Elastic properties of lanthanum gallogermanate glasses

Room temperature ultrasonic velocities of eight lanthanum gallogermanate glasses were determined by pulse-echo technique. The results indicate that both longitudinal and transverse velocities of these glasses are composition dependent. The density and index of refraction of the samples were also studied. The experimental results were used to obtain elastic constants. The measured values of Young's modulus and bulk modulus for our glasses show good agreement with the theoretically calculated results based on the model of Makishima and Mackenzie. (C) 1999 Kluwer Academic Publishers

Temperature dependence of elastic moduli of lanthanum gallogermanate glasses

Temperature dependence of sound velocities of a series of Lanthanum Gallogermanate glasses have been determined from ultrasonic pulse-echo and Brillouin scattering measurements ranging from room temperature up to and through the glass transition temperature. Both longitudinal and transverse velocities of these glasses are composition dependent. The density and index of refraction of the samples were also studied. The experimental results are used to obtain elastic moduli. The correlation of elastic stiffness, the crosslink density, and the fractal bond connectivity of the glass are discussed. The normal behavior of negative temperature dependence of elastic properties is observed in these glasses. A possible explanation of the observed discrepancy of high temperature sound velocity of these glasses from two different measurements is given. (C) 2002 Kluwer Academic Publishers

Electromagnetic probes

We introduce the seminal developments in the theory and experiments of electromagnetic probes for the study of the dynamics of relativistic heavy ion collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200

Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions

We review the most important experimental results from the first three years of nucleus-nucleus collision studies at RHIC, with emphasis on results from the STAR experiment, and we assess their interpretation and comparison to theory. The theory-experiment comparison suggests that central Au+Au collisions at RHIC produce dense, rapidly thermalizing matter characterized by: (1) initial energy densities above the critical values predicted by lattice QCD for establishment of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by constituent interactions of very short mean free path, established most probably at a stage preceding hadron formation; and (3) opacity to jets. Many of the observations are consistent with models incorporating QGP formation in the early collision stages, and have not found ready explanation in a hadronic framework. However, the measurements themselves do not yet establish unequivocal evidence for a transition to this new form of matter. The theoretical treatment of the collision evolution, despite impressive successes, invokes a suite of distinct models, degrees of freedom and assumptions of as yet unknown quantitative consequence. We pose a set of important open questions, and suggest additional measurements, at least some of which should be addressed in order to establish a compelling basis to conclude definitively that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.

Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV

We report the STAR measurement of Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi spectra and yields are obtained at mid-rapidity for five centrality bins in Au+Au collisions and for non-singly-diffractive p+p collisions. It is found that the Phi transverse momentum distributions from Au+Au collisions are better fitted with a single-exponential while the p+p spectrum is better described by a double-exponential distribution. The measured nuclear modification factors indicate that Phi production in central Au+Au collisions is suppressed relative to peripheral collisions when scaled by the number of binary collisions. The systematics of versus centrality and the constant Phi/K- ratio versus beam species, centrality, and collision energy rule out kaon coalescence as the dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let

Longitudinal scaling property of the charge balance function in Au + Au collisions at 200 GeV

We present measurements of the charge balance function, from the charged particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au collisions at 200 GeV using the STAR detector at RHIC. We observe that the balance function is boost-invariant within the pseudorapidity coverage [-1.3, 1.3]. The balance function properly scaled by the width of the observed pseudorapidity window does not depend on the position or size of the pseudorapidity window. This scaling property also holds for particles in different transverse momentum ranges. In addition, we find that the width of the balance function decreases monotonically with increasing transverse momentum for all centrality classes.Comment: 6 pages, 3 figure

Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions

We study the beam-energy and system-size dependence of \phi meson production (using the hadronic decay mode \phi -- K+K-) by comparing the new results from Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV measured in the STAR experiment at RHIC. Data presented are from mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the transverse momentum distributions for \phi mesons are observed to be similar in yield and shape for Cu+Cu and Au+Au colliding systems with similar average numbers of participating nucleons. The \phi meson yields in nucleus-nucleus collisions, normalised by the average number of participating nucleons, are found to be enhanced relative to those from p+p collisions with a different trend compared to strange baryons. The enhancement for \phi mesons is observed to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision energies, the source of enhancement of strange hadrons is related to the formation of a dense partonic medium in high energy nucleus-nucleus collisions and cannot be alone due to canonical suppression of their production in smaller systems.Comment: 20 pages and 5 figure

Polarized Raman scattering in lanthanum gallogermanate glasses

Polarized Raman scattering has been used to characterize the structure of two series of lanthanum gallogermanate glasses with the composition xLa(2)O(3)-GeO2-0.25Ga(2)O(3) and 0.33La(2)O(3)-GeO2-yGa(2)O(3), where x, y = 0.2, 0.25, 0.33, and 0.5, We assigned the vibrational modes to different types of atomic motions in the glass network. No direct evidence of the six-fold coordinated (octahedral) germanium or gallium ions in the glass structure has been observed. The nature of the low frequency Raman peak - the so called Boson peak - is discussed in terms of the existing theories. (C) 1999 Elsevier Science B.V. All rights reserved

Structure of properties of lanthanum galliogermanate glasses

Lanthanum galliogermanate glasses were prepared. Raman spectra, molar volumes, glass transition temperatures acid activation energies for glass transition and crystallization were obtained. For glasses having the same La2O3/GeO2 ratio, the molar volumes increase with the Ga2O3 content, and the glass transition temperatures, activation energies for glass transition and crystallization, increase initially then decrease as the ratio of Ga2O3/GeO2 increases. For glasses having the same Ga2O3/GeO2 ratio, the molar volumes increase with La2O3 content, and the glass transition temperatures increase as the ratio of La2O3/GeO2 increases. The change of glass structure and its properties with composition is correlated with the concentration of lanthanum ion. (C) 1998 Elsevier Science B.V. All rights reserved

Optical and physical properties of lanthanum gallogermanate glasses

Optical properties of lanthanum gallogermanate glasses were investigated by infrared (IR) transmission and IR reflectivity measurements. Several physical properties of these glasses, including density, index of refraction and ultrasonic velocities, were also measured. The experimental results are used to obtain elastic constants. These glasses are transparent over frequencies ranging from the near ultraviolet to the mid-IR (similar to 8 mu m) and have ionic bond properties in their structure. (C) 1998 Elsevier Science B.V. All rights reserved