaling of binary nucleon-nucleon collisions. The scaling matches with peripheral collisions. Transverse momentum spectra of identified neutral pions from 1 to 4 GeV/c in peripheral collisions show consistency with point-like scaling with the average number of binary collisions. Yields in central collisions are significantly suppressed. Transverse momentum spectra of identified charged hadrons up to 3.5 GeV/c were measured in minimum bias events. The mass and centrality dependencies of inverse slope parameters and mean transverse momenta were determined. Inclusive spectra of electrons were measured for momenta from a few hundred MeV/c to 4 GeV/c. Inclusive photon spectra from a few hundred MeV/c to 3 GeV/c were obtained from conversion pair measurements.     

Charged hadron suppression in Au+Au collisions at high p T from STAR

We report high statistics measurements of inclusive charged hadron production in Au+Au collisions at $\sqrt {s_{NN} } = 200$ GeV and 130 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for 5 ‖p _T ‖ 12 GeV/c. The collision energy dependence of the yields and the centrality and p _T dependence of the suppression provide stringent constraints on theoretical models of suppression. Models incorporating initial-state gluon saturation or partonic energy loss in dense matter are largely consistent with observations. The p _T -dependent suppression expected from models incorporating jet attenuation in cold nuclear matter or absorption of fragmentation hadrons is not observed.     

Scaling properties of azimuthal anisotropy of mesons and baryons at RHIC

Detailed measurements of the azimuthal anisotropy (v ₂) for identified charged particles are reported as a function of transverse momentum (pT) and centrality for Au+Au collisions at $\sqrt {s_{NN} } = 200$ GeV. The measurements indicate clear evidence for eccentricity and particle flavor scaling over a broad range of centralities and transverse rapidity yT, indicating a hydrodynamical origin of the fine structure of azimuthal anisotropy at RHIC. The observed scaling supports the picture of a suddenly hadronizing (recombining) fluid of quarks. An apparent breaking of flavor scaling at relatively large values of yT points to an important change in the mechanism for particle emission.     

Hadron production at forward rapidity in nuclear collisions at RHIC

The main experimental results obtained by the BRAHMS experiment at Relativistic Heavy Ion Collider (RHIC) for Au+Au collisions at \(\sqrt {s_{NN} } \) =62.4, 200 GeV and d+Au collisions at \(\sqrt {s_{NN} } \) = 200GeV are presented. The m _T spectra and the Gaussian-like rapidity densities of produced pions and kaons in Au+Au central collisions at \(\sqrt {s_{NN} } \) = 200 are GeV shown, and their rapidity densities are compared with results from models. The net-proton yield in the same system is compared with that from AGS and SPS energies to study the high energy collision scenario-transparency and stopping. The rapidity, energy and centrality dependence of the nuclear modification factors in both systems are compared with models to differentiate between the initial and final state effect.     

Probing the QCD phase boundary with elliptic flow in relativistic heavy ion collisions at STAR

We present measurement of elliptic flow, v ₂, for charged and identified particles at midrapidity in Au+Au collisions at $\sqrt {s_{NN} } $ = 7.7?C39 GeV. We compare the inclusive charged hadron v ₂ to those from transport model calculations, such as the UrQMD model, AMPT default model and AMPT string-melting model. We discuss the energy dependence of the difference in v ₂ between particles and anti-particles. The v ₂ of ? meson is observed to be systematically lower than other particles in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 GeV.     

Self-assembled strontium ferrite dot array on Au underlayer

Strontium ferrite (SrM) thin films were deposited on thermally oxidized silicon wafer with Au underlayer. Gold underlayers were prepared at various substrate temperatures by using a magnetron sputtering system. C-axis oriented SrM perpendicular films and preferred (1 1 1) orientation of underlayer have confirmed by X-ray diffraction patterns. The intensity of (1 1 1) diffraction line for Au and that of (0 0 l) diffraction line for strontium ferrite decrease with increase in substrate temperature (T_u) The maximum coercivity and remanent squareness ratio in perpendicular direction, at T_u of 500 °C, are 5.4 kOe and 0.68, respectively. The strength of the intergranular interaction of SrM magnetic particles is described by the parameter Δm. The SrM/Au films prepared at T_u above 100 °C have smaller Δm peak values than that for SrM/Au films prepared at T_u of room temperature. This behavior is related to low magnetostatic coupling between the magnetic particles separated by the non-magnetic amorphous phase.     

Au/SiO2纳米复合薄膜的微结构及光吸收特性研究

用多靶磁控溅射技术制备了Au/SiO₂纳米多层薄膜.利用透射电子显微镜以及吸 收光谱对Au/SiO₂复合薄膜的微观结构、表面形貌及光学性能进行了表征和测试 .研究结果表明：单层Au/SiO₂薄膜中Au沉积时间小于10s时，分散在SiO_{2< /sub>中的Au颗粒随Au的沉积时间的延长而增大；当沉积时间超过10s后，Au颗粒的尺寸几乎 不随沉积时间变化，但Au颗粒的形状由网络状结构变为薄膜状结构.［Au(t1关键词： 尺寸效应 纳米复合薄膜 吸收光谱 有效媒质理论}     

The near-ultraviolet spectrum of diacetylene trapped in solid argon at 9 K

The absorption spectra of normal and deuterated diacetylene trapped in solid argon at 9 K were investigated in the near-ultraviolet region between 2000 and 3000 Å. The vibrational structure observed at low temperature for the band system at 2448 Å, which was previously reported by Haink and Jungen in the gas phase, and identified as a ¹Δ_u ← X¹Σ_g⁺ transition, was analyzed. A comparison between the spectra for C₄H₂ and C₄D₂ suggests some revisions in the upper-state vibrational assignments. The possibility that the upper state assumes a C_2htrans configuration of ¹A_u symmetry is examined. The matrix spectra also appear to indicate that the absorption spectrum observed at 2576 Å in the gas phase and which has been assigned to a ¹Σ_u^? ← X¹Σ_g⁺ transition may not originate in the ground state of C₄H₂.     

The reconstructed final state of Au+AU collisions from PHENIX and STAR data at √s=130 AgeV— Indication for quark deconfinement at RHIC

The final state of Au+Au collisions at √s=130 AGeV at RHIC has been reconstructed within the framework of the Buda-Lund hydrodynamical model, by performing a simultaneous fit to final data on twoparticle Bose-Einstein correlations of the STAR and PHENIX Collaboration, and final identified single-particle spectra as measured by the PHENIX Collaboration. The results indicate a strongly three dimensional expansion, with a four-velocity field that is almost a spherically symmetric Hubble flow. We find large transverse geometrical source sizes, R _G=9.8±1.2 fm, relatively short mean freeze-out time, τ₀=6.1±0.3 fm/c and a short duration of particle emission, Δτ=0.02±1.5 fm/c. Most strikingsly, we find an indication for a hot central part of the hydrodynamically evolving core, characterized by a central temperature T ₀=202±13 MeV that is close to (or even above) the deconfinement temperature of the quark-hadron phase transition. The best fit indicates a cold surface temperature T _s=110±16 MeV. When the possibility of the hot center is excluded, the confidence level of the fit decreases from 28.9% to 1.0%. Predictions are made for the rapidity dependence of the slope parameters and for the transverse mass depedence of the rapidity width of the single-particle spectra, and the transverse mass dependence of the non-identical particle correlations.     

Resonance production in RHIC collisions

Short lived resonances are sensitive to the properties of the medium produced in heavy ion collision, in particular the temperature, density and expansion velocity. Thermal models underpredict the yield of K(892) and Λ(1520) in Au+Au collisions which allows us to conclude that an extended hadronic interaction phase exists between chemical and thermal freeze-out. During this time the decay particles of resonances will re-scatter and coalesce to regenerate resonances. These mechanisms affect the resonance yield mostly in the low momentum region below 1 GeV/c. Therefore the nuclear suppression factor R_AA of resonances with more re-scattering than regeneration will be suppressed compared to stable particles in that p_T range. It is interesting to study the R_AA of resonances at higher momenta where the spectra of non-resonant particles exhibit effects such as enhancement through constituent quark recombination and quenching in the dense partonic medium. In addition the R_AA’s of strange particles show the effect of canonical suppression on the nuclear suppression factor which leads to a significant difference between R_AA and R_CP, in particular for strange baryons. Therefore the R_AA and the elliptic flow v₂ for strange resonances in comparison to strange particles are investigated.     

The A dependence of fast-particle spectra in π +, K +, and p interactions with Al and Au targets at 250 GeV/c

The A dependence of charged-particle spectra in π ⁺, K ⁺, and p interactions with Al and Au targets at 250 GeV/c are presented and compared to predictions of the Quark-Gluon String Model (QGSM). It is shown that the A dependence of invariant inclusive charged-particle spectra on the Feynman variable x is very weak between Al and Au targets. The QGSM shows a larger difference between fast-particle spectra for both Al and Au targets and different beam particles. The QGSM prediction for the leading-particle spectrum over an energy range from 250 GeV to 10 TeV in pAu(Pb) reactions is in a reasonable agreement with the results of NA22 data and a cosmic-ray experiment.     

Measurement of Neutral pions in √NN=200 GeV and 62.4 GeV Au+Au collisions at RHIC-PHENIX

Neutral pions (π⁰) in √_NN=200 GeV and 62.4 GeV Au+Au collisions were measured at RHIC-PHENIX Year-4 Run. In √_NN=200 GeV, π⁰ spectra are measured up to p _T=20 GeV/c. A strong suppression by a factor of ～5 is observed and stays almost constant up to 20 GeV/c.     

Dissipation and fragmentation of low-Q 2 scattered partons in Au−Au collisions at RHIC

Two-particle correlations and event-wise fluctuations in transverse momentum p _tare reported for Au?Au collisions at √s _NN =62 and 200 GeV on pseudorapidity η and azimuth ?. Distributions of all pairs of particles (no leading trigger particle) reveal jet-like correlations, or peaks at pair-wise opening angles of order 1 radian or less. The width of this same-side correlation peak increases dramatically on pseudorapidity and decreases on azimuth for increasing collision centrality. Evolution of the same-side peak with centrality suggests dissipation of low-Q ² partons via strong couplign to an expanding bulk medium. p _t correlations, which provide access to temperature and/or velocity distributions in the colliding system, are also presented.     

I.R. Lattice-vibration spectra of MnF2

The room temperature reflectivity of MnF₂ has been measured in the far i.r. between 50 and 800 cm^?1. The reflectivity spectra show four i.r.-active modes which can be identified as E_u and A_2u modes. The spectra also show structure which might be related to multiphonon effects. The dielectric functions were determined by fitting the reflectivity data with classical oscillator parameters.     

Characteristics of charged particle production in relativistic heavy-ion collisions

Inclusive spectra of charged particles at midrapidity in Au+Au collisions at $\sqrt {s_{NN} } = 130$ GeV and 200 GeV were measured with the STAR detector at RHIC. The measured mean transverse momentum 〈p _T 〉 shows a characteristic dependence on charged particle multiplicity and beam energy in Au+Au collisions that is distinctly different from pp, $p\bar p$ and e⁺e^? collisions. A 32%±3%(syst) increase in 〈p _T 〉 from pp to Au+Au collisions was observed at 200 GeV. While the charged multiplicity was found to increase by 19%±5%(syst) from $\sqrt {s_{NN} } = 130$ GeV to 200 GeV, no significant difference in 〈p _T 〉 was found between the two energies. A comparison with model predictions is discussed.     

Infrared dispersion of lead phosphate at room temperature

Infrared reflection spectra [15–4000 cm^-1] along the b (binary axis) and c axes (A_u and B_u-type modes) are reported at room temperature as obtained with a Fourier-transform scanning interferometer. The spectra are analyzed with the factorized form of the dielectric function and the infrared-active mode parameters are reported.     

Cems study of corrosion on iron foil at low temperatures

Conversion electron Mössbauer measurements with a proportional counter at 6.3, 78 and 300 K have been done to investigate the corrosion of the surface of iron foils, which consists of small particles of γ-Fe₂O₃. When the average particle sizes of the corroded layer are approximately 4 and 5 nm, magnetic hyperfine splitting was observed in the spectra at 6.3 and 78 K. However, for a corroded layer composed of smaller particles, the splitting was noticed only at 6.3 K. The anisotropy constantK of the small particles was estimated using the magnetic hyperfine fields obtained from the spectra at 6.3 and 78 K.     

F-center induced Raman scattering in RbCl

Experimental Raman spectra of RbCl containing F-centers are reported. Lines of A_1u, E_u and F_2u symmetry were observed. Calculations of the first-order Raman spectra are presented; they have been based on the assumption that the electron-phonon interaction is linear with displacements of F-center nearest neighbours. A shell-model fitted to neutron data was used to evaluate the Green-function matrix elements and the projected densities of states. The best agreement between theory and experiment was found to occur when using a zero-force-constant change for the F_2u spectrum and a 0·35 fractional decrease in the longitudinal force-constant A₁₂ for the A_3u and E_u spectra.     

Positron lines from subcritical heavy ion-atom collisions

Positron lines were observed in heavy ion-atom collisions at bombarding energies close to the Coulomb barrier in subcritical systems with the sum of the atomic numbers of the colliding nucleiZ _u =Z ₁+Z ₂ being smaller thanZ _u =172. Each collision system, studied,²⁰⁸Pb +²⁰⁸Pb(Z_u=164),²³⁸U+¹⁸¹Ta(Z_u=165), and²³⁸Au(Z_u=171), exhibits the emission of two positron lines withZ _u -independent c.m. energies of ～ 258 keV and ～ 340 keV, and with widths of about 30 keV, superimposed on continuous positron spectra from nuclear pair decay and pair emission induced by the time changing Coulomb field of the collision. The production cross section of thee ⁺-lines rises with a high power ofZ _u (ocZ _u ²²), which is comparable to theZ _u ²⁰-dependence for the collision induced positrons.