arXiv subjects

Charles B. Chiu

Publications and source records attributed to Charles B. Chiu.

14 recordsLinked to original sources

arXiv2012

Ridge and Transverse Correlation at Separated Rapidities

A simple phenomenological relationship between the ridge distribution in $Δη$ and the single-particle distribution in $η$ can be established from the PHOBOS data on both distributions. The implication points to the possibility that there is no long-range longitudinal correlation. An interpretation of the relationship is then developed, based on the recognition that longitudinal uncertainty of the initial configuration allows for non-Hubble-like expansion at early time. It is shown that the main features of the ridge structure can be explained in a model where transverse correlation stimulated by semihard partons is the principal mechanism.

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arXiv2011

Classical color field modified minijet model for $pp$ and $\bar{p} p$ total cross section

In a recent paper, we have evaluated the $gg\rightarrow gg$ scattering amplitude in the presence of classical color field generated by the colliding protons in the leading order approximation within the pQCD. In this work, we show that this amplitude can be resumed to obtain the classical color field modified $gg \rightarrow gg$ elastic scattering amplitude. This modified amplitude is suppressed when the longitudinal momentum fraction, $x$, of the incident gluon is small. Minijet cross section is calculated using the modified amplitude. We show that the $pp$ and $\bar{p} p$ cross section from $\sqrt{s} = 5$ GeV to 30 TeV can be described as a sum of a hard component contributed by the modified minijet model and a soft component due to the exchange of the pomeron and of the I=0 exchange-degenerate $ω$ and $f$ trajectories. The predicted cross section has a $\ln^2 s$ asymptotic behavior which satisfies the Froissart bound.

hep-ph↗

arXiv2011

Gluon-gluon elastic scattering amplitude in classical color field of colliding protons

We present a formalism for gluon-gluon elastic scattering in the presence of the classical color field of the protons in high energy collision. The classical field is obtained by solving the classical Yang-Mills equation in the covariant gauge and treated as a prescribed background for the quantum gluons involved in the scattering process. The interaction between the classical field and the quantum gluon modifies the gluon propagator, and, in turn, the $gg\rightarrow gg$ amplitude. The modified gluon propagator is derived to the first non-zero order of the classical field using the Gaussian approximation in Color Glass Condensate and shown to satisfy the generalized Slavnov-Taylor identity. This formalism is the theoretical basis for our recently proposed classical color field modified minijet model where we show that the $pp$ and $\pbar p$ cross section data from $\sqrt{s}=5$ GeV to 30 TeV can be satisfactorily fitted and the model predicts a $(\ln s)^2$ behavior for large $s$, which saturates the asymptotic behaviour of Froissart bound.

hep-ph↗

arXiv2010

Phenomenological Relationship between the Ridge and Inclusive Distributions

A relationship between the ridge distribution in $Δη$ and the single-particle distribution in $η$ is proposed. It is then verified by use of the data from PHOBOS on both distributions. The implication seems to point to the possibility that there is no long-range longitudinal correlation. An interpretation of the phenomenological observation along that possibility is developed.

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arXiv2009

Dependence of Ridge Formation on Trigger Azimuth: Correlated Emission Model

Ridge formation in near-side correlation in heavy-ion collisions is studied in the framework of a phenomenological model, called Correlated Emission Model (CEM). Successive soft emissions due to jet-medium interaction lead to the enhancement of thermal partons which follow the local flow directions. The correlation between the flow direction and the semihard parton direction is the major factor that causes the ridge formation to depend on the trigger direction relative to the reaction plane. With the use of a few parameters we have been able to reproduce the data on the ridge yields as functions of the trigger azimuthal angle for different centralities. An inside-outside asymmetry function is proposed to further probe the characteristics of the azimuthal correlation function. Insights are provided for the understanding of some detailed aspects of the centrality dependence.

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arXiv2008

Azimuthal Anisotropy: Ridges, Recombination and Breaking of Quark Number Scaling

Azimuthal anisotropy is studied by taking into account the ridges created by semi-hard scattering, which is sensitive to the initial spatial configuration in non-central heavy-ion collisions. No rapid thermalization is required. Although hydrodynamics is not used in this study, the validity of hydrodynamical expansion is not excluded at later time after equilibration is achieved. Phenomenological properties of the bulk and ridge behaviors are used as inputs to determine the elliptic flow of pion and proton at low p_T. At intermediate p_T the recombination of shower partons with thermal partons becomes more important. The phi dependence arises from the variation of the in-medium path length of the hard parton that generates the shower. The p_T dependence of v_2 is therefore very different at intermediate p_T compared to that at low p_T. Quark number scaling of v_2 is shown to be only approximately valid at low p_T, but is broken at intermediate p_T, even though recombination is the mechanism of hadronization in all p_T regions considered.

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arXiv2007

Particles Associated with Omega Produced at Intermediate p_T

The dual observation of the Omega production in central Au+Au collisions having both an exponential p_T distribution and also associated particles above the background has been referred to as the Omega puzzle. We give a quantitative description of how that puzzle can be understood in terms of phantom jets, where only ridges without peaks are produced to give rise to both the Omega trigger and its associated particles. In the framework of recombination of thermal partons we are able to reproduce both the Δϕdistribution and the trigger-momentum dependence of the yield of the associated particles. We make predictions on other observables that can be checked by further analyses of the data.

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arXiv2006

Away-side azimuthal distribution in a Markovian parton scattering model

An event generator is constructed on the basis of a model of multiple scattering of partons so that the trajectory of a parton traversing a dense and expanding medium can be tracked. The parameters in the code are adjusted to fit the Δϕazimuthal distribution on the far side when the trigger momentum is in the non-perturbative region, p_T(trigger)<4 GeV/c. The dip-bump structure for 1 8 GeV/c, the model reproduces the single-peak structure observed by STAR without invoking any new dynamical mechanism.

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arXiv2006

Away-side distribution in a parton multiple scattering model and background-suppressed measures

A model of parton multiple scattering in a dense and expanding medium is described. The simulated results reproduce the general features of the data. In particular, in the intermediate trigger momentum region there is a dip-bump structure, while at higher trigger momentum the double bumps merge into a central peak. Also, a new measure is proposed to quantify the azimuthal distribution with the virtue that it suppresses the statistical fluctuations event-by-event, while enhancing the even-structure of the signal.

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arXiv2006

Suppression of statistical background in the event structure of away-side $Δϕ$ distribution

An approach is proposed to analyze the azimuthal distribution of particles produced on the away side in heavy-ion collisions without background subtraction. Measures in terms of factorial moments are suggested that can suppress the statistical background, while giving clear distinction between one-jet and two-jet event structures on the away side. It is also possible to map the position and strength of the recoil jet to suitably chosen asymmetry moments.

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arXiv2005

Autocorrelation of Hadrons in Jets Produced in Heavy-Ion Collisions

Autocorrelation of two pions produced in heavy-ion collisions at intermediate $p_T$ is calculated in the framework of the recombination model. The differences of the pseudo-rapidities and azimuthal angles of the two pions are related to the angle between two shower partons in a jet. It is shown how the autocorrelation distribution reveals the properties of jet cone of the shower partons created by high-$p_T$ partons in hard collisions.

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arXiv2005

Pedestal and Peak Structure in Jet Correlation

We study the characteristics of correlation between particles in jets produced in heavy-ion collisions. In the framework of parton recombination we calculate the $η$ and $ϕ$ distributions of a pion associated with a trigger particle. The origin of the pedestal in $Δη$ is related to the longitudinal expansion of the thermal partons that are enhanced by the energy loss of hard partons traversing the bulk medium. The peaks in $Δη$ and $Δϕ$ are related to the same angular spread of the shower partons in a jet cone. No artificial short- or long-range correlations are put in by hand. A large part of the correlation between hadrons in jets is due to the correlation among the shower partons arising from momentum conservation. Recombination between thermal and shower partons dominates the correlation characterisitics in the intermediate $p_T$ region.

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arXiv1994

Dips in Partial Wave Amplitudes from Final State Interactions

We consider the dip-peak structures in the J=0 partial wave amplitudes for processes $γγ\rightarrow W^+W^-~ \mbox{and}~γγ,gg\rightarrow t\overline{t}$ taking into account the corresponding Born term process and the rescattering process where the intermediate state is rescattered through the exchange of Higgs resonance state in the direct channel.

hep-ph↗

arXiv1993

Direct Channel Dominance in Goldstone Boson Scattering in the Resonance Region

We consider the scattering of Goldstone bosons in the range of intermediate energies, and in particular focus our attention on the scattering of pions in the $ρ$-resonance region. The chiral perturbation series is obtained to order $E^4$ from a chiral $SU(2)\times SU(2)$ invariant effective Lagrangian. At order $E^4$, we isolate the low-energy manifestation of heavy particle exchange in the s-channel. We find that the contributions of this type to the I=1 and I=2 amplitudes have a one parameter dependence. This observation provides a symmetry rationale for Chanowitz's recent observation that in a chiral model with an explicitly coupled $ρ$, the I=1 and I=2 channels are strongly correlated. In order to realize, in a quantitative way, the fact that in the resonance region the direct-channel dominates, we make use of a simple and intuitive unitarization scheme. This allows us to derive a renormalization constant-independent relation for the I=1 and I=2 phase shifts. With the assumption of a $ρ$-resonance, this relation determines the position of a pole at euclidean momentum in the I=2 channel. Through an analysis based on the theory of redundant poles and the Adler sum rule we show that this ``tachyon'' pole actually represents a physical contribution to the unitary amplitude which accounts for $ρ$ and $ε$ exchange in the u-channel.

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