arXiv subjects

Rudolph C. Hwa

Publications and source records attributed to Rudolph C. Hwa.

At least 91 records · Page 5Linked to original sources

arXiv2001

The effect of gluon depletion on J/psi suppression in pA and AA collisions

The enhanced suppression of $J/ψ$ production at large $x_F$ in $pA$ collisions is studied in the framework of gluon depletion at large $x_1$. The nonperturbative process that modifies the gluon distribution as the gluons propagate in nuclear matter is described by an evolution equation with a kernal to be determined by phenomenology. With nuclear shadowing and anti-shadowing taken into account, the effect on the gluon distribution is shown to be a depletion in excess of 40% at $x_1 \approx 0.8$ for $A > 100$. There is a small amount of enhancement of the gluon distribution at small $x_1$, but it does not lead to any contradiction with the existing data on $J/ψ$ suppression in the central region. Extentions to $ψ^{\prime}$ suppression and $AB$ collisions are also investigated in the framework of gluon redistribution.

nucl-th↗

arXiv2000

Observable measures of critical behavior in high-energy nuclear collisions

Critical behaviors of quark-hadron phase transition in high-energy heavy-ion collisions are investigated with the aim of identifying hadronic observables. The surface of the plasma cylinder is mapped onto a 2D lattice. The Ising model is used to simulate configurations corresponding to cross-over transitions in accordance to the findings of QCD lattice gauge theory. Hadrons are formed in clusters of all sizes. Various measures are examined to quantify the fluctuations of the cluster sizes and of the voids among the clusters. The canonical power-law behaviors near the critical temperature are found for appropriately chosen measures. Since the temperature is not directly observable, attention is given to the problem of finding observable measures. It is demonstrated that for the measures considered the dependence on the final-state randomization is weak. Thus the critical behavior of the measures proposed is likely to survive the scattering effect of the hadron gas in the final state.

nucl-th↗

arXiv2000

Fluctuation of Voids in Hadronization at Phase Transition

Starting from the recognition that hadrons are not produced smoothly at phase transition, the fluctuation of spatial patterns is investigated by finding a measure of the voids that exhibits scaling behavior. The Ising model is used to simulate a cross-over in quark-hadron phase transition. A threshold in hadron density is used to define a void. The dependence of the scaling exponents on that threshold is found to provide useful information on some properties of the hadronization process. The complication in heavy-ion collision introduces the possibility of configuration mixing, which can also be studied in this approach. Numerical criteria on the scaling exponents have been found that can be used to discriminate phase-transition processes from other hadronization processes having nothing to do with critical phenomena.

nucl-th↗

arXiv1999

Erraticity of Rapidity Gaps

The use of rapidity gaps is proposed as a measure of the spatial pattern of an event. When the event multiplicity is low, the gaps between neighboring particles carry far more information about an event than multiplicity spikes, which may occur very rarely. Two moments of the gap distrubiton are suggested for characterizing an event. The fluctuations of those moments from event to event are then quantified by an entropy-like measure, which serves to describe erraticity. We use ECOMB to simulate the exclusive rapidity distribution of each event, from which the erraticity measures are calculated. The dependences of those measures on the order of $q$ of the moments provide single-parameter characterizations of erraticity.

hep-ph↗

arXiv1998

Entropy Index as a Measure of Heartbeat Irregularity

A method is proposed to analyze the heartbeat waveform that can yield a reliable characterization of the structure after only a few pulses. The measure suggested is entropy index that is related to the one found effective in describing chaotic behaviors in a wide variety of physical systems. When applied to the ECG data that include ventricular fibrillation, the index is shown to change drastically within a few pulses. Wavelet analysis is used to exhibit different scaling behaviors in different phases.

physics.med-ph↗

arXiv1998

A Color Mutation Model of Soft Interaction in High Energy Hadronic Collisions

A comprehensive model, called ECOMB, is proposed to describe multiparticle production by soft interaction. It incorporates the eikonal formalism, parton model, color mutation, branching and recombination. The physics is conceptually opposite to the dynamics that underlies the fragmentation of a string. The partons are present initially in a hadronic collision; they form a single, large, color-neutral cluster until color mutation of the quarks leads to a fission of the cluster into two color-neutral subclusters. The mutation and branching processes continue until only $q\bar q$ pairs are left in each small cluster. The model contains self-similar dynamics and exhibits scaling behavior in the factorial moments. It can satisfactorily reproduce the intermittency data that no other model has been able to fit.

hep-ph↗

arXiv1997

Fluctuations of Spatial Patterns as a Measure of Classical Chaos

In problems where the temporal evolution of a nonlinear system cannot be followed, a method for studying the fluctuations of spatial patterns has been developed. That method is applied to well-known problems in deterministic chaos (the logistic map and the Lorenz model) to check its effectiveness in characterizing the dynamical behaviors. It is found that the indices $μ_q$ are as useful as the Lyapunov exponents in providing a quantitative measure of chaos.

nucl-th↗

arXiv1996

Summary of the Nijmegen Workshop on Multiparticle Production

This is the summary talk of the Nijmegen Workshop. The topics are: 1. Introduction, 2. Phenomenology of mature topics, 2.1 Bose-Einstein correlations, 2.2 Fluctuations, 2.3 Phenomenology of QCD and other dynamics, 3. Experiments not driven by conventional theory, 3.1 Search for DCC, 3.2 Soft-photon production, 4. Theory not driven by conventional experiments, 4.1 Criticality, 4.2 Erraticity and chaos, 5. Other comments.

hep-ph↗

arXiv1996

Critical and Chaotic Behaviors of Quarks

The critical behavior of quarks undergoing phase transition to hadrons is considered in the framework of the Ising model. It is found that spatial fluctuations do not alter the F-scaling result obtained earlier in the Ginzberg-Landau formalism. For the study of chaos a new measure must be found for the quark-gluon system, for which the usual description appropriate for classical nonlinear systems is inapplicable. It is shown that the entropy indices $μ_q$ which characterize the fluctuations of spatial patterns, are as effective as the Lyapunov exponent in measuring chaos. When applied to the QCD parton showers, it is found that the quark jets are more chaotic than gluon jets. The analysis is highly appropriate for a quantitative treatment of the erratic fluctuations of multiparticle production in leptonic, hadronic and nuclear collision processes. It represents a step beyond the traditional intermittency analysis.

hep-ph↗

arXiv1996

Beyond Intermittency: Erraticity

Erraticity analysis of multiparticle production data is introduced as a way of extracting the maximum amount of information on self-similar fluctuations. It is presented as the next logical step to take beyond the intermittency analysis. An erraticity spectrum $e(α)$ can be determined analogous to the multifractal spectrum $f(α)$. An analytical example is presented to elucidate the method of analysis and the type of results that can be obtained.

hep-ph↗

arXiv1996

Fluctuations and Entropy Indices of QCD Parton Showers

The branching processes in parton showers are studied in perturbative QCD for both quark and gluon jets. The emphasis is on the nature of fluctuations of both the parton multiplicities and the spatial patterns of the final states. Effective measures of such fluctuations are calculated from the data obtained by Monte Carlo simulations. The entropy indices are used to characterize chaoticity. Both running and fixed couplings are considered. The fixed coupling case is used to study the onset of chaos. Implications of the results are discussed.

hep-ph↗

arXiv1996

Quark-hadron phase transition with surface fluctuation

The effect of surface fluctuation on the observables of quark-hadron phase transition is studied. The Ginzburg-Landau formalism is extended by the inclusion of an extra term in the free energy that depends on the vertical displacements from a flat surface. The probability that a bin has a particular net displacement is determined by lattice simulation, where the physics input is color confinement. The surface fluctuation from bin to bin is related to multiplicity fluctuation, which in turn is measured by the factorial moments. It is found that both the F-scaling behavior and the scaling exponent are essentially unaffected by the inclusion of surface fluctuation.

nucl-th↗

arXiv1996

Scaling Properties of Hadron Production in the Ising Model for Quark-Hadron Phase Transition

Earlier study of quark-hadron phase transition in the Ginzberg-Landau theory is reexamined in the Ising model, so that spatial fluctuations during the transition can be taken into account. Although the dimension of the physical system is 2, as will be argued, both d=2 and d=4 Ising systems are studied, the latter being theoretically closer to the Ginzberg-Landau theory. The normalized factorial moments F_q are used to quantify multiplicity fluctuations, and the scaling exponent νis used to characterize the scaling properties. It is found by simulation on the Ising lattice that νbecomes a function of the temperature T near T_c. The average value of νover a range of T<T_c agrees with the value of 1.3 derived analytically from the Ginzberg-Landau theory. Thus the implications of the mean-field theory are not invalidated by either the introduction of spatial fluctuations or the restriction to a 2D system.

nucl-th↗

arXiv1995

Chaotic Behavior of Particle Production in Branching Processes

The notion of chaotic behavior is examined for particle production in branching processes. Two types of branching are considered: non-Abelian gauge interaction and an Abelian cascade model. Properties of the production processes are investigated by Monte Carlo stimulation. The ``temporal'' behavior is studied by following the fluctuations in the multiplicities of each generation as the branching evolves. The ``spatial'' behavior is described in terms of the fluctuations of the normalized factorial moments from event to event. The information dimension and a new entropy index are determined. When all the measures are taken together, they collectively give a strong suggestion that the QCD branching process is chaotic, while the Abelian cascade model is not.

hep-ph↗

arXiv1995

Phase Transition in Evolutionary Games

The evolution of cooperative behaviour is studied in the deterministic version of the Prisoners' Dilemma on a two-dimensional lattice. The payoff parameter is set at the critical region $1.8 < b < 2.0$ , where clusters of cooperators are formed in all spatial sizes. Using the factorial moments developed in particle and nuclear physics for the study of phase transition, the distribution of cooperators is studied as a function of the bin size covering varying numbers of lattice cells. From the scaling behaviour of the moments a scaling exponent is determined and is found to lie in the range where phase transitions are known to take place in physical systems. It is therefore inferred that when the payoff parameter is increased through the critical region the biological system of cooperators undergoes a phase transition to defectors. The universality of the critical behaviour is thus extended to include also this particular model of evolution dynamics.

nucl-th↗

arXiv1995

Self-Organized Criticality in Quark-Hadron Phase Transition

The problem of clusters growth in quark-hadron phase transition in heavy-ion collision is investigated by cellular automata. The system is found to exhibit self-organized criticality with the distribution of cluster sizes having universal scaling behavior.

hep-ph↗

arXiv1995

Cluster Production with Coalescence and Breakup

The problem of hadronic cluster production in quark-hadron phase transition in heavy-ion collisions is studied by cellular automata. Previous result on the scaling behavior is extended to include variation in the drift speed. It is also shown that coalescence is more important than growth in generating scaling. A new set of rules is adopted to free the clusters from being rigid. It is found that the scaling exponent is independent of not only the shapes of the clusters, but also the probability of breakup of the clusters. The universality of the scaling behavior is now extended to a wide range of physical properties characterizing the geometry and dynamics of the phase transition process.

hep-ph↗

arXiv1995

In Search for Signs of Chaos in Branching Processes

For systems that involve particle production through branching processes the concept of chaos is explored. The measures that can describe their behaviors are investigated. Monte Carlo simulation is used to generate events according to perturbative QCD and an Abelian model. It is shown how the measures proposed distinguish the two cases in ways that characterize the chaotic behavior.

hep-ph↗