Rapidity equilibration and longitudinal expansion at RHIC

The evolution of net-proton rapidity spectra with sqrt(s_NN) in heavy relativistic systems is proposed as an indicator for local equilibration and longitudinal expansion. In a Relativistic Diffusion Model, bell-shaped distributions in central collisions at AGS energies and double-humped nonequilibrium spectra at SPS show pronounced longitudinal collective expansion when compared to the available data. The broad midrapidity valley recently discovered at RHIC in central Au+Au collisions at sqrt(s_NN) = 200 GeV indicates rapid local equilibration which is most likely due to deconfinement, and fast longitudinal expansion of the locally equilibrated subsystem. A prediction is made for Au+Au at sqrt(s_NN)= 62.4 GeV.Comment: 11 pages, 1 table, 2 figures; changes/additions in text, table, fig

Is there more than one thermal source?

BRAHMS has the ability to study relativistic heavy ion collisions over a wide range of pT and rapidity. This allows us to test whether thermal models can be generalized to describe the rapidity dependence of particle ratios. This appears to work with the baryo-chemical potential changing more rapidly than the temperature. Using fits to BRAHMS data for the 5% most central Au+Au collisions we are able to describe Xi and Omega ratios from other experiments. This paper is dedicated to Julia Thompson who worked to bring South African teachers into physics.Comment: 5 pages, 4 figures, proceedings for SQM04 conference, Cape Town South Afric

A note on the calculation of the effective range

The closed form of the first order non-linear differential equation that is satisfied by the effective range within the variable phase formulation of scattering theory is discussed. It is shown that the conventional method of determining the effective range, by fitting a numerical solution of the Schr\"odinger equation to known asymptotic boundary conditions, can be modified to include the first order contribution of a long range interaction.Comment: 4 page

Internal convection in thermoelectric generator models

Coupling between heat and electrical currents is at the heart of thermoelectric processes. From a thermal viewpoint this may be seen as an additional thermal flux linked to the appearance of electrical current in a given thermoelectric system. Since this additional flux is associated to the global displacement of charge carriers in the system, it can be qualified as convective in opposition to the conductive part associated with both phonons transport and heat transport by electrons under open circuit condition, as, e.g., in the Wiedemann-Franz relation. In this article we demonstrate that considering the convective part of the thermal flux allows both new insight into the thermoelectric energy conversion and the derivation of the maximum power condition for generators with realistic thermal coupling.Comment: 8 pages, 3 figure

p-wave phase shift and scattering length of 6^6Li

We have calculated the p-wave phase shifts and scattering length of $^6$Li. For this we solve the $p$ partial wave Schr\"odinger equation and analyze the validity of adopting the semiclassical solution to evaluate the constant factors in the solution. Unlike in the $s$ wave case, the semiclassical solution does not provide unique value of the constants. We suggest an approximate analytic solution, which provides reliable results in special cases. Further more, we also use the variable phase method to evaluate the phase shifts. The p-wave scattering lengths of $^{132}$Cs and $^{134}$Cs are calculated to validate the schemes followed. Based on our calculations, the value of the $p$ wave scattering length of $^6$Li is $-45a_o$.Comment: 10 figure

Baryon Junction Loops in HIJING/B\=Bv2.0 and the Baryon/Meson Anomaly at RHIC

A new version, v2.0, of the HIJING/B\=B Monte Carlo nuclear collision event generator is introduced in order to explore further the possible role of baryon junctions loops in the baryon/meson anomaly (2 $< p_{T} <$ 5 GeV/c) observed in 200A GeV Au+Au reactions at RHIC. We show that junction loops with an enhanced intrinsic $k_T\approx 1$ GeV/c transverse momentum kick may provide a partial explanation of the anomaly as well as other important baryon stopping observables.Comment: 27 pages, Latex(revtex), 8 figure

The variable phase method used to calculate and correct scattering lengths

It is shown that the scattering length can be obtained by solving a Riccati equation derived from variable phase theory. Two methods of solving it are presented. The equation is used to predict how long-range interactions influence the scattering length, and upper and lower bounds on the scattering length are determined. The predictions are compared with others and it is shown how they may be obtained from secular perturbation theory.Comment: 7 pages including 3 figure

Pseudorapidity distributions of charged particles from Au+Au collisions at the maximum RHIC energy, Sqrt(s_NN) = 200 GeV

We present charged particle densities as a function of pseudorapidity and collision centrality for the 197Au+197Au reaction at Sqrt{s_NN}=200 GeV. For the 5% most central events we obtain dN_ch/deta(eta=0) = 625 +/- 55 and N_ch(-4.7<= eta <= 4.7) = 4630+-370, i.e. 14% and 21% increases, respectively, relative to Sqrt{s_NN}=130 GeV collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around mid-rapidity. These results constrain current models of particle production at the highest RHIC energy.Comment: 4 pages, 5 figures; fixed fig. 5 caption; revised text and figures to show corrected calculation of and ; final version accepted for publicatio

The New Physics at RHIC. From Transparency to High pt_t Suppression

Heavy ion collisions at RHIC energies (Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV) exhibit significant new features as compared to earlier experiments at lower energies. The reaction is characterized by a high degree of transparency of the collisions partners leading to the formation of a baryon-poor central region. In this zone, particle production occurs mainly from the stretching of the color field. The initial energy density is well above the one considered necessary for the formation of the Quark Gluon Plasma, QGP. The production of charged particles of various masses is consistent with chemical and thermal equilibrium. Recently, a suppression of the high transverse momentum component of hadron spectra has been observed in central Au+Au collisions. This can be explained by the energy loss experienced by leading partons in a medium with a high density of unscreened color charges. In contrast, such high $p_t$ jets are not suppressed in d+Au collisions suggesting that the high $p_t$ suppression is not due to initial state effects in the ultrarelativistic colliding nuclei.Comment: 15 pages, 11 figures. to appear in Nucl. Physics A. Invited talk at 'Nucleus-Nucleus Collisions 2003' conference, Mosco

Rapidity dependence of deuteron production in Au+Au collisions at sNN\sqrt{s_{NN}} = 200 GeV

We have measured the distributions of protons and deuterons produced in high energy heavy ion Au+Au collisions at RHIC over a very wide range of transverse and longitudinal momentum. Near mid-rapidity we have also measured the distribution of anti-protons and anti-deuterons. We present our results in the context of coalescence models. In particular we extract the "volume of homogeneity" and the average phase-space density for protons and anti-protons. Near central rapidity the coalescence parameter $B_2(p_T)$ and the space averaged phase-space density $(p_T)$ are very similar for both protons and anti-protons. For protons we see little variation of either $B_2(p_T)$ or the space averaged phase-space density as the rapidity increases from 0 to 3. However both these quantities depend strongly on $p_T$ at all rapidities. These results are in contrast to lower energy data where the proton and anti-proton phase-space densities are different at $y$=0 and both $B_2$ and $f$ depend strongly on rapidity.Comment: Document updated after proofs received from PR