Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration

Extensive experimental data from high-energy nucleus-nucleus collisions were recorded using the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The comprehensive set of measurements from the first three years of RHIC operation includes charged particle multiplicities, transverse energy, yield ratios and spectra of identified hadrons in a wide range of transverse momenta (p_T), elliptic flow, two-particle correlations, non-statistical fluctuations, and suppression of particle production at high p_T. The results are examined with an emphasis on implications for the formation of a new state of dense matter. We find that the state of matter created at RHIC cannot be described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted to Nuclear Physics A as a regular article; v3 has minor changes in response to referee comments. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

Correlated Production of p and p^bar in Au+Au Collisions at sqrt(s_NN) = 200 GeV

Correlations between p and pbar's at transverse momenta typical of enhanced baryon production in Au+Au collisions are reported. The PHENIX experiment measures same and opposite sign baryon pairs in Au+Au collisions at sqrt(s_NN) = 200 GeV. Correlated production of p and p^bar with the trigger particle from the range 2.5 < p_T < 4.0 GeV/c and the associated particle with 1.8 < p_T < 2.5 GeV/c is observed to be nearly independent of the centrality of the collisions. Same sign pairs show no correlation at any centrality. The conditional yield of mesons triggered by baryons (and anti-baryons) and mesons in the same pT range rises with increasing centrality, except for the most central collisions, where baryons show a significantly smaller number of associated mesons. These data are consistent with a picture in which hard scattered partons produce correlated p and p^bar in the p_T region of the baryon excess.Comment: 420 authors from 58 institutions, 21 pages,5 figures. Submitted to Physics Letters B. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

Buoyancy effects on the 3D MHD stagnation-point flow of a Newtonian fluid

This work examines the steady three-dimensional stagnation-point flow of an electrically conducting Newtonian fluid in the presence of a uniform external magnetic field H0 under the Oberbeck–Boussinesq approximation. We neglect the induced magnetic field and examine the three possible directions of H0 which coincide with the directions of the axes. In all cases it is shown that the governing nonlinear partial differential equations admit similarity solutions. We find that the flow has to satisfy an ordinary differential problem whose solution depends on the Hartmann number M, the buoyancy parameter λ and the Prandtl number Pr. The skin-friction components along the axes are computed and the stagnation-point is classified. The numerical integration shows the existence of dual solutions and the occurrence of the reverse flow for some values of the parameters

Transport phenomena in the mixed state and fluctuation regime in (Bi1.6Pb0.4)Sr2Ca1-x Hox (Cu1-yZny)2O8+d

Measurements of the magnetoresistivity, Seebeck, Nernst and Hall coefficients in Bi:2212 superconductors doped with Ho and Zn are reported. The critical temperature and the transport coefficients depend strongly on the Ho and Zn contents. The tails of the transport coefficients versus temperature curves are caused by fluctuation effects, which increase with increasing magnetic field. An anomalous suppression of superconductivity at x = 0.25-0.35 and y = 0.025-0.032 was also found when the hole concentration per Cu is PH = 1/8 and the transport properties exhibit metallic behavior. It was found that dBc2/dT = -2.4 ± 0.2 T/K, corresponding to a Ginzburg-Landau coherence length ε = 15 Å. The Hall resistivity ρxy scaling with the longitudinal resistivity ρxx as ρxy(T) = a-1ρα xx with α ≒ 1.8 is in agreement with the theory of Vinokur et al. The experimental data in the mixed state are in agreement with the prediction of the time-dependent Ginzburg-Landau theory

Magnetic and structural properties of Fe65Co35 alloys obtained by melting, high-energy milling and heat treatment

International audienc

Transport and magnetic properties in MgB2

Magneto-transport and magnetic data on MgB2 polycrystalline samples are reported for applied magnetic fields up to 9 T. In the normal state we find that MgB2 compound has a temperature and field-dependent resistivity behavior like a simple metal. The critical magnetic field H c2 (T) and the irreversibility field Hirr(T) curves were determined. The Hall coefficient RH is slightly temperature dependent. Using the extracted data, we calculated the electronic mean free path, coherency length ξ0 and London penetration depth λL

Influence of mechanical milling on the physical properties of SmCo5/Fe65Co35 type hard/soft magnetic nanocomposite

International audienceThe influence of milling type on the structural and magnetic behaviour of mechanically milled SmCo5/Fe65Co35 has been studied. By adjusting the mill speed parameters, (Omega/omega), three types of milling have been performed: shock mode process (SMP), friction mode process (FMP) and a combined shock followed by a friction mode process. It was found that in SMP conditions the remanent magnetization and composite coercivity increase with increasing milling time. The best exchange coupling, with a coercivity of 1.05 T, was obtained for samples milled for 8 h in SMP and annealed for 2 h at 550 degrees C. On the other hand, the low energy of FMP does not succeed in producing a microstructure adapted to favour the interphase exchange interactions between the soft and hard magnetic phases. A combined milling process does not change significantly the microstructure obtained previously after 8 h of SMP. This indicates that the microstructure of the composite is formed primarily during SMP while FMP, less energetic, does not drastically affect the crystallite size and crystallite shape of SMP samples. X-ray diffraction patterns were used to follow the evolution of the structure and microstructure. The diffusion of Fe and Co from Fe65Co35 to SmCo5 phase leads to the formation of Sm-2(Co,Fe)(17)/Fe-Co composite. The magnetic behaviour was checked from hysteresis curves and dM/dH vs. H plots