Three-particle Correlation Research Articles

Proton-proton correlations observed in two-proton decay ofMg19andNe16

Proton-proton correlations were observed for the two-proton decays of the ground states of Mg19 and Ne16. The trajectories of the respective decay products, Ne17+p+p and O14+p+p, were measured by using a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of fragments projected on planes transverse to the precursor momenta. The measured three-particle correlations reflect a genuine three-body decay mechanism and allowed us to obtain spectroscopic information on the precursors with valence protons in the sd shell.Received 4 February 2008DOI:https://doi.org/10.1103/PhysRevC.77.061303©2008 American Physical Society

Simulation of pair and three-particle correlations in a binary solid solution with a hexagonal lattice

The correlations revealed in an AyB1 −y disordered solid solution in which atoms occupy sites in the planar hexagonal lattice are investigated. It is demonstrated that pair correlations in the first coordination shell necessarily result in the appearance of pair correlations in the second and subsequent coordination shells. These induced pair correlations decay to the tenth coordination shell. The atomic ordering in solid solutions of all compositions is studied using the computer simulation. It is shown that, within the limits of computational error, the functional dependence between the pair correlation parameter of the first coordination shell and the parameters of the induced pair correlations in the second to ninth coordination shells is described by a third-degree polynomial. The results of the computer simulation of three-particle correlations are in agreement with the analytical solution for the corresponding correlations in the first coordination shell of the hexagonal lattice.

Comment on the magnetic dipole hyperfine interaction in the gold atom ground state

The multiconfiguration Dirac–Hartree–Fock (MCDHF) model has been employed to calculate the magnetic dipole hyperfine constant A of the 5d106s 2S1/2 ground state of atomic gold. Electron correlation effects contribute more than 20% to the total value of A. We investigated the effects of single, double, and a subset of triple substitutions. The calculations reveal strong cancellations between one-, two- and three-particle correlation effects. It is demonstrated that in the case of the ground state of atomic gold the three-particle effects are comparable in size to the one- and two-particle ones.

Transverse radial flow effects on two- and three-particle angular correlations

We use a simple a transverse radial boost scenario coupled to PYTHIA events to illustrate the impact radial flow may have of two- and three-particle correlation functions measured in heavy-ion collisions. We show that modest radial velocities can impart strong modifications to the correlation functions, some of which may be interpreted as same side ridge and away side structure that can mimic conical emission.

THREE PARTICLE CORRELATIONS FROM STAR

Two-particle correlations have shown modification to the away-side shape in central Au + Au collisions relative to pp , d + Au and peripheral Au + Au collisions. Different scenarios can explain this modification including: large angle gluon radiation, jets deflected by transverse flow, path length dependent energy loss, Cerenkov gluon radiation of fast moving particles, and conical flow generated by hydrodynamic Mach-cone shock-waves. Three-particle correlations have the power to distinguish the scenarios with conical emission, conical flow and Cerenkov radiation, from other scenarios. In addition, the dependence of the observed shapes on the pT of the associated particles can be used to distinguish conical emission from a sonic boom (Mach-cone) and from QCD-Čerenkov radiation. We present results from STAR on 3-particle azimuthal correlations for a high pT trigger particle with two softer particles. Results are shown for pp , d + Au and high statistics Au + Au collisions at [Formula: see text]. An important aspect of the analysis is the subtraction of combinatorial backgrounds. Systematic uncertainties due to this subtraction and the flow harmonics v2 and v4 are investigated in detail. The implications of the results for the presence or absence of conical flow from Mach-cones are discussed.

Tracer diffusion in ordered lattice-gas systems with defect-controlled transport mechanisms

Tracer diffusion in an ordered two-dimensional lattice-gas system with square lattice symmetry is studied theoretically and by means of computer simulations. It is well known that the ordering with $c(2\ifmmode\times\else\texttimes\fi{}2)$ symmetry formed in the vicinity of half-filling of lattice sites is due to strong nearest neighbor repulsive interaction. In this case, the tracer migration occurs mainly by elementary displacements of structural defects. This paper focuses on the dimer transport mechanism which was accounted for with insufficient accuracy in previous publications. The long-time asymptotics of the dimer-tracer correlation function (i.e., a three-particle correlation function), which describes concerted tracer-dimer motion, is obtained analytically. We analyze a specific exchange mechanism, relevant to tracer diffusion only. Also, the contribution of generation-recombination jumps to tracer diffusion is taken into account. The theoretical data agree well with the results of intensive Monte Carlo simulations.

METHODS FOR JET STUDIES WITH THREE-PARTICLE CORRELATIONS

We present a method based on three-particle azimuthal correlation cumulants for the study of the interaction of jets with the medium produced in heavy ion collisions at RHIC and LHC where jets cannot be reconstructed on an event-by-event basis with conventional jet finding algorithms. The method is specifically designed to distinguish a range of jet interaction mechanisms such as Mach cone emission, gluon Cerenkov emission, jet scattering, and jet broadening. We discuss how anisotropic flow background conti-butions of second order (e.g. [Formula: see text]) are suppressed in three-particle azimuthal correlation cumulants, and discussed specific model representations of di-jets, away-side scattering, and Mach cone emission.

COHERENCE OF PION SOURCES FROM MULTI-PION INTERFEROMETRY IN RELATIVISTIC HEAVY ION COLLISIONS AT SPS AND RHIC

We study degree of coherence of pion sources by making use of two- and three-particle momentum intensity correlation functions in S + Pb , Pb + Pb , and Au + Au collisions at SPS and RHIC. For each system, we calculate a chaotic fraction ε and the number of coherent sources α from the chaoticity λ of the two-pion correlation function and the weight factor ω of the three-pion correlator. We take account of long-lived resonance decay contribution to the λ factor by making a correction with the help of a statistical model. The result gives strong constraints on the source and shows roughly increasing number of coherent sources as multiplicity increases.

Three-particle azimuthal correlations and Mach shocks

Measurements of angular correlations of hadrons with a (semi)hard trigger hadron in heavy-ion collisions at RHIC show large angular structures opposite to the trigger which were a priori unexpected. These away side large angle correlations were first observed in two-particle correlations [S. S. Adler et al. (PHENIX Collaboration), Phys. Rev. Lett. 97, 052301 (2006) and J. Adams et al. (STAR Collaboration), Phys. Rev. Lett. 95, 152301 (2005)] and have recently also been investigated in three-particle correlation measurements [J. G. Ulery (STAR Collaboration), Nucl. Phys. A774, 581 (2006) and F. Wang, arXiv:nucl-ex/0610027]. We show that the correlation signal can be understood in terms of sonic shockwaves (`Mach cones') excited by hard partons supersonically traversing the medium. The propagation of such shocks through the medium evolution is treated in a Monte Carlo (MC) framework [T. Renk and J. Ruppert, Phys. Rev. C 73, 011901(R) (2006) and Phys. Lett. B646, 19 (2007)]. We demonstrate that two- and especially three-particle correlations offer nontrivial insight into the medium-averaged speed of sound and the evolution of flow. Our findings imply that the assumption of ``deflected jets'' is not necessary to account for the observed correlations.

Two- and three-particle azimuthal correlations of high-pt charged hadrons in Pb–Au collisions at 158 A GeV/c

Azimuthal correlations of hadrons with high transverse momenta serve as a measure to study the energy loss and the fragmentation pattern of jets emerging from hard parton–parton interactions in heavy-ion collisions. Preliminary results from the CERES experiment on two- and three-particle correlations in central Pb–Au collisions are presented. A strongly non-Gaussian shape on the away-side of the two-particle correlation function is observed, indicating significant interactions of the emerging partons with the medium. Mechanisms like deflection of the initial partons or the evolution of a mach cone in the medium can lead to similar modifications of the jet structure on the away-side. An analysis based on three-particle correlations is presented which helps us to shed light on the origin of the observed away-side pattern.

Two- and three-particle correlations in a partonic transport model

Two- and three-particle azimuthal correlations have been investigated in central Au + Au collisions at = 200 GeV with a partonic transport model. A hump structure on the away side, so-called ‘Mach-like structure’, which was observed in two- (three-) particle correlations in RHIC experiments, has been reproduced by the partonic transport model. It indicates that a strong parton cascade can couple partons together to show an apparent collective behaviour, i.e. a partonic Mach-like shock wave, due to a big partonic interaction cross section.

Search for conical emission with three-particle correlations

We present preliminary STAR results on three-particle azimuthal angle correlation studies in Au+Au collisions at GeV. The studies are carried out at mid-rapidity between a trigger particle with 3 ⩽p⊥⩽ 4 GeV/c and two associated particles in 1 ⩽p⊥⩽ 2 GeV/c. A cumulant analysis reveals finite three-particle azimuthal correlations, dominated by near- and away-side particle correlations consistent with jet production, and jet-flow correlations. We use a two-component model to remove underlying background correlations. This analysis indicates the presence of the conical emission signals in central Au+Au collisions within the model assumptions about background composition and normalization.

Studying the medium modification of jets via high-pT hadron angular correlations

We report the analysis of high-pT hadron angular correlation performed by the PHENIX collaboration. The goal of the analysis is to investigate the medium modification of jets in the RHIC heavy-ion collisions. Two angular correlation techniques are used in our analysis: two-particle azimuthal correlation (2-p) and three-particle correlation (3-p). In the 2-p analysis, we focus on the pT and collision system evolution of the jets medium modification. In the 3-p analysis, we focus on the discrimination of two scenarios of jets medium modification, Mach Cone (Casalderrey-Solana J et al 2006 Preprint hep-ph/0602183) and deflected jets (Hwa Chiu 2006 Preprint nucl-th/0609038).

Algebraic perturbation theory for dense liquids with discrete potentials

A simple theory for the leading-order correction g{1}(r) to the structure of a hard-sphere liquid with discrete (e.g., square-well) potential perturbations is proposed. The theory makes use of a general approximation that effectively eliminates four-particle correlations from g{1}(r) with good accuracy at high densities. For the particular case of discrete perturbations, the remaining three-particle correlations can be modeled with a simple volume-exclusion argument, resulting in an algebraic and surprisingly accurate expression for g{1}(r). The structure of a discrete "core-softened" model for liquids with anomalous thermodynamic properties is reproduced as an application.

Jet shapes in opaque media

We present general arguments, based on the medium-induced radiative energy loss, to explain the presence of nontrivial angular structures within this perturbative mechanism. Simple analytical estimates of this effect are provided which are relevant to the current discussion on the interpretation of the data on two- and three-particle correlations of semihard particles at BNL's Relativistic Heavy Ion Collider.

Multiscale coarse-graining and structural correlations: connections to liquid-state theory.

A statistical mechanical framework elucidates the significance of structural correlations between coarse-grained (CG) sites in the multiscale coarse-graining (MS-CG) method (Izvekov, S.; Voth, G. A. J. Phys. Chem. B 2005, 109, 2469; J. Chem. Phys. 2005, 123, 134105). If no approximations are made, then the MS-CG method yields a many-body multidimensional potential of mean force describing the interactions between CG sites. However, numerical applications of the MS-CG method typically employ a set of pair potentials to describe nonbonded interactions. The analogy between coarse-graining and the inverse problem of liquid-state theory clarifies the general significance of three-particle correlations for the development of such CG pair potentials. It is demonstrated that the MS-CG methodology incorporates critical three-body correlation effects and that, for isotropic homogeneous systems evolving under a central pair potential, the MS-CG equations are a discretized representation of the well-known Yvon-Born-Green equation. Numerical calculations validate the theory and illustrate the role of these structural correlations in the MS-CG method.

Is there a Sonic Boom in the Little Bang at RHIC?

The use of elliptic flow and correlation measurements as constraints to establish the transport properties of hot and dense QCD matter is discussed. Measured Two- and three-particle correlation functions give initial hints for a “sonic boom”. Elliptic flow measurements give the estimates c s ∼ 0.35 and η / s ∼ 0.1 for the sound speed and viscosity to entropy ratio.

Momentum conservation and correlation analyses in heavy-ion collisions at ultrarelativistic energies

Global transverse-momentum conservation induces correlations between any number of particles, which contribute in particular to the two- and three-particle correlations measured in heavy-ion collisions. These correlations are examined in detail, and their importance for studies of jets and their interaction with the medium is discussed.

Three-particle correlations from parton cascades in Au+Au collisions

Abstract We present a study of three-particle correlations among a trigger particle and two associated particles in Au + Au collisions at s N N = 200 GeV using a multi-phase transport model (AMPT) with both partonic and hadronic interactions. We found that three-particle correlation densities in different angular directions with respect to the triggered particle (‘center’, ‘cone’, ‘deflected’, ‘near’ and ‘near-away’) increase with the number of participants. The ratio of ‘deflected’ to ‘cone’ density approaches to 1.0 with the increasing of number of participants, which indicates that partonic Mach-like shock waves can be produced by strong parton cascades in central Au + Au collisions.

Three-Particle Azimuthal Correlations

Two-particle azimuthal correlations reveal broadened and softened away-side correlations. Several different physics mechanisms are possible: large angle gluon radiation, deflected jets, and conical flow or Cerenkov radiation. Three-particle correlations are investigated to try to discriminate these mechanisms. We present results on 3-particle azimuthal correlations between a trigger particle of 3 < p T < 4 GeV / c and two softer particles of 1 < p T < 2 GeV / c for pp, d+Au and Au+Au collisions at s N N = 200 GeV . Implications of the results are discussed.