arXiv subjects
Publications and source records attributed to C. B. Yang.
We treat the mass of a proton as the total static energy which can be separated into two parts that come from the contribution of quarks and gluons respectively. We adopt the essential of the bag model of hadron to discuss the structure of a proton and find that the calculated temperature, proton radius, the bag constant are compare well with QCD results if a proton is a thermal equilibrium system of quarks and gluons.
A model is constructed for the origin of the double-humped structure found in the di-hahron azimuthal correlation on the away-side in heavy ion collisions. The parameters in the model are determined by fitting $Δϕ$ azimuthal distribution in central Au+Au collisions at RHIC given by STAR collaboration when the trigger momentum is in $3-4\rm {GeV/c}$ and the associated particle momentum is in $1.3-1.8\rm{GeV/c}$. Then we apply our model to the semi-central and peripheral Au+Au collisions at RHIC and the responding $\triangle ϕ$ azimuthal distribution are reproduced respectively. Our results show that the transverse flow effect plays an essential role in the experimentally observed di-hadron azimuthal distribution structure. The spread of the hard parton creation point and initial moving direction is also necessary for the double-humped structure.
Correlation between trigger and associated particles in jets produced on near and away sides of high-p_T triggers in heavy-ion collisions is studied. Hadronization of jets on both sides is treated by thermal-shower and shower-shower recombination. Energy loss of semihard and hard partons traversing the nuclear medium is parametrized in a way that renders good fit of the single-particle inclusive distributions at all centralities. The associated hadron distribution in the near-side jet can be determined showing weak dependence on system size because of trigger bias. The inverse slope increases with trigger momentum in agreement with data. The distribution of associated particle in the away-side jet is also studied with careful attention given to antitrigger bias that is due to the longer path length that the away-side jet recoiling against the trigger jet must propagate in the medium to reach the opposite side. Centrality dependence is taken into account after determining a realistic probability distribution of the dynamical path length of the parton trajectory within each class of centrality. For symmetric dijets with p_T^{trig}=p_T^{assoc}(away) it is shown that the per-trigger yield is dominated by tangential jets. The average parton momentum for the recoil jet is shown to be always larger than that of the trigger jet for fixed p_T^{trig} and centrality and for any measurable p_T^{assoc}(away). With the comprehensive treatment of dijet production described here it is possible to answer many questions regarding the behavior of partons in the medium under conditions that can be specified on measurable hadron momenta.
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.
With the experimental data from STAR on the centrality dependence of transverse momentum $p_T$ spectra of pions and protons in Au+Au collisions at $\sqrt{s_{NN}}=200 {\rm GeV}$, we investigate the scaling properties of transverse energy $E_T$ distributions at different centralities. In the framework of cluster formation and decay mechanism for particle production, the universal transverse energy distributions for pion and proton can be described separately but not simultaneously.
With the experimental data from STAR and PHENIX on the centrality dependence of the $p_T$ spectra of protons and anti-protons produced at mid-rapidity in Au+Au collisions at 200 GeV, we show that for protons and anti-protons there exists a scaling distribution independent of the colliding centrality. The scaling functions can also describe data from BRAHMS for both proton and anti-proton spectra at $y=2.2$ and 3.2. The scaling behaviors are shown to be incompatible with the usual string fragmentation scenario for particle production.
In this paper is investigated the influence of net baryon density on baryon and meson yields in relativistic nucleus-nucleus collisions, based on the recombination model for hadronization. Unitarity condition is used as a constraint on the model. Three cases with different assumptions on the expansion of partonic system are considered and the baryon to meson ratio is calculated for those situations.
Particle production in the forward region of heavy-ion collisions is shown to be due to parton recombination without shower partons. The regeneration of soft partons due to momentum degradation through the nuclear medium is considered. The degree of degradation is determined by fitting the $\bar p/p$ ratio. The data at $\sqrt s=62.4$ GeV and $η=3.2$ from BRAHMS on the $p_T$ distribution of average charged particles are well reproduced. Large proton-to-pion ratio is predicted. The particles produced at any $p_T$ should have no associated particles above background to manifest any jet structure.
Forward-backward correlation in pp collisions is studied in an approach that emphasizes the partonic scattering angles and circumvents the intractable problem related to the transverse momenta that are low. Assuming the back-to-back scattering of partons to be the origin of hadronic correlation, the properties of forward-backward multiplicity covariance can be derived essentially independent of details of hadronization. The range of correlation in pseudo-rapidity emerges from the study without any dynamical input, thus dispelling the notion that correlation length has any fundamental significance. An attempt is made to relate the results to the two-component structure seen in autocorrelation.
With the experimental data from STAR, PHENIX and BRAHMS on the centrality and rapidity dependence of the $p_T$ spectrum in Au+Au and d+Au collisions, we show that there exists a scaling distribution which is independent of the colliding system, centrality and rapidity. The parameter for the average transverse momentum $ $ increases from peripheral to central d+Au collisions. This increase accounts for the enhancement of particle production in those collisions. A non-extensive entropy is used to derive the scaling function.
The recombination model is applied to the production of $K, ϕ, Λ$ and $Ω$ at all $p_T$ in central Au+Au collisions. The thermal-shower component of the recombination is found to be important for $K$ and $Λ$, but only in a minor way for $ϕ$ and $Ω$ in the intermediate to high $p_T$ region. The normalization and inverse slope of the thermal partons in the strange sector are determined by fitting the low-$p_T$ data. At higher $p_T$ the data of $K, ϕ, Λ$ and $Ω$ in the log scale are all well reproduced in our study that extends the thermal contribution and includes the shower contribution. The calculated result on the $Λ/K$ ratio rises to a maximum of around 2 at $p_T\approx 4$ GeV/c, arching over the data in linear scale. The production of $ϕ$ and $Ω$ are shown to arise mainly from the recombination of thermal partons, thus exhibiting exponential $p_T$ dependences in agreement with the data. Their ratio, $R_{Ω/ϕ}$, rises linearly to $p_T\approx 4$ GeV/c and develops a maximum at $p_T\approx 5.5$ GeV/c. It is argued that the $p_T$ spectra of $ϕ$ and $Ω$ reveal directly the partonic nature of the thermal source that characterizes quark-gluon plasma. Comments are made on the $Ω$ puzzle due to the simultaneous observation of both the exponential behavior of the $Ω$ spectrum in $p_T$ and the existence of low-$p_T$ particles associated with $Ω$ as trigger.
With a simple attack and repair evolution model, we investigate the stability and structural changes of the Erdos-Renyi random graphs (RG) and Barabasi-Albert scale-free (SF) networks. We introduce a new quantity, invulnerability I(s), to describe the stability of the system. We find that both RG and SF networks can evolve to a stationary state. The stationary value I_c has a power-law dependence on the repair probability p_re. We also analyze the effects of the repair strategy to the attack tolerance of the networks. We observe that there is a threshold, (k_max)_c, for the maximum degree. The maximum degree k_max at time s will be no smaller than (k_max)_c. We give further information on the evolution of the networks by comparing the changes of the topological parameters, such as degree distribution P(k), average degree , shortest path length L, clustering coefficient C, assortativity r, under the initial and stationary states.
The production of pions and protons in the $p_T$ range between 10 and 20 GeV/c for Pb+Pb collisions at LHC is studied in the recombination model. It is shown that the dominant mechanism for hadronization is the recombination of shower partons from neighboring jets when the jet density is high. Protons are more copiously produced than pions in that $p_T$ range because the coalescing partons can have lower momentum fractions, but no thermal partons are involved. The proton-to-pion ratio can rise beyond 20. When such a high $p_T$ hadron is used as a trigger particle, there will not be any associated particles that are not in the background.
The transverse momentum distribution of produced charged particles is investigated for gold-gold collisions at $\sqrt{s_{NN}}=200$ GeV. A simple parameterization is suggested for the particle distribution based on the nuclear stopping effect. The model can fit very well both the transverse momentum distributions at different pseudo-rapidities and the pseudo-rapidity distributions at different centralities. The ratio of rapidity distributions for peripheral and central collisions is calculated and compared with the data.
We relate the fragmentation functions of partons into mesons and baryons in the framework of recombination of shower partons. The results are in reasonable agreement with the data. The implication is that the meson and baryon fragmentation functions are not independent when hadronization of the shower partons are taken into account. The conclusion therefore closes a conceptual gap in the system of fragmentation functions whose $Q^2$ evolution has been more extensively studied than their interrelationship.
We study the production of hadrons in Au+Au collisions in the region $0.6 0$, where $η'=η-y_{\rm beam}$, depending on $p_T$. We show how hadrons can be produced in that region when the hadronization process is parton recombination. The inclusive $x$-distributions for proton and pion production are calculated with momentum degradation taken into account. The results show that the proton yield is significantly higher than that of the pions in the TFR. Without particle identification the existing data cannot be used for comparison with our result on the $p/π$ ratio. Without $p_T$ determination it is not feasible to relate the $x$ distribution to the experimental $η'$ distribution. Nevertheless, on theoretical grounds we have shown why the production of hadrons in the TFR is not forbidden by momentum conservation.
The effect of finite hadronization time is considered in the recombination model, and it is shown that the hadron multiplicity turns out to be proportional to the initial quark density and unitarity is conserved in the model. The baryon to meson ratio increases rapidly with the initial quark density due to competition among different channels.
We analyze the correlation properties of the Erdos-Renyi random graph (RG) and the Barabasi-Albert scale-free network (SF) under the attack and repair strategy with detrended fluctuation analysis (DFA). The maximum degree k_max, representing the local property of the system, shows similar scaling behaviors for random graphs and scale-free networks. The fluctuations are quite random at short time scales but display strong anticorrelation at longer time scales under the same system size N and different repair probability p_re. The average degree , revealing the statistical property of the system, exhibits completely different scaling behaviors for random graphs and scale-free networks. Random graphs display long-range power-law correlations. Scale-free networks are uncorrelated at short time scales; while anticorrelated at longer time scales and the anticorrelation becoming stronger with the increase of p_re.