Long ranged correlations at a solid-fluid interface A signature of the approach to complete wetting

We have investigated the behaviour of the pairwise distribution function for Sullivan's model of a gas adsorbed on a solid substrate. We show that in the approach to complete wetting, when a thick film of liquid density is adsorbed on the substrate, long ranged transverse correlations (parallel to the surface) develop at the edge of the film where the density profile of the fluid resembles that of a liquid-gas interface. The long ranged correlations can be attributed to damped capillary-wave-like fluctuations; for a class I wetting situation the damping decreases and the range of the correlations increases and ultimately diverges as the bulk gas pressure approaches the saturated vapour pressure.

Our analysis provides a physical explanation of the long ranged transverse correlations calculated by Foiles and Ashcroft in their recent study of a model of argon at a carbon dioxide substrate. We also predict that long range transverse correlations will occur for the case of adsorption from a dense liquid provided the solid-fluid potential is such that a thick film of gas forms between the substrate and the bulk liquid.     

Scaling behaviour and correlations in the string fusion model for heavy ion collisions

The KNO scaling, the scaling of multiplicities, the behaviour of fluctuations in the transverse momentum as a function of the multiplicity and the long range correlations in nucleus-nucleus collisions are studied by a Monte Carlo code based on the string fusion model. It is shown that the fusion of strings produces a strong reduction of the long range correlations at high multiplicities, which could be detected experimentally. On the contrary the KNO scaling, the scaling of multiplicities and the behaviour of fluctuations in the transverse momentum are not modified when string fusion is included.On leave of absence from the Department of High Energy Physics, University of St. Petersburg, 198904 St. Petersburg, Russia     

Modeling of exclusive parton distributions and long-range rapidity correlations in proton-proton collisions at the LHC energies

The soft part of proton-proton interaction is considered within a phenomenological model that involves the formation of color strings. Under the assumption that an elementary collision is associated with the interaction of two color dipoles, the total inelastic cross section and the multiplicity of charged particles are estimated in order to fix model parameters. Particular attention is given to modeling of exclusive parton distributions with allowance for the energy-conservation law and for fixing the center of mass, which are necessary for describing correlations. An algorithm that describes the fusion of strings in the transverse plane and which takes into account their finite rapidity width is developed. The influence of string-fusion effects on long-range correlations is found within this mechanism.     

Pairwise correlations and wetting transitions at a solid-gas interface

We summarize the main results of our study of the density-density correlation function for Sullivan's model of a gas adsorbed on a solid substrate. In the approach to complete wetting, when a thick film of liquid density is adsorbed at the substrate, long-ranged transverse (parallel to the surface) correlations develop at the edge of the film where the density profile is similar to that of a liquid-gas interface. For a class I wetting situation the range of the transverse correlations increases and ultimately diverges as the bulk gas pressure approaches the saturated vapour pressure. We comment on other situations where long-ranged correlations arise and mention the possibility of observing these in diffraction experiments and in computer simulations. Sullivan's model always predicts a second-order phase transition between class II and class I wetting. By extending his model and allowing the attractive part of the solid-fluid potential to be longer-ranged than the attractive fluid-fluid potential we find that this wetting transition can become a first-order (Cahn) transition.     

Flavour tagging of parton jets and separation of parton subprocesses in hard proton-proton collisions at the ISR

High energy proton-proton interactions yielding a single trigger particle with large transverse momentum give rise to a four-jet event structure with two transverse jets and two jets along the beam direction. The transverse jets are due to the fragmentation of point like scattered partons. It is shown that the quantum numbers of triggering charged pions and positive kaons are correlated with the flavour of the scattered parent parton; thus one can enhance data samples with a particular flavour of a scattered parton. The analysis, which is independent of detailed model calculations, exploits (a) the identification of the leading particles in the trigger jets (trigger particles), (b) the measurement of their relative production rates, (c) short range quantum number correlations within the trigger jets, and (d) long range correlations between leading particles from different jets. The data were obtained at \(\sqrt s \) =62 GeV with the Split Field Magnet detector at the CERN ISR.     

Inclusive processes at large transverse momenta

A general model for processes at large transverse momentum is constructed on the assumption that events with large transverse momentum particles posses short range correlations. It is shown that particle ratios and scaling properties are not sensitive to the detailed dynamics of large angle scattering, and also that the character of the inclusive spectrum can be understood in terms of (quasi-) elastic scattering.     

Two-particle correlations in 360 GeV/cp p interactions

Two particle correlations of hadrons produced in 360 GeV/cpp interactions are investigated in the transverse plane and in rapidity. The data were obtained at the European hybrid spectrometer equipped with a rapid cycling bubble chamber. The observed transverse and rapidity correlations are compared with the one string LUND-and a two string dual parton-model. These models predict in general stronger correlations in the transverse plane and much weaker correlations in rapidity than found in the data. The LUND-FRITIOF-and multichain dual parton models provide a better reproduction of the data, although the agreement is not yet satisfactory. Only the UA5 cluster model GENCL shows agreement with the data.     

部分子相互作用与(S_(NN))~(1/2)=130GeV Au-Au碰撞中两粒子的横向动量关联(英文)

采用蒙特卡罗模型AMPT 究了(S_(NN))~(1/2)=130GeV Au Au碰撞中部分子相互作用对两粒子横向动量关联的影响,结果表明部分子相互作用对两粒子的横向动量关联有重要的贡献．还计算了AMPT模型中(S_(NN))~(1/2)=130GeV Au Au碰撞的两粒子横向动量关联与碰撞对心性的依赖关系并与来自STAR的实验数据进行了比较,发现AMPT的理论预言很好地符合实验数据．     

Glasma flux tubes and the near side ridge phenomenon at RHIC

We investigate the consequences of long range rapidity correlations in the Glasma. Particles produced locally in the transverse plane are correlated by approximately boost invariant flux tubes of longitudinal color electric and magnetic fields that are formed when two sheets of Colored Glass Condensate pass through one another, each acquiring a modified color charge density in the collision. We argue that such long range rapidity correlations persist during the evolution of the Quark–Gluon Plasma formed later in the collision. When combined with transverse flow, these correlations reproduce many of the features of the recently observed ridge events in heavy ion collisions at RHIC.     

Partonic interactions and two particle transverse momentum correlations in Au + Au collisions at √sNN=130GeV

Partonic effects on two-particle transverse momentum correlations are studied for Au+Au collisions at \sqrt{s_{_{\rm NN}}}=130GeV in the Monte Carlo model, AMPT. This study demonstrates that in these collisions partonic interactions contribute significantly to the correlations. Additionally, model calculations are compared with data of the two-particle transverse momentum correlations measured by the STAR Collaboration at RHIC, and it is found that AMPT with string melting can well reproduce the measured centrality dependence of the two-particle transverse momentum correlations in Au+Au collisions at \sqrt{s_{_{\rm NN}}}=130GeV.     

Rapidity correlations in π+ p,K + p andpp interactions at 250 GeV/c

Two- and three-particle rapidity correlations are analyzed inK ⁺ p and π⁺ p-interactions at 250 GeV/c. The main contribution to the two- and three-particle correlation functions comes from mixing of events of different multiplicity. The (short range) two-particle correlation remaining after exclusion of mixing is significantly larger for (+?) than for the equal charge combinations, and is positive for a wider range in rapidity difference. FRITIOF and a 2-string DPM are excluded by our data. A quark-gluon (multi-)string model can describe our inclusive correlation function, but needs to be tuned on the short range part. The multiplicity mixing part increases much faster with increasing energy than the short range part. In the central region, our correlation is similar to that observed ine ⁺ e ^? and μp collisions at similar energy.     

A three-dimensional model for quark and gluon jets

Based on the assumption that a color force-field has a stringlike character (like a stretchedout bag_ with no excited degrees of freedom transverse to the field direction (which is strongly supported by the observed polarization of inclusively produced Λ-particles) we derive the probability to produce heavy flavor quark-antiquark pairs and pairs with transverse momentum in the field. We show how to incorporate the results into a soft hadronisation scheme for particle distributions in quark and gluon jets. We point to some non-trivial effects from the finite (longitudinal) size of the force-field which result on the one hand in important correlations between the longitudinal scaling variable and the transverse momentum and on the other hand leads to correstions to the simple iterative cascade scheme.     

Two-particle azimuthal and rapidity correlations in intervals of transverse momentum in π+ p-interactions at 250 GeV/c

A multi-dimensional analysis of two-particle correlations in π⁺ p-interactions at 250 GeV/c shows interesting structure. Particularly strong positive shortrange rapidity and azimuthal correlations are observed for low-p _T like sign pairs. This observation is not reproduced by models used for comparison (FRITIOF, DPM, quark gluon (multi)string model). A possible explanation is Bose-Einstein interference not included in these models.     

Phase Diagram and Tricritical Behavior of a Spin-2 Transverse Ising Model in a Random Field

The phase diagrams of a spin-2 transverse Ising model with a random field on honeycomb, square, and simple-cubic lattices, respectively, are investigated within the framework of an effective-field theory with correlations.We find the behavior of the tricritical point and the reentrant phenomenon for the system with any coordination number z, when the applied random field is bimodal. The behavior of the tricritical point is also examined as a function of applied transverse field. The reentrant phenomenon comes from the competition between the transverse field and the random field.     

Study of transverse momenta of charged hadrons produced in νp and\bar vp charged current interactions

Data from a neutrino and antineutrino hydrogen experiment with BEBC are used to investigate transverse properties of the produced charged hadrons. Measurements are presented on average transverse momenta of charged pions as functions of Feynman-x and the hadronic mass, on the transverse momentum flow within an event and on jet-related quantities. The main features of the data are well described by the LUND model. The data favour a version of the model in which soft gluon effects are included and the primordial transverse momentum of the quarks in the proton is small. Effects from 1^st order QCD (hard gluon emission) are negligible.     

Influence of varying magnetic order in an external magnetic field on the electronic structure and Fermi surface within the <Emphasis Type="Italic">t</Emphasis>–<Emphasis Type="Italic">J</Emphasis> model

We investigate the electronic structure of the two-dimensional t–J model in a transverse external static magnetic field with canted long-range magnetic order using cluster perturbation theory. The distribution of the spectral weight in the whole range of fields from zero to ferromagnetic saturation is explored. We demonstrate the possibility of a sharp change in a distribution of spectral weight at the Fermi level associated with the magnetic correlations when varying magnetic field.     

Effect of Bose-Einstein statistics on two-particle azimuthal and rapidity correlations

The short-range effect in azimuthal and rapidity correlations can be explained within the independent cluster model taking into account the cluster transverse momentum and the Bose-effect (identical particle effect) in the single as well as the two-cluster term. Good agreement with data from Dubna, NAL and ISR is obtained. From the data we determine parameters related to the longitudinal and transverse dimensions of the clusters.     

Saturation of azimuthal anisotropy in Au + Au collisions at (square root)s(NN) = 62-200 GeV

New measurements are presented for charged hadron azimuthal correlations at midrapidity in Au+Au collisions at (square root)s(NN) = 62.4 and 200 GeV. They are compared to earlier measurements obtained at (square root)s(NN) = 130 GeV and in Pb + Pb collisions at (square root)s(NN) = 17.2 GeV. Sizeable anisotropies are observed with centrality and transverse momentum (pT) dependence characteristic of elliptic flow (upsilon2). For a broad range of centralities, the observed magnitudes and trends of the differential anisotropy, upsilon2(pT), change very little over the collision energy range (square root)s(NN) = 62-200 GeV, indicating saturation of the excitation function for upsilon2 at these energies. Such a saturation may be indicative of the dominance of a very soft equation of state for (square root)s(NN) approximately 60-200 GeV.     

Properties of the ground state in a spin-2 transverse Ising model with the presence of a crystal field

The properties of the ground state in the spin-2 transverse Ising model with the presence of a crystal field are studied by using the effective-field theory with correlations. The longitudinal and transverse magnetizations, the phase diagram and the internal energy in the ground state are given numerically for a honeycomb lattice (z=3).