Effect Of Transverse Flow Research Articles

Proton and pion production in Au+Au collisions at10.8AGeV/c

We present proton and pion tranverse momentum spectra and rapidity distributions for Au+Au collisions at 10.8A GeV/c. The proton spectra exhibit collective transverse flow effects. Evidence of the influence of the Coulomb interaction from the fireball is found in the pion transverse momentum spectra. The data are compared with the predictions of the RQMD event generator.

Proton and deuteron production in Au+Au reactions at11.6A GeV/c

Proton and deuteron distributions from 11.6A GeV/c Au + Au collisions measured by the E802 Collaboration in experiment E-866 are presented. The invariant yield of protons and deuterons is studied as a function of the transverse mass for different cuts of rapidity and centrality. At low mt−m0 the proton and deuteron invariant spectra deviate from a single exponential shape. The average mt as function of centrality and rapidity is used to explore the effect of collective transverse flow in the reaction. The ratio of the deuteron to squared proton yield as a function of transverse momentum, rapidity, and centrality is used to probe the coalescence model of deuteron production. This ratio is constant as a function of rapidity only for the most central cuts and decreases with the centrality for every rapidity cut. The ratio of the differential cross section of the deuteron to the squared differential cross section of the proton, for the most central cut, is not constant as a function of mt−m0.

Anisotropic transverse flow and the Hanbury-Brown-Twiss correlation function.

Utilizing the Lorentz invariance of the correlation function we study the effects of anisotropic transverse flow on the Hanbury-Brown--Twiss (HBT) correlation function. In particular we show that directed flow would evidence itself by nonzero ``side-long'' and ``side-out'' terms in the correlation function. We also show that the study of ratios of the correlation functions evaluated on different event subsamples and/or different Lorentz systems provides information on the source dimensions and velocity which could be less biased by corrections of different kinds. We present a fitting technique appropriate for HBT analysis which does not require binning and is especially useful for multidimensional fitting. \textcopyright{} 1996 The American Physical Society.

Hadron yields and spectra in Au+Au collisions at the AGS

Inclusive double differential multiplicities and rapidity density distributions of hadrons are presented for 10.8·A GeV/c Au+Au collisions as measured at the AGS by the E877 collaboration. The results indicate that large amounts of stopping and collective transverse flow effects are present. The data are also compared to the results from the lighter Si+Al system.

A scheme to identify collective transverse flow in relativistic heavy ion collisions at CERN SPS

A judicious selection of projectile-target combinations in relativistic heavy ion collisions at CERN SPS may provide us with a number of systems having a similar particle rapidity density per unit transverse area. There may be a formation of quark gluon plasma, followed by hadronization, if the energy density attained is large enough. Electromagnetic radiations from such systems normalized to the initial transverse area would be identical if they do not undergo a transverse expansion. A deviation from this scaling behaviour is shown to provide a novel signature for the transverse flow effects in such experiments. Such a deviation is expected to emerge clearly in a comparison of results for Pb+Pb system, e.g., with those for S+Au.

Flow study in relativistic nuclear collisions by Fourier expansion of azimuthal particle distributions

We propose a new method to study transverse flow effects in relativistic nuclear collisions by Fourier analysis of the azimuthal distribution on an event-by-event basis in relatively narrow rapidity windows. The distributions of Fourier coefficients provide direct information on the magnitude and type of flow. Directivity and two dimensional sphericity tensor, widely used to analyze flow, emerge naturally in our approach, since they correspond to the distributions of the first and second harmonic coefficients, respectively. The role of finite particle fluctuations and particle correlations is discussed.

Hanbury-Brown-Twiss analysis of anisotropic transverse flow.

The effects of anisotropic transverse collective flow on the Hanbury-Brown--Twiss (HBT) correlation function is studied. There exist three different physics contributions related to flow which affect the correlation function: anisotropic source shape, anisotropic space-momentum correlations in pion emission, and the effects related to the HBT measurement of the size of a moving source in different reference frames. Resolution of these contributions experimentally can lead to a detailed understanding of both collective flow in nucleus-nucleus collisions and the HBT technique itself. A method is presented which permits the derivation of model independent relations between the radius of a source measured in a frame in which it is moving and in its rest frame. \textcopyright{} 1996 The American Physical Society.

Calculation of the distribution of the concentration of pollutants in a stream course, incorporating the effect of transverse flow

Calculation of the distribution of the concentration of pollutants in a stream course, incorporating the effect of transverse flow

The effect of body dimensions on the free convection from inclined slender cylinders with uniform heat flux / Der Einfluß der Körperabmessungen auf die freie Konvektion in der Umgebung schlanker geneigter Zylinder bei einheitlicher Wärmestromdichte

Experimental local heat transfer data are presented for the free convection from inclined slender cylinders in air and water with uniform heat flux. The temperature distributions in axial and circumferential direction are presented for different angles of inclination. The data cover the range of modified Rayleigh numbers Raq from 10 7 to 10 15 for inclinations of 15° to 75° from the vertical position. A mathematical correlation of the data is proposed which takes into account the cylinder dimensions, the inclination angle and the transverse flow effect

Transverse flow effects on photon spectra

High energy photons in ultra-relativistic nucleus nucleus collisions at RHIC and LHC energies are discussed as a source of information on the collision dynamics and as a signature of deconfining phase transition. The photon emission rates from an expanding quark gluon plasma undergoing transverse expansion have been evaluated.

Transverse flow effects on high-energy photons emitted by expanding quark-gluon plasma.

High-energy photons emitted in ultrarelativistic nucleus-nucleus collisions at energies reached at the CERN SPS and LHC and the BNL RHIC are discussed as a source of information on the collision dynamics and as a signature of the deconfining phase transition. The energy density and velocity fields of the expanding matter have been computed assuming cylindrical symmetry along the transverse direction and boost invariance along the longitudinal direction. The emission of photons from an expanding quark-gluon plasma undergoing a first-order phase transition has been evaluated. When the transverse flow of the system is accounted for, it is found that the photons having their origin in the hadronic matter are comparable to those originating in the quark-gluon plasma for [ital p][sub [ital T]] greater than 2 GeV, at energies reached at the SPS and RHIC. At energies reached at the LHC, photons having a [ital p][sub [ital T]] larger than about 4 GeV are shown to have their origin predominantly in the quark-gluon plasma. The location of the [ital p][sub [ital T]] window is shown to be very sensitive to the value of the freeze-out temperature chosen. The feasibility of evaluating the direct (QCD) photons has been studied. Photons fragmented off final more » state quarks in parton-parton scattering are shown to provide the largest background beyond [ital p][sub [ital T]][approx]3 GeV at energies reached at the LHC. Accounting for hadronic degrees of freedom beyond the pion is found to be important. « less

Transverse expansion and effective radii of sources in high energy collisions

We investigate the effects of transverse flow on Bose-Einstein correlations by using an exact three-dimensional solution of the equations of hydrodynamics. Contrary to what one might expect it is found that transverse flow does not increase the transverse radius. On the other hand, a strong dependence of the longitudinal radius on the transverse expansion is found.

Transverse flow due to minijets in [formula omitted] collisions at √ s=1.8 TeV

The multiplicity and flavor dependence of average transverse momentum of charged particles produced in high energy pp and p p collisions is studied in a PQCD inspired model. The experimentally observed transverse flow effect at √ s=1.8 TeV is naturally explained in the context of the fragmentation of multiple minijets which dominate the hadronic interaction mechanism at high collider energies.

Correlations between dilepton yields and pion multiplicities as probe of the deconfinement transition

The correlation between dilepton yields and pion multiplicities from the thermalized baryon-poor central region matter produced in ultra-relativistic nucleus-nucleus collisions is analyzed within a hydrodynamical framework. A “cut-in” (or a concave section) in the correlation function is predicted as signal of the deconfinement transition. Transverse flow effects, finite hadronization times of the deconfined matter and realistic initial matter distribution tend to enhance this signal. The need of a refined background subtraction is pointed out to discriminate the dileptons stemming from hard initial interactions and pre-equilibrium processes.

Volume-selective NMR spectroscopy with self-refocusing pulses

If the 90° selective pulses that are normally used for volume localization are replaced with self-refocusing 270° pulses having a Gaussian time-domain amplitude profile, various pulse sequences can be made shorter, thus reducing the effects of transverse relaxation, flow, or diffusion. The sensitivity advantage is ascertained quantitatively for some of the commonly used sequences. The volume of interest defined in these experiments is determined by the offset dependence (spatial profile) of the conversion of transverse xy magnetization into z magnetization and vice versa. It is demonstrated that the gradients can be switched on the off within the intervals where the radiofrequency pulses are applied without affecting the spatial profile. We compare the shapes of the volumes of interest defined by (i) 90° Gaussian pulses, (ii) 90° sinc pulses, and (iii) self-refocusing 270° Gaussian pulses. In the first two cases, refocusing or predefocusing is necessary, while in the latter case it is not. The comparisonslead us to propose three new methods, (i) self- refocusing spatial and chemical-shift-encoded excitation (SR-SPACE), (ii) self- refocusing s patially resolved spectroscopy (SR-SPARS), and (iii) self- refocusing selected- volume excitation using stimulated echoes (SR-VEST).

Relativistic quantum molecular dynamics approach to nuclear collisions at ultrarelativistic energies

A Lorentz invariant extension of the well-known quantum molecular dynamics approach is employed to investigate the space-time evolution of heavy ion collision at Dubna, AGS and CERN energies ( E kin = 3A GeV …200 AGeV). The model combines multiple twobody elastic and inelastic scattering plus soft many body potential interactions. The predicted multiplicity and rapidity distributions, transverse energy production and flow effects compare well with the experimental data at these energies. Predictions to the stopping power at the AGS-Booster are also presented. The RQMD results demonstrate the importance of nuclear stopping and secondary scattering up to the highest beam energies currently available. This is of particular importance for the recently observed enhancement of strangeness production compared to pp data, which was proposed as a signal for quark gluon plasma formation.

Strangeness evolution in the central region of a heavy-ion collision with transverse flow effects

Strangeness evolution in the central region of an ultra-relativistic nucleus-nucleus collision is studied by using a numerically computed boost invariant cylindrically symmetric hydrodynamic flow. Kinetic equations describing the evolution through quark-gluon plasma, mixed and hadron phases are derived. With reasonable collision terms the conclusion is that the strangeness density (=weighted sum of the strange quark density and the sum of K − and K̄ 0 densities) evolves close to or up to a factor 2 below the equilibrium density until the end of the mixed phase. With transverse expansion the dilution of matter in hadron phase is so fast that strangeness creation and annihilation process effectively decouple. This implies that the observed N K / N π is rather independent of the assumed decoupling temperature and lies in the range 0.15-0.3.

Transverse-flow effects in dilepton emission.

Dilepton emission from expanding QCD matter formed in ultrarelativistic nuclear collisions is computed. The energy density and the velocity field of the expanding matter are computed numerically with a (1+3)-dimensional numerical code which assumes cylindrical invariance in the transverse and boost invariance in the longitudinal direction. Effects of transverse flow are studied and shown to be important in the region of pair mass M\ensuremath{\lesssim}1.2 GeV. The existence of transverse flow results in the persistent appearance of the \ensuremath{\rho} peak in the M distribution at fixed transverse mass ${M}_{T}$ for large ${M}_{T}$. The initial temperature ${T}_{i}$ and the thermalization time ${\ensuremath{\tau}}_{i}$ of the hydrodynamical flow are related to the associated pion multiplicity dN/dy and the dilepton emission rate at M>1.5 GeV.

Water and Sediment Routing Through Curved Channels

A mathematical model for water and sediment routing through curved alluvial channels is developed and applied in a case study. This model, which is for alluvial streams with nonerodible banks, may be employed to simulate stream bed changes during a given flow, thereby providing the necessary information for the design of dikes, levees, or other bank protection. This model incorporates the major effects of transverse circulation, inherent in curved channels, on the flow and sediment processes. In the simulation of the evolution in stream bed profile, the effect of transverse flow is tied in with the aggradation and degradation development. River flow through curved channels is characterized by the changing curvature, to which variations of flow pattern and bed topography are closely related. Simulation of these changing features is based upon the fluid dynamics governing the growth and decay of transverse circulation along the channel.

“The Effects of Transverse Flow through Graphite on Fission Product Movement in HTGR-Type Systems”

“The Effects of Transverse Flow through Graphite on Fission Product Movement in HTGR-Type Systems”